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/sha.h>
18 #include <linux/fsverity.h>
19
20 struct ahash_request;
21
22 /*
23 * Implementation limit: maximum depth of the Merkle tree. For now 8 is plenty;
24 * it's enough for over U64_MAX bytes of data using SHA-256 and 4K blocks.
25 */
26 #define FS_VERITY_MAX_LEVELS 8
27
28 /*
29 * Largest digest size among all hash algorithms supported by fs-verity.
30 * Currently assumed to be <= size of fsverity_descriptor::root_hash.
31 */
32 #define FS_VERITY_MAX_DIGEST_SIZE SHA512_DIGEST_SIZE
33
34 /* A hash algorithm supported by fs-verity */
35 struct fsverity_hash_alg {
36 struct crypto_ahash *tfm; /* hash tfm, allocated on demand */
37 const char *name; /* crypto API name, e.g. sha256 */
38 unsigned int digest_size; /* digest size in bytes, e.g. 32 for SHA-256 */
39 unsigned int block_size; /* block size in bytes, e.g. 64 for SHA-256 */
40 };
41
42 /* Merkle tree parameters: hash algorithm, initial hash state, and topology */
43 struct merkle_tree_params {
44 const struct fsverity_hash_alg *hash_alg; /* the hash algorithm */
45 const u8 *hashstate; /* initial hash state or NULL */
46 unsigned int digest_size; /* same as hash_alg->digest_size */
47 unsigned int block_size; /* size of data and tree blocks */
48 unsigned int hashes_per_block; /* number of hashes per tree block */
49 unsigned int log_blocksize; /* log2(block_size) */
50 unsigned int log_arity; /* log2(hashes_per_block) */
51 unsigned int num_levels; /* number of levels in Merkle tree */
52 u64 tree_size; /* Merkle tree size in bytes */
53
54 /*
55 * Starting block index for each tree level, ordered from leaf level (0)
56 * to root level ('num_levels - 1')
57 */
58 u64 level_start[FS_VERITY_MAX_LEVELS];
59 };
60
61 /**
62 * fsverity_info - cached verity metadata for an inode
63 *
64 * When a verity file is first opened, an instance of this struct is allocated
65 * and stored in ->i_verity_info; it remains until the inode is evicted. It
66 * caches information about the Merkle tree that's needed to efficiently verify
67 * data read from the file. It also caches the file measurement. The Merkle
68 * tree pages themselves are not cached here, but the filesystem may cache them.
69 */
70 struct fsverity_info {
71 struct merkle_tree_params tree_params;
72 u8 root_hash[FS_VERITY_MAX_DIGEST_SIZE];
73 u8 measurement[FS_VERITY_MAX_DIGEST_SIZE];
74 const struct inode *inode;
75 };
76
77 /*
78 * Merkle tree properties. The file measurement is the hash of this structure
79 * excluding the signature and with the sig_size field set to 0.
80 */
81 struct fsverity_descriptor {
82 __u8 version; /* must be 1 */
83 __u8 hash_algorithm; /* Merkle tree hash algorithm */
84 __u8 log_blocksize; /* log2 of size of data and tree blocks */
85 __u8 salt_size; /* size of salt in bytes; 0 if none */
86 __le32 sig_size; /* size of signature in bytes; 0 if none */
87 __le64 data_size; /* size of file the Merkle tree is built over */
88 __u8 root_hash[64]; /* Merkle tree root hash */
89 __u8 salt[32]; /* salt prepended to each hashed block */
90 __u8 __reserved[144]; /* must be 0's */
91 __u8 signature[]; /* optional PKCS#7 signature */
92 };
93
94 /* Arbitrary limit to bound the kmalloc() size. Can be changed. */
95 #define FS_VERITY_MAX_DESCRIPTOR_SIZE 16384
96
97 #define FS_VERITY_MAX_SIGNATURE_SIZE (FS_VERITY_MAX_DESCRIPTOR_SIZE - \
98 sizeof(struct fsverity_descriptor))
99
100 /*
101 * Format in which verity file measurements are signed. This is the same as
102 * 'struct fsverity_digest', except here some magic bytes are prepended to
103 * provide some context about what is being signed in case the same key is used
104 * for non-fsverity purposes, and here the fields have fixed endianness.
105 */
106 struct fsverity_signed_digest {
107 char magic[8]; /* must be "FSVerity" */
108 __le16 digest_algorithm;
109 __le16 digest_size;
110 __u8 digest[];
111 };
112
113 /* hash_algs.c */
114
115 extern struct fsverity_hash_alg fsverity_hash_algs[];
116
117 const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
118 unsigned int num);
119 const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,
120 const u8 *salt, size_t salt_size);
121 int fsverity_hash_page(const struct merkle_tree_params *params,
122 const struct inode *inode,
123 struct ahash_request *req, struct page *page, u8 *out);
124 int fsverity_hash_buffer(const struct fsverity_hash_alg *alg,
125 const void *data, size_t size, u8 *out);
126 void __init fsverity_check_hash_algs(void);
127
128 /* init.c */
129
130 extern void __printf(3, 4) __cold
131 fsverity_msg(const struct inode *inode, const char *level,
132 const char *fmt, ...);
133
134 #define fsverity_warn(inode, fmt, ...) \
135 fsverity_msg((inode), KERN_WARNING, fmt, ##__VA_ARGS__)
136 #define fsverity_err(inode, fmt, ...) \
137 fsverity_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__)
138
139 /* open.c */
140
141 int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
142 const struct inode *inode,
143 unsigned int hash_algorithm,
144 unsigned int log_blocksize,
145 const u8 *salt, size_t salt_size);
146
147 struct fsverity_info *fsverity_create_info(const struct inode *inode,
148 void *desc, size_t desc_size);
149
150 void fsverity_set_info(struct inode *inode, struct fsverity_info *vi);
151
152 void fsverity_free_info(struct fsverity_info *vi);
153
154 int __init fsverity_init_info_cache(void);
155 void __init fsverity_exit_info_cache(void);
156
157 /* signature.c */
158
159 #ifdef CONFIG_FS_VERITY_BUILTIN_SIGNATURES
160 int fsverity_verify_signature(const struct fsverity_info *vi,
161 const struct fsverity_descriptor *desc,
162 size_t desc_size);
163
164 int __init fsverity_init_signature(void);
165 #else /* !CONFIG_FS_VERITY_BUILTIN_SIGNATURES */
166 static inline int
fsverity_verify_signature(const struct fsverity_info * vi,const struct fsverity_descriptor * desc,size_t desc_size)167 fsverity_verify_signature(const struct fsverity_info *vi,
168 const struct fsverity_descriptor *desc,
169 size_t desc_size)
170 {
171 return 0;
172 }
173
fsverity_init_signature(void)174 static inline int fsverity_init_signature(void)
175 {
176 return 0;
177 }
178 #endif /* !CONFIG_FS_VERITY_BUILTIN_SIGNATURES */
179
180 /* verify.c */
181
182 int __init fsverity_init_workqueue(void);
183 void __init fsverity_exit_workqueue(void);
184
185 #endif /* _FSVERITY_PRIVATE_H */
186