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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288// SPDX-License-Identifier: GPL-2.0-only/* * This implements the various checks for CONFIG_HARDENED_USERCOPY*, * which are designed to protect kernel memory from needless exposure * and overwrite under many unintended conditions. This code is based * on PAX_USERCOPY, which is: * * Copyright (C) 2001-2016 PaX Team, Bradley Spengler, Open Source * Security Inc. */#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/mm.h>#include <linux/highmem.h>#include <linux/kstrtox.h>#include <linux/slab.h>#include <linux/sched.h>#include <linux/sched/task.h>#include <linux/sched/task_stack.h>#include <linux/ucopysize.h>#include <linux/vmalloc.h>#include <linux/atomic.h>#include <linux/jump_label.h>#include <asm/sections.h>#include "slab.h"
/* * Checks if a given pointer and length is contained by the current * stack frame (if possible). * * Returns: * NOT_STACK: not at all on the stack * GOOD_FRAME: fully within a valid stack frame * GOOD_STACK: within the current stack (when can't frame-check exactly) * BAD_STACK: error condition (invalid stack position or bad stack frame) */static noinline int check_stack_object(const void *obj, unsigned long len){ const void * const stack = task_stack_page(current); const void * const stackend = stack + THREAD_SIZE; int ret;
/* Object is not on the stack at all. */ if (obj + len <= stack || stackend <= obj) return NOT_STACK;
/* * Reject: object partially overlaps the stack (passing the * check above means at least one end is within the stack, * so if this check fails, the other end is outside the stack). */ if (obj < stack || stackend < obj + len) return BAD_STACK;
/* Check if object is safely within a valid frame. */ ret = arch_within_stack_frames(stack, stackend, obj, len); if (ret) return ret;
/* Finally, check stack depth if possible. */#ifdef CONFIG_ARCH_HAS_CURRENT_STACK_POINTER if (IS_ENABLED(CONFIG_STACK_GROWSUP)) { if ((void *)current_stack_pointer < obj + len) return BAD_STACK; } else { if (obj < (void *)current_stack_pointer) return BAD_STACK; }#endif
return GOOD_STACK;}
/* * If these functions are reached, then CONFIG_HARDENED_USERCOPY has found * an unexpected state during a copy_from_user() or copy_to_user() call. * There are several checks being performed on the buffer by the * __check_object_size() function. Normal stack buffer usage should never * trip the checks, and kernel text addressing will always trip the check. * For cache objects, it is checking that only the whitelisted range of * bytes for a given cache is being accessed (via the cache's usersize and * useroffset fields). To adjust a cache whitelist, use the usercopy-aware * kmem_cache_create_usercopy() function to create the cache (and * carefully audit the whitelist range). */void __noreturn usercopy_abort(const char *name, const char *detail, bool to_user, unsigned long offset, unsigned long len){ pr_emerg("Kernel memory %s attempt detected %s %s%s%s%s (offset %lu, size %lu)!\n", to_user ? "exposure" : "overwrite", to_user ? "from" : "to", name ? : "unknown?!", detail ? " '" : "", detail ? : "", detail ? "'" : "", offset, len);
/* * For greater effect, it would be nice to do do_group_exit(), * but BUG() actually hooks all the lock-breaking and per-arch * Oops code, so that is used here instead. */ BUG();}
/* Returns true if any portion of [ptr,ptr+n) over laps with [low,high). */static bool overlaps(const unsigned long ptr, unsigned long n, unsigned long low, unsigned long high){ const unsigned long check_low = ptr; unsigned long check_high = check_low + n;
/* Does not overlap if entirely above or entirely below. */ if (check_low >= high || check_high <= low) return false;
return true;}
/* Is this address range in the kernel text area? */static inline void check_kernel_text_object(const unsigned long ptr, unsigned long n, bool to_user){ unsigned long textlow = (unsigned long)_stext; unsigned long texthigh = (unsigned long)_etext; unsigned long textlow_linear, texthigh_linear;
if (overlaps(ptr, n, textlow, texthigh)) usercopy_abort("kernel text", NULL, to_user, ptr - textlow, n);
