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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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SPDX-License-Identifier: GPL-2.0-only/* * mm/userfaultfd.c * * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org> * Copyright (C) 2008-2009 Red Hat, Inc. * Copyright (C) 2015 Red Hat, Inc. * * Some part derived from fs/eventfd.c (anon inode setup) and * mm/ksm.c (mm hashing). */
#include <linux/mm.h>#include <linux/sched/signal.h>#include <linux/pagemap.h>#include <linux/rmap.h>#include <linux/swap.h>#include <linux/leafops.h>#include <linux/userfaultfd_k.h>#include <linux/mmu_notifier.h>#include <linux/hugetlb.h>#include <linux/list.h>#include <linux/sched/mm.h>#include <linux/mm_inline.h>#include <linux/poll.h>#include <linux/slab.h>#include <linux/seq_file.h>#include <linux/bug.h>#include <linux/anon_inodes.h>#include <linux/syscalls.h>#include <linux/miscdevice.h>#include <linux/uio.h>#include <linux/file.h>#include <linux/cleanup.h>#include <asm/tlbflush.h>#include <asm/tlb.h>#include "internal.h"#include "swap.h"
struct mfill_state { struct userfaultfd_ctx *ctx; unsigned long src_start; unsigned long dst_start; unsigned long len; uffd_flags_t flags;
struct vm_area_struct *vma; unsigned long src_addr; unsigned long dst_addr; pmd_t *pmd;};
static bool anon_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags){ /* anonymous memory does not support MINOR mode */ if (vm_flags & VM_UFFD_MINOR) return false; return true;}
static struct folio *anon_alloc_folio(struct vm_area_struct *vma, unsigned long addr){ struct folio *folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, addr);
if (!folio) return NULL;
if (mem_cgroup_charge(folio, vma->vm_mm, GFP_KERNEL)) { folio_put(folio); return NULL; }
return folio;}
static const struct vm_uffd_ops anon_uffd_ops = { .can_userfault = anon_can_userfault, .alloc_folio = anon_alloc_folio,};
static const struct vm_uffd_ops *vma_uffd_ops(struct vm_area_struct *vma){ if (vma_is_anonymous(vma)) return &anon_uffd_ops; return vma->vm_ops->uffd_ops;}
static __always_inlinebool validate_dst_vma(struct vm_area_struct *dst_vma, unsigned long dst_end){ /* Make sure that the dst range is fully within dst_vma. */ if (dst_end > dst_vma->vm_end) return false;
/* * Check the vma is registered in uffd, this is required to * enforce the VM_MAYWRITE check done at uffd registration * time. */ if (!dst_vma->vm_userfaultfd_ctx.ctx) return false;
return true;}
static __always_inlinestruct vm_area_struct *find_vma_and_prepare_anon(struct mm_struct *mm, unsigned long addr){ struct vm_area_struct *vma;
mmap_assert_locked(mm); vma = vma_lookup(mm, addr); if (!vma) vma = ERR_PTR(-ENOENT); else if (!(vma->vm_flags & VM_SHARED) && unlikely(anon_vma_prepare(vma))) vma = ERR_PTR(-ENOMEM);
return vma;}
#ifdef CONFIG_PER_VMA_LOCK/* * uffd_lock_vma() - Lookup and lock vma corresponding to @address. * @mm: mm to search vma in. * @address: address that the vma should contain. * * Should be called without holding mmap_lock. * * Return: A locked vma containing @address, -ENOENT if no vma is found, or * -ENOMEM if anon_vma couldn't be allocated. */static struct vm_area_struct *uffd_lock_vma(struct mm_struct *mm, unsigned long address){ struct vm_area_struct *vma;
vma = lock_vma_under_rcu(mm, address); if (vma) { /* * We know we're going to need to use anon_vma, so check * that early. */ if (!(vma->vm_flags & VM_SHARED) && unlikely(!vma->anon_vma)) vma_end_read(vma); else return vma; }
mmap_read_lock(mm); vma = find_vma_and_prepare_anon(mm, address); if (!IS_ERR(vma)) { bool locked = vma_start_read_locked(vma);
if (!locked) vma = ERR_PTR(-EAGAIN); }
mmap_read_unlock(mm); return vma;}
static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm, unsigned long dst_start, unsigned long len){ struct vm_area_struct *dst_vma;
dst_vma = uffd_lock_vma(dst_mm, dst_start); if (IS_ERR(dst_vma) || validate_dst_vma(dst_vma, dst_start + len)) return dst_vma;
vma_end_read(dst_vma); return ERR_PTR(-ENOENT);}
static void uffd_mfill_unlock(struct vm_area_struct *vma){ vma_end_read(vma);}
#else
static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm, unsigned long dst_start, unsigned long len){ struct vm_area_struct *dst_vma;
mmap_read_lock(dst_mm); dst_vma = find_vma_and_prepare_anon(dst_mm, dst_start); if (IS_ERR(dst_vma)) goto out_unlock;
if (validate_dst_vma(dst_vma, dst_start + len)) return dst_vma;
dst_vma = ERR_PTR(-ENOENT);out_unlock: mmap_read_unlock(dst_mm); return dst_vma;}
static void uffd_mfill_unlock(struct vm_area_struct *vma){ mmap_read_unlock(vma->vm_mm);}#endif
static void mfill_put_vma(struct mfill_state *state){ if (!state->vma) return;
up_read(&state->ctx->map_changing_lock); uffd_mfill_unlock(state->vma); state->vma = NULL;}
static int mfill_get_vma(struct mfill_state *state){ struct userfaultfd_ctx *ctx = state->ctx; uffd_flags_t flags = state->flags; struct vm_area_struct *dst_vma; const struct vm_uffd_ops *ops; int err;
/* * Make sure the vma is not shared, that the dst range is * both valid and fully within a single existing vma. */ dst_vma = uffd_mfill_lock(ctx->mm, state->dst_start, state->len); if (IS_ERR(dst_vma)) return PTR_ERR(dst_vma);
/* * If memory mappings are changing because of non-cooperative * operation (e.g. mremap) running in parallel, bail out and * request the user to retry later */ down_read(&ctx->map_changing_lock); state->vma = dst_vma; err = -EAGAIN; if (atomic_read(&ctx->mmap_changing)) goto out_unlock;
err = -EINVAL;
/* * shmem_zero_setup is invoked in mmap for MAP_ANONYMOUS|MAP_SHARED but * it will overwrite vm_ops, so vma_is_anonymous must return false. */ if (WARN_ON_ONCE(vma_is_anonymous(dst_vma) && dst_vma->vm_flags & VM_SHARED)) goto out_unlock;
/* * validate 'mode' now that we know the dst_vma: don't allow * a wrprotect copy if the userfaultfd didn't register as WP. */ if ((flags & MFILL_ATOMIC_WP) && !(dst_vma->vm_flags & VM_UFFD_WP)) goto out_unlock;
if (is_vm_hugetlb_page(dst_vma)) return 0;
ops = vma_uffd_ops(dst_vma); if (!ops) goto out_unlock;
if (uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE) && !ops->get_folio_noalloc) goto out_unlock;
return 0;
out_unlock: mfill_put_vma(state); return err;}
static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address){ pgd_t *pgd; p4d_t *p4d; pud_t *pud;
pgd = pgd_offset(mm, address); p4d = p4d_alloc(mm, pgd, address); if (!p4d) return NULL; pud = pud_alloc(mm, p4d, address); if (!pud) return NULL; /* * Note that we didn't run this because the pmd was * missing, the *pmd may be already established and in * turn it may also be a trans_huge_pmd. */ return pmd_alloc(mm, pud, address);}
static int mfill_establish_pmd(struct mfill_state *state){ struct mm_struct *dst_mm = state->ctx->mm; pmd_t *dst_pmd, dst_pmdval;
dst_pmd = mm_alloc_pmd(dst_mm, state->dst_addr); if (unlikely(!dst_pmd)) return -ENOMEM;
dst_pmdval = pmdp_get_lockless(dst_pmd); if (unlikely(pmd_none(dst_pmdval)) && unlikely(__pte_alloc(dst_mm, dst_pmd))) return -ENOMEM;
dst_pmdval = pmdp_get_lockless(dst_pmd); /* * If the dst_pmd is THP don't override it and just be strict. * (This includes the case where the PMD used to be THP and * changed back to none after __pte_alloc().) */ if (unlikely(!pmd_present(dst_pmdval) || pmd_leaf(dst_pmdval))) return -EEXIST; if (unlikely(pmd_bad(dst_pmdval))) return -EFAULT;
state->pmd = dst_pmd; return 0;}
/* Check if dst_addr is outside of file's size. Must be called with ptl held. */static bool mfill_file_over_size(struct vm_area_struct *dst_vma, unsigned long dst_addr){ struct inode *inode; pgoff_t offset, max_off;
if (!dst_vma->vm_file) return false;
inode = dst_vma->vm_file->f_inode; offset = linear_page_index(dst_vma, dst_addr); max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE); return offset >= max_off;}
/* * Install PTEs, to map dst_addr (within dst_vma) to page. * * This function handles both MCOPY_ATOMIC_NORMAL and _CONTINUE for both shmem * and anon, and for both shared and private VMAs. */static int mfill_atomic_install_pte(pmd_t *dst_pmd, struct vm_area_struct *dst_vma, unsigned long dst_addr, struct page *page, uffd_flags_t flags){ int ret; struct mm_struct *dst_mm = dst_vma->vm_mm; pte_t _dst_pte, *dst_pte; bool writable = dst_vma->vm_flags & VM_WRITE; bool vm_shared = dst_vma->vm_flags & VM_SHARED; spinlock_t *ptl; struct folio *folio = page_folio(page); bool page_in_cache = folio_mapping(folio); pte_t dst_ptep;
_dst_pte = mk_pte(page, dst_vma->vm_page_prot); _dst_pte = pte_mkdirty(_dst_pte); if (page_in_cache && !vm_shared) writable = false; if (writable) _dst_pte = pte_mkwrite(_dst_pte, dst_vma); if (flags & MFILL_ATOMIC_WP) _dst_pte = pte_mkuffd_wp(_dst_pte);
ret = -EAGAIN; dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl); if (!dst_pte) goto out;
if (mfill_file_over_size(dst_vma, dst_addr)) { ret = -EFAULT; goto out_unlock; }
ret = -EEXIST;
dst_ptep = ptep_get(dst_pte);
/* * We are allowed to overwrite a UFFD pte marker: consider when both * MISSING|WP registered, we firstly wr-protect a none pte which has no * page cache page backing it, then access the page. */ if (!pte_none(dst_ptep) && !pte_is_uffd_marker(dst_ptep)) goto out_unlock;
if (page_in_cache) { folio_add_file_rmap_pte(folio, page, dst_vma); } else { folio_add_new_anon_rmap(folio, dst_vma, dst_addr, RMAP_EXCLUSIVE); folio_add_lru_vma(folio, dst_vma); }
/* * Must happen after rmap, as mm_counter() checks mapping (via * PageAnon()), which is set by __page_set_anon_rmap(). */ inc_mm_counter(dst_mm, mm_counter(folio));
set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
if (page_in_cache) folio_unlock(folio);
/* No need to invalidate - it was non-present before */ update_mmu_cache(dst_vma, dst_addr, dst_pte); ret = 0;out_unlock: pte_unmap_unlock(dst_pte, ptl);out: return ret;}
static int mfill_copy_folio_locked(struct folio *folio, unsigned long src_addr){ void *kaddr; int ret;
kaddr = kmap_local_folio(folio, 0); /* * The read mmap_lock is held here. Despite the * mmap_lock being read recursive a deadlock is still * possible if a writer has taken a lock. For example: * * process A thread 1 takes read lock on own mmap_lock * process A thread 2 calls mmap, blocks taking write lock * process B thread 1 takes page fault, read lock on own mmap lock * process B thread 2 calls mmap, blocks taking write lock * process A thread 1 blocks taking read lock on process B * process B thread 1 blocks taking read lock on process A * * Disable page faults to prevent potential deadlock * and retry the copy outside the mmap_lock. */ pagefault_disable(); ret = copy_from_user(kaddr, (const void __user *) src_addr, PAGE_SIZE); pagefault_enable(); kunmap_local(kaddr);
if (ret) return -EFAULT;
flush_dcache_folio(folio); return ret;}
#define MFILL_RETRY_STATE_VMA_FLAGS \ append_vma_flags(__VMA_UFFD_FLAGS, VMA_SHARED_BIT)
/* * VMA state saved before dropping the locks in mfill_copy_folio_retry(). * Used to detect VMA replacement or incompatible changes after reacquiring the * locks. */struct mfill_retry_state { const struct vm_uffd_ops *ops; struct file *file; vma_flags_t flags; pgoff_t pgoff;};
static void mfill_retry_state_save(struct mfill_retry_state *s, struct vm_area_struct *vma){ s->flags = vma_flags_and_mask(&vma->flags, MFILL_RETRY_STATE_VMA_FLAGS); s->ops = vma_uffd_ops(vma); s->pgoff = vma->vm_pgoff;
if (vma->vm_file) s->file = get_file(vma->vm_file);}
static bool mfill_retry_state_changed(struct mfill_retry_state *state, struct vm_area_struct *vma){ vma_flags_t flags = vma_flags_and_mask(&vma->flags, MFILL_RETRY_STATE_VMA_FLAGS);
/* Have any UFFD flags (missing, WP, minor) changed? */ if (!vma_flags_same_pair(&state->flags, &flags)) return true;
/* VMA type or effective uffd_ops changed while the lock was dropped */ if (state->ops != vma_uffd_ops(vma)) return true;
/* VMA was anonymous before; changed only if it no longer is */ if (!state->file) return !vma_is_anonymous(vma);
/* VMA was file backed, but file, inode or offset has changed */ if (!vma->vm_file || vma->vm_file->f_inode != state->file->f_inode || state->file != vma->vm_file || vma->vm_pgoff != state->pgoff) return true;
return false;}
static void mfill_retry_state_put(struct mfill_retry_state *s){ if (s->file) fput(s->file);}
DEFINE_FREE(retry_put, struct mfill_retry_state *, if (_T) mfill_retry_state_put(_T));
static int mfill_copy_folio_retry(struct mfill_state *mfill_state, struct folio *folio){ struct mfill_retry_state retry_state = { 0 }; struct mfill_retry_state *for_free __free(retry_put) = &retry_state; unsigned long src_addr = mfill_state->src_addr; void *kaddr; int err;
mfill_retry_state_save(&retry_state, mfill_state->vma);
/* retry copying with mm_lock dropped */ mfill_put_vma(mfill_state);
kaddr = kmap_local_folio(folio, 0); err = copy_from_user(kaddr, (const void __user *) src_addr, PAGE_SIZE); kunmap_local(kaddr); if (unlikely(err)) return -EFAULT;
flush_dcache_folio(folio);
/* reget VMA and PMD, they could change underneath us */ err = mfill_get_vma(mfill_state); if (err) return err;
if (mfill_retry_state_changed(&retry_state, mfill_state->vma)) return -EAGAIN;
err = mfill_establish_pmd(mfill_state); if (err) return err;
return 0;}
static int __mfill_atomic_pte(struct mfill_state *state, const struct vm_uffd_ops *ops){ unsigned long dst_addr = state->dst_addr; unsigned long src_addr = state->src_addr; uffd_flags_t flags = state->flags; struct folio *folio; int ret;
if (!ops) { VM_WARN_ONCE(1, "UFFDIO_COPY for unsupported VMA"); return -EOPNOTSUPP; }
folio = ops->alloc_folio(state->vma, state->dst_addr); if (!folio) return -ENOMEM;
if (uffd_flags_mode_is(flags, MFILL_ATOMIC_COPY)) { ret = mfill_copy_folio_locked(folio, src_addr); /* * Fallback to copy_from_user outside mmap_lock. * If retry is successful, mfill_copy_folio_locked() returns * with locks retaken by mfill_get_vma(). * If there was an error, we must mfill_put_vma() anyway and it * will take care of unlocking if needed. */ if (unlikely(ret)) { ret = mfill_copy_folio_retry(state, folio); if (ret) goto err_folio_put; } } else if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) { clear_user_highpage(&folio->page, state->dst_addr); } else { VM_WARN_ONCE(1, "Unknown UFFDIO operation, flags: %x", flags); }
