1 // SPDX-License-Identifier: GPL-2.0
3 * This file contains core tag-based KASAN code.
5 * Copyright (c) 2018 Google, Inc.
6 * Author: Andrey Konovalov <andreyknvl@google.com>
9 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
11 #include <linux/export.h>
12 #include <linux/interrupt.h>
13 #include <linux/init.h>
14 #include <linux/kasan.h>
15 #include <linux/kernel.h>
16 #include <linux/kmemleak.h>
17 #include <linux/linkage.h>
18 #include <linux/memblock.h>
19 #include <linux/memory.h>
21 #include <linux/module.h>
22 #include <linux/printk.h>
23 #include <linux/random.h>
24 #include <linux/sched.h>
25 #include <linux/sched/task_stack.h>
26 #include <linux/slab.h>
27 #include <linux/stacktrace.h>
28 #include <linux/string.h>
29 #include <linux/types.h>
30 #include <linux/vmalloc.h>
31 #include <linux/bug.h>
36 static DEFINE_PER_CPU(u32, prng_state);
38 void kasan_init_tags(void)
42 for_each_possible_cpu(cpu)
43 per_cpu(prng_state, cpu) = (u32)get_cycles();
47 * If a preemption happens between this_cpu_read and this_cpu_write, the only
48 * side effect is that we'll give a few allocated in different contexts objects
49 * the same tag. Since tag-based KASAN is meant to be used a probabilistic
50 * bug-detection debug feature, this doesn't have significant negative impact.
52 * Ideally the tags use strong randomness to prevent any attempts to predict
53 * them during explicit exploit attempts. But strong randomness is expensive,
54 * and we did an intentional trade-off to use a PRNG. This non-atomic RMW
55 * sequence has in fact positive effect, since interrupts that randomly skew
56 * PRNG at unpredictable points do only good.
60 u32 state = this_cpu_read(prng_state);
62 state = 1664525 * state + 1013904223;
63 this_cpu_write(prng_state, state);
65 return (u8)(state % (KASAN_TAG_MAX + 1));
68 void *kasan_reset_tag(const void *addr)
70 return reset_tag(addr);
73 bool check_memory_region(unsigned long addr, size_t size, bool write,
77 u8 *shadow_first, *shadow_last, *shadow;
80 if (unlikely(size == 0))
83 if (unlikely(addr + size < addr))
84 return !kasan_report(addr, size, write, ret_ip);
86 tag = get_tag((const void *)addr);
89 * Ignore accesses for pointers tagged with 0xff (native kernel
90 * pointer tag) to suppress false positives caused by kmap.
92 * Some kernel code was written to account for archs that don't keep
93 * high memory mapped all the time, but rather map and unmap particular
94 * pages when needed. Instead of storing a pointer to the kernel memory,
95 * this code saves the address of the page structure and offset within
96 * that page for later use. Those pages are then mapped and unmapped
97 * with kmap/kunmap when necessary and virt_to_page is used to get the
98 * virtual address of the page. For arm64 (that keeps the high memory
99 * mapped all the time), kmap is turned into a page_address call.
101 * The issue is that with use of the page_address + virt_to_page
102 * sequence the top byte value of the original pointer gets lost (gets
103 * set to KASAN_TAG_KERNEL (0xFF)).
105 if (tag == KASAN_TAG_KERNEL)
108 untagged_addr = reset_tag((const void *)addr);
109 if (unlikely(untagged_addr <
110 kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) {
111 return !kasan_report(addr, size, write, ret_ip);
113 shadow_first = kasan_mem_to_shadow(untagged_addr);
114 shadow_last = kasan_mem_to_shadow(untagged_addr + size - 1);
115 for (shadow = shadow_first; shadow <= shadow_last; shadow++) {
116 if (*shadow != tag) {
117 return !kasan_report(addr, size, write, ret_ip);
124 #define DEFINE_HWASAN_LOAD_STORE(size) \
125 void __hwasan_load##size##_noabort(unsigned long addr) \
127 check_memory_region(addr, size, false, _RET_IP_); \
129 EXPORT_SYMBOL(__hwasan_load##size##_noabort); \
130 void __hwasan_store##size##_noabort(unsigned long addr) \
132 check_memory_region(addr, size, true, _RET_IP_); \
134 EXPORT_SYMBOL(__hwasan_store##size##_noabort)
136 DEFINE_HWASAN_LOAD_STORE(1);
137 DEFINE_HWASAN_LOAD_STORE(2);
138 DEFINE_HWASAN_LOAD_STORE(4);
139 DEFINE_HWASAN_LOAD_STORE(8);
140 DEFINE_HWASAN_LOAD_STORE(16);
142 void __hwasan_loadN_noabort(unsigned long addr, unsigned long size)
144 check_memory_region(addr, size, false, _RET_IP_);
146 EXPORT_SYMBOL(__hwasan_loadN_noabort);
148 void __hwasan_storeN_noabort(unsigned long addr, unsigned long size)
150 check_memory_region(addr, size, true, _RET_IP_);
152 EXPORT_SYMBOL(__hwasan_storeN_noabort);
154 void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size)
156 poison_range((void *)addr, size, tag);
158 EXPORT_SYMBOL(__hwasan_tag_memory);
160 void kasan_set_free_info(struct kmem_cache *cache,
161 void *object, u8 tag)
163 struct kasan_alloc_meta *alloc_meta;
166 alloc_meta = get_alloc_info(cache, object);
168 #ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
169 idx = alloc_meta->free_track_idx;
170 alloc_meta->free_pointer_tag[idx] = tag;
171 alloc_meta->free_track_idx = (idx + 1) % KASAN_NR_FREE_STACKS;
174 kasan_set_track(&alloc_meta->free_track[idx], GFP_NOWAIT);
177 struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
178 void *object, u8 tag)
180 struct kasan_alloc_meta *alloc_meta;
183 alloc_meta = get_alloc_info(cache, object);
185 #ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
186 for (i = 0; i < KASAN_NR_FREE_STACKS; i++) {
187 if (alloc_meta->free_pointer_tag[i] == tag)
190 if (i == KASAN_NR_FREE_STACKS)
191 i = alloc_meta->free_track_idx;
194 return &alloc_meta->free_track[i];