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(I'm so sorry!) Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel os linux
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/* * This driver exists to allow userspace programs in Linux to allocate kernel * memory that will later be shared with another domain. Without this device, * Linux userspace programs cannot create grant references. * * How this stuff works: * X -> granting a page to Y * Y -> mapping the grant from X * * 1. X uses the gntalloc device to allocate a page of kernel memory, P. * 2. X creates an entry in the grant table that says domid(Y) can access P. * This is done without a hypercall unless the grant table needs expansion. * 3. X gives the grant reference identifier, GREF, to Y. * 4. Y maps the page, either directly into kernel memory for use in a backend * driver, or via a the gntdev device to map into the address space of an * application running in Y. This is the first point at which Xen does any * tracking of the page. * 5. A program in X mmap()s a segment of the gntalloc device that corresponds * to the shared page, and can now communicate with Y over the shared page. * * * NOTE TO USERSPACE LIBRARIES: * The grant allocation and mmap()ing are, naturally, two separate operations. * You set up the sharing by calling the create ioctl() and then the mmap(). * Teardown requires munmap() and either close() or ioctl(). * * WARNING: Since Xen does not allow a guest to forcibly end the use of a grant * reference, this device can be used to consume kernel memory by leaving grant * references mapped by another domain when an application exits. Therefore, * there is a global limit on the number of pages that can be allocated. When * all references to the page are unmapped, it will be freed during the next * grant operation. */
#define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt
#include <linux/atomic.h>#include <linux/module.h>#include <linux/miscdevice.h>#include <linux/kernel.h>#include <linux/init.h>#include <linux/slab.h>#include <linux/fs.h>#include <linux/device.h>#include <linux/mm.h>#include <linux/uaccess.h>#include <linux/types.h>#include <linux/list.h>#include <linux/highmem.h>
#include <xen/xen.h>#include <xen/page.h>#include <xen/grant_table.h>#include <xen/gntalloc.h>#include <xen/events.h>
static unsigned int limit = 1024;module_param(limit, uint, 0644);MODULE_PARM_DESC(limit, "Maximum number of grants that may be allocated by " "the gntalloc device");
static LIST_HEAD(gref_list);static DEFINE_MUTEX(gref_mutex);static unsigned int gref_size;
struct notify_info { uint16_t pgoff:12; /* Bits 0-11: Offset of the byte to clear */ uint16_t flags:2; /* Bits 12-13: Unmap notification flags */ int event; /* Port (event channel) to notify */};
/* Metadata on a grant reference. */struct gntalloc_gref { struct list_head next_gref; /* list entry gref_list */ struct list_head next_file; /* list entry file->list, if open */ struct page *page; /* The shared page */ uint64_t file_index; /* File offset for mmap() */ unsigned int users; /* Use count - when zero, waiting on Xen */ grant_ref_t gref_id; /* The grant reference number */ struct notify_info notify; /* Unmap notification */};
struct gntalloc_file_private_data { struct list_head list; uint64_t index;};
struct gntalloc_vma_private_data { struct gntalloc_gref *gref; int users; int count;};
static void __del_gref(struct gntalloc_gref *gref);
static void do_cleanup(void){ struct gntalloc_gref *gref, *n; list_for_each_entry_safe(gref, n, &gref_list, next_gref) { if (!gref->users) __del_gref(gref); }}