/* * The memory barrier inside __folio_mark_uptodate makes sure that * preceding stores to the page contents become visible before * the set_pte_at() write. */ __folio_mark_uptodate(folio);
if (ops->filemap_add) { ret = ops->filemap_add(folio, state->vma, state->dst_addr); if (ret) goto err_folio_put; }
ret = mfill_atomic_install_pte(state->pmd, state->vma, dst_addr, &folio->page, flags); if (ret) goto err_filemap_remove;
return 0;
err_filemap_remove: if (ops->filemap_remove) ops->filemap_remove(folio, state->vma);err_folio_put: folio_put(folio); return ret;}
static int mfill_atomic_pte_copy(struct mfill_state *state){ const struct vm_uffd_ops *ops = vma_uffd_ops(state->vma);
/* * The normal page fault path for a MAP_PRIVATE mapping in a * file-backed VMA will invoke the fault, fill the hole in the file and * COW it right away. The result generates plain anonymous memory. * So when we are asked to fill a hole in a MAP_PRIVATE mapping, we'll * generate anonymous memory directly without actually filling the * hole. For the MAP_PRIVATE case the robustness check only happens in * the pagetable (to verify it's still none) and not in the page cache. */ if (!(state->vma->vm_flags & VM_SHARED)) ops = &anon_uffd_ops;
return __mfill_atomic_pte(state, ops);}
static int mfill_atomic_pte_zeroed_folio(struct mfill_state *state){ const struct vm_uffd_ops *ops = vma_uffd_ops(state->vma);
return __mfill_atomic_pte(state, ops);}
static int mfill_atomic_pte_zeropage(struct mfill_state *state){ struct vm_area_struct *dst_vma = state->vma; unsigned long dst_addr = state->dst_addr; pmd_t *dst_pmd = state->pmd; pte_t _dst_pte, *dst_pte; spinlock_t *ptl; int ret;
if (mm_forbids_zeropage(dst_vma->vm_mm) || (dst_vma->vm_flags & VM_SHARED)) return mfill_atomic_pte_zeroed_folio(state);
_dst_pte = pte_mkspecial(pfn_pte(zero_pfn(dst_addr), dst_vma->vm_page_prot)); ret = -EAGAIN; dst_pte = pte_offset_map_lock(dst_vma->vm_mm, dst_pmd, dst_addr, &ptl); if (!dst_pte) goto out; if (mfill_file_over_size(dst_vma, dst_addr)) { ret = -EFAULT; goto out_unlock; } ret = -EEXIST; if (!pte_none(ptep_get(dst_pte))) goto out_unlock; set_pte_at(dst_vma->vm_mm, dst_addr, dst_pte, _dst_pte); /* No need to invalidate - it was non-present before */ update_mmu_cache(dst_vma, dst_addr, dst_pte); ret = 0;out_unlock: pte_unmap_unlock(dst_pte, ptl);out: return ret;}
/* Handles UFFDIO_CONTINUE for all shmem VMAs (shared or private). */static int mfill_atomic_pte_continue(struct mfill_state *state){ struct vm_area_struct *dst_vma = state->vma; const struct vm_uffd_ops *ops = vma_uffd_ops(dst_vma); unsigned long dst_addr = state->dst_addr; pgoff_t pgoff = linear_page_index(dst_vma, dst_addr); struct inode *inode = file_inode(dst_vma->vm_file); uffd_flags_t flags = state->flags; pmd_t *dst_pmd = state->pmd; struct folio *folio; struct page *page; int ret;
if (!ops) { VM_WARN_ONCE(1, "UFFDIO_CONTINUE for unsupported VMA"); return -EOPNOTSUPP; }
folio = ops->get_folio_noalloc(inode, pgoff); /* Our caller expects us to return -EFAULT if we failed to find folio */ if (IS_ERR_OR_NULL(folio)) return -EFAULT;
page = folio_file_page(folio, pgoff); if (PageHWPoison(page)) { ret = -EIO; goto out_release; }
ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr, page, flags); if (ret) goto out_release;
return 0;
out_release: folio_unlock(folio); folio_put(folio); return ret;}
/* Handles UFFDIO_POISON for all non-hugetlb VMAs. */static int mfill_atomic_pte_poison(struct mfill_state *state){ struct vm_area_struct *dst_vma = state->vma; struct mm_struct *dst_mm = dst_vma->vm_mm; unsigned long dst_addr = state->dst_addr; pmd_t *dst_pmd = state->pmd; pte_t _dst_pte, *dst_pte; spinlock_t *ptl; int ret;
_dst_pte = make_pte_marker(PTE_MARKER_POISONED); ret = -EAGAIN; dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl); if (!dst_pte) goto out;
if (mfill_file_over_size(dst_vma, dst_addr)) { ret = -EFAULT; goto out_unlock; }
ret = -EEXIST; /* Refuse to overwrite any PTE, even a PTE marker (e.g. UFFD WP). */ if (!pte_none(ptep_get(dst_pte))) goto out_unlock;
set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
/* No need to invalidate - it was non-present before */ update_mmu_cache(dst_vma, dst_addr, dst_pte); ret = 0;out_unlock: pte_unmap_unlock(dst_pte, ptl);out: return ret;}
#ifdef CONFIG_HUGETLB_PAGE/* * mfill_atomic processing for HUGETLB vmas. Note that this routine is * called with either vma-lock or mmap_lock held, it will release the lock * before returning. */static __always_inline ssize_t mfill_atomic_hugetlb( struct userfaultfd_ctx *ctx, struct vm_area_struct *dst_vma, unsigned long dst_start, unsigned long src_start, unsigned long len, uffd_flags_t flags){ struct mm_struct *dst_mm = dst_vma->vm_mm; ssize_t err; pte_t *dst_pte; unsigned long src_addr, dst_addr; long copied; struct folio *folio; unsigned long vma_hpagesize; pgoff_t idx; u32 hash; struct address_space *mapping;
/* * There is no default zero huge page for all huge page sizes as * supported by hugetlb. A PMD_SIZE huge pages may exist as used * by THP. Since we can not reliably insert a zero page, this * feature is not supported. */ if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) { up_read(&ctx->map_changing_lock); uffd_mfill_unlock(dst_vma); return -EINVAL; }
src_addr = src_start; dst_addr = dst_start; copied = 0; folio = NULL; vma_hpagesize = vma_kernel_pagesize(dst_vma);
/* * Validate alignment based on huge page size */ err = -EINVAL; if (dst_start & (vma_hpagesize - 1) || len & (vma_hpagesize - 1)) goto out_unlock;
retry: /* * On routine entry dst_vma is set. If we had to drop mmap_lock and * retry, dst_vma will be set to NULL and we must lookup again. */ if (!dst_vma) { dst_vma = uffd_mfill_lock(dst_mm, dst_start, len); if (IS_ERR(dst_vma)) { err = PTR_ERR(dst_vma); goto out; }
err = -ENOENT; if (!is_vm_hugetlb_page(dst_vma)) goto out_unlock_vma;
err = -EINVAL; if (vma_hpagesize != vma_kernel_pagesize(dst_vma)) goto out_unlock_vma;
/* * If memory mappings are changing because of non-cooperative * operation (e.g. mremap) running in parallel, bail out and * request the user to retry later */ down_read(&ctx->map_changing_lock); err = -EAGAIN; if (atomic_read(&ctx->mmap_changing)) goto out_unlock; }
while (src_addr < src_start + len) { VM_WARN_ON_ONCE(dst_addr >= dst_start + len);
/* * Serialize via vma_lock and hugetlb_fault_mutex. * vma_lock ensures the dst_pte remains valid even * in the case of shared pmds. fault mutex prevents * races with other faulting threads. */ idx = hugetlb_linear_page_index(dst_vma, dst_addr); mapping = dst_vma->vm_file->f_mapping; hash = hugetlb_fault_mutex_hash(mapping, idx); mutex_lock(&hugetlb_fault_mutex_table[hash]); hugetlb_vma_lock_read(dst_vma);
err = -ENOMEM; dst_pte = huge_pte_alloc(dst_mm, dst_vma, dst_addr, vma_hpagesize); if (!dst_pte) { hugetlb_vma_unlock_read(dst_vma); mutex_unlock(&hugetlb_fault_mutex_table[hash]); goto out_unlock; }
if (!uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) { const pte_t ptep = huge_ptep_get(dst_mm, dst_addr, dst_pte);
if (!huge_pte_none(ptep) && !pte_is_uffd_marker(ptep)) { err = -EEXIST; hugetlb_vma_unlock_read(dst_vma); mutex_unlock(&hugetlb_fault_mutex_table[hash]); goto out_unlock; } }
err = hugetlb_mfill_atomic_pte(dst_pte, dst_vma, dst_addr, src_addr, flags, &folio);
hugetlb_vma_unlock_read(dst_vma); mutex_unlock(&hugetlb_fault_mutex_table[hash]);
cond_resched();
if (unlikely(err == -ENOENT)) { up_read(&ctx->map_changing_lock); uffd_mfill_unlock(dst_vma); VM_WARN_ON_ONCE(!folio);
err = copy_folio_from_user(folio, (const void __user *)src_addr, true); if (unlikely(err)) { err = -EFAULT; goto out; }
dst_vma = NULL; goto retry; } else VM_WARN_ON_ONCE(folio);
if (!err) { dst_addr += vma_hpagesize; src_addr += vma_hpagesize; copied += vma_hpagesize;
if (fatal_signal_pending(current)) err = -EINTR; } if (err) break; }
out_unlock: up_read(&ctx->map_changing_lock);out_unlock_vma: uffd_mfill_unlock(dst_vma);out: if (folio) folio_put(folio); VM_WARN_ON_ONCE(copied < 0); VM_WARN_ON_ONCE(err > 0); VM_WARN_ON_ONCE(!copied && !err); return copied ? copied : err;}#else /* !CONFIG_HUGETLB_PAGE *//* fail at build time if gcc attempts to use this */extern ssize_t mfill_atomic_hugetlb(struct userfaultfd_ctx *ctx, struct vm_area_struct *dst_vma, unsigned long dst_start, unsigned long src_start, unsigned long len, uffd_flags_t flags);#endif /* CONFIG_HUGETLB_PAGE */
static __always_inline ssize_t mfill_atomic_pte(struct mfill_state *state){ uffd_flags_t flags = state->flags;
if (uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) return mfill_atomic_pte_continue(state); if (uffd_flags_mode_is(flags, MFILL_ATOMIC_POISON)) return mfill_atomic_pte_poison(state); if (uffd_flags_mode_is(flags, MFILL_ATOMIC_COPY)) return mfill_atomic_pte_copy(state); if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) return mfill_atomic_pte_zeropage(state);
VM_WARN_ONCE(1, "Unknown UFFDIO operation, flags: %x", flags); return -EOPNOTSUPP;}
static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, unsigned long dst_start, unsigned long src_start, unsigned long len, uffd_flags_t flags){ struct mfill_state state = (struct mfill_state){ .ctx = ctx, .dst_start = dst_start, .src_start = src_start, .flags = flags, .len = len, .src_addr = src_start, .dst_addr = dst_start, }; long copied = 0; ssize_t err;
/* * Sanitize the command parameters: */ VM_WARN_ON_ONCE(dst_start & ~PAGE_MASK); VM_WARN_ON_ONCE(len & ~PAGE_MASK);
/* Does the address range wrap, or is the span zero-sized? */ VM_WARN_ON_ONCE(src_start + len <= src_start); VM_WARN_ON_ONCE(dst_start + len <= dst_start);
err = mfill_get_vma(&state); if (err) goto out;
/* * If this is a HUGETLB vma, pass off to appropriate routine */ if (is_vm_hugetlb_page(state.vma)) return mfill_atomic_hugetlb(ctx, state.vma, dst_start, src_start, len, flags);
while (state.src_addr < src_start + len) { VM_WARN_ON_ONCE(state.dst_addr >= dst_start + len);
err = mfill_establish_pmd(&state); if (err) break;
/* * For shmem mappings, khugepaged is allowed to remove page * tables under us; pte_offset_map_lock() will deal with that. */
err = mfill_atomic_pte(&state); cond_resched();
if (!err) { state.dst_addr += PAGE_SIZE; state.src_addr += PAGE_SIZE; copied += PAGE_SIZE;
if (fatal_signal_pending(current)) err = -EINTR; } if (err) break; }
mfill_put_vma(&state);out: VM_WARN_ON_ONCE(copied < 0); VM_WARN_ON_ONCE(err > 0); VM_WARN_ON_ONCE(!copied && !err); return copied ? copied : err;}
static ssize_t mfill_atomic_copy(struct userfaultfd_ctx *ctx, unsigned long dst_start, unsigned long src_start, unsigned long len, uffd_flags_t flags){ return mfill_atomic(ctx, dst_start, src_start, len, uffd_flags_set_mode(flags, MFILL_ATOMIC_COPY));}
static ssize_t mfill_atomic_zeropage(struct userfaultfd_ctx *ctx, unsigned long start, unsigned long len){ return mfill_atomic(ctx, start, 0, len, uffd_flags_set_mode(0, MFILL_ATOMIC_ZEROPAGE));}
static ssize_t mfill_atomic_continue(struct userfaultfd_ctx *ctx, unsigned long start, unsigned long len, uffd_flags_t flags){
/* * A caller might reasonably assume that UFFDIO_CONTINUE contains an * smp_wmb() to ensure that any writes to the about-to-be-mapped page by * the thread doing the UFFDIO_CONTINUE are guaranteed to be visible to * subsequent loads from the page through the newly mapped address range. */ smp_wmb();
return mfill_atomic(ctx, start, 0, len, uffd_flags_set_mode(flags, MFILL_ATOMIC_CONTINUE));}
static ssize_t mfill_atomic_poison(struct userfaultfd_ctx *ctx, unsigned long start, unsigned long len, uffd_flags_t flags){ return mfill_atomic(ctx, start, 0, len, uffd_flags_set_mode(flags, MFILL_ATOMIC_POISON));}
long uffd_wp_range(struct vm_area_struct *dst_vma, unsigned long start, unsigned long len, bool enable_wp){ unsigned int mm_cp_flags; struct mmu_gather tlb; long ret;
VM_WARN_ONCE(start < dst_vma->vm_start || start + len > dst_vma->vm_end, "The address range exceeds VMA boundary.\n"); if (enable_wp) mm_cp_flags = MM_CP_UFFD_WP; else mm_cp_flags = MM_CP_UFFD_WP_RESOLVE;
/* * vma->vm_page_prot already reflects that uffd-wp is enabled for this * VMA (see userfaultfd_set_vm_flags()) and that all PTEs are supposed * to be write-protected as default whenever protection changes. * Try upgrading write permissions manually. */ if (!enable_wp && vma_wants_manual_pte_write_upgrade(dst_vma)) mm_cp_flags |= MM_CP_TRY_CHANGE_WRITABLE; tlb_gather_mmu(&tlb, dst_vma->vm_mm); ret = change_protection(&tlb, dst_vma, start, start + len, mm_cp_flags); tlb_finish_mmu(&tlb);
return ret;}
static int mwriteprotect_range(struct userfaultfd_ctx *ctx, unsigned long start, unsigned long len, bool enable_wp){ struct mm_struct *dst_mm = ctx->mm; unsigned long end = start + len; unsigned long _start, _end; struct vm_area_struct *dst_vma; unsigned long page_mask; long err; VMA_ITERATOR(vmi, dst_mm, start);
/* * Sanitize the command parameters: */ VM_WARN_ON_ONCE(start & ~PAGE_MASK); VM_WARN_ON_ONCE(len & ~PAGE_MASK);
/* Does the address range wrap, or is the span zero-sized? */ VM_WARN_ON_ONCE(start + len <= start);
mmap_read_lock(dst_mm);
/* * If memory mappings are changing because of non-cooperative * operation (e.g. mremap) running in parallel, bail out and * request the user to retry later */ down_read(&ctx->map_changing_lock); err = -EAGAIN; if (atomic_read(&ctx->mmap_changing)) goto out_unlock;
err = -ENOENT; for_each_vma_range(vmi, dst_vma, end) {
if (!userfaultfd_wp(dst_vma)) { err = -ENOENT; break; }
if (is_vm_hugetlb_page(dst_vma)) { err = -EINVAL; page_mask = vma_kernel_pagesize(dst_vma) - 1; if ((start & page_mask) || (len & page_mask)) break; }
_start = max(dst_vma->vm_start, start); _end = min(dst_vma->vm_end, end);
err = uffd_wp_range(dst_vma, _start, _end - _start, enable_wp);
/* Return 0 on success, <0 on failures */ if (err < 0) break; err = 0; }out_unlock: up_read(&ctx->map_changing_lock); mmap_read_unlock(dst_mm); return err;}
