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- // 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/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 (strtobool(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);
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