static int add_grefs(struct ioctl_gntalloc_alloc_gref *op, uint32_t *gref_ids, struct gntalloc_file_private_data *priv){ int i, rc, readonly; LIST_HEAD(queue_gref); LIST_HEAD(queue_file); struct gntalloc_gref *gref, *next;
readonly = !(op->flags & GNTALLOC_FLAG_WRITABLE); for (i = 0; i < op->count; i++) { gref = kzalloc_obj(*gref); if (!gref) { rc = -ENOMEM; goto undo; } list_add_tail(&gref->next_gref, &queue_gref); list_add_tail(&gref->next_file, &queue_file); gref->users = 1; gref->file_index = op->index + i * PAGE_SIZE; gref->page = alloc_page(GFP_KERNEL|__GFP_ZERO); if (!gref->page) { rc = -ENOMEM; goto undo; }
/* Grant foreign access to the page. */ rc = gnttab_grant_foreign_access(op->domid, xen_page_to_gfn(gref->page), readonly); if (rc < 0) goto undo; gref_ids[i] = gref->gref_id = rc; }
/* Add to gref lists. */ mutex_lock(&gref_mutex); list_splice_tail(&queue_gref, &gref_list); list_splice_tail(&queue_file, &priv->list); mutex_unlock(&gref_mutex);
return 0;
undo: mutex_lock(&gref_mutex); gref_size -= (op->count - i);
list_for_each_entry_safe(gref, next, &queue_file, next_file) { list_del(&gref->next_file); __del_gref(gref); }
mutex_unlock(&gref_mutex); return rc;}
static void __del_gref(struct gntalloc_gref *gref){ if (gref->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) { uint8_t *tmp = kmap_local_page(gref->page); tmp[gref->notify.pgoff] = 0; kunmap_local(tmp); } if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT) { notify_remote_via_evtchn(gref->notify.event); evtchn_put(gref->notify.event); }
gref->notify.flags = 0;
if (gref->gref_id) { if (gref->page) gnttab_end_foreign_access(gref->gref_id, gref->page); else gnttab_free_grant_reference(gref->gref_id); }
gref_size--; list_del(&gref->next_gref);
kfree(gref);}
/* finds contiguous grant references in a file, returns the first */static struct gntalloc_gref *find_grefs(struct gntalloc_file_private_data *priv, uint64_t index, uint32_t count){ struct gntalloc_gref *rv = NULL, *gref; list_for_each_entry(gref, &priv->list, next_file) { if (gref->file_index == index && !rv) rv = gref; if (rv) { if (gref->file_index != index) return NULL; index += PAGE_SIZE; count--; if (count == 0) return rv; } } return NULL;}
/* * ------------------------------------- * File operations. * ------------------------------------- */static int gntalloc_open(struct inode *inode, struct file *filp){ struct gntalloc_file_private_data *priv;
priv = kzalloc_obj(*priv); if (!priv) goto out_nomem; INIT_LIST_HEAD(&priv->list);
filp->private_data = priv;
pr_debug("%s: priv %p\n", __func__, priv);
return 0;
out_nomem: return -ENOMEM;}
static int gntalloc_release(struct inode *inode, struct file *filp){ struct gntalloc_file_private_data *priv = filp->private_data; struct gntalloc_gref *gref;
pr_debug("%s: priv %p\n", __func__, priv);
mutex_lock(&gref_mutex); while (!list_empty(&priv->list)) { gref = list_entry(priv->list.next, struct gntalloc_gref, next_file); list_del(&gref->next_file); gref->users--; if (gref->users == 0) __del_gref(gref); } kfree(priv); mutex_unlock(&gref_mutex);
return 0;}
static long gntalloc_ioctl_alloc(struct gntalloc_file_private_data *priv, struct ioctl_gntalloc_alloc_gref __user *arg){ int rc = 0; struct ioctl_gntalloc_alloc_gref op; uint32_t *gref_ids; unsigned int limit_snapshot;
pr_debug("%s: priv %p\n", __func__, priv);
if (copy_from_user(&op, arg, sizeof(op))) { rc = -EFAULT; goto out; }