void double_pt_lock(spinlock_t *ptl1, spinlock_t *ptl2) __acquires(ptl1) __acquires(ptl2){ if (ptl1 > ptl2) swap(ptl1, ptl2); /* lock in virtual address order to avoid lock inversion */ spin_lock(ptl1); if (ptl1 != ptl2) spin_lock_nested(ptl2, SINGLE_DEPTH_NESTING); else __acquire(ptl2);}
void double_pt_unlock(spinlock_t *ptl1, spinlock_t *ptl2) __releases(ptl1) __releases(ptl2){ spin_unlock(ptl1); if (ptl1 != ptl2) spin_unlock(ptl2); else __release(ptl2);}
static inline bool is_pte_pages_stable(pte_t *dst_pte, pte_t *src_pte, pte_t orig_dst_pte, pte_t orig_src_pte, pmd_t *dst_pmd, pmd_t dst_pmdval){ return pte_same(ptep_get(src_pte), orig_src_pte) && pte_same(ptep_get(dst_pte), orig_dst_pte) && pmd_same(dst_pmdval, pmdp_get_lockless(dst_pmd));}
/* * Checks if the two ptes and the corresponding folio are eligible for batched * move. If so, then returns pointer to the locked folio. Otherwise, returns NULL. * * NOTE: folio's reference is not required as the whole operation is within * PTL's critical section. */static struct folio *check_ptes_for_batched_move(struct vm_area_struct *src_vma, unsigned long src_addr, pte_t *src_pte, pte_t *dst_pte){ pte_t orig_dst_pte, orig_src_pte; struct folio *folio;
orig_dst_pte = ptep_get(dst_pte); if (!pte_none(orig_dst_pte)) return NULL;
orig_src_pte = ptep_get(src_pte); if (!pte_present(orig_src_pte) || is_zero_pfn(pte_pfn(orig_src_pte))) return NULL;
folio = vm_normal_folio(src_vma, src_addr, orig_src_pte); if (!folio || !folio_trylock(folio)) return NULL; if (!PageAnonExclusive(&folio->page) || folio_test_large(folio)) { folio_unlock(folio); return NULL; } return folio;}
/* * Moves src folios to dst in a batch as long as they are not large, and can * successfully take the lock via folio_trylock(). */static long move_present_ptes(struct mm_struct *mm, struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, unsigned long dst_addr, unsigned long src_addr, pte_t *dst_pte, pte_t *src_pte, pte_t orig_dst_pte, pte_t orig_src_pte, pmd_t *dst_pmd, pmd_t dst_pmdval, spinlock_t *dst_ptl, spinlock_t *src_ptl, struct folio **first_src_folio, unsigned long len){ int err = 0; struct folio *src_folio = *first_src_folio; unsigned long src_start = src_addr; unsigned long src_end;
len = pmd_addr_end(dst_addr, dst_addr + len) - dst_addr; src_end = pmd_addr_end(src_addr, src_addr + len); flush_cache_range(src_vma, src_addr, src_end); double_pt_lock(dst_ptl, src_ptl);
if (!is_pte_pages_stable(dst_pte, src_pte, orig_dst_pte, orig_src_pte, dst_pmd, dst_pmdval)) { err = -EAGAIN; goto out; } if (folio_test_large(src_folio) || folio_maybe_dma_pinned(src_folio) || !PageAnonExclusive(&src_folio->page)) { err = -EBUSY; goto out; } /* It's safe to drop the reference now as the page-table is holding one. */ folio_put(*first_src_folio); *first_src_folio = NULL; lazy_mmu_mode_enable();
while (true) { orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte); /* Folio got pinned from under us. Put it back and fail the move. */ if (folio_maybe_dma_pinned(src_folio)) { set_pte_at(mm, src_addr, src_pte, orig_src_pte); err = -EBUSY; break; }
folio_move_anon_rmap(src_folio, dst_vma); src_folio->index = linear_page_index(dst_vma, dst_addr);
orig_dst_pte = folio_mk_pte(src_folio, dst_vma->vm_page_prot); /* Set soft dirty bit so userspace can notice the pte was moved */ if (pgtable_supports_soft_dirty()) orig_dst_pte = pte_mksoft_dirty(orig_dst_pte); if (pte_dirty(orig_src_pte)) orig_dst_pte = pte_mkdirty(orig_dst_pte); orig_dst_pte = pte_mkwrite(orig_dst_pte, dst_vma); set_pte_at(mm, dst_addr, dst_pte, orig_dst_pte);
src_addr += PAGE_SIZE; if (src_addr == src_end) break; dst_addr += PAGE_SIZE; dst_pte++; src_pte++;
folio_unlock(src_folio); src_folio = check_ptes_for_batched_move(src_vma, src_addr, src_pte, dst_pte); if (!src_folio) break; }
lazy_mmu_mode_disable(); if (src_addr > src_start) flush_tlb_range(src_vma, src_start, src_addr);
if (src_folio) folio_unlock(src_folio);out: double_pt_unlock(dst_ptl, src_ptl); return src_addr > src_start ? src_addr - src_start : err;}
static int move_swap_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma, unsigned long dst_addr, unsigned long src_addr, pte_t *dst_pte, pte_t *src_pte, pte_t orig_dst_pte, pte_t orig_src_pte, pmd_t *dst_pmd, pmd_t dst_pmdval, spinlock_t *dst_ptl, spinlock_t *src_ptl, struct folio *src_folio, struct swap_info_struct *si, swp_entry_t entry){ /* * Check if the folio still belongs to the target swap entry after * acquiring the lock. Folio can be freed in the swap cache while * not locked. */ if (src_folio && unlikely(!folio_test_swapcache(src_folio) || entry.val != src_folio->swap.val)) return -EAGAIN;
double_pt_lock(dst_ptl, src_ptl);
if (!is_pte_pages_stable(dst_pte, src_pte, orig_dst_pte, orig_src_pte, dst_pmd, dst_pmdval)) { double_pt_unlock(dst_ptl, src_ptl); return -EAGAIN; }
/* * The src_folio resides in the swapcache, requiring an update to its * index and mapping to align with the dst_vma, where a swap-in may * occur and hit the swapcache after moving the PTE. */ if (src_folio) { folio_move_anon_rmap(src_folio, dst_vma); src_folio->index = linear_page_index(dst_vma, dst_addr); } else { /* * Check if the swap entry is cached after acquiring the src_pte * lock. Otherwise, we might miss a newly loaded swap cache folio. * * We are trying to catch newly added swap cache, the only possible case is * when a folio is swapped in and out again staying in swap cache, using the * same entry before the PTE check above. The PTL is acquired and released * twice, each time after updating the swap table. So holding * the PTL here ensures we see the updated value. */ if (swap_cache_has_folio(entry)) { double_pt_unlock(dst_ptl, src_ptl); return -EAGAIN; } }
orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte); if (pgtable_supports_soft_dirty()) orig_src_pte = pte_swp_mksoft_dirty(orig_src_pte); set_pte_at(mm, dst_addr, dst_pte, orig_src_pte); double_pt_unlock(dst_ptl, src_ptl);
return PAGE_SIZE;}
static int move_zeropage_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, unsigned long dst_addr, unsigned long src_addr, pte_t *dst_pte, pte_t *src_pte, pte_t orig_dst_pte, pte_t orig_src_pte, pmd_t *dst_pmd, pmd_t dst_pmdval, spinlock_t *dst_ptl, spinlock_t *src_ptl){ pte_t zero_pte;
double_pt_lock(dst_ptl, src_ptl); if (!is_pte_pages_stable(dst_pte, src_pte, orig_dst_pte, orig_src_pte, dst_pmd, dst_pmdval)) { double_pt_unlock(dst_ptl, src_ptl); return -EAGAIN; }
zero_pte = pte_mkspecial(pfn_pte(zero_pfn(dst_addr), dst_vma->vm_page_prot)); ptep_clear_flush(src_vma, src_addr, src_pte); set_pte_at(mm, dst_addr, dst_pte, zero_pte); double_pt_unlock(dst_ptl, src_ptl);
return PAGE_SIZE;}
/* * The mmap_lock for reading is held by the caller. Just move the page(s) * from src_pmd to dst_pmd if possible, and return number of bytes moved. * On failure, an error code is returned. */static long move_pages_ptes(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, unsigned long dst_addr, unsigned long src_addr, unsigned long len, __u64 mode){ struct swap_info_struct *si = NULL; pte_t orig_src_pte, orig_dst_pte; pte_t src_folio_pte; spinlock_t *src_ptl, *dst_ptl; pte_t *src_pte = NULL; pte_t *dst_pte = NULL; pmd_t dummy_pmdval; pmd_t dst_pmdval; struct folio *src_folio = NULL; struct mmu_notifier_range range; long ret = 0;
mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, src_addr, src_addr + len); mmu_notifier_invalidate_range_start(&range);retry: /* * Use the maywrite version to indicate that dst_pte will be modified, * since dst_pte needs to be none, the subsequent pte_same() check * cannot prevent the dst_pte page from being freed concurrently, so we * also need to obtain dst_pmdval and recheck pmd_same() later. */ dst_pte = pte_offset_map_rw_nolock(mm, dst_pmd, dst_addr, &dst_pmdval, &dst_ptl);
/* Retry if a huge pmd materialized from under us */ if (unlikely(!dst_pte)) { ret = -EAGAIN; goto out; }
/* * Unlike dst_pte, the subsequent pte_same() check can ensure the * stability of the src_pte page, so there is no need to get pmdval, * just pass a dummy variable to it. */ src_pte = pte_offset_map_rw_nolock(mm, src_pmd, src_addr, &dummy_pmdval, &src_ptl);
/* * We held the mmap_lock for reading so MADV_DONTNEED * can zap transparent huge pages under us, or the * transparent huge page fault can establish new * transparent huge pages under us. */ if (unlikely(!src_pte)) { ret = -EAGAIN; goto out; }
/* Sanity checks before the operation */ if (pmd_none(*dst_pmd) || pmd_none(*src_pmd) || pmd_trans_huge(*dst_pmd) || pmd_trans_huge(*src_pmd)) { ret = -EINVAL; goto out; }
spin_lock(dst_ptl); orig_dst_pte = ptep_get(dst_pte); spin_unlock(dst_ptl); if (!pte_none(orig_dst_pte)) { ret = -EEXIST; goto out; }
spin_lock(src_ptl); orig_src_pte = ptep_get(src_pte); spin_unlock(src_ptl); if (pte_none(orig_src_pte)) { if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) ret = -ENOENT; else /* nothing to do to move a hole */ ret = PAGE_SIZE; goto out; }
/* If PTE changed after we locked the folio then start over */ if (src_folio && unlikely(!pte_same(src_folio_pte, orig_src_pte))) { ret = -EAGAIN; goto out; }
if (pte_present(orig_src_pte)) { if (is_zero_pfn(pte_pfn(orig_src_pte))) { ret = move_zeropage_pte(mm, dst_vma, src_vma, dst_addr, src_addr, dst_pte, src_pte, orig_dst_pte, orig_src_pte, dst_pmd, dst_pmdval, dst_ptl, src_ptl); goto out; }
/* * Pin and lock source folio. Since we are in RCU read section, * we can't block, so on contention have to unmap the ptes, * obtain the lock and retry. */ if (!src_folio) { struct folio *folio; bool locked;
/* * Pin the page while holding the lock to be sure the * page isn't freed under us */ spin_lock(src_ptl); if (!pte_same(orig_src_pte, ptep_get(src_pte))) { spin_unlock(src_ptl); ret = -EAGAIN; goto out; }
folio = vm_normal_folio(src_vma, src_addr, orig_src_pte); if (!folio || !PageAnonExclusive(&folio->page)) { spin_unlock(src_ptl); ret = -EBUSY; goto out; }
locked = folio_trylock(folio); /* * We avoid waiting for folio lock with a raised * refcount for large folios because extra refcounts * will result in split_folio() failing later and * retrying. If multiple tasks are trying to move a * large folio we can end up livelocking. */ if (!locked && folio_test_large(folio)) { spin_unlock(src_ptl); ret = -EAGAIN; goto out; }
folio_get(folio); src_folio = folio; src_folio_pte = orig_src_pte; spin_unlock(src_ptl);
if (!locked) { pte_unmap(src_pte); pte_unmap(dst_pte); src_pte = dst_pte = NULL; /* now we can block and wait */ folio_lock(src_folio); goto retry; }
if (WARN_ON_ONCE(!folio_test_anon(src_folio))) { ret = -EBUSY; goto out; } }
/* at this point we have src_folio locked */ if (folio_test_large(src_folio)) { /* split_folio() can block */ pte_unmap(src_pte); pte_unmap(dst_pte); src_pte = dst_pte = NULL; ret = split_folio(src_folio); if (ret) goto out; /* have to reacquire the folio after it got split */ folio_unlock(src_folio); folio_put(src_folio); src_folio = NULL; goto retry; }
ret = move_present_ptes(mm, dst_vma, src_vma, dst_addr, src_addr, dst_pte, src_pte, orig_dst_pte, orig_src_pte, dst_pmd, dst_pmdval, dst_ptl, src_ptl, &src_folio, len); } else { /* !pte_present() */ struct folio *folio = NULL; const softleaf_t entry = softleaf_from_pte(orig_src_pte);
if (softleaf_is_migration(entry)) { pte_unmap(src_pte); pte_unmap(dst_pte); src_pte = dst_pte = NULL; migration_entry_wait(mm, src_pmd, src_addr);
ret = -EAGAIN; goto out; } else if (!softleaf_is_swap(entry)) { ret = -EFAULT; goto out; }
if (!pte_swp_exclusive(orig_src_pte)) { ret = -EBUSY; goto out; }
si = get_swap_device(entry); if (unlikely(!si)) { ret = -EAGAIN; goto out; } /* * Verify the existence of the swapcache. If present, the folio's * index and mapping must be updated even when the PTE is a swap * entry. The anon_vma lock is not taken during this process since * the folio has already been unmapped, and the swap entry is * exclusive, preventing rmap walks. * * For large folios, return -EBUSY immediately, as split_folio() * also returns -EBUSY when attempting to split unmapped large * folios in the swapcache. This issue needs to be resolved * separately to allow proper handling. */ if (!src_folio) folio = swap_cache_get_folio(entry); if (folio) { if (folio_test_large(folio)) { ret = -EBUSY; folio_put(folio); goto out; } src_folio = folio; src_folio_pte = orig_src_pte; if (!folio_trylock(src_folio)) { pte_unmap(src_pte); pte_unmap(dst_pte); src_pte = dst_pte = NULL; put_swap_device(si); si = NULL; /* now we can block and wait */ folio_lock(src_folio); goto retry; } } ret = move_swap_pte(mm, dst_vma, dst_addr, src_addr, dst_pte, src_pte, orig_dst_pte, orig_src_pte, dst_pmd, dst_pmdval, dst_ptl, src_ptl, src_folio, si, entry); }
out: if (src_folio) { folio_unlock(src_folio); folio_put(src_folio); } /* * Unmap in reverse order (LIFO) to maintain proper kmap_local * index ordering when CONFIG_HIGHPTE is enabled. We mapped dst_pte * first, then src_pte, so we must unmap src_pte first, then dst_pte. */ if (src_pte) pte_unmap(src_pte); if (dst_pte) pte_unmap(dst_pte); mmu_notifier_invalidate_range_end(&range); if (si) put_swap_device(si);
return ret;}
#ifdef CONFIG_TRANSPARENT_HUGEPAGEstatic inline bool move_splits_huge_pmd(unsigned long dst_addr, unsigned long src_addr, unsigned long src_end){ return (src_addr & ~HPAGE_PMD_MASK) || (dst_addr & ~HPAGE_PMD_MASK) || src_end - src_addr < HPAGE_PMD_SIZE;}#elsestatic inline bool move_splits_huge_pmd(unsigned long dst_addr, unsigned long src_addr, unsigned long src_end){ /* This is unreachable anyway, just to avoid warnings when HPAGE_PMD_SIZE==0 */ return false;}#endif
static inline bool vma_move_compatible(struct vm_area_struct *vma){ return !(vma->vm_flags & (VM_PFNMAP | VM_IO | VM_HUGETLB | VM_MIXEDMAP | VM_SHADOW_STACK));}
static int validate_move_areas(struct userfaultfd_ctx *ctx, struct vm_area_struct *src_vma, struct vm_area_struct *dst_vma){ /* Only allow moving if both have the same access and protection */ if ((src_vma->vm_flags & VM_ACCESS_FLAGS) != (dst_vma->vm_flags & VM_ACCESS_FLAGS) || pgprot_val(src_vma->vm_page_prot) != pgprot_val(dst_vma->vm_page_prot)) return -EINVAL;
