1 // SPDX-License-Identifier: GPL-2.0
3 * This file contains core software tag-based KASAN code.
5 * Copyright (c) 2018 Google, Inc.
6 * Author: Andrey Konovalov <andreyknvl@google.com>
9 #define pr_fmt(fmt) "kasan: " 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 __init kasan_init_sw_tags(void)
42 for_each_possible_cpu(cpu)
43 per_cpu(prng_state, cpu) = (u32)get_cycles();
45 pr_info("KernelAddressSanitizer initialized (sw-tags)\n");
49 * If a preemption happens between this_cpu_read and this_cpu_write, the only
50 * side effect is that we'll give a few allocated in different contexts objects
51 * the same tag. Since tag-based KASAN is meant to be used a probabilistic
52 * bug-detection debug feature, this doesn't have significant negative impact.
54 * Ideally the tags use strong randomness to prevent any attempts to predict
55 * them during explicit exploit attempts. But strong randomness is expensive,
56 * and we did an intentional trade-off to use a PRNG. This non-atomic RMW
57 * sequence has in fact positive effect, since interrupts that randomly skew
58 * PRNG at unpredictable points do only good.
60 u8 kasan_random_tag(void)
62 u32 state = this_cpu_read(prng_state);
64 state = 1664525 * state + 1013904223;
65 this_cpu_write(prng_state, state);
67 return (u8)(state % (KASAN_TAG_MAX + 1));
70 bool kasan_check_range(unsigned long addr, size_t size, bool write,
74 u8 *shadow_first, *shadow_last, *shadow;
77 if (unlikely(size == 0))
80 if (unlikely(addr + size < addr))
81 return !kasan_report(addr, size, write, ret_ip);
83 tag = get_tag((const void *)addr);
86 * Ignore accesses for pointers tagged with 0xff (native kernel
87 * pointer tag) to suppress false positives caused by kmap.
89 * Some kernel code was written to account for archs that don't keep
90 * high memory mapped all the time, but rather map and unmap particular
91 * pages when needed. Instead of storing a pointer to the kernel memory,
92 * this code saves the address of the page structure and offset within
93 * that page for later use. Those pages are then mapped and unmapped
94 * with kmap/kunmap when necessary and virt_to_page is used to get the
95 * virtual address of the page. For arm64 (that keeps the high memory
96 * mapped all the time), kmap is turned into a page_address call.
98 * The issue is that with use of the page_address + virt_to_page
99 * sequence the top byte value of the original pointer gets lost (gets
100 * set to KASAN_TAG_KERNEL (0xFF)).
102 if (tag == KASAN_TAG_KERNEL)
105 untagged_addr = kasan_reset_tag((const void *)addr);
106 if (unlikely(untagged_addr <
107 kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) {
108 return !kasan_report(addr, size, write, ret_ip);
110 shadow_first = kasan_mem_to_shadow(untagged_addr);
111 shadow_last = kasan_mem_to_shadow(untagged_addr + size - 1);
112 for (shadow = shadow_first; shadow <= shadow_last; shadow++) {
113 if (*shadow != tag) {
114 return !kasan_report(addr, size, write, ret_ip);
121 bool kasan_byte_accessible(const void *addr)
123 u8 tag = get_tag(addr);
124 void *untagged_addr = kasan_reset_tag(addr);
127 if (untagged_addr < kasan_shadow_to_mem((void *)KASAN_SHADOW_START))
130 shadow_byte = READ_ONCE(*(u8 *)kasan_mem_to_shadow(untagged_addr));
131 return tag == KASAN_TAG_KERNEL || tag == shadow_byte;
134 #define DEFINE_HWASAN_LOAD_STORE(size) \
135 void __hwasan_load##size##_noabort(unsigned long addr) \
137 kasan_check_range(addr, size, false, _RET_IP_); \
139 EXPORT_SYMBOL(__hwasan_load##size##_noabort); \
140 void __hwasan_store##size##_noabort(unsigned long addr) \
142 kasan_check_range(addr, size, true, _RET_IP_); \
144 EXPORT_SYMBOL(__hwasan_store##size##_noabort)
146 DEFINE_HWASAN_LOAD_STORE(1);
147 DEFINE_HWASAN_LOAD_STORE(2);
148 DEFINE_HWASAN_LOAD_STORE(4);
149 DEFINE_HWASAN_LOAD_STORE(8);
150 DEFINE_HWASAN_LOAD_STORE(16);
152 void __hwasan_loadN_noabort(unsigned long addr, unsigned long size)
154 kasan_check_range(addr, size, false, _RET_IP_);
156 EXPORT_SYMBOL(__hwasan_loadN_noabort);
158 void __hwasan_storeN_noabort(unsigned long addr, unsigned long size)
160 kasan_check_range(addr, size, true, _RET_IP_);
162 EXPORT_SYMBOL(__hwasan_storeN_noabort);
164 void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size)
166 kasan_poison((void *)addr, size, tag, false);
168 EXPORT_SYMBOL(__hwasan_tag_memory);
170 void kasan_tag_mismatch(unsigned long addr, unsigned long access_info,
171 unsigned long ret_ip)
173 kasan_report(addr, 1 << (access_info & 0xf), access_info & 0x10,