1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * This file contains core tag-based KASAN code.
4 *
5 * Copyright (c) 2018 Google, Inc.
6 * Author: Andrey Konovalov <andreyknvl@google.com>
7 *
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License version 2 as
10 * published by the Free Software Foundation.
11 *
12 */
13
14 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
15 #define DISABLE_BRANCH_PROFILING
16
17 #include <linux/export.h>
18 #include <linux/interrupt.h>
19 #include <linux/init.h>
20 #include <linux/kasan.h>
21 #include <linux/kernel.h>
22 #include <linux/kmemleak.h>
23 #include <linux/linkage.h>
24 #include <linux/memblock.h>
25 #include <linux/memory.h>
26 #include <linux/mm.h>
27 #include <linux/module.h>
28 #include <linux/printk.h>
29 #include <linux/random.h>
30 #include <linux/sched.h>
31 #include <linux/sched/task_stack.h>
32 #include <linux/slab.h>
33 #include <linux/stacktrace.h>
34 #include <linux/string.h>
35 #include <linux/types.h>
36 #include <linux/vmalloc.h>
37 #include <linux/bug.h>
38
39 #include "kasan.h"
40 #include "../slab.h"
41
42 static DEFINE_PER_CPU(u32, prng_state);
43
kasan_init_tags(void)44 void kasan_init_tags(void)
45 {
46 int cpu;
47
48 for_each_possible_cpu(cpu)
49 per_cpu(prng_state, cpu) = (u32)get_cycles();
50 }
51
52 /*
53 * If a preemption happens between this_cpu_read and this_cpu_write, the only
54 * side effect is that we'll give a few allocated in different contexts objects
55 * the same tag. Since tag-based KASAN is meant to be used a probabilistic
56 * bug-detection debug feature, this doesn't have significant negative impact.
57 *
58 * Ideally the tags use strong randomness to prevent any attempts to predict
59 * them during explicit exploit attempts. But strong randomness is expensive,
60 * and we did an intentional trade-off to use a PRNG. This non-atomic RMW
61 * sequence has in fact positive effect, since interrupts that randomly skew
62 * PRNG at unpredictable points do only good.
63 */
random_tag(void)64 u8 random_tag(void)
65 {
66 u32 state = this_cpu_read(prng_state);
67
68 state = 1664525 * state + 1013904223;
69 this_cpu_write(prng_state, state);
70
71 return (u8)(state % (KASAN_TAG_MAX + 1));
72 }
73
kasan_reset_tag(const void * addr)74 void *kasan_reset_tag(const void *addr)
75 {
76 return reset_tag(addr);
77 }
78
check_memory_region(unsigned long addr,size_t size,bool write,unsigned long ret_ip)79 bool check_memory_region(unsigned long addr, size_t size, bool write,
80 unsigned long ret_ip)
81 {
82 u8 tag;
83 u8 *shadow_first, *shadow_last, *shadow;
84 void *untagged_addr;
85
86 if (unlikely(size == 0))
87 return true;
88
89 tag = get_tag((const void *)addr);
90
91 /*
92 * Ignore accesses for pointers tagged with 0xff (native kernel
93 * pointer tag) to suppress false positives caused by kmap.
94 *
95 * Some kernel code was written to account for archs that don't keep
96 * high memory mapped all the time, but rather map and unmap particular
97 * pages when needed. Instead of storing a pointer to the kernel memory,
98 * this code saves the address of the page structure and offset within
99 * that page for later use. Those pages are then mapped and unmapped
100 * with kmap/kunmap when necessary and virt_to_page is used to get the
101 * virtual address of the page. For arm64 (that keeps the high memory
102 * mapped all the time), kmap is turned into a page_address call.
103
104 * The issue is that with use of the page_address + virt_to_page
105 * sequence the top byte value of the original pointer gets lost (gets
106 * set to KASAN_TAG_KERNEL (0xFF)).
107 */
108 if (tag == KASAN_TAG_KERNEL)
109 return true;
110
111 untagged_addr = reset_tag((const void *)addr);
112 if (unlikely(untagged_addr <
113 kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) {
114 kasan_report(addr, size, write, ret_ip);
115 return false;
116 }
117 shadow_first = kasan_mem_to_shadow(untagged_addr);
118 shadow_last = kasan_mem_to_shadow(untagged_addr + size - 1);
119 for (shadow = shadow_first; shadow <= shadow_last; shadow++) {
120 if (*shadow != tag) {
121 kasan_report(addr, size, write, ret_ip);
122 return false;
123 }
124 }
125
126 return true;
127 }
128
129 #define DEFINE_HWASAN_LOAD_STORE(size) \
130 void __hwasan_load##size##_noabort(unsigned long addr) \
131 { \
132 check_memory_region(addr, size, false, _RET_IP_); \
133 } \
134 EXPORT_SYMBOL(__hwasan_load##size##_noabort); \
135 void __hwasan_store##size##_noabort(unsigned long addr) \
136 { \
137 check_memory_region(addr, size, true, _RET_IP_); \
138 } \
139 EXPORT_SYMBOL(__hwasan_store##size##_noabort)
140
141 DEFINE_HWASAN_LOAD_STORE(1);
142 DEFINE_HWASAN_LOAD_STORE(2);
143 DEFINE_HWASAN_LOAD_STORE(4);
144 DEFINE_HWASAN_LOAD_STORE(8);
145 DEFINE_HWASAN_LOAD_STORE(16);
146
__hwasan_loadN_noabort(unsigned long addr,unsigned long size)147 void __hwasan_loadN_noabort(unsigned long addr, unsigned long size)
148 {
149 check_memory_region(addr, size, false, _RET_IP_);
150 }
151 EXPORT_SYMBOL(__hwasan_loadN_noabort);
152
__hwasan_storeN_noabort(unsigned long addr,unsigned long size)153 void __hwasan_storeN_noabort(unsigned long addr, unsigned long size)
154 {
155 check_memory_region(addr, size, true, _RET_IP_);
156 }
157 EXPORT_SYMBOL(__hwasan_storeN_noabort);
158
__hwasan_tag_memory(unsigned long addr,u8 tag,unsigned long size)159 void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size)
160 {
161 kasan_poison_shadow((void *)addr, size, tag);
162 }
163 EXPORT_SYMBOL(__hwasan_tag_memory);
164