/* Only allow moving if both are mlocked or both aren't */ if ((src_vma->vm_flags & VM_LOCKED) != (dst_vma->vm_flags & VM_LOCKED)) return -EINVAL;
/* * For now, we keep it simple and only move between writable VMAs. * Access flags are equal, therefore checking only the source is enough. */ if (!(src_vma->vm_flags & VM_WRITE)) return -EINVAL;
/* Check if vma flags indicate content which can be moved */ if (!vma_move_compatible(src_vma) || !vma_move_compatible(dst_vma)) return -EINVAL;
/* Ensure dst_vma is registered in uffd we are operating on */ if (!dst_vma->vm_userfaultfd_ctx.ctx || dst_vma->vm_userfaultfd_ctx.ctx != ctx) return -EINVAL;
/* Only allow moving across anonymous vmas */ if (!vma_is_anonymous(src_vma) || !vma_is_anonymous(dst_vma)) return -EINVAL;
return 0;}
static __always_inlineint find_vmas_mm_locked(struct mm_struct *mm, unsigned long dst_start, unsigned long src_start, struct vm_area_struct **dst_vmap, struct vm_area_struct **src_vmap){ struct vm_area_struct *vma;
mmap_assert_locked(mm); vma = find_vma_and_prepare_anon(mm, dst_start); if (IS_ERR(vma)) return PTR_ERR(vma);
*dst_vmap = vma; /* Skip finding src_vma if src_start is in dst_vma */ if (src_start >= vma->vm_start && src_start < vma->vm_end) goto out_success;
vma = vma_lookup(mm, src_start); if (!vma) return -ENOENT;out_success: *src_vmap = vma; return 0;}
#ifdef CONFIG_PER_VMA_LOCKstatic int uffd_move_lock(struct mm_struct *mm, unsigned long dst_start, unsigned long src_start, struct vm_area_struct **dst_vmap, struct vm_area_struct **src_vmap){ struct vm_area_struct *vma; int err;
vma = uffd_lock_vma(mm, dst_start); if (IS_ERR(vma)) return PTR_ERR(vma);
*dst_vmap = vma; /* * Skip finding src_vma if src_start is in dst_vma. This also ensures * that we don't lock the same vma twice. */ if (src_start >= vma->vm_start && src_start < vma->vm_end) { *src_vmap = vma; return 0; }
/* * Using uffd_lock_vma() to get src_vma can lead to following deadlock: * * Thread1 Thread2 * ------- ------- * vma_start_read(dst_vma) * mmap_write_lock(mm) * vma_start_write(src_vma) * vma_start_read(src_vma) * mmap_read_lock(mm) * vma_start_write(dst_vma) */ *src_vmap = lock_vma_under_rcu(mm, src_start); if (likely(*src_vmap)) return 0;
/* Undo any locking and retry in mmap_lock critical section */ vma_end_read(*dst_vmap);
mmap_read_lock(mm); err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap); if (err) goto out;
if (!vma_start_read_locked(*dst_vmap)) { err = -EAGAIN; goto out; }
/* Nothing further to do if both vmas are locked. */ if (*dst_vmap == *src_vmap) goto out;
if (!vma_start_read_locked_nested(*src_vmap, SINGLE_DEPTH_NESTING)) { /* Undo dst_vmap locking if src_vmap failed to lock */ vma_end_read(*dst_vmap); err = -EAGAIN; }out: mmap_read_unlock(mm); return err;}
static void uffd_move_unlock(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma){ vma_end_read(src_vma); if (src_vma != dst_vma) vma_end_read(dst_vma);}
#else
static int uffd_move_lock(struct mm_struct *mm, unsigned long dst_start, unsigned long src_start, struct vm_area_struct **dst_vmap, struct vm_area_struct **src_vmap){ int err;
mmap_read_lock(mm); err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap); if (err) mmap_read_unlock(mm); return err;}
static void uffd_move_unlock(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma){ mmap_assert_locked(src_vma->vm_mm); mmap_read_unlock(dst_vma->vm_mm);}#endif
/** * move_pages - move arbitrary anonymous pages of an existing vma * @ctx: pointer to the userfaultfd context * @dst_start: start of the destination virtual memory range * @src_start: start of the source virtual memory range * @len: length of the virtual memory range * @mode: flags from uffdio_move.mode * * It will either use the mmap_lock in read mode or per-vma locks * * move_pages() remaps arbitrary anonymous pages atomically in zero * copy. It only works on non shared anonymous pages because those can * be relocated without generating non linear anon_vmas in the rmap * code. * * It provides a zero copy mechanism to handle userspace page faults. * The source vma pages should have mapcount == 1, which can be * enforced by using madvise(MADV_DONTFORK) on src vma. * * The thread receiving the page during the userland page fault * will receive the faulting page in the source vma through the network, * storage or any other I/O device (MADV_DONTFORK in the source vma * avoids move_pages() to fail with -EBUSY if the process forks before * move_pages() is called), then it will call move_pages() to map the * page in the faulting address in the destination vma. * * This userfaultfd command works purely via pagetables, so it's the * most efficient way to move physical non shared anonymous pages * across different virtual addresses. Unlike mremap()/mmap()/munmap() * it does not create any new vmas. The mapping in the destination * address is atomic. * * It only works if the vma protection bits are identical from the * source and destination vma. * * It can remap non shared anonymous pages within the same vma too. * * If the source virtual memory range has any unmapped holes, or if * the destination virtual memory range is not a whole unmapped hole, * move_pages() will fail respectively with -ENOENT or -EEXIST. This * provides a very strict behavior to avoid any chance of memory * corruption going unnoticed if there are userland race conditions. * Only one thread should resolve the userland page fault at any given * time for any given faulting address. This means that if two threads * try to both call move_pages() on the same destination address at the * same time, the second thread will get an explicit error from this * command. * * The command retval will return "len" is successful. The command * however can be interrupted by fatal signals or errors. If * interrupted it will return the number of bytes successfully * remapped before the interruption if any, or the negative error if * none. It will never return zero. Either it will return an error or * an amount of bytes successfully moved. If the retval reports a * "short" remap, the move_pages() command should be repeated by * userland with src+retval, dst+reval, len-retval if it wants to know * about the error that interrupted it. * * The UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES flag can be specified to * prevent -ENOENT errors to materialize if there are holes in the * source virtual range that is being remapped. The holes will be * accounted as successfully remapped in the retval of the * command. This is mostly useful to remap hugepage naturally aligned * virtual regions without knowing if there are transparent hugepage * in the regions or not, but preventing the risk of having to split * the hugepmd during the remap. */static ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start, unsigned long src_start, unsigned long len, __u64 mode){ struct mm_struct *mm = ctx->mm; struct vm_area_struct *src_vma, *dst_vma; unsigned long src_addr, dst_addr, src_end; pmd_t *src_pmd, *dst_pmd; long err = -EINVAL; ssize_t moved = 0;
/* Sanitize the command parameters. */ VM_WARN_ON_ONCE(src_start & ~PAGE_MASK); VM_WARN_ON_ONCE(dst_start & ~PAGE_MASK); VM_WARN_ON_ONCE(len & ~PAGE_MASK);
/* Does the address range wrap, or is the span zero-sized? */ VM_WARN_ON_ONCE(src_start + len < src_start); VM_WARN_ON_ONCE(dst_start + len < dst_start);
err = uffd_move_lock(mm, dst_start, src_start, &dst_vma, &src_vma); if (err) goto out;
/* Re-check after taking map_changing_lock */ err = -EAGAIN; down_read(&ctx->map_changing_lock); if (likely(atomic_read(&ctx->mmap_changing))) goto out_unlock; /* * Make sure the vma is not shared, that the src and dst remap * ranges are both valid and fully within a single existing * vma. */ err = -EINVAL; if (src_vma->vm_flags & VM_SHARED) goto out_unlock; if (src_start + len > src_vma->vm_end) goto out_unlock;
if (dst_vma->vm_flags & VM_SHARED) goto out_unlock; if (dst_start + len > dst_vma->vm_end) goto out_unlock;
err = validate_move_areas(ctx, src_vma, dst_vma); if (err) goto out_unlock;
for (src_addr = src_start, dst_addr = dst_start, src_end = src_start + len; src_addr < src_end;) { spinlock_t *ptl; pmd_t dst_pmdval; unsigned long step_size;
/* * Below works because anonymous area would not have a * transparent huge PUD. If file-backed support is added, * that case would need to be handled here. */ src_pmd = mm_find_pmd(mm, src_addr); if (unlikely(!src_pmd)) { if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) { err = -ENOENT; break; } src_pmd = mm_alloc_pmd(mm, src_addr); if (unlikely(!src_pmd)) { err = -ENOMEM; break; } } dst_pmd = mm_alloc_pmd(mm, dst_addr); if (unlikely(!dst_pmd)) { err = -ENOMEM; break; }
dst_pmdval = pmdp_get_lockless(dst_pmd); /* * If the dst_pmd is mapped as THP don't override it and just * be strict. If dst_pmd changes into TPH after this check, the * move_pages_huge_pmd() will detect the change and retry * while move_pages_pte() will detect the change and fail. */ if (unlikely(pmd_trans_huge(dst_pmdval))) { err = -EEXIST; break; }
ptl = pmd_trans_huge_lock(src_pmd, src_vma); if (ptl) { /* Check if we can move the pmd without splitting it. */ if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) || !pmd_none(dst_pmdval)) { /* Can be a migration entry */ if (pmd_present(*src_pmd)) { struct folio *folio = pmd_folio(*src_pmd);
if (!is_huge_zero_folio(folio) && !PageAnonExclusive(&folio->page)) { spin_unlock(ptl); err = -EBUSY; break; } }
spin_unlock(ptl); split_huge_pmd(src_vma, src_pmd, src_addr); /* The folio will be split by move_pages_pte() */ continue; }
err = move_pages_huge_pmd(mm, dst_pmd, src_pmd, dst_pmdval, dst_vma, src_vma, dst_addr, src_addr); step_size = HPAGE_PMD_SIZE; } else { long ret;
if (pmd_none(*src_pmd)) { if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) { err = -ENOENT; break; } if (unlikely(__pte_alloc(mm, src_pmd))) { err = -ENOMEM; break; } }
if (unlikely(pte_alloc(mm, dst_pmd))) { err = -ENOMEM; break; }
ret = move_pages_ptes(mm, dst_pmd, src_pmd, dst_vma, src_vma, dst_addr, src_addr, src_end - src_addr, mode); if (ret < 0) err = ret; else step_size = ret; }
cond_resched();
if (fatal_signal_pending(current)) { /* Do not override an error */ if (!err || err == -EAGAIN) err = -EINTR; break; }
if (err) { if (err == -EAGAIN) continue; break; }
/* Proceed to the next page */ dst_addr += step_size; src_addr += step_size; moved += step_size; }
out_unlock: up_read(&ctx->map_changing_lock); uffd_move_unlock(dst_vma, src_vma);out: VM_WARN_ON_ONCE(moved < 0); VM_WARN_ON_ONCE(err > 0); VM_WARN_ON_ONCE(!moved && !err); return moved ? moved : err;}
static bool vma_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags, bool wp_async){ const struct vm_uffd_ops *ops = vma_uffd_ops(vma);
if (vma->vm_flags & (VM_DROPPABLE | VM_SHADOW_STACK)) return false;
if (!is_vm_hugetlb_page(vma) && (vma->vm_flags & VM_SPECIAL)) return false;
vm_flags &= __VM_UFFD_FLAGS;
/* * If WP is the only mode enabled and context is wp async, allow any * memory type. */ if (wp_async && (vm_flags == VM_UFFD_WP)) return true;
/* For any other mode reject VMAs that don't implement vm_uffd_ops */ if (!ops) return false;
/* * If user requested uffd-wp but not enabled pte markers for * uffd-wp, then only anonymous memory is supported */ if (!uffd_supports_wp_marker() && (vm_flags & VM_UFFD_WP) && !vma_is_anonymous(vma)) return false;
return ops->can_userfault(vma, vm_flags);}
static void userfaultfd_set_vm_flags(struct vm_area_struct *vma, vm_flags_t vm_flags){ const bool uffd_wp_changed = (vma->vm_flags ^ vm_flags) & VM_UFFD_WP;
vm_flags_reset(vma, vm_flags); /* * For shared mappings, we want to enable writenotify while * userfaultfd-wp is enabled (see vma_wants_writenotify()). We'll simply * recalculate vma->vm_page_prot whenever userfaultfd-wp changes. */ if ((vma->vm_flags & VM_SHARED) && uffd_wp_changed) vma_set_page_prot(vma);}
static void userfaultfd_set_ctx(struct vm_area_struct *vma, struct userfaultfd_ctx *ctx, vm_flags_t vm_flags){ vma_start_write(vma); vma->vm_userfaultfd_ctx = (struct vm_userfaultfd_ctx){ctx}; userfaultfd_set_vm_flags(vma, (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags);}
static void userfaultfd_reset_ctx(struct vm_area_struct *vma){ userfaultfd_set_ctx(vma, NULL, 0);}
static struct vm_area_struct *userfaultfd_clear_vma(struct vma_iterator *vmi, struct vm_area_struct *prev, struct vm_area_struct *vma, unsigned long start, unsigned long end){ struct vm_area_struct *ret; bool give_up_on_oom = false; vma_flags_t new_vma_flags = vma->flags;
vma_flags_clear_mask(&new_vma_flags, __VMA_UFFD_FLAGS);
/* * If we are modifying only and not splitting, just give up on the merge * if OOM prevents us from merging successfully. */ if (start == vma->vm_start && end == vma->vm_end) give_up_on_oom = true;
/* Reset ptes for the whole vma range if wr-protected */ if (userfaultfd_wp(vma)) uffd_wp_range(vma, start, end - start, false);
ret = vma_modify_flags_uffd(vmi, prev, vma, start, end, &new_vma_flags, NULL_VM_UFFD_CTX, give_up_on_oom);
/* * In the vma_merge() successful mprotect-like case 8: * the next vma was merged into the current one and * the current one has not been updated yet. */ if (!IS_ERR(ret)) userfaultfd_reset_ctx(ret);
return ret;}
/* Assumes mmap write lock taken, and mm_struct pinned. */static int userfaultfd_register_range(struct userfaultfd_ctx *ctx, struct vm_area_struct *vma, vm_flags_t vm_flags, unsigned long start, unsigned long end, bool wp_async){ vma_flags_t vma_flags = legacy_to_vma_flags(vm_flags); VMA_ITERATOR(vmi, ctx->mm, start); struct vm_area_struct *prev = vma_prev(&vmi); unsigned long vma_end; vma_flags_t new_vma_flags;
if (vma->vm_start < start) prev = vma;
for_each_vma_range(vmi, vma, end) { cond_resched();
VM_WARN_ON_ONCE(!vma_can_userfault(vma, vm_flags, wp_async)); VM_WARN_ON_ONCE(vma->vm_userfaultfd_ctx.ctx && vma->vm_userfaultfd_ctx.ctx != ctx); VM_WARN_ON_ONCE(!vma_test(vma, VMA_MAYWRITE_BIT));
