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 
kasan_init_sw_tags(void)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  */
kasan_random_tag(void)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 
kasan_check_range(const void * addr,size_t size,bool write,unsigned long ret_ip)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, write, 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((const void *)addr);
109 	if (unlikely(!addr_has_metadata(untagged_addr)))
110 		return !kasan_report(addr, size, write, 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, write, ret_ip);
116 		}
117 	}
118 
119 	return true;
120 }
121 
kasan_byte_accessible(const void * addr)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(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 
__hwasan_loadN_noabort(void * addr,ssize_t size)153 void __hwasan_loadN_noabort(void *addr, ssize_t size)
154 {
155 	kasan_check_range(addr, size, false, _RET_IP_);
156 }
157 EXPORT_SYMBOL(__hwasan_loadN_noabort);
158 
__hwasan_storeN_noabort(void * addr,ssize_t size)159 void __hwasan_storeN_noabort(void *addr, ssize_t size)
160 {
161 	kasan_check_range(addr, size, true, _RET_IP_);
162 }
163 EXPORT_SYMBOL(__hwasan_storeN_noabort);
164 
__hwasan_tag_memory(void * addr,u8 tag,ssize_t size)165 void __hwasan_tag_memory(void *addr, u8 tag, ssize_t size)
166 {
167 	kasan_poison(addr, size, tag, false);
168 }
169 EXPORT_SYMBOL(__hwasan_tag_memory);
170 
kasan_tag_mismatch(void * addr,unsigned long access_info,unsigned long ret_ip)171 void kasan_tag_mismatch(void *addr, unsigned long access_info,
172 			unsigned long ret_ip)
173 {
174 	kasan_report(addr, 1 << (access_info & 0xf), access_info & 0x10,
175 		     ret_ip);
176 }
177