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Diffstat (limited to 'mm/kasan/tags.c')
-rw-r--r-- | mm/kasan/tags.c | 200 |
1 files changed, 200 insertions, 0 deletions
diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c new file mode 100644 index 000000000..e02a36a51 --- /dev/null +++ b/mm/kasan/tags.c @@ -0,0 +1,200 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * This file contains core tag-based KASAN code. + * + * Copyright (c) 2018 Google, Inc. + * Author: Andrey Konovalov <andreyknvl@google.com> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + * + */ + +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include <linux/export.h> +#include <linux/interrupt.h> +#include <linux/init.h> +#include <linux/kasan.h> +#include <linux/kernel.h> +#include <linux/kmemleak.h> +#include <linux/linkage.h> +#include <linux/memblock.h> +#include <linux/memory.h> +#include <linux/mm.h> +#include <linux/module.h> +#include <linux/printk.h> +#include <linux/random.h> +#include <linux/sched.h> +#include <linux/sched/task_stack.h> +#include <linux/slab.h> +#include <linux/stacktrace.h> +#include <linux/string.h> +#include <linux/types.h> +#include <linux/vmalloc.h> +#include <linux/bug.h> + +#include "kasan.h" +#include "../slab.h" + +static DEFINE_PER_CPU(u32, prng_state); + +void kasan_init_tags(void) +{ + int cpu; + + for_each_possible_cpu(cpu) + per_cpu(prng_state, cpu) = (u32)get_cycles(); +} + +/* + * If a preemption happens between this_cpu_read and this_cpu_write, the only + * side effect is that we'll give a few allocated in different contexts objects + * the same tag. Since tag-based KASAN is meant to be used a probabilistic + * bug-detection debug feature, this doesn't have significant negative impact. + * + * Ideally the tags use strong randomness to prevent any attempts to predict + * them during explicit exploit attempts. But strong randomness is expensive, + * and we did an intentional trade-off to use a PRNG. This non-atomic RMW + * sequence has in fact positive effect, since interrupts that randomly skew + * PRNG at unpredictable points do only good. + */ +u8 random_tag(void) +{ + u32 state = this_cpu_read(prng_state); + + state = 1664525 * state + 1013904223; + this_cpu_write(prng_state, state); + + return (u8)(state % (KASAN_TAG_MAX + 1)); +} + +void *kasan_reset_tag(const void *addr) +{ + return reset_tag(addr); +} + +bool check_memory_region(unsigned long addr, size_t size, bool write, + unsigned long ret_ip) +{ + u8 tag; + u8 *shadow_first, *shadow_last, *shadow; + void *untagged_addr; + + if (unlikely(size == 0)) + return true; + + if (unlikely(addr + size < addr)) + return !kasan_report(addr, size, write, ret_ip); + + tag = get_tag((const void *)addr); + + /* + * Ignore accesses for pointers tagged with 0xff (native kernel + * pointer tag) to suppress false positives caused by kmap. + * + * Some kernel code was written to account for archs that don't keep + * high memory mapped all the time, but rather map and unmap particular + * pages when needed. Instead of storing a pointer to the kernel memory, + * this code saves the address of the page structure and offset within + * that page for later use. Those pages are then mapped and unmapped + * with kmap/kunmap when necessary and virt_to_page is used to get the + * virtual address of the page. For arm64 (that keeps the high memory + * mapped all the time), kmap is turned into a page_address call. + + * The issue is that with use of the page_address + virt_to_page + * sequence the top byte value of the original pointer gets lost (gets + * set to KASAN_TAG_KERNEL (0xFF)). + */ + if (tag == KASAN_TAG_KERNEL) + return true; + + untagged_addr = reset_tag((const void *)addr); + if (unlikely(untagged_addr < + kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) { + return !kasan_report(addr, size, write, ret_ip); + } + shadow_first = kasan_mem_to_shadow(untagged_addr); + shadow_last = kasan_mem_to_shadow(untagged_addr + size - 1); + for (shadow = shadow_first; shadow <= shadow_last; shadow++) { + if (*shadow != tag) { + return !kasan_report(addr, size, write, ret_ip); + } + } + + return true; +} + +#define DEFINE_HWASAN_LOAD_STORE(size) \ + void __hwasan_load##size##_noabort(unsigned long addr) \ + { \ + check_memory_region(addr, size, false, _RET_IP_); \ + } \ + EXPORT_SYMBOL(__hwasan_load##size##_noabort); \ + void __hwasan_store##size##_noabort(unsigned long addr) \ + { \ + check_memory_region(addr, size, true, _RET_IP_); \ + } \ + EXPORT_SYMBOL(__hwasan_store##size##_noabort) + +DEFINE_HWASAN_LOAD_STORE(1); +DEFINE_HWASAN_LOAD_STORE(2); +DEFINE_HWASAN_LOAD_STORE(4); +DEFINE_HWASAN_LOAD_STORE(8); +DEFINE_HWASAN_LOAD_STORE(16); + +void __hwasan_loadN_noabort(unsigned long addr, unsigned long size) +{ + check_memory_region(addr, size, false, _RET_IP_); +} +EXPORT_SYMBOL(__hwasan_loadN_noabort); + +void __hwasan_storeN_noabort(unsigned long addr, unsigned long size) +{ + check_memory_region(addr, size, true, _RET_IP_); +} +EXPORT_SYMBOL(__hwasan_storeN_noabort); + +void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size) +{ + kasan_poison_shadow((void *)addr, size, tag); +} +EXPORT_SYMBOL(__hwasan_tag_memory); + +void kasan_set_free_info(struct kmem_cache *cache, + void *object, u8 tag) +{ + struct kasan_alloc_meta *alloc_meta; + u8 idx = 0; + + alloc_meta = get_alloc_info(cache, object); + +#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY + idx = alloc_meta->free_track_idx; + alloc_meta->free_pointer_tag[idx] = tag; + alloc_meta->free_track_idx = (idx + 1) % KASAN_NR_FREE_STACKS; +#endif + + kasan_set_track(&alloc_meta->free_track[idx], GFP_NOWAIT); +} + +struct kasan_track *kasan_get_free_track(struct kmem_cache *cache, + void *object, u8 tag) +{ + struct kasan_alloc_meta *alloc_meta; + int i = 0; + + alloc_meta = get_alloc_info(cache, object); + +#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY + for (i = 0; i < KASAN_NR_FREE_STACKS; i++) { + if (alloc_meta->free_pointer_tag[i] == tag) + break; + } + if (i == KASAN_NR_FREE_STACKS) + i = alloc_meta->free_track_idx; +#endif + + return &alloc_meta->free_track[i]; +} |