| // 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/slab.h> |
| #include <linux/sched.h> |
| #include <linux/sched/task.h> |
| #include <linux/sched/task_stack.h> |
| #include <linux/thread_info.h> |
| #include <linux/atomic.h> |
| #include <linux/jump_label.h> |
| #include <asm/sections.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: fully on the stack (when can't do frame-checking) |
| * 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 |
| * 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; |
| |
| 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 usercopy_warn(const char *name, const char *detail, bool to_user, |
| unsigned long offset, unsigned long len) |
| { |
| WARN_ONCE(1, "Bad or missing usercopy whitelist? 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); |
| } |
| |
| 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 < 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); |
| } |
| |
| /* Checks for allocs that are marked in some way as spanning multiple pages. */ |
| static inline void check_page_span(const void *ptr, unsigned long n, |
| struct page *page, bool to_user) |
| { |
| #ifdef CONFIG_HARDENED_USERCOPY_PAGESPAN |
| const void *end = ptr + n - 1; |
| struct page *endpage; |
| bool is_reserved, is_cma; |
| |
| /* |
| * Sometimes the kernel data regions are not marked Reserved (see |
| * check below). And sometimes [_sdata,_edata) does not cover |
| * rodata and/or bss, so check each range explicitly. |
| */ |
| |
| /* Allow reads of kernel rodata region (if not marked as Reserved). */ |
| if (ptr >= (const void *)__start_rodata && |
| end <= (const void *)__end_rodata) { |
| if (!to_user) |
| usercopy_abort("rodata", NULL, to_user, 0, n); |
| return; |
| } |
| |
| /* Allow kernel data region (if not marked as Reserved). */ |
| if (ptr >= (const void *)_sdata && end <= (const void *)_edata) |
| return; |
| |
| /* Allow kernel bss region (if not marked as Reserved). */ |
| if (ptr >= (const void *)__bss_start && |
| end <= (const void *)__bss_stop) |
| return; |
| |
| /* Is the object wholly within one base page? */ |
| if (likely(((unsigned long)ptr & (unsigned long)PAGE_MASK) == |
| ((unsigned long)end & (unsigned long)PAGE_MASK))) |
| return; |
| |
| /* Allow if fully inside the same compound (__GFP_COMP) page. */ |
| endpage = virt_to_head_page(end); |
| if (likely(endpage == page)) |
| return; |
| |
| /* |
| * Reject if range is entirely either Reserved (i.e. special or |
| * device memory), or CMA. Otherwise, reject since the object spans |
| * several independently allocated pages. |
| */ |
| is_reserved = PageReserved(page); |
| is_cma = is_migrate_cma_page(page); |
| if (!is_reserved && !is_cma) |
| usercopy_abort("spans multiple pages", NULL, to_user, 0, n); |
| |
| for (ptr += PAGE_SIZE; ptr <= end; ptr += PAGE_SIZE) { |
| page = virt_to_head_page(ptr); |
| if (is_reserved && !PageReserved(page)) |
| usercopy_abort("spans Reserved and non-Reserved pages", |
| NULL, to_user, 0, n); |
| if (is_cma && !is_migrate_cma_page(page)) |
| usercopy_abort("spans CMA and non-CMA pages", NULL, |
| to_user, 0, n); |
| } |
| #endif |
| } |
| |
| static inline void check_heap_object(const void *ptr, unsigned long n, |
| bool to_user) |
| { |
| struct page *page; |
| |
| if (!virt_addr_valid(ptr)) |
| return; |
| |
| page = virt_to_head_page(ptr); |
| |
| if (PageSlab(page)) { |
| /* Check slab allocator for flags and size. */ |
| __check_heap_object(ptr, n, page, to_user); |
| } else { |
| /* Verify object does not incorrectly span multiple pages. */ |
| check_page_span(ptr, n, page, to_user); |
| } |
| } |
| |
| 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, 0, 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) |
| { |
| return strtobool(str, &enable_checks); |
| } |
| |
| __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); |