/* * Some architectures have virtual memory mappings with a secondary * mapping of the kernel text, i.e. there is more than one virtual * kernel address that points to the kernel image. It is usually * when there is a separate linear physical memory mapping, in that * __pa() is not just the reverse of __va(). This can be detected * and checked: */ textlow_linear = (unsigned long)lm_alias(textlow); /* No different mapping: we're done. */ if (textlow_linear == textlow) return;
/* Check the secondary mapping... */ texthigh_linear = (unsigned long)lm_alias(texthigh); if (overlaps(ptr, n, textlow_linear, texthigh_linear)) usercopy_abort("linear kernel text", NULL, to_user, ptr - textlow_linear, n);}
static inline void check_bogus_address(const unsigned long ptr, unsigned long n, bool to_user){ /* Reject if object wraps past end of memory. */ if (ptr + (n - 1) < ptr) usercopy_abort("wrapped address", NULL, to_user, 0, ptr + n);
/* Reject if NULL or ZERO-allocation. */ if (ZERO_OR_NULL_PTR(ptr)) usercopy_abort("null address", NULL, to_user, ptr, n);}
static inline void check_heap_object(const void *ptr, unsigned long n, bool to_user){ unsigned long addr = (unsigned long)ptr; unsigned long offset; struct page *page; struct slab *slab;
if (is_kmap_addr(ptr)) { offset = offset_in_page(ptr); if (n > PAGE_SIZE - offset) usercopy_abort("kmap", NULL, to_user, offset, n); return; }
if (is_vmalloc_addr(ptr) && !pagefault_disabled()) { struct vmap_area *area = find_vmap_area(addr);
if (!area) usercopy_abort("vmalloc", "no area", to_user, 0, n);
if (n > area->va_end - addr) { offset = addr - area->va_start; usercopy_abort("vmalloc", NULL, to_user, offset, n); } return; }
if (!virt_addr_valid(ptr)) return;
page = virt_to_page(ptr); slab = page_slab(page); if (slab) { /* Check slab allocator for flags and size. */ __check_heap_object(ptr, n, slab, to_user); } else if (PageCompound(page)) { page = compound_head(page); offset = ptr - page_address(page); if (n > page_size(page) - offset) usercopy_abort("page alloc", NULL, to_user, offset, n); }
/* * We cannot check non-compound pages. They might be part of * a large allocation, in which case crossing a page boundary * is fine. */}
DEFINE_STATIC_KEY_MAYBE_RO(CONFIG_HARDENED_USERCOPY_DEFAULT_ON, validate_usercopy_range);EXPORT_SYMBOL(validate_usercopy_range);
/* * Validates that the given object is: * - not bogus address * - fully contained by stack (or stack frame, when available) * - fully within SLAB object (or object whitelist area, when available) * - not in kernel text */void __check_object_size(const void *ptr, unsigned long n, bool to_user){ /* Skip all tests if size is zero. */ if (!n) return;
/* Check for invalid addresses. */ check_bogus_address((const unsigned long)ptr, n, to_user);
/* Check for bad stack object. */ switch (check_stack_object(ptr, n)) { case NOT_STACK: /* Object is not touching the current process stack. */ break; case GOOD_FRAME: case GOOD_STACK: /* * Object is either in the correct frame (when it * is possible to check) or just generally on the * process stack (when frame checking not available). */ return; default: usercopy_abort("process stack", NULL, to_user,#ifdef CONFIG_ARCH_HAS_CURRENT_STACK_POINTER IS_ENABLED(CONFIG_STACK_GROWSUP) ? ptr - (void *)current_stack_pointer : (void *)current_stack_pointer - ptr,#else 0,#endif n); }
/* Check for bad heap object. */ check_heap_object(ptr, n, to_user);
/* Check for object in kernel to avoid text exposure. */ check_kernel_text_object((const unsigned long)ptr, n, to_user);}EXPORT_SYMBOL(__check_object_size);
static bool enable_checks __initdata = IS_ENABLED(CONFIG_HARDENED_USERCOPY_DEFAULT_ON);
static int __init parse_hardened_usercopy(char *str){ if (kstrtobool(str, &enable_checks)) pr_warn("Invalid option string for hardened_usercopy: '%s'\n", str); return 1;}
__setup("hardened_usercopy=", parse_hardened_usercopy);
static int __init set_hardened_usercopy(void){ if (enable_checks) static_branch_enable(&validate_usercopy_range); else static_branch_disable(&validate_usercopy_range); return 1;}
late_initcall(set_hardened_usercopy);