1 /* SPDX-License-Identifier: GPL-2.0 */
2 /*
3 * fs-verity: read-only file-based authenticity protection
4 *
5 * Copyright 2019 Google LLC
6 */
7
8 #ifndef _FSVERITY_PRIVATE_H
9 #define _FSVERITY_PRIVATE_H
10
11 #ifdef CONFIG_FS_VERITY_DEBUG
12 #define DEBUG
13 #endif
14
15 #define pr_fmt(fmt) "fs-verity: " fmt
16
17 #include <crypto/sha2.h>
18 #include <linux/fsverity.h>
19 #include <linux/mempool.h>
20
21 struct ahash_request;
22
23 /*
24 * Implementation limit: maximum depth of the Merkle tree. For now 8 is plenty;
25 * it's enough for over U64_MAX bytes of data using SHA-256 and 4K blocks.
26 */
27 #define FS_VERITY_MAX_LEVELS 8
28
29 /*
30 * Largest digest size among all hash algorithms supported by fs-verity.
31 * Currently assumed to be <= size of fsverity_descriptor::root_hash.
32 */
33 #define FS_VERITY_MAX_DIGEST_SIZE SHA512_DIGEST_SIZE
34
35 /* A hash algorithm supported by fs-verity */
36 struct fsverity_hash_alg {
37 struct crypto_ahash *tfm; /* hash tfm, allocated on demand */
38 const char *name; /* crypto API name, e.g. sha256 */
39 unsigned int digest_size; /* digest size in bytes, e.g. 32 for SHA-256 */
40 unsigned int block_size; /* block size in bytes, e.g. 64 for SHA-256 */
41 mempool_t req_pool; /* mempool with a preallocated hash request */
42 };
43
44 /* Merkle tree parameters: hash algorithm, initial hash state, and topology */
45 struct merkle_tree_params {
46 struct fsverity_hash_alg *hash_alg; /* the hash algorithm */
47 const u8 *hashstate; /* initial hash state or NULL */
48 unsigned int digest_size; /* same as hash_alg->digest_size */
49 unsigned int block_size; /* size of data and tree blocks */
50 unsigned int hashes_per_block; /* number of hashes per tree block */
51 unsigned int log_blocksize; /* log2(block_size) */
52 unsigned int log_arity; /* log2(hashes_per_block) */
53 unsigned int num_levels; /* number of levels in Merkle tree */
54 u64 tree_size; /* Merkle tree size in bytes */
55 unsigned long level0_blocks; /* number of blocks in tree level 0 */
56
57 /*
58 * Starting block index for each tree level, ordered from leaf level (0)
59 * to root level ('num_levels - 1')
60 */
61 u64 level_start[FS_VERITY_MAX_LEVELS];
62 };
63
64 /*
65 * fsverity_info - cached verity metadata for an inode
66 *
67 * When a verity file is first opened, an instance of this struct is allocated
68 * and stored in ->i_verity_info; it remains until the inode is evicted. It
69 * caches information about the Merkle tree that's needed to efficiently verify
70 * data read from the file. It also caches the file digest. The Merkle tree
71 * pages themselves are not cached here, but the filesystem may cache them.
72 */
73 struct fsverity_info {
74 struct merkle_tree_params tree_params;
75 u8 root_hash[FS_VERITY_MAX_DIGEST_SIZE];
76 u8 file_digest[FS_VERITY_MAX_DIGEST_SIZE];
77 const struct inode *inode;
78 };
79
80 /* Arbitrary limit to bound the kmalloc() size. Can be changed. */
81 #define FS_VERITY_MAX_DESCRIPTOR_SIZE 16384
82
83 #define FS_VERITY_MAX_SIGNATURE_SIZE (FS_VERITY_MAX_DESCRIPTOR_SIZE - \
84 sizeof(struct fsverity_descriptor))
85
86 /* hash_algs.c */
87
88 extern struct fsverity_hash_alg fsverity_hash_algs[];
89
90 struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
91 unsigned int num);
92 struct ahash_request *fsverity_alloc_hash_request(struct fsverity_hash_alg *alg,
93 gfp_t gfp_flags);
94 void fsverity_free_hash_request(struct fsverity_hash_alg *alg,
95 struct ahash_request *req);
96 const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg,
97 const u8 *salt, size_t salt_size);
98 int fsverity_hash_page(const struct merkle_tree_params *params,
99 const struct inode *inode,
100 struct ahash_request *req, struct page *page, u8 *out);
101 int fsverity_hash_buffer(struct fsverity_hash_alg *alg,
102 const void *data, size_t size, u8 *out);
103 void __init fsverity_check_hash_algs(void);
104
105 /* init.c */
106
107 void __printf(3, 4) __cold
108 fsverity_msg(const struct inode *inode, const char *level,
109 const char *fmt, ...);
110
111 #define fsverity_warn(inode, fmt, ...) \
112 fsverity_msg((inode), KERN_WARNING, fmt, ##__VA_ARGS__)
113 #define fsverity_err(inode, fmt, ...) \
114 fsverity_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__)
115
116 /* open.c */
117
118 int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
119 const struct inode *inode,
120 unsigned int hash_algorithm,
121 unsigned int log_blocksize,
122 const u8 *salt, size_t salt_size);
123
124 struct fsverity_info *fsverity_create_info(const struct inode *inode,
125 struct fsverity_descriptor *desc,
126 size_t desc_size);
127
128 void fsverity_set_info(struct inode *inode, struct fsverity_info *vi);
129
130 void fsverity_free_info(struct fsverity_info *vi);
131
132 int fsverity_get_descriptor(struct inode *inode,
133 struct fsverity_descriptor **desc_ret,
134 size_t *desc_size_ret);
135
136 int __init fsverity_init_info_cache(void);
137 void __init fsverity_exit_info_cache(void);
138
139 /* signature.c */
140
141 #ifdef CONFIG_FS_VERITY_BUILTIN_SIGNATURES
142 int fsverity_verify_signature(const struct fsverity_info *vi,
143 const u8 *signature, size_t sig_size);
144
145 int __init fsverity_init_signature(void);
146 #else /* !CONFIG_FS_VERITY_BUILTIN_SIGNATURES */
147 static inline int
fsverity_verify_signature(const struct fsverity_info * vi,const u8 * signature,size_t sig_size)148 fsverity_verify_signature(const struct fsverity_info *vi,
149 const u8 *signature, size_t sig_size)
150 {
151 return 0;
152 }
153
fsverity_init_signature(void)154 static inline int fsverity_init_signature(void)
155 {
156 return 0;
157 }
158 #endif /* !CONFIG_FS_VERITY_BUILTIN_SIGNATURES */
159
160 /* verify.c */
161
162 int __init fsverity_init_workqueue(void);
163 void __init fsverity_exit_workqueue(void);
164
165 #endif /* _FSVERITY_PRIVATE_H */
166