/* * Nothing to do: this vma is already registered into this * userfaultfd and with the right tracking mode too. */ if (vma->vm_userfaultfd_ctx.ctx == ctx && vma_test_all_mask(vma, vma_flags)) goto skip;
if (vma->vm_start > start) start = vma->vm_start; vma_end = min(end, vma->vm_end);
new_vma_flags = vma->flags; vma_flags_clear_mask(&new_vma_flags, __VMA_UFFD_FLAGS); vma_flags_set_mask(&new_vma_flags, vma_flags);
vma = vma_modify_flags_uffd(&vmi, prev, vma, start, vma_end, &new_vma_flags, (struct vm_userfaultfd_ctx){ctx}, /* give_up_on_oom = */false); if (IS_ERR(vma)) return PTR_ERR(vma);
/* * In the vma_merge() successful mprotect-like case 8: * the next vma was merged into the current one and * the current one has not been updated yet. */ userfaultfd_set_ctx(vma, ctx, vm_flags);
if (is_vm_hugetlb_page(vma) && uffd_disable_huge_pmd_share(vma)) hugetlb_unshare_all_pmds(vma);
skip: prev = vma; start = vma->vm_end; }
return 0;}
static void userfaultfd_release_new(struct userfaultfd_ctx *ctx){ struct mm_struct *mm = ctx->mm; struct vm_area_struct *vma; VMA_ITERATOR(vmi, mm, 0);
/* the various vma->vm_userfaultfd_ctx still points to it */ mmap_write_lock(mm); for_each_vma(vmi, vma) { if (vma->vm_userfaultfd_ctx.ctx == ctx) userfaultfd_reset_ctx(vma); } mmap_write_unlock(mm);}
static void userfaultfd_release_all(struct mm_struct *mm, struct userfaultfd_ctx *ctx){ struct vm_area_struct *vma, *prev; VMA_ITERATOR(vmi, mm, 0);
if (!mmget_not_zero(mm)) return;
/* * Flush page faults out of all CPUs. NOTE: all page faults * must be retried without returning VM_FAULT_SIGBUS if * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx * changes while handle_userfault released the mmap_lock. So * it's critical that released is set to true (above), before * taking the mmap_lock for writing. */ mmap_write_lock(mm); prev = NULL; for_each_vma(vmi, vma) { cond_resched(); VM_WARN_ON_ONCE(!!vma->vm_userfaultfd_ctx.ctx ^ !!(vma->vm_flags & __VM_UFFD_FLAGS)); if (vma->vm_userfaultfd_ctx.ctx != ctx) { prev = vma; continue; }
vma = userfaultfd_clear_vma(&vmi, prev, vma, vma->vm_start, vma->vm_end); prev = vma; } mmap_write_unlock(mm); mmput(mm);}
static int sysctl_unprivileged_userfaultfd __read_mostly;
#ifdef CONFIG_SYSCTLstatic const struct ctl_table vm_userfaultfd_table[] = { { .procname = "unprivileged_userfaultfd", .data = &sysctl_unprivileged_userfaultfd, .maxlen = sizeof(sysctl_unprivileged_userfaultfd), .mode = 0644, .proc_handler = proc_dointvec_minmax, .extra1 = SYSCTL_ZERO, .extra2 = SYSCTL_ONE, },};#endif
static struct kmem_cache *userfaultfd_ctx_cachep __ro_after_init;
struct userfaultfd_fork_ctx { struct userfaultfd_ctx *orig; struct userfaultfd_ctx *new; struct list_head list;};
struct userfaultfd_unmap_ctx { struct userfaultfd_ctx *ctx; unsigned long start; unsigned long end; struct list_head list;};
struct userfaultfd_wait_queue { struct uffd_msg msg; wait_queue_entry_t wq; struct userfaultfd_ctx *ctx; bool waken;};
struct userfaultfd_wake_range { unsigned long start; unsigned long len;};
/* internal indication that UFFD_API ioctl was successfully executed */#define UFFD_FEATURE_INITIALIZED (1u << 31)
static bool userfaultfd_is_initialized(struct userfaultfd_ctx *ctx){ return ctx->features & UFFD_FEATURE_INITIALIZED;}
static bool userfaultfd_wp_async_ctx(struct userfaultfd_ctx *ctx){ return ctx && (ctx->features & UFFD_FEATURE_WP_ASYNC);}
/* * Whether WP_UNPOPULATED is enabled on the uffd context. It is only * meaningful when userfaultfd_wp()==true on the vma and when it's * anonymous. */bool userfaultfd_wp_unpopulated(struct vm_area_struct *vma){ struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
if (!ctx) return false;
return ctx->features & UFFD_FEATURE_WP_UNPOPULATED;}
static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode, int wake_flags, void *key){ struct userfaultfd_wake_range *range = key; int ret; struct userfaultfd_wait_queue *uwq; unsigned long start, len;
uwq = container_of(wq, struct userfaultfd_wait_queue, wq); ret = 0; /* len == 0 means wake all */ start = range->start; len = range->len; if (len && (start > uwq->msg.arg.pagefault.address || start + len <= uwq->msg.arg.pagefault.address)) goto out; WRITE_ONCE(uwq->waken, true); /* * The Program-Order guarantees provided by the scheduler * ensure uwq->waken is visible before the task is woken. */ ret = wake_up_state(wq->private, mode); if (ret) { /* * Wake only once, autoremove behavior. * * After the effect of list_del_init is visible to the other * CPUs, the waitqueue may disappear from under us, see the * !list_empty_careful() in handle_userfault(). * * try_to_wake_up() has an implicit smp_mb(), and the * wq->private is read before calling the extern function * "wake_up_state" (which in turns calls try_to_wake_up). */ list_del_init(&wq->entry); }out: return ret;}
/** * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd * context. * @ctx: [in] Pointer to the userfaultfd context. */static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx){ refcount_inc(&ctx->refcount);}
/** * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd * context. * @ctx: [in] Pointer to userfaultfd context. * * The userfaultfd context reference must have been previously acquired either * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget(). */static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx){ if (refcount_dec_and_test(&ctx->refcount)) { VM_WARN_ON_ONCE(spin_is_locked(&ctx->fault_pending_wqh.lock)); VM_WARN_ON_ONCE(waitqueue_active(&ctx->fault_pending_wqh)); VM_WARN_ON_ONCE(spin_is_locked(&ctx->fault_wqh.lock)); VM_WARN_ON_ONCE(waitqueue_active(&ctx->fault_wqh)); VM_WARN_ON_ONCE(spin_is_locked(&ctx->event_wqh.lock)); VM_WARN_ON_ONCE(waitqueue_active(&ctx->event_wqh)); VM_WARN_ON_ONCE(spin_is_locked(&ctx->fd_wqh.lock)); VM_WARN_ON_ONCE(waitqueue_active(&ctx->fd_wqh)); mmdrop(ctx->mm); kmem_cache_free(userfaultfd_ctx_cachep, ctx); }}
static inline void msg_init(struct uffd_msg *msg){ BUILD_BUG_ON(sizeof(struct uffd_msg) != 32); /* * Must use memset to zero out the paddings or kernel data is * leaked to userland. */ memset(msg, 0, sizeof(struct uffd_msg));}
static inline struct uffd_msg userfault_msg(unsigned long address, unsigned long real_address, unsigned int flags, unsigned long reason, unsigned int features){ struct uffd_msg msg;
msg_init(&msg); msg.event = UFFD_EVENT_PAGEFAULT;
msg.arg.pagefault.address = (features & UFFD_FEATURE_EXACT_ADDRESS) ? real_address : address;
/* * These flags indicate why the userfault occurred: * - UFFD_PAGEFAULT_FLAG_WP indicates a write protect fault. * - UFFD_PAGEFAULT_FLAG_MINOR indicates a minor fault. * - Neither of these flags being set indicates a MISSING fault. * * Separately, UFFD_PAGEFAULT_FLAG_WRITE indicates it was a write * fault. Otherwise, it was a read fault. */ if (flags & FAULT_FLAG_WRITE) msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE; if (reason & VM_UFFD_WP) msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP; if (reason & VM_UFFD_MINOR) msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_MINOR; if (features & UFFD_FEATURE_THREAD_ID) msg.arg.pagefault.feat.ptid = task_pid_vnr(current); return msg;}
#ifdef CONFIG_HUGETLB_PAGE/* * Same functionality as userfaultfd_must_wait below with modifications for * hugepmd ranges. */static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx, struct vm_fault *vmf, unsigned long reason){ struct vm_area_struct *vma = vmf->vma; pte_t *ptep, pte;
assert_fault_locked(vmf);
ptep = hugetlb_walk(vma, vmf->address, vma_mmu_pagesize(vma)); if (!ptep) return true;
pte = huge_ptep_get(vma->vm_mm, vmf->address, ptep);
/* * Lockless access: we're in a wait_event so it's ok if it * changes under us. */
/* Entry is still missing, wait for userspace to resolve the fault. */ if (huge_pte_none(pte)) return true; /* UFFD PTE markers require userspace to resolve the fault. */ if (pte_is_uffd_marker(pte)) return true; /* * Concurrent migration may have replaced the present PTE with a * non-marker swap entry between fault delivery and this lockless * re-check. huge_pte_write() on a swap entry decodes random offset * bits, so gate it on pte_present(). The migration completion path * will re-deliver the fault if it still needs userspace. */ if (!pte_present(pte)) return false; /* * If VMA has UFFD WP faults enabled and WP fault, wait for userspace to * resolve the fault. */ if (!huge_pte_write(pte) && (reason & VM_UFFD_WP)) return true;
return false;}#elsestatic inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx, struct vm_fault *vmf, unsigned long reason){ /* Should never get here. */ VM_WARN_ON_ONCE(1); return false;}#endif /* CONFIG_HUGETLB_PAGE */
/* * Verify the pagetables are still not ok after having registered into * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any * userfault that has already been resolved, if userfaultfd_read_iter and * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different * threads. */static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx, struct vm_fault *vmf, unsigned long reason){ struct mm_struct *mm = ctx->mm; unsigned long address = vmf->address; pgd_t *pgd; p4d_t *p4d; pud_t *pud; pmd_t *pmd, _pmd; pte_t *pte; pte_t ptent; bool ret;
assert_fault_locked(vmf);
pgd = pgd_offset(mm, address); if (!pgd_present(*pgd)) return true; p4d = p4d_offset(pgd, address); if (!p4d_present(*p4d)) return true; pud = pud_offset(p4d, address); if (!pud_present(*pud)) return true; pmd = pmd_offset(pud, address);again: _pmd = pmdp_get_lockless(pmd); if (pmd_none(_pmd)) return true;
/* * A race could arise which would result in a softleaf entry such as * migration entry unexpectedly being present in the PMD, so explicitly * check for this and bail out if so. */ if (!pmd_present(_pmd)) return false;
if (pmd_trans_huge(_pmd)) return !pmd_write(_pmd) && (reason & VM_UFFD_WP);
pte = pte_offset_map(pmd, address); if (!pte) goto again;
/* * Lockless access: we're in a wait_event so it's ok if it * changes under us. */ ptent = ptep_get(pte);
ret = true; /* Entry is still missing, wait for userspace to resolve the fault. */ if (pte_none(ptent)) goto out; /* UFFD PTE markers require userspace to resolve the fault. */ if (pte_is_uffd_marker(ptent)) goto out; /* * Concurrent swap-out / migration may have replaced the present PTE * with a non-marker swap entry between fault delivery and this * lockless re-check. pte_write() on a swap entry decodes random * offset bits, so gate it on pte_present(). The page-in path will * re-deliver the fault if it still needs userspace. */ if (!pte_present(ptent)) { ret = false; goto out; } /* * If VMA has UFFD WP faults enabled and WP fault, wait for userspace to * resolve the fault. */ if (!pte_write(ptent) && (reason & VM_UFFD_WP)) goto out;
ret = false;out: pte_unmap(pte); return ret;}
static inline unsigned int userfaultfd_get_blocking_state(unsigned int flags){ if (flags & FAULT_FLAG_INTERRUPTIBLE) return TASK_INTERRUPTIBLE;
if (flags & FAULT_FLAG_KILLABLE) return TASK_KILLABLE;
return TASK_UNINTERRUPTIBLE;}
/* * The locking rules involved in returning VM_FAULT_RETRY depending on * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and * FAULT_FLAG_KILLABLE are not straightforward. The "Caution" * recommendation in __lock_page_or_retry is not an understatement. * * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_lock must be released * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is * not set. * * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not * set, VM_FAULT_RETRY can still be returned if and only if there are * fatal_signal_pending()s, and the mmap_lock must be released before * returning it. */vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason){ struct vm_area_struct *vma = vmf->vma; struct mm_struct *mm = vma->vm_mm; struct userfaultfd_ctx *ctx; struct userfaultfd_wait_queue uwq; vm_fault_t ret = VM_FAULT_SIGBUS; bool must_wait; unsigned int blocking_state;
/* * We don't do userfault handling for the final child pid update * and when coredumping (faults triggered by get_dump_page()). */ if (current->flags & (PF_EXITING|PF_DUMPCORE)) goto out;
assert_fault_locked(vmf);
ctx = vma->vm_userfaultfd_ctx.ctx; if (!ctx) goto out;
VM_WARN_ON_ONCE(ctx->mm != mm);
/* Any unrecognized flag is a bug. */ VM_WARN_ON_ONCE(reason & ~__VM_UFFD_FLAGS); /* 0 or > 1 flags set is a bug; we expect exactly 1. */ VM_WARN_ON_ONCE(!reason || (reason & (reason - 1)));
if (ctx->features & UFFD_FEATURE_SIGBUS) goto out; if (!(vmf->flags & FAULT_FLAG_USER) && (ctx->flags & UFFD_USER_MODE_ONLY)) goto out;
/* * Check that we can return VM_FAULT_RETRY. * * NOTE: it should become possible to return VM_FAULT_RETRY * even if FAULT_FLAG_TRIED is set without leading to gup() * -EBUSY failures, if the userfaultfd is to be extended for * VM_UFFD_WP tracking and we intend to arm the userfault * without first stopping userland access to the memory. For * VM_UFFD_MISSING userfaults this is enough for now. */ if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) { /* * Validate the invariant that nowait must allow retry * to be sure not to return SIGBUS erroneously on * nowait invocations. */ VM_WARN_ON_ONCE(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);#ifdef CONFIG_DEBUG_VM if (printk_ratelimit()) { pr_warn("FAULT_FLAG_ALLOW_RETRY missing %x\n", vmf->flags); dump_stack(); }#endif goto out; }
/* * Handle nowait, not much to do other than tell it to retry * and wait. */ ret = VM_FAULT_RETRY; if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT) goto out;
if (unlikely(READ_ONCE(ctx->released))) { /* * If a concurrent release is detected, do not return * VM_FAULT_SIGBUS or VM_FAULT_NOPAGE, but instead always * return VM_FAULT_RETRY with lock released proactively. * * If we were to return VM_FAULT_SIGBUS here, the non * cooperative manager would be instead forced to * always call UFFDIO_UNREGISTER before it can safely * close the uffd, to avoid involuntary SIGBUS triggered. * * If we were to return VM_FAULT_NOPAGE, it would work for * the fault path, in which the lock will be released * later. However for GUP, faultin_page() does nothing * special on NOPAGE, so GUP would spin retrying without * releasing the mmap read lock, causing possible livelock. * * Here only VM_FAULT_RETRY would make sure the mmap lock * be released immediately, so that the thread concurrently * releasing the userfault would always make progress. */ release_fault_lock(vmf); goto out; }
