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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-11 08:27:49 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-11 08:27:49 +0000 |
commit | ace9429bb58fd418f0c81d4c2835699bddf6bde6 (patch) | |
tree | b2d64bc10158fdd5497876388cd68142ca374ed3 /mm/usercopy.c | |
parent | Initial commit. (diff) | |
download | linux-ace9429bb58fd418f0c81d4c2835699bddf6bde6.tar.xz linux-ace9429bb58fd418f0c81d4c2835699bddf6bde6.zip |
Adding upstream version 6.6.15.upstream/6.6.15
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'mm/usercopy.c')
-rw-r--r-- | mm/usercopy.c | 277 |
1 files changed, 277 insertions, 0 deletions
diff --git a/mm/usercopy.c b/mm/usercopy.c new file mode 100644 index 0000000000..83c164aba6 --- /dev/null +++ b/mm/usercopy.c @@ -0,0 +1,277 @@ +// 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/thread_info.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 folio *folio; + + 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; + + folio = virt_to_folio(ptr); + + if (folio_test_slab(folio)) { + /* Check slab allocator for flags and size. */ + __check_heap_object(ptr, n, folio_slab(folio), to_user); + } else if (folio_test_large(folio)) { + offset = ptr - folio_address(folio); + if (n > folio_size(folio) - offset) + usercopy_abort("page alloc", NULL, to_user, offset, n); + } +} + +static DEFINE_STATIC_KEY_FALSE_RO(bypass_usercopy_checks); + +/* + * 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) +{ + if (static_branch_unlikely(&bypass_usercopy_checks)) + return; + + /* 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 = true; + +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 == false) + static_branch_enable(&bypass_usercopy_checks); + return 1; +} + +late_initcall(set_hardened_usercopy); |