limit_snapshot = READ_ONCE(limit); if (op.count > limit_snapshot) { rc = -ENOSPC; goto out; }
gref_ids = kcalloc(op.count, sizeof(gref_ids[0]), GFP_KERNEL); if (!gref_ids) { rc = -ENOMEM; goto out; }
mutex_lock(&gref_mutex); /* Clean up pages that were at zero (local) users but were still mapped * by remote domains. Since those pages count towards the limit that we * are about to enforce, removing them here is a good idea. */ do_cleanup(); limit_snapshot = READ_ONCE(limit); if (gref_size > limit_snapshot || op.count > limit_snapshot - gref_size) { mutex_unlock(&gref_mutex); rc = -ENOSPC; goto out_free; } gref_size += op.count; op.index = priv->index; priv->index += (uint64_t)op.count * PAGE_SIZE; mutex_unlock(&gref_mutex);
rc = add_grefs(&op, gref_ids, priv); if (rc < 0) goto out_free;
/* Once we finish add_grefs, it is unsafe to touch the new reference, * since it is possible for a concurrent ioctl to remove it (by guessing * its index). If the userspace application doesn't provide valid memory * to write the IDs to, then it will need to close the file in order to * release - which it will do by segfaulting when it tries to access the * IDs to close them. */ if (copy_to_user(arg, &op, sizeof(op))) { rc = -EFAULT; goto out_free; } if (copy_to_user(arg->gref_ids_flex, gref_ids, sizeof(gref_ids[0]) * op.count)) { rc = -EFAULT; goto out_free; }
out_free: kfree(gref_ids);out: return rc;}
static long gntalloc_ioctl_dealloc(struct gntalloc_file_private_data *priv, void __user *arg){ int i, rc = 0; struct ioctl_gntalloc_dealloc_gref op; struct gntalloc_gref *gref, *n;
pr_debug("%s: priv %p\n", __func__, priv);
if (copy_from_user(&op, arg, sizeof(op))) { rc = -EFAULT; goto dealloc_grant_out; }
mutex_lock(&gref_mutex); gref = find_grefs(priv, op.index, op.count); if (gref) { /* Remove from the file list only, and decrease reference count. * The later call to do_cleanup() will remove from gref_list and * free the memory if the pages aren't mapped anywhere. */ for (i = 0; i < op.count; i++) { n = list_entry(gref->next_file.next, struct gntalloc_gref, next_file); list_del(&gref->next_file); gref->users--; gref = n; } } else { rc = -EINVAL; }
do_cleanup();
mutex_unlock(&gref_mutex);dealloc_grant_out: return rc;}
static long gntalloc_ioctl_unmap_notify(struct gntalloc_file_private_data *priv, void __user *arg){ struct ioctl_gntalloc_unmap_notify op; struct gntalloc_gref *gref; uint64_t index; int pgoff; int rc;
if (copy_from_user(&op, arg, sizeof(op))) return -EFAULT;
index = op.index & ~(PAGE_SIZE - 1); pgoff = op.index & (PAGE_SIZE - 1);
mutex_lock(&gref_mutex);
gref = find_grefs(priv, index, 1); if (!gref) { rc = -ENOENT; goto unlock_out; }
if (op.action & ~(UNMAP_NOTIFY_CLEAR_BYTE|UNMAP_NOTIFY_SEND_EVENT)) { rc = -EINVAL; goto unlock_out; }
/* We need to grab a reference to the event channel we are going to use * to send the notify before releasing the reference we may already have * (if someone has called this ioctl twice). This is required so that * it is possible to change the clear_byte part of the notification * without disturbing the event channel part, which may now be the last * reference to that event channel. */ if (op.action & UNMAP_NOTIFY_SEND_EVENT) { if (evtchn_get(op.event_channel_port)) { rc = -EINVAL; goto unlock_out; } }
if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT) evtchn_put(gref->notify.event);
gref->notify.flags = op.action; gref->notify.pgoff = pgoff; gref->notify.event = op.event_channel_port; rc = 0;
unlock_out: mutex_unlock(&gref_mutex); return rc;}