/* take the reference before dropping the mmap_lock */ userfaultfd_ctx_get(ctx);
init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function); uwq.wq.private = current; uwq.msg = userfault_msg(vmf->address, vmf->real_address, vmf->flags, reason, ctx->features); uwq.ctx = ctx; uwq.waken = false;
blocking_state = userfaultfd_get_blocking_state(vmf->flags);
/* * Take the vma lock now, in order to safely call * userfaultfd_huge_must_wait() later. Since acquiring the * (sleepable) vma lock can modify the current task state, that * must be before explicitly calling set_current_state(). */ if (is_vm_hugetlb_page(vma)) hugetlb_vma_lock_read(vma);
spin_lock_irq(&ctx->fault_pending_wqh.lock); /* * After the __add_wait_queue the uwq is visible to userland * through poll/read(). */ __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq); /* * The smp_mb() after __set_current_state prevents the reads * following the spin_unlock to happen before the list_add in * __add_wait_queue. */ set_current_state(blocking_state); spin_unlock_irq(&ctx->fault_pending_wqh.lock);
if (is_vm_hugetlb_page(vma)) { must_wait = userfaultfd_huge_must_wait(ctx, vmf, reason); hugetlb_vma_unlock_read(vma); } else { must_wait = userfaultfd_must_wait(ctx, vmf, reason); }
release_fault_lock(vmf);
if (likely(must_wait && !READ_ONCE(ctx->released))) { wake_up_poll(&ctx->fd_wqh, EPOLLIN); schedule(); }
__set_current_state(TASK_RUNNING);
/* * Here we race with the list_del; list_add in * userfaultfd_ctx_read(), however because we don't ever run * list_del_init() to refile across the two lists, the prev * and next pointers will never point to self. list_add also * would never let any of the two pointers to point to * self. So list_empty_careful won't risk to see both pointers * pointing to self at any time during the list refile. The * only case where list_del_init() is called is the full * removal in the wake function and there we don't re-list_add * and it's fine not to block on the spinlock. The uwq on this * kernel stack can be released after the list_del_init. */ if (!list_empty_careful(&uwq.wq.entry)) { spin_lock_irq(&ctx->fault_pending_wqh.lock); /* * No need of list_del_init(), the uwq on the stack * will be freed shortly anyway. */ list_del(&uwq.wq.entry); spin_unlock_irq(&ctx->fault_pending_wqh.lock); }
/* * ctx may go away after this if the userfault pseudo fd is * already released. */ userfaultfd_ctx_put(ctx);
out: return ret;}
static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx, struct userfaultfd_wait_queue *ewq){ struct userfaultfd_ctx *release_new_ctx;
if (WARN_ON_ONCE(current->flags & PF_EXITING)) goto out;
ewq->ctx = ctx; init_waitqueue_entry(&ewq->wq, current); release_new_ctx = NULL;
spin_lock_irq(&ctx->event_wqh.lock); /* * After the __add_wait_queue the uwq is visible to userland * through poll/read(). */ __add_wait_queue(&ctx->event_wqh, &ewq->wq); for (;;) { set_current_state(TASK_KILLABLE); if (ewq->msg.event == 0) break; if (READ_ONCE(ctx->released) || fatal_signal_pending(current)) { /* * &ewq->wq may be queued in fork_event, but * __remove_wait_queue ignores the head * parameter. It would be a problem if it * didn't. */ __remove_wait_queue(&ctx->event_wqh, &ewq->wq); if (ewq->msg.event == UFFD_EVENT_FORK) { struct userfaultfd_ctx *new;
new = (struct userfaultfd_ctx *) (unsigned long) ewq->msg.arg.reserved.reserved1; release_new_ctx = new; } break; }
spin_unlock_irq(&ctx->event_wqh.lock);
wake_up_poll(&ctx->fd_wqh, EPOLLIN); schedule();
spin_lock_irq(&ctx->event_wqh.lock); } __set_current_state(TASK_RUNNING); spin_unlock_irq(&ctx->event_wqh.lock);
if (release_new_ctx) { userfaultfd_release_new(release_new_ctx); userfaultfd_ctx_put(release_new_ctx); }
/* * ctx may go away after this if the userfault pseudo fd is * already released. */out: atomic_dec(&ctx->mmap_changing); VM_WARN_ON_ONCE(atomic_read(&ctx->mmap_changing) < 0); userfaultfd_ctx_put(ctx);}
static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx, struct userfaultfd_wait_queue *ewq){ ewq->msg.event = 0; wake_up_locked(&ctx->event_wqh); __remove_wait_queue(&ctx->event_wqh, &ewq->wq);}
int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs){ struct userfaultfd_ctx *ctx = NULL, *octx; struct userfaultfd_fork_ctx *fctx;
octx = vma->vm_userfaultfd_ctx.ctx; if (!octx) return 0;
if (!(octx->features & UFFD_FEATURE_EVENT_FORK)) { userfaultfd_reset_ctx(vma); return 0; }
list_for_each_entry(fctx, fcs, list) if (fctx->orig == octx) { ctx = fctx->new; break; }
if (!ctx) { fctx = kmalloc_obj(*fctx); if (!fctx) return -ENOMEM;
ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL); if (!ctx) { kfree(fctx); return -ENOMEM; }
refcount_set(&ctx->refcount, 1); ctx->flags = octx->flags; ctx->features = octx->features; ctx->released = false; init_rwsem(&ctx->map_changing_lock); atomic_set(&ctx->mmap_changing, 0); ctx->mm = vma->vm_mm; mmgrab(ctx->mm);
userfaultfd_ctx_get(octx); down_write(&octx->map_changing_lock); atomic_inc(&octx->mmap_changing); up_write(&octx->map_changing_lock); fctx->orig = octx; fctx->new = ctx; list_add_tail(&fctx->list, fcs); }
vma->vm_userfaultfd_ctx.ctx = ctx; return 0;}
static void dup_fctx(struct userfaultfd_fork_ctx *fctx){ struct userfaultfd_ctx *ctx = fctx->orig; struct userfaultfd_wait_queue ewq;
msg_init(&ewq.msg);
ewq.msg.event = UFFD_EVENT_FORK; ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new;
userfaultfd_event_wait_completion(ctx, &ewq);}
void dup_userfaultfd_complete(struct list_head *fcs){ struct userfaultfd_fork_ctx *fctx, *n;
list_for_each_entry_safe(fctx, n, fcs, list) { dup_fctx(fctx); list_del(&fctx->list); kfree(fctx); }}
void dup_userfaultfd_fail(struct list_head *fcs){ struct userfaultfd_fork_ctx *fctx, *n;
/* * An error has occurred on fork, we will tear memory down, but have * allocated memory for fctx's and raised reference counts for both the * original and child contexts (and on the mm for each as a result). * * These would ordinarily be taken care of by a user handling the event, * but we are no longer doing so, so manually clean up here. * * mm tear down will take care of cleaning up VMA contexts. */ list_for_each_entry_safe(fctx, n, fcs, list) { struct userfaultfd_ctx *octx = fctx->orig; struct userfaultfd_ctx *ctx = fctx->new;
atomic_dec(&octx->mmap_changing); VM_WARN_ON_ONCE(atomic_read(&octx->mmap_changing) < 0); userfaultfd_ctx_put(octx); userfaultfd_ctx_put(ctx);
list_del(&fctx->list); kfree(fctx); }}
void mremap_userfaultfd_prep(struct vm_area_struct *vma, struct vm_userfaultfd_ctx *vm_ctx){ struct userfaultfd_ctx *ctx;
ctx = vma->vm_userfaultfd_ctx.ctx;
if (!ctx) return;
if (ctx->features & UFFD_FEATURE_EVENT_REMAP) { vm_ctx->ctx = ctx; userfaultfd_ctx_get(ctx); down_write(&ctx->map_changing_lock); atomic_inc(&ctx->mmap_changing); up_write(&ctx->map_changing_lock); } else { /* Drop uffd context if remap feature not enabled */ userfaultfd_reset_ctx(vma); }}
void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx, unsigned long from, unsigned long to, unsigned long len){ struct userfaultfd_ctx *ctx = vm_ctx->ctx; struct userfaultfd_wait_queue ewq;
if (!ctx) return;
msg_init(&ewq.msg);
ewq.msg.event = UFFD_EVENT_REMAP; ewq.msg.arg.remap.from = from; ewq.msg.arg.remap.to = to; ewq.msg.arg.remap.len = len;
userfaultfd_event_wait_completion(ctx, &ewq);}
void mremap_userfaultfd_fail(struct vm_userfaultfd_ctx *vm_ctx){ struct userfaultfd_ctx *ctx = vm_ctx->ctx;
if (!ctx) return;
atomic_dec(&ctx->mmap_changing); VM_WARN_ON_ONCE(atomic_read(&ctx->mmap_changing) < 0); userfaultfd_ctx_put(ctx);}
bool userfaultfd_remove(struct vm_area_struct *vma, unsigned long start, unsigned long end){ struct mm_struct *mm = vma->vm_mm; struct userfaultfd_ctx *ctx; struct userfaultfd_wait_queue ewq;
ctx = vma->vm_userfaultfd_ctx.ctx; if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE)) return true;
userfaultfd_ctx_get(ctx); down_write(&ctx->map_changing_lock); atomic_inc(&ctx->mmap_changing); up_write(&ctx->map_changing_lock); mmap_read_unlock(mm);
msg_init(&ewq.msg);
ewq.msg.event = UFFD_EVENT_REMOVE; ewq.msg.arg.remove.start = start; ewq.msg.arg.remove.end = end;
userfaultfd_event_wait_completion(ctx, &ewq);
return false;}
static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps, unsigned long start, unsigned long end){ struct userfaultfd_unmap_ctx *unmap_ctx;
list_for_each_entry(unmap_ctx, unmaps, list) if (unmap_ctx->ctx == ctx && unmap_ctx->start == start && unmap_ctx->end == end) return true;
return false;}
int userfaultfd_unmap_prep(struct vm_area_struct *vma, unsigned long start, unsigned long end, struct list_head *unmaps){ struct userfaultfd_unmap_ctx *unmap_ctx; struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) || has_unmap_ctx(ctx, unmaps, start, end)) return 0;
unmap_ctx = kzalloc_obj(*unmap_ctx); if (!unmap_ctx) return -ENOMEM;
userfaultfd_ctx_get(ctx); down_write(&ctx->map_changing_lock); atomic_inc(&ctx->mmap_changing); up_write(&ctx->map_changing_lock); unmap_ctx->ctx = ctx; unmap_ctx->start = start; unmap_ctx->end = end; list_add_tail(&unmap_ctx->list, unmaps);
return 0;}
void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf){ struct userfaultfd_unmap_ctx *ctx, *n; struct userfaultfd_wait_queue ewq;
list_for_each_entry_safe(ctx, n, uf, list) { msg_init(&ewq.msg);
ewq.msg.event = UFFD_EVENT_UNMAP; ewq.msg.arg.remove.start = ctx->start; ewq.msg.arg.remove.end = ctx->end;
userfaultfd_event_wait_completion(ctx->ctx, &ewq);
list_del(&ctx->list); kfree(ctx); }}
static int userfaultfd_release(struct inode *inode, struct file *file){ struct userfaultfd_ctx *ctx = file->private_data; struct mm_struct *mm = ctx->mm; /* len == 0 means wake all */ struct userfaultfd_wake_range range = { .len = 0, };
WRITE_ONCE(ctx->released, true);
userfaultfd_release_all(mm, ctx);
/* * After no new page faults can wait on this fault_*wqh, flush * the last page faults that may have been already waiting on * the fault_*wqh. */ spin_lock_irq(&ctx->fault_pending_wqh.lock); __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range); __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range); spin_unlock_irq(&ctx->fault_pending_wqh.lock);
/* Flush pending events that may still wait on event_wqh */ wake_up_all(&ctx->event_wqh);
wake_up_poll(&ctx->fd_wqh, EPOLLHUP); userfaultfd_ctx_put(ctx); return 0;}
/* fault_pending_wqh.lock must be hold by the caller */static inline struct userfaultfd_wait_queue *find_userfault_in( wait_queue_head_t *wqh){ wait_queue_entry_t *wq; struct userfaultfd_wait_queue *uwq;
lockdep_assert_held(&wqh->lock);
uwq = NULL; if (!waitqueue_active(wqh)) goto out; /* walk in reverse to provide FIFO behavior to read userfaults */ wq = list_last_entry(&wqh->head, typeof(*wq), entry); uwq = container_of(wq, struct userfaultfd_wait_queue, wq);out: return uwq;}
static inline struct userfaultfd_wait_queue *find_userfault( struct userfaultfd_ctx *ctx){ return find_userfault_in(&ctx->fault_pending_wqh);}
static inline struct userfaultfd_wait_queue *find_userfault_evt( struct userfaultfd_ctx *ctx){ return find_userfault_in(&ctx->event_wqh);}
static __poll_t userfaultfd_poll(struct file *file, poll_table *wait){ struct userfaultfd_ctx *ctx = file->private_data; __poll_t ret;
poll_wait(file, &ctx->fd_wqh, wait);
if (!userfaultfd_is_initialized(ctx)) return EPOLLERR;
/* * poll() never guarantees that read won't block. * userfaults can be waken before they're read(). */ if (unlikely(!(file->f_flags & O_NONBLOCK))) return EPOLLERR; /* * lockless access to see if there are pending faults * __pollwait last action is the add_wait_queue but * the spin_unlock would allow the waitqueue_active to * pass above the actual list_add inside * add_wait_queue critical section. So use a full * memory barrier to serialize the list_add write of * add_wait_queue() with the waitqueue_active read * below. */ ret = 0; smp_mb(); if (waitqueue_active(&ctx->fault_pending_wqh)) ret = EPOLLIN; else if (waitqueue_active(&ctx->event_wqh)) ret = EPOLLIN;
return ret;}
static const struct file_operations userfaultfd_fops;
static int resolve_userfault_fork(struct userfaultfd_ctx *new, struct inode *inode, struct uffd_msg *msg){ int fd;
fd = anon_inode_create_getfd("[userfaultfd]", &userfaultfd_fops, new, O_RDONLY | (new->flags & UFFD_SHARED_FCNTL_FLAGS), inode); if (fd < 0) return fd;
msg->arg.reserved.reserved1 = 0; msg->arg.fork.ufd = fd; return 0;}
static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait, struct uffd_msg *msg, struct inode *inode){ ssize_t ret; DECLARE_WAITQUEUE(wait, current); struct userfaultfd_wait_queue *uwq; /* * Handling fork event requires sleeping operations, so * we drop the event_wqh lock, then do these ops, then * lock it back and wake up the waiter. While the lock is * dropped the ewq may go away so we keep track of it * carefully. */ LIST_HEAD(fork_event); struct userfaultfd_ctx *fork_nctx = NULL;
/* always take the fd_wqh lock before the fault_pending_wqh lock */ spin_lock_irq(&ctx->fd_wqh.lock); __add_wait_queue(&ctx->fd_wqh, &wait); for (;;) { set_current_state(TASK_INTERRUPTIBLE); spin_lock(&ctx->fault_pending_wqh.lock); uwq = find_userfault(ctx); if (uwq) { /* * Use a seqcount to repeat the lockless check * in wake_userfault() to avoid missing * wakeups because during the refile both * waitqueue could become empty if this is the * only userfault. */ write_seqcount_begin(&ctx->refile_seq);
