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(addr) ((u8)0xaa ^ (u8)((unsigned long)(addr) & 0x7))
25
26 /* Maximum stack depth for reports. */
27 #define KFENCE_STACK_DEPTH 64
28
29 /* KFENCE object states. */
30 enum kfence_object_state {
31 KFENCE_OBJECT_UNUSED, /* Object is unused. */
32 KFENCE_OBJECT_ALLOCATED, /* Object is currently allocated. */
33 KFENCE_OBJECT_FREED, /* Object was allocated, and then freed. */
34 };
35
36 /* Alloc/free tracking information. */
37 struct kfence_track {
38 pid_t pid;
39 int cpu;
40 u64 ts_nsec;
41 int num_stack_entries;
42 unsigned long stack_entries[KFENCE_STACK_DEPTH];
43 };
44
45 /* KFENCE metadata per guarded allocation. */
46 struct kfence_metadata {
47 struct list_head list; /* Freelist node; access under kfence_freelist_lock. */
48 struct rcu_head rcu_head; /* For delayed freeing. */
49
50 /*
51 * Lock protecting below data; to ensure consistency of the below data,
52 * since the following may execute concurrently: __kfence_alloc(),
53 * __kfence_free(), kfence_handle_page_fault(). However, note that we
54 * cannot grab the same metadata off the freelist twice, and multiple
55 * __kfence_alloc() cannot run concurrently on the same metadata.
56 */
57 raw_spinlock_t lock;
58
59 /* The current state of the object; see above. */
60 enum kfence_object_state state;
61
62 /*
63 * Allocated object address; cannot be calculated from size, because of
64 * alignment requirements.
65 *
66 * Invariant: ALIGN_DOWN(addr, PAGE_SIZE) is constant.
67 */
68 unsigned long addr;
69
70 /*
71 * The size of the original allocation.
72 */
73 size_t size;
74
75 /*
76 * The kmem_cache cache of the last allocation; NULL if never allocated
77 * or the cache has already been destroyed.
78 */
79 struct kmem_cache *cache;
80
81 /*
82 * In case of an invalid access, the page that was unprotected; we
83 * optimistically only store one address.
84 */
85 unsigned long unprotected_page;
86
87 /* Allocation and free stack information. */
88 struct kfence_track alloc_track;
89 struct kfence_track free_track;
90 /* For updating alloc_covered on frees. */
91 u32 alloc_stack_hash;
92 #ifdef CONFIG_MEMCG
93 struct obj_cgroup *objcg;
94 #endif
95 };
96
97 extern struct kfence_metadata kfence_metadata[CONFIG_KFENCE_NUM_OBJECTS];
98
addr_to_metadata(unsigned long addr)99 static inline struct kfence_metadata *addr_to_metadata(unsigned long addr)
100 {
101 long index;
102
103 /* The checks do not affect performance; only called from slow-paths. */
104
105 if (!is_kfence_address((void *)addr))
106 return NULL;
107
108 /*
109 * May be an invalid index if called with an address at the edge of
110 * __kfence_pool, in which case we would report an "invalid access"
111 * error.
112 */
113 index = (addr - (unsigned long)__kfence_pool) / (PAGE_SIZE * 2) - 1;
114 if (index < 0 || index >= CONFIG_KFENCE_NUM_OBJECTS)
115 return NULL;
116
117 return &kfence_metadata[index];
118 }
119
120 /* KFENCE error types for report generation. */
121 enum kfence_error_type {
122 KFENCE_ERROR_OOB, /* Detected a out-of-bounds access. */
123 KFENCE_ERROR_UAF, /* Detected a use-after-free access. */
124 KFENCE_ERROR_CORRUPTION, /* Detected a memory corruption on free. */
125 KFENCE_ERROR_INVALID, /* Invalid access of unknown type. */
126 KFENCE_ERROR_INVALID_FREE, /* Invalid free. */
127 };
128
129 void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *regs,
130 const struct kfence_metadata *meta, enum kfence_error_type type);
131
132 void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta);
133
134 #endif /* MM_KFENCE_KFENCE_H */
135