1 /* SPDX-License-Identifier: GPL-2.0 */
2 /*
3 * Kernel Electric-Fence (KFENCE). For more info please see
4 * Documentation/dev-tools/kfence.rst.
5 *
6 * Copyright (C) 2020, Google LLC.
7 */
8
9 #ifndef MM_KFENCE_KFENCE_H
10 #define MM_KFENCE_KFENCE_H
11
12 #include <linux/mm.h>
13 #include <linux/slab.h>
14 #include <linux/spinlock.h>
15 #include <linux/types.h>
16
17 #include "../slab.h" /* for struct kmem_cache */
18
19 /*
20 * Get the canary byte pattern for @addr. Use a pattern that varies based on the
21 * lower 3 bits of the address, to detect memory corruptions with higher
22 * probability, where similar constants are used.
23 */
24 #define KFENCE_CANARY_PATTERN_U8(addr) ((u8)0xaa ^ (u8)((unsigned long)(addr) & 0x7))
25
26 /*
27 * Define a continuous 8-byte canary starting from a multiple of 8. The canary
28 * of each byte is only related to the lowest three bits of its address, so the
29 * canary of every 8 bytes is the same. 64-bit memory can be filled and checked
30 * at a time instead of byte by byte to improve performance.
31 */
32 #define KFENCE_CANARY_PATTERN_U64 ((u64)0xaaaaaaaaaaaaaaaa ^ (u64)(le64_to_cpu(0x0706050403020100)))
33
34 /* Maximum stack depth for reports. */
35 #define KFENCE_STACK_DEPTH 64
36
37 /* KFENCE object states. */
38 enum kfence_object_state {
39 KFENCE_OBJECT_UNUSED, /* Object is unused. */
40 KFENCE_OBJECT_ALLOCATED, /* Object is currently allocated. */
41 KFENCE_OBJECT_FREED, /* Object was allocated, and then freed. */
42 };
43
44 /* Alloc/free tracking information. */
45 struct kfence_track {
46 pid_t pid;
47 int cpu;
48 u64 ts_nsec;
49 int num_stack_entries;
50 unsigned long stack_entries[KFENCE_STACK_DEPTH];
51 };
52
53 /* KFENCE metadata per guarded allocation. */
54 struct kfence_metadata {
55 struct list_head list; /* Freelist node; access under kfence_freelist_lock. */
56 struct rcu_head rcu_head; /* For delayed freeing. */
57
58 /*
59 * Lock protecting below data; to ensure consistency of the below data,
60 * since the following may execute concurrently: __kfence_alloc(),
61 * __kfence_free(), kfence_handle_page_fault(). However, note that we
62 * cannot grab the same metadata off the freelist twice, and multiple
63 * __kfence_alloc() cannot run concurrently on the same metadata.
64 */
65 raw_spinlock_t lock;
66
67 /* The current state of the object; see above. */
68 enum kfence_object_state state;
69
70 /*
71 * Allocated object address; cannot be calculated from size, because of
72 * alignment requirements.
73 *
74 * Invariant: ALIGN_DOWN(addr, PAGE_SIZE) is constant.
75 */
76 unsigned long addr;
77
78 /*
79 * The size of the original allocation.
80 */
81 size_t size;
82
83 /*
84 * The kmem_cache cache of the last allocation; NULL if never allocated
85 * or the cache has already been destroyed.
86 */
87 struct kmem_cache *cache;
88
89 /*
90 * In case of an invalid access, the page that was unprotected; we
91 * optimistically only store one address.
92 */
93 unsigned long unprotected_page;
94
95 /* Allocation and free stack information. */
96 struct kfence_track alloc_track;
97 struct kfence_track free_track;
98 /* For updating alloc_covered on frees. */
99 u32 alloc_stack_hash;
100 #ifdef CONFIG_MEMCG
101 struct slabobj_ext obj_exts;
102 #endif
103 };
104
105 #define KFENCE_METADATA_SIZE PAGE_ALIGN(sizeof(struct kfence_metadata) * \
106 CONFIG_KFENCE_NUM_OBJECTS)
107
108 extern struct kfence_metadata *kfence_metadata;
109
110 static inline struct kfence_metadata *addr_to_metadata(unsigned long addr)
111 {
112 long index;
113
114 /* The checks do not affect performance; only called from slow-paths. */
115
116 if (!is_kfence_address((void *)addr))
117 return NULL;
118
119 /*
120 * May be an invalid index if called with an address at the edge of
121 * __kfence_pool, in which case we would report an "invalid access"
122 * error.
123 */
124 index = (addr - (unsigned long)__kfence_pool) / (PAGE_SIZE * 2) - 1;
125 if (index < 0 || index >= CONFIG_KFENCE_NUM_OBJECTS)
126 return NULL;
127
128 return &kfence_metadata[index];
129 }
130
131 /* KFENCE error types for report generation. */
132 enum kfence_error_type {
133 KFENCE_ERROR_OOB, /* Detected a out-of-bounds access. */
134 KFENCE_ERROR_UAF, /* Detected a use-after-free access. */
135 KFENCE_ERROR_CORRUPTION, /* Detected a memory corruption on free. */
136 KFENCE_ERROR_INVALID, /* Invalid access of unknown type. */
137 KFENCE_ERROR_INVALID_FREE, /* Invalid free. */
138 };
139
140 void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *regs,
141 const struct kfence_metadata *meta, enum kfence_error_type type);
142
143 void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta);
144
145 #endif /* MM_KFENCE_KFENCE_H */
146
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