/* * The fault_pending_wqh.lock prevents the uwq * to disappear from under us. * * Refile this userfault from * fault_pending_wqh to fault_wqh, it's not * pending anymore after we read it. * * Use list_del() by hand (as * userfaultfd_wake_function also uses * list_del_init() by hand) to be sure nobody * changes __remove_wait_queue() to use * list_del_init() in turn breaking the * !list_empty_careful() check in * handle_userfault(). The uwq->wq.head list * must never be empty at any time during the * refile, or the waitqueue could disappear * from under us. The "wait_queue_head_t" * parameter of __remove_wait_queue() is unused * anyway. */ list_del(&uwq->wq.entry); add_wait_queue(&ctx->fault_wqh, &uwq->wq);
write_seqcount_end(&ctx->refile_seq);
/* careful to always initialize msg if ret == 0 */ *msg = uwq->msg; spin_unlock(&ctx->fault_pending_wqh.lock); ret = 0; break; } spin_unlock(&ctx->fault_pending_wqh.lock);
spin_lock(&ctx->event_wqh.lock); uwq = find_userfault_evt(ctx); if (uwq) { *msg = uwq->msg;
if (uwq->msg.event == UFFD_EVENT_FORK) { fork_nctx = (struct userfaultfd_ctx *) (unsigned long) uwq->msg.arg.reserved.reserved1; list_move(&uwq->wq.entry, &fork_event); /* * fork_nctx can be freed as soon as * we drop the lock, unless we take a * reference on it. */ userfaultfd_ctx_get(fork_nctx); spin_unlock(&ctx->event_wqh.lock); ret = 0; break; }
userfaultfd_event_complete(ctx, uwq); spin_unlock(&ctx->event_wqh.lock); ret = 0; break; } spin_unlock(&ctx->event_wqh.lock);
if (signal_pending(current)) { ret = -ERESTARTSYS; break; } if (no_wait) { ret = -EAGAIN; break; } spin_unlock_irq(&ctx->fd_wqh.lock); schedule(); spin_lock_irq(&ctx->fd_wqh.lock); } __remove_wait_queue(&ctx->fd_wqh, &wait); __set_current_state(TASK_RUNNING); spin_unlock_irq(&ctx->fd_wqh.lock);
if (!ret && msg->event == UFFD_EVENT_FORK) { ret = resolve_userfault_fork(fork_nctx, inode, msg); spin_lock_irq(&ctx->event_wqh.lock); if (!list_empty(&fork_event)) { /* * The fork thread didn't abort, so we can * drop the temporary refcount. */ userfaultfd_ctx_put(fork_nctx);
uwq = list_first_entry(&fork_event, typeof(*uwq), wq.entry); /* * If fork_event list wasn't empty and in turn * the event wasn't already released by fork * (the event is allocated on fork kernel * stack), put the event back to its place in * the event_wq. fork_event head will be freed * as soon as we return so the event cannot * stay queued there no matter the current * "ret" value. */ list_del(&uwq->wq.entry); __add_wait_queue(&ctx->event_wqh, &uwq->wq);
/* * Leave the event in the waitqueue and report * error to userland if we failed to resolve * the userfault fork. */ if (likely(!ret)) userfaultfd_event_complete(ctx, uwq); } else { /* * Here the fork thread aborted and the * refcount from the fork thread on fork_nctx * has already been released. We still hold * the reference we took before releasing the * lock above. If resolve_userfault_fork * failed we've to drop it because the * fork_nctx has to be freed in such case. If * it succeeded we'll hold it because the new * uffd references it. */ if (ret) userfaultfd_ctx_put(fork_nctx); } spin_unlock_irq(&ctx->event_wqh.lock); }
return ret;}
static ssize_t userfaultfd_read_iter(struct kiocb *iocb, struct iov_iter *to){ struct file *file = iocb->ki_filp; struct userfaultfd_ctx *ctx = file->private_data; ssize_t _ret, ret = 0; struct uffd_msg msg; struct inode *inode = file_inode(file); bool no_wait;
if (!userfaultfd_is_initialized(ctx)) return -EINVAL;
no_wait = file->f_flags & O_NONBLOCK || iocb->ki_flags & IOCB_NOWAIT; for (;;) { if (iov_iter_count(to) < sizeof(msg)) return ret ? ret : -EINVAL; _ret = userfaultfd_ctx_read(ctx, no_wait, &msg, inode); if (_ret < 0) return ret ? ret : _ret; _ret = !copy_to_iter_full(&msg, sizeof(msg), to); if (_ret) return ret ? ret : -EFAULT; ret += sizeof(msg); /* * Allow to read more than one fault at time but only * block if waiting for the very first one. */ no_wait = true; }}
static void __wake_userfault(struct userfaultfd_ctx *ctx, struct userfaultfd_wake_range *range){ spin_lock_irq(&ctx->fault_pending_wqh.lock); /* wake all in the range and autoremove */ if (waitqueue_active(&ctx->fault_pending_wqh)) __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, range); if (waitqueue_active(&ctx->fault_wqh)) __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, range); spin_unlock_irq(&ctx->fault_pending_wqh.lock);}
static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx, struct userfaultfd_wake_range *range){ unsigned seq; bool need_wakeup;
/* * To be sure waitqueue_active() is not reordered by the CPU * before the pagetable update, use an explicit SMP memory * barrier here. PT lock release or mmap_read_unlock(mm) still * have release semantics that can allow the * waitqueue_active() to be reordered before the pte update. */ smp_mb();
/* * Use waitqueue_active because it's very frequent to * change the address space atomically even if there are no * userfaults yet. So we take the spinlock only when we're * sure we've userfaults to wake. */ do { seq = read_seqcount_begin(&ctx->refile_seq); need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) || waitqueue_active(&ctx->fault_wqh); cond_resched(); } while (read_seqcount_retry(&ctx->refile_seq, seq)); if (need_wakeup) __wake_userfault(ctx, range);}
static __always_inline int validate_unaligned_range( struct mm_struct *mm, __u64 start, __u64 len){ __u64 task_size = mm->task_size;
if (len & ~PAGE_MASK) return -EINVAL; if (!len) return -EINVAL; if (start >= task_size) return -EINVAL; if (len > task_size - start) return -EINVAL; if (start + len <= start) return -EINVAL; return 0;}
static __always_inline int validate_range(struct mm_struct *mm, __u64 start, __u64 len){ if (start & ~PAGE_MASK) return -EINVAL;
return validate_unaligned_range(mm, start, len);}
static int userfaultfd_register(struct userfaultfd_ctx *ctx, unsigned long arg){ struct mm_struct *mm = ctx->mm; struct vm_area_struct *vma, *cur; int ret; struct uffdio_register uffdio_register; struct uffdio_register __user *user_uffdio_register; vm_flags_t vm_flags; bool found; bool basic_ioctls; unsigned long start, end; struct vma_iterator vmi; bool wp_async = userfaultfd_wp_async_ctx(ctx);
user_uffdio_register = (struct uffdio_register __user *) arg;
ret = -EFAULT; if (copy_from_user(&uffdio_register, user_uffdio_register, sizeof(uffdio_register)-sizeof(__u64))) goto out;
ret = -EINVAL; if (!uffdio_register.mode) goto out; if (uffdio_register.mode & ~UFFD_API_REGISTER_MODES) goto out; vm_flags = 0; if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING) vm_flags |= VM_UFFD_MISSING; if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) { if (!pgtable_supports_uffd_wp()) goto out;
vm_flags |= VM_UFFD_WP; } if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR goto out;#endif vm_flags |= VM_UFFD_MINOR; }
ret = validate_range(mm, uffdio_register.range.start, uffdio_register.range.len); if (ret) goto out;
start = uffdio_register.range.start; end = start + uffdio_register.range.len;
ret = -ENOMEM; if (!mmget_not_zero(mm)) goto out;
ret = -EINVAL; mmap_write_lock(mm); vma_iter_init(&vmi, mm, start); vma = vma_find(&vmi, end); if (!vma) goto out_unlock;
/* * If the first vma contains huge pages, make sure start address * is aligned to huge page size. */ if (is_vm_hugetlb_page(vma)) { unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
if (start & (vma_hpagesize - 1)) goto out_unlock; }
/* * Search for not compatible vmas. */ found = false; basic_ioctls = false; cur = vma; do { cond_resched();
VM_WARN_ON_ONCE(!!cur->vm_userfaultfd_ctx.ctx ^ !!(cur->vm_flags & __VM_UFFD_FLAGS));
/* check not compatible vmas */ ret = -EINVAL; if (!vma_can_userfault(cur, vm_flags, wp_async)) goto out_unlock;
/* * UFFDIO_COPY will fill file holes even without * PROT_WRITE. This check enforces that if this is a * MAP_SHARED, the process has write permission to the backing * file. If VM_MAYWRITE is set it also enforces that on a * MAP_SHARED vma: there is no F_WRITE_SEAL and no further * F_WRITE_SEAL can be taken until the vma is destroyed. */ ret = -EPERM; if (unlikely(!(cur->vm_flags & VM_MAYWRITE))) goto out_unlock;
/* * If this vma contains ending address, and huge pages * check alignment. */ if (is_vm_hugetlb_page(cur) && end <= cur->vm_end && end > cur->vm_start) { unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
ret = -EINVAL;
if (end & (vma_hpagesize - 1)) goto out_unlock; } if ((vm_flags & VM_UFFD_WP) && !(cur->vm_flags & VM_MAYWRITE)) goto out_unlock;
/* * Check that this vma isn't already owned by a * different userfaultfd. We can't allow more than one * userfaultfd to own a single vma simultaneously or we * wouldn't know which one to deliver the userfaults to. */ ret = -EBUSY; if (cur->vm_userfaultfd_ctx.ctx && cur->vm_userfaultfd_ctx.ctx != ctx) goto out_unlock;
/* * Note vmas containing huge pages */ if (is_vm_hugetlb_page(cur)) basic_ioctls = true;
found = true; } for_each_vma_range(vmi, cur, end); VM_WARN_ON_ONCE(!found);
ret = userfaultfd_register_range(ctx, vma, vm_flags, start, end, wp_async);
out_unlock: mmap_write_unlock(mm); mmput(mm); if (!ret) { __u64 ioctls_out;
ioctls_out = basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC : UFFD_API_RANGE_IOCTLS;
/* * Declare the WP ioctl only if the WP mode is * specified and all checks passed with the range */ if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_WP)) ioctls_out &= ~((__u64)1 << _UFFDIO_WRITEPROTECT);
/* CONTINUE ioctl is only supported for MINOR ranges. */ if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR)) ioctls_out &= ~((__u64)1 << _UFFDIO_CONTINUE);
/* * Now that we scanned all vmas we can already tell * userland which ioctls methods are guaranteed to * succeed on this range. */ if (put_user(ioctls_out, &user_uffdio_register->ioctls)) ret = -EFAULT; }out: return ret;}
static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, unsigned long arg){ struct mm_struct *mm = ctx->mm; struct vm_area_struct *vma, *prev, *cur; int ret; struct uffdio_range uffdio_unregister; bool found; unsigned long start, end, vma_end; const void __user *buf = (void __user *)arg; struct vma_iterator vmi; bool wp_async = userfaultfd_wp_async_ctx(ctx);
ret = -EFAULT; if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister))) goto out;
ret = validate_range(mm, uffdio_unregister.start, uffdio_unregister.len); if (ret) goto out;
start = uffdio_unregister.start; end = start + uffdio_unregister.len;
ret = -ENOMEM; if (!mmget_not_zero(mm)) goto out;
mmap_write_lock(mm); ret = -EINVAL; vma_iter_init(&vmi, mm, start); vma = vma_find(&vmi, end); if (!vma) goto out_unlock;
/* * If the first vma contains huge pages, make sure start address * is aligned to huge page size. */ if (is_vm_hugetlb_page(vma)) { unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
if (start & (vma_hpagesize - 1)) goto out_unlock; }
/* * Search for not compatible vmas. */ found = false; cur = vma; do { cond_resched();
VM_WARN_ON_ONCE(!!cur->vm_userfaultfd_ctx.ctx ^ !!(cur->vm_flags & __VM_UFFD_FLAGS));
/* * Prevent unregistering through a different userfaultfd than * the one used for registration. */ if (cur->vm_userfaultfd_ctx.ctx && cur->vm_userfaultfd_ctx.ctx != ctx) goto out_unlock;
/* * Check not compatible vmas, not strictly required * here as not compatible vmas cannot have an * userfaultfd_ctx registered on them, but this * provides for more strict behavior to notice * unregistration errors. */ if (!vma_can_userfault(cur, cur->vm_flags, wp_async)) goto out_unlock;
found = true; } for_each_vma_range(vmi, cur, end); VM_WARN_ON_ONCE(!found);
vma_iter_set(&vmi, start); prev = vma_prev(&vmi); if (vma->vm_start < start) prev = vma;
ret = 0; for_each_vma_range(vmi, vma, end) { cond_resched();
/* VMA not registered with userfaultfd. */ if (!vma->vm_userfaultfd_ctx.ctx) goto skip;
VM_WARN_ON_ONCE(vma->vm_userfaultfd_ctx.ctx != ctx); VM_WARN_ON_ONCE(!vma_can_userfault(vma, vma->vm_flags, wp_async)); VM_WARN_ON_ONCE(!(vma->vm_flags & VM_MAYWRITE));
if (vma->vm_start > start) start = vma->vm_start; vma_end = min(end, vma->vm_end);
if (userfaultfd_missing(vma)) { /* * Wake any concurrent pending userfault while * we unregister, so they will not hang * permanently and it avoids userland to call * UFFDIO_WAKE explicitly. */ struct userfaultfd_wake_range range; range.start = start; range.len = vma_end - start; wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range); }
vma = userfaultfd_clear_vma(&vmi, prev, vma, start, vma_end); if (IS_ERR(vma)) { ret = PTR_ERR(vma); break; }
skip: prev = vma; start = vma->vm_end; }
out_unlock: mmap_write_unlock(mm); mmput(mm);out: return ret;}
/* * userfaultfd_wake may be used in combination with the * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches. */static int userfaultfd_wake(struct userfaultfd_ctx *ctx, unsigned long arg){ int ret; struct uffdio_range uffdio_wake; struct userfaultfd_wake_range range; const void __user *buf = (void __user *)arg;
ret = -EFAULT; if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake))) goto out;
ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len); if (ret) goto out;
range.start = uffdio_wake.start; range.len = uffdio_wake.len;
/* * len == 0 means wake all and we don't want to wake all here, * so check it again to be sure. */ VM_WARN_ON_ONCE(!range.len);
wake_userfault(ctx, &range); ret = 0;
out: return ret;}
static int userfaultfd_copy(struct userfaultfd_ctx *ctx, unsigned long arg){ __s64 ret; struct uffdio_copy uffdio_copy; struct uffdio_copy __user *user_uffdio_copy; struct userfaultfd_wake_range range; uffd_flags_t flags = 0;
user_uffdio_copy = (struct uffdio_copy __user *) arg;
ret = -EAGAIN; if (unlikely(atomic_read(&ctx->mmap_changing))) { if (unlikely(put_user(ret, &user_uffdio_copy->copy))) return -EFAULT; goto out; }
ret = -EFAULT; if (copy_from_user(&uffdio_copy, user_uffdio_copy, /* don't copy "copy" last field */ sizeof(uffdio_copy)-sizeof(__s64))) goto out;
ret = validate_unaligned_range(ctx->mm, uffdio_copy.src, uffdio_copy.len); if (ret) goto out; ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len); if (ret) goto out;
