1 | // SPDX-License-Identifier: GPL-2.0 |
2 | /* |
3 | * This file contains core software tag-based KASAN code. |
4 | * |
5 | * Copyright (c) 2018 Google, Inc. |
6 | * Author: Andrey Konovalov <andreyknvl@google.com> |
7 | */ |
8 | |
9 | #define pr_fmt(fmt) "kasan: " fmt |
10 | |
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> |
20 | #include <linux/mm.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> |
32 | |
33 | #include "kasan.h" |
34 | #include "../slab.h" |
35 | |
36 | static DEFINE_PER_CPU(u32, prng_state); |
37 | |
38 | void __init kasan_init_sw_tags(void) |
39 | { |
40 | int cpu; |
41 | |
42 | for_each_possible_cpu(cpu) |
43 | per_cpu(prng_state, cpu) = (u32)get_cycles(); |
44 | |
45 | kasan_init_tags(); |
46 | |
47 | pr_info("KernelAddressSanitizer initialized (sw-tags, stacktrace=%s)\n" , |
48 | kasan_stack_collection_enabled() ? "on" : "off" ); |
49 | } |
50 | |
51 | /* |
52 | * If a preemption happens between this_cpu_read and this_cpu_write, the only |
53 | * side effect is that we'll give a few allocated in different contexts objects |
54 | * the same tag. Since tag-based KASAN is meant to be used a probabilistic |
55 | * bug-detection debug feature, this doesn't have significant negative impact. |
56 | * |
57 | * Ideally the tags use strong randomness to prevent any attempts to predict |
58 | * them during explicit exploit attempts. But strong randomness is expensive, |
59 | * and we did an intentional trade-off to use a PRNG. This non-atomic RMW |
60 | * sequence has in fact positive effect, since interrupts that randomly skew |
61 | * PRNG at unpredictable points do only good. |
62 | */ |
63 | u8 kasan_random_tag(void) |
64 | { |
65 | u32 state = this_cpu_read(prng_state); |
66 | |
67 | state = 1664525 * state + 1013904223; |
68 | this_cpu_write(prng_state, state); |
69 | |
70 | return (u8)(state % (KASAN_TAG_MAX + 1)); |
71 | } |
72 | |
73 | bool kasan_check_range(const void *addr, size_t size, bool write, |
74 | unsigned long ret_ip) |
75 | { |
76 | u8 tag; |
77 | u8 *shadow_first, *shadow_last, *shadow; |
78 | void *untagged_addr; |
79 | |
80 | if (unlikely(size == 0)) |
81 | return true; |
82 | |
83 | if (unlikely(addr + size < addr)) |
84 | return !kasan_report(addr, size, is_write: write, ip: ret_ip); |
85 | |
86 | tag = get_tag((const void *)addr); |
87 | |
88 | /* |
89 | * Ignore accesses for pointers tagged with 0xff (native kernel |
90 | * pointer tag) to suppress false positives caused by kmap. |
91 | * |
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. |
100 | |
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)). |
104 | */ |
105 | if (tag == KASAN_TAG_KERNEL) |
106 | return true; |
107 | |
108 | untagged_addr = kasan_reset_tag(addr: (const void *)addr); |
109 | if (unlikely(!addr_has_metadata(untagged_addr))) |
110 | return !kasan_report(addr, size, is_write: write, ip: ret_ip); |
111 | shadow_first = kasan_mem_to_shadow(untagged_addr); |
112 | shadow_last = kasan_mem_to_shadow(untagged_addr + size - 1); |
113 | for (shadow = shadow_first; shadow <= shadow_last; shadow++) { |
114 | if (*shadow != tag) { |
115 | return !kasan_report(addr, size, is_write: write, ip: ret_ip); |
116 | } |
117 | } |
118 | |
119 | return true; |
120 | } |
121 | |
122 | bool kasan_byte_accessible(const void *addr) |
123 | { |
124 | u8 tag = get_tag(addr); |
125 | void *untagged_addr = kasan_reset_tag(addr); |
126 | u8 shadow_byte; |
127 | |
128 | if (!addr_has_metadata(addr: untagged_addr)) |
129 | return false; |
130 | |
131 | shadow_byte = READ_ONCE(*(u8 *)kasan_mem_to_shadow(untagged_addr)); |
132 | return tag == KASAN_TAG_KERNEL || tag == shadow_byte; |
133 | } |
134 | |
135 | #define DEFINE_HWASAN_LOAD_STORE(size) \ |
136 | void __hwasan_load##size##_noabort(void *addr) \ |
137 | { \ |
138 | kasan_check_range(addr, size, false, _RET_IP_); \ |
139 | } \ |
140 | EXPORT_SYMBOL(__hwasan_load##size##_noabort); \ |
141 | void __hwasan_store##size##_noabort(void *addr) \ |
142 | { \ |
143 | kasan_check_range(addr, size, true, _RET_IP_); \ |
144 | } \ |
145 | EXPORT_SYMBOL(__hwasan_store##size##_noabort) |
146 | |
147 | DEFINE_HWASAN_LOAD_STORE(1); |
148 | DEFINE_HWASAN_LOAD_STORE(2); |
149 | DEFINE_HWASAN_LOAD_STORE(4); |
150 | DEFINE_HWASAN_LOAD_STORE(8); |
151 | DEFINE_HWASAN_LOAD_STORE(16); |
152 | |
153 | void __hwasan_loadN_noabort(void *addr, ssize_t size) |
154 | { |
155 | kasan_check_range(addr, size, write: false, _RET_IP_); |
156 | } |
157 | EXPORT_SYMBOL(__hwasan_loadN_noabort); |
158 | |
159 | void __hwasan_storeN_noabort(void *addr, ssize_t size) |
160 | { |
161 | kasan_check_range(addr, size, write: true, _RET_IP_); |
162 | } |
163 | EXPORT_SYMBOL(__hwasan_storeN_noabort); |
164 | |
165 | void __hwasan_tag_memory(void *addr, u8 tag, ssize_t size) |
166 | { |
167 | kasan_poison(addr, size, value: tag, init: false); |
168 | } |
169 | EXPORT_SYMBOL(__hwasan_tag_memory); |
170 | |
171 | void kasan_tag_mismatch(void *addr, unsigned long access_info, |
172 | unsigned long ret_ip) |
173 | { |
174 | kasan_report(addr, size: 1 << (access_info & 0xf), is_write: access_info & 0x10, |
175 | ip: ret_ip); |
176 | } |
177 | |