static long gntalloc_ioctl(struct file *filp, unsigned int cmd, unsigned long arg){ struct gntalloc_file_private_data *priv = filp->private_data;
switch (cmd) { case IOCTL_GNTALLOC_ALLOC_GREF: return gntalloc_ioctl_alloc(priv, (void __user *)arg);
case IOCTL_GNTALLOC_DEALLOC_GREF: return gntalloc_ioctl_dealloc(priv, (void __user *)arg);
case IOCTL_GNTALLOC_SET_UNMAP_NOTIFY: return gntalloc_ioctl_unmap_notify(priv, (void __user *)arg);
default: return -ENOIOCTLCMD; }
return 0;}
static void gntalloc_vma_open(struct vm_area_struct *vma){ struct gntalloc_vma_private_data *priv = vma->vm_private_data;
if (!priv) return;
mutex_lock(&gref_mutex); priv->users++; mutex_unlock(&gref_mutex);}
static void gntalloc_vma_close(struct vm_area_struct *vma){ struct gntalloc_vma_private_data *priv = vma->vm_private_data; struct gntalloc_gref *gref, *next; int i;
if (!priv) return;
mutex_lock(&gref_mutex); priv->users--; if (priv->users == 0) { gref = priv->gref; for (i = 0; i < priv->count; i++) { gref->users--; next = list_entry(gref->next_gref.next, struct gntalloc_gref, next_gref); if (gref->users == 0) __del_gref(gref); gref = next; } kfree(priv); } mutex_unlock(&gref_mutex);}
static const struct vm_operations_struct gntalloc_vmops = { .open = gntalloc_vma_open, .close = gntalloc_vma_close,};
static int gntalloc_mmap(struct file *filp, struct vm_area_struct *vma){ struct gntalloc_file_private_data *priv = filp->private_data; struct gntalloc_vma_private_data *vm_priv; struct gntalloc_gref *gref; int count = vma_pages(vma); int rv, i;
if (!(vma->vm_flags & VM_SHARED)) { pr_err("%s: Mapping must be shared\n", __func__); return -EINVAL; }
vm_priv = kmalloc_obj(*vm_priv); if (!vm_priv) return -ENOMEM;
mutex_lock(&gref_mutex);
pr_debug("%s: priv %p,%p, page %lu+%d\n", __func__, priv, vm_priv, vma->vm_pgoff, count);
gref = find_grefs(priv, vma->vm_pgoff << PAGE_SHIFT, count); if (gref == NULL) { rv = -ENOENT; pr_debug("%s: Could not find grant reference", __func__); kfree(vm_priv); goto out_unlock; }
vm_priv->gref = gref; vm_priv->users = 1; vm_priv->count = count;
vma->vm_private_data = vm_priv;
vm_flags_set(vma, VM_DONTEXPAND | VM_DONTDUMP);
vma->vm_ops = &gntalloc_vmops;
for (i = 0; i < count; i++) { gref->users++; rv = vm_insert_page(vma, vma->vm_start + i * PAGE_SIZE, gref->page); if (rv) goto out_unlock;
gref = list_entry(gref->next_file.next, struct gntalloc_gref, next_file); } rv = 0;
out_unlock: mutex_unlock(&gref_mutex); return rv;}
static const struct file_operations gntalloc_fops = { .owner = THIS_MODULE, .open = gntalloc_open, .release = gntalloc_release, .unlocked_ioctl = gntalloc_ioctl, .mmap = gntalloc_mmap};
/* * ------------------------------------- * Module creation/destruction. * ------------------------------------- */static struct miscdevice gntalloc_miscdev = { .minor = MISC_DYNAMIC_MINOR, .name = "xen/gntalloc", .fops = &gntalloc_fops,};
static int __init gntalloc_init(void){ int err;
if (!xen_domain()) return -ENODEV;
err = misc_register(&gntalloc_miscdev); if (err != 0) { pr_err("Could not register misc gntalloc device\n"); return err; }
pr_debug("Created grant allocation device at %d,%d\n", MISC_MAJOR, gntalloc_miscdev.minor);
return 0;}
static void __exit gntalloc_exit(void){ misc_deregister(&gntalloc_miscdev);}
module_init(gntalloc_init);module_exit(gntalloc_exit);
MODULE_LICENSE("GPL");MODULE_AUTHOR("Carter Weatherly <carter.weatherly@jhuapl.edu>, " "Daniel De Graaf <dgdegra@tycho.nsa.gov>");MODULE_DESCRIPTION("User-space grant reference allocator driver");