ret = -EINVAL; if (uffdio_copy.mode & ~(UFFDIO_COPY_MODE_DONTWAKE|UFFDIO_COPY_MODE_WP)) goto out; if (uffdio_copy.mode & UFFDIO_COPY_MODE_WP) flags |= MFILL_ATOMIC_WP; if (mmget_not_zero(ctx->mm)) { ret = mfill_atomic_copy(ctx, uffdio_copy.dst, uffdio_copy.src, uffdio_copy.len, flags); mmput(ctx->mm); } else { return -ESRCH; } if (unlikely(put_user(ret, &user_uffdio_copy->copy))) return -EFAULT; if (ret < 0) goto out; VM_WARN_ON_ONCE(!ret); /* len == 0 would wake all */ range.len = ret; if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) { range.start = uffdio_copy.dst; wake_userfault(ctx, &range); } ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;out: return ret;}
static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx, unsigned long arg){ __s64 ret; struct uffdio_zeropage uffdio_zeropage; struct uffdio_zeropage __user *user_uffdio_zeropage; struct userfaultfd_wake_range range;
user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
ret = -EAGAIN; if (unlikely(atomic_read(&ctx->mmap_changing))) { if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage))) return -EFAULT; goto out; }
ret = -EFAULT; if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage, /* don't copy "zeropage" last field */ sizeof(uffdio_zeropage)-sizeof(__s64))) goto out;
ret = validate_range(ctx->mm, uffdio_zeropage.range.start, uffdio_zeropage.range.len); if (ret) goto out; ret = -EINVAL; if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE) goto out;
if (mmget_not_zero(ctx->mm)) { ret = mfill_atomic_zeropage(ctx, uffdio_zeropage.range.start, uffdio_zeropage.range.len); mmput(ctx->mm); } else { return -ESRCH; } if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage))) return -EFAULT; if (ret < 0) goto out; /* len == 0 would wake all */ VM_WARN_ON_ONCE(!ret); range.len = ret; if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) { range.start = uffdio_zeropage.range.start; wake_userfault(ctx, &range); } ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;out: return ret;}
static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx, unsigned long arg){ int ret; struct uffdio_writeprotect uffdio_wp; struct uffdio_writeprotect __user *user_uffdio_wp; struct userfaultfd_wake_range range; bool mode_wp, mode_dontwake;
if (atomic_read(&ctx->mmap_changing)) return -EAGAIN;
user_uffdio_wp = (struct uffdio_writeprotect __user *) arg;
if (copy_from_user(&uffdio_wp, user_uffdio_wp, sizeof(struct uffdio_writeprotect))) return -EFAULT;
ret = validate_range(ctx->mm, uffdio_wp.range.start, uffdio_wp.range.len); if (ret) return ret;
if (uffdio_wp.mode & ~(UFFDIO_WRITEPROTECT_MODE_DONTWAKE | UFFDIO_WRITEPROTECT_MODE_WP)) return -EINVAL;
mode_wp = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP; mode_dontwake = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE;
if (mode_wp && mode_dontwake) return -EINVAL;
if (mmget_not_zero(ctx->mm)) { ret = mwriteprotect_range(ctx, uffdio_wp.range.start, uffdio_wp.range.len, mode_wp); mmput(ctx->mm); } else { return -ESRCH; }
if (ret) return ret;
if (!mode_wp && !mode_dontwake) { range.start = uffdio_wp.range.start; range.len = uffdio_wp.range.len; wake_userfault(ctx, &range); } return ret;}
static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg){ __s64 ret; struct uffdio_continue uffdio_continue; struct uffdio_continue __user *user_uffdio_continue; struct userfaultfd_wake_range range; uffd_flags_t flags = 0;
user_uffdio_continue = (struct uffdio_continue __user *)arg;
ret = -EAGAIN; if (unlikely(atomic_read(&ctx->mmap_changing))) { if (unlikely(put_user(ret, &user_uffdio_continue->mapped))) return -EFAULT; goto out; }
ret = -EFAULT; if (copy_from_user(&uffdio_continue, user_uffdio_continue, /* don't copy the output fields */ sizeof(uffdio_continue) - (sizeof(__s64)))) goto out;
ret = validate_range(ctx->mm, uffdio_continue.range.start, uffdio_continue.range.len); if (ret) goto out;
ret = -EINVAL; if (uffdio_continue.mode & ~(UFFDIO_CONTINUE_MODE_DONTWAKE | UFFDIO_CONTINUE_MODE_WP)) goto out; if (uffdio_continue.mode & UFFDIO_CONTINUE_MODE_WP) flags |= MFILL_ATOMIC_WP;
if (mmget_not_zero(ctx->mm)) { ret = mfill_atomic_continue(ctx, uffdio_continue.range.start, uffdio_continue.range.len, flags); mmput(ctx->mm); } else { return -ESRCH; }
if (unlikely(put_user(ret, &user_uffdio_continue->mapped))) return -EFAULT; if (ret < 0) goto out;
/* len == 0 would wake all */ VM_WARN_ON_ONCE(!ret); range.len = ret; if (!(uffdio_continue.mode & UFFDIO_CONTINUE_MODE_DONTWAKE)) { range.start = uffdio_continue.range.start; wake_userfault(ctx, &range); } ret = range.len == uffdio_continue.range.len ? 0 : -EAGAIN;
out: return ret;}
static inline int userfaultfd_poison(struct userfaultfd_ctx *ctx, unsigned long arg){ __s64 ret; struct uffdio_poison uffdio_poison; struct uffdio_poison __user *user_uffdio_poison; struct userfaultfd_wake_range range;
user_uffdio_poison = (struct uffdio_poison __user *)arg;
ret = -EAGAIN; if (unlikely(atomic_read(&ctx->mmap_changing))) { if (unlikely(put_user(ret, &user_uffdio_poison->updated))) return -EFAULT; goto out; }
ret = -EFAULT; if (copy_from_user(&uffdio_poison, user_uffdio_poison, /* don't copy the output fields */ sizeof(uffdio_poison) - (sizeof(__s64)))) goto out;
ret = validate_range(ctx->mm, uffdio_poison.range.start, uffdio_poison.range.len); if (ret) goto out;
ret = -EINVAL; if (uffdio_poison.mode & ~UFFDIO_POISON_MODE_DONTWAKE) goto out;
if (mmget_not_zero(ctx->mm)) { ret = mfill_atomic_poison(ctx, uffdio_poison.range.start, uffdio_poison.range.len, 0); mmput(ctx->mm); } else { return -ESRCH; }
if (unlikely(put_user(ret, &user_uffdio_poison->updated))) return -EFAULT; if (ret < 0) goto out;
/* len == 0 would wake all */ VM_WARN_ON_ONCE(!ret); range.len = ret; if (!(uffdio_poison.mode & UFFDIO_POISON_MODE_DONTWAKE)) { range.start = uffdio_poison.range.start; wake_userfault(ctx, &range); } ret = range.len == uffdio_poison.range.len ? 0 : -EAGAIN;
out: return ret;}
bool userfaultfd_wp_async(struct vm_area_struct *vma){ return userfaultfd_wp_async_ctx(vma->vm_userfaultfd_ctx.ctx);}
static inline unsigned int uffd_ctx_features(__u64 user_features){ /* * For the current set of features the bits just coincide. Set * UFFD_FEATURE_INITIALIZED to mark the features as enabled. */ return (unsigned int)user_features | UFFD_FEATURE_INITIALIZED;}
static int userfaultfd_move(struct userfaultfd_ctx *ctx, unsigned long arg){ __s64 ret; struct uffdio_move uffdio_move; struct uffdio_move __user *user_uffdio_move; struct userfaultfd_wake_range range; struct mm_struct *mm = ctx->mm;
user_uffdio_move = (struct uffdio_move __user *) arg;
ret = -EAGAIN; if (unlikely(atomic_read(&ctx->mmap_changing))) { if (unlikely(put_user(ret, &user_uffdio_move->move))) return -EFAULT; goto out; }
if (copy_from_user(&uffdio_move, user_uffdio_move, /* don't copy "move" last field */ sizeof(uffdio_move)-sizeof(__s64))) return -EFAULT;
/* Do not allow cross-mm moves. */ if (mm != current->mm) return -EINVAL;
ret = validate_range(mm, uffdio_move.dst, uffdio_move.len); if (ret) return ret;
ret = validate_range(mm, uffdio_move.src, uffdio_move.len); if (ret) return ret;
if (uffdio_move.mode & ~(UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES| UFFDIO_MOVE_MODE_DONTWAKE)) return -EINVAL;
if (mmget_not_zero(mm)) { ret = move_pages(ctx, uffdio_move.dst, uffdio_move.src, uffdio_move.len, uffdio_move.mode); mmput(mm); } else { return -ESRCH; }
if (unlikely(put_user(ret, &user_uffdio_move->move))) return -EFAULT; if (ret < 0) goto out;
/* len == 0 would wake all */ VM_WARN_ON(!ret); range.len = ret; if (!(uffdio_move.mode & UFFDIO_MOVE_MODE_DONTWAKE)) { range.start = uffdio_move.dst; wake_userfault(ctx, &range); } ret = range.len == uffdio_move.len ? 0 : -EAGAIN;
out: return ret;}
/* * userland asks for a certain API version and we return which bits * and ioctl commands are implemented in this kernel for such API * version or -EINVAL if unknown. */static int userfaultfd_api(struct userfaultfd_ctx *ctx, unsigned long arg){ struct uffdio_api uffdio_api; void __user *buf = (void __user *)arg; unsigned int ctx_features; int ret; __u64 features;
ret = -EFAULT; if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api))) goto out; features = uffdio_api.features; ret = -EINVAL; if (uffdio_api.api != UFFD_API) goto err_out; ret = -EPERM; if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE)) goto err_out;
/* WP_ASYNC relies on WP_UNPOPULATED, choose it unconditionally */ if (features & UFFD_FEATURE_WP_ASYNC) features |= UFFD_FEATURE_WP_UNPOPULATED;
/* report all available features and ioctls to userland */ uffdio_api.features = UFFD_API_FEATURES;#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR uffdio_api.features &= ~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);#endif if (!pgtable_supports_uffd_wp()) uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
if (!uffd_supports_wp_marker()) { uffdio_api.features &= ~UFFD_FEATURE_WP_HUGETLBFS_SHMEM; uffdio_api.features &= ~UFFD_FEATURE_WP_UNPOPULATED; uffdio_api.features &= ~UFFD_FEATURE_WP_ASYNC; }
ret = -EINVAL; if (features & ~uffdio_api.features) goto err_out;
uffdio_api.ioctls = UFFD_API_IOCTLS; ret = -EFAULT; if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api))) goto out;
/* only enable the requested features for this uffd context */ ctx_features = uffd_ctx_features(features); ret = -EINVAL; if (cmpxchg(&ctx->features, 0, ctx_features) != 0) goto err_out;
ret = 0;out: return ret;err_out: memset(&uffdio_api, 0, sizeof(uffdio_api)); if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api))) ret = -EFAULT; goto out;}
static long userfaultfd_ioctl(struct file *file, unsigned cmd, unsigned long arg){ int ret = -EINVAL; struct userfaultfd_ctx *ctx = file->private_data;
if (cmd != UFFDIO_API && !userfaultfd_is_initialized(ctx)) return -EINVAL;
switch (cmd) { case UFFDIO_API: ret = userfaultfd_api(ctx, arg); break; case UFFDIO_REGISTER: ret = userfaultfd_register(ctx, arg); break; case UFFDIO_UNREGISTER: ret = userfaultfd_unregister(ctx, arg); break; case UFFDIO_WAKE: ret = userfaultfd_wake(ctx, arg); break; case UFFDIO_COPY: ret = userfaultfd_copy(ctx, arg); break; case UFFDIO_ZEROPAGE: ret = userfaultfd_zeropage(ctx, arg); break; case UFFDIO_MOVE: ret = userfaultfd_move(ctx, arg); break; case UFFDIO_WRITEPROTECT: ret = userfaultfd_writeprotect(ctx, arg); break; case UFFDIO_CONTINUE: ret = userfaultfd_continue(ctx, arg); break; case UFFDIO_POISON: ret = userfaultfd_poison(ctx, arg); break; } return ret;}
#ifdef CONFIG_PROC_FSstatic void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f){ struct userfaultfd_ctx *ctx = f->private_data; wait_queue_entry_t *wq; unsigned long pending = 0, total = 0;
spin_lock_irq(&ctx->fault_pending_wqh.lock); list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) { pending++; total++; } list_for_each_entry(wq, &ctx->fault_wqh.head, entry) { total++; } spin_unlock_irq(&ctx->fault_pending_wqh.lock);
/* * If more protocols will be added, there will be all shown * separated by a space. Like this: * protocols: aa:... bb:... */ seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n", pending, total, UFFD_API, ctx->features, UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);}#endif
static const struct file_operations userfaultfd_fops = {#ifdef CONFIG_PROC_FS .show_fdinfo = userfaultfd_show_fdinfo,#endif .release = userfaultfd_release, .poll = userfaultfd_poll, .read_iter = userfaultfd_read_iter, .unlocked_ioctl = userfaultfd_ioctl, .compat_ioctl = compat_ptr_ioctl, .llseek = noop_llseek,};
static void init_once_userfaultfd_ctx(void *mem){ struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
init_waitqueue_head(&ctx->fault_pending_wqh); init_waitqueue_head(&ctx->fault_wqh); init_waitqueue_head(&ctx->event_wqh); init_waitqueue_head(&ctx->fd_wqh); seqcount_spinlock_init(&ctx->refile_seq, &ctx->fault_pending_wqh.lock);}
static int new_userfaultfd(int flags){ struct userfaultfd_ctx *ctx __free(kfree) = NULL;
VM_WARN_ON_ONCE(!current->mm);
/* Check the UFFD_* constants for consistency. */ BUILD_BUG_ON(UFFD_USER_MODE_ONLY & UFFD_SHARED_FCNTL_FLAGS);
if (flags & ~(UFFD_SHARED_FCNTL_FLAGS | UFFD_USER_MODE_ONLY)) return -EINVAL;
ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL); if (!ctx) return -ENOMEM;
refcount_set(&ctx->refcount, 1); ctx->flags = flags; ctx->features = 0; ctx->released = false; init_rwsem(&ctx->map_changing_lock); atomic_set(&ctx->mmap_changing, 0); ctx->mm = current->mm;
FD_PREPARE(fdf, flags & UFFD_SHARED_FCNTL_FLAGS, anon_inode_create_getfile("[userfaultfd]", &userfaultfd_fops, ctx, O_RDONLY | (flags & UFFD_SHARED_FCNTL_FLAGS), NULL)); if (fdf.err) return fdf.err;
/* prevent the mm struct to be freed */ mmgrab(ctx->mm); fd_prepare_file(fdf)->f_mode |= FMODE_NOWAIT; retain_and_null_ptr(ctx); return fd_publish(fdf);}
static inline bool userfaultfd_syscall_allowed(int flags){ /* Userspace-only page faults are always allowed */ if (flags & UFFD_USER_MODE_ONLY) return true;
/* * The user is requesting a userfaultfd which can handle kernel faults. * Privileged users are always allowed to do this. */ if (capable(CAP_SYS_PTRACE)) return true;
/* Otherwise, access to kernel fault handling is sysctl controlled. */ return sysctl_unprivileged_userfaultfd;}
SYSCALL_DEFINE1(userfaultfd, int, flags){ if (!userfaultfd_syscall_allowed(flags)) return -EPERM;
return new_userfaultfd(flags);}
static long userfaultfd_dev_ioctl(struct file *file, unsigned int cmd, unsigned long flags){ if (cmd != USERFAULTFD_IOC_NEW) return -EINVAL;
return new_userfaultfd(flags);}
static const struct file_operations userfaultfd_dev_fops = { .unlocked_ioctl = userfaultfd_dev_ioctl, .compat_ioctl = userfaultfd_dev_ioctl, .owner = THIS_MODULE, .llseek = noop_llseek,};
static struct miscdevice userfaultfd_misc = { .minor = MISC_DYNAMIC_MINOR, .name = "userfaultfd", .fops = &userfaultfd_dev_fops};
static int __init userfaultfd_init(void){ int ret;
ret = misc_register(&userfaultfd_misc); if (ret) return ret;
userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache", sizeof(struct userfaultfd_ctx), 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, init_once_userfaultfd_ctx);#ifdef CONFIG_SYSCTL register_sysctl_init("vm", vm_userfaultfd_table);#endif return 0;}__initcall(userfaultfd_init);