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. */
38enum 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. */
45struct 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. */
54struct 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 obj_cgroup *objcg;
102#endif
103};
104
105#define KFENCE_METADATA_SIZE PAGE_ALIGN(sizeof(struct kfence_metadata) * \
106					CONFIG_KFENCE_NUM_OBJECTS)
107
108extern struct kfence_metadata *kfence_metadata;
109
110static 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. */
132enum 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
140void 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
143void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta);
144
145#endif /* MM_KFENCE_KFENCE_H */
146