1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * fs/verity/hash_algs.c: fs-verity hash algorithms
4 *
5 * Copyright 2019 Google LLC
6 */
7
8 #include "fsverity_private.h"
9
10 #include <crypto/hash.h>
11 #include <linux/scatterlist.h>
12
13 /* The hash algorithms supported by fs-verity */
14 struct fsverity_hash_alg fsverity_hash_algs[] = {
15 [FS_VERITY_HASH_ALG_SHA256] = {
16 .name = "sha256",
17 .digest_size = SHA256_DIGEST_SIZE,
18 .block_size = SHA256_BLOCK_SIZE,
19 },
20 [FS_VERITY_HASH_ALG_SHA512] = {
21 .name = "sha512",
22 .digest_size = SHA512_DIGEST_SIZE,
23 .block_size = SHA512_BLOCK_SIZE,
24 },
25 };
26
27 /**
28 * fsverity_get_hash_alg() - validate and prepare a hash algorithm
29 * @inode: optional inode for logging purposes
30 * @num: the hash algorithm number
31 *
32 * Get the struct fsverity_hash_alg for the given hash algorithm number, and
33 * ensure it has a hash transform ready to go. The hash transforms are
34 * allocated on-demand so that we don't waste resources unnecessarily, and
35 * because the crypto modules may be initialized later than fs/verity/.
36 *
37 * Return: pointer to the hash alg on success, else an ERR_PTR()
38 */
fsverity_get_hash_alg(const struct inode * inode,unsigned int num)39 const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
40 unsigned int num)
41 {
42 struct fsverity_hash_alg *alg;
43 struct crypto_ahash *tfm;
44 int err;
45
46 if (num >= ARRAY_SIZE(fsverity_hash_algs) ||
47 !fsverity_hash_algs[num].name) {
48 fsverity_warn(inode, "Unknown hash algorithm number: %u", num);
49 return ERR_PTR(-EINVAL);
50 }
51 alg = &fsverity_hash_algs[num];
52
53 /* pairs with cmpxchg() below */
54 tfm = READ_ONCE(alg->tfm);
55 if (likely(tfm != NULL))
56 return alg;
57 /*
58 * Using the shash API would make things a bit simpler, but the ahash
59 * API is preferable as it allows the use of crypto accelerators.
60 */
61 tfm = crypto_alloc_ahash(alg->name, 0, 0);
62 if (IS_ERR(tfm)) {
63 if (PTR_ERR(tfm) == -ENOENT) {
64 fsverity_warn(inode,
65 "Missing crypto API support for hash algorithm \"%s\"",
66 alg->name);
67 return ERR_PTR(-ENOPKG);
68 }
69 fsverity_err(inode,
70 "Error allocating hash algorithm \"%s\": %ld",
71 alg->name, PTR_ERR(tfm));
72 return ERR_CAST(tfm);
73 }
74
75 err = -EINVAL;
76 if (WARN_ON(alg->digest_size != crypto_ahash_digestsize(tfm)))
77 goto err_free_tfm;
78 if (WARN_ON(alg->block_size != crypto_ahash_blocksize(tfm)))
79 goto err_free_tfm;
80
81 pr_info("%s using implementation \"%s\"\n",
82 alg->name, crypto_ahash_driver_name(tfm));
83
84 /* pairs with READ_ONCE() above */
85 if (cmpxchg(&alg->tfm, NULL, tfm) != NULL)
86 crypto_free_ahash(tfm);
87
88 return alg;
89
90 err_free_tfm:
91 crypto_free_ahash(tfm);
92 return ERR_PTR(err);
93 }
94
95 /**
96 * fsverity_prepare_hash_state() - precompute the initial hash state
97 * @alg: hash algorithm
98 * @salt: a salt which is to be prepended to all data to be hashed
99 * @salt_size: salt size in bytes, possibly 0
100 *
101 * Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed
102 * initial hash state on success or an ERR_PTR() on failure.
103 */
fsverity_prepare_hash_state(const struct fsverity_hash_alg * alg,const u8 * salt,size_t salt_size)104 const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,
105 const u8 *salt, size_t salt_size)
106 {
107 u8 *hashstate = NULL;
108 struct ahash_request *req = NULL;
109 u8 *padded_salt = NULL;
110 size_t padded_salt_size;
111 struct scatterlist sg;
112 DECLARE_CRYPTO_WAIT(wait);
113 int err;
114
115 if (salt_size == 0)
116 return NULL;
117
118 hashstate = kmalloc(crypto_ahash_statesize(alg->tfm), GFP_KERNEL);
119 if (!hashstate)
120 return ERR_PTR(-ENOMEM);
121
122 req = ahash_request_alloc(alg->tfm, GFP_KERNEL);
123 if (!req) {
124 err = -ENOMEM;
125 goto err_free;
126 }
127
128 /*
129 * Zero-pad the salt to the next multiple of the input size of the hash
130 * algorithm's compression function, e.g. 64 bytes for SHA-256 or 128
131 * bytes for SHA-512. This ensures that the hash algorithm won't have
132 * any bytes buffered internally after processing the salt, thus making
133 * salted hashing just as fast as unsalted hashing.
134 */
135 padded_salt_size = round_up(salt_size, alg->block_size);
136 padded_salt = kzalloc(padded_salt_size, GFP_KERNEL);
137 if (!padded_salt) {
138 err = -ENOMEM;
139 goto err_free;
140 }
141 memcpy(padded_salt, salt, salt_size);
142
143 sg_init_one(&sg, padded_salt, padded_salt_size);
144 ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
145 CRYPTO_TFM_REQ_MAY_BACKLOG,
146 crypto_req_done, &wait);
147 ahash_request_set_crypt(req, &sg, NULL, padded_salt_size);
148
149 err = crypto_wait_req(crypto_ahash_init(req), &wait);
150 if (err)
151 goto err_free;
152
153 err = crypto_wait_req(crypto_ahash_update(req), &wait);
154 if (err)
155 goto err_free;
156
157 err = crypto_ahash_export(req, hashstate);
158 if (err)
159 goto err_free;
160 out:
161 ahash_request_free(req);
162 kfree(padded_salt);
163 return hashstate;
164
165 err_free:
166 kfree(hashstate);
167 hashstate = ERR_PTR(err);
168 goto out;
169 }
170
171 /**
172 * fsverity_hash_page() - hash a single data or hash page
173 * @params: the Merkle tree's parameters
174 * @inode: inode for which the hashing is being done
175 * @req: preallocated hash request
176 * @page: the page to hash
177 * @out: output digest, size 'params->digest_size' bytes
178 *
179 * Hash a single data or hash block, assuming block_size == PAGE_SIZE.
180 * The hash is salted if a salt is specified in the Merkle tree parameters.
181 *
182 * Return: 0 on success, -errno on failure
183 */
fsverity_hash_page(const struct merkle_tree_params * params,const struct inode * inode,struct ahash_request * req,struct page * page,u8 * out)184 int fsverity_hash_page(const struct merkle_tree_params *params,
185 const struct inode *inode,
186 struct ahash_request *req, struct page *page, u8 *out)
187 {
188 struct scatterlist sg;
189 DECLARE_CRYPTO_WAIT(wait);
190 int err;
191
192 if (WARN_ON(params->block_size != PAGE_SIZE))
193 return -EINVAL;
194
195 sg_init_table(&sg, 1);
196 sg_set_page(&sg, page, PAGE_SIZE, 0);
197 ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
198 CRYPTO_TFM_REQ_MAY_BACKLOG,
199 crypto_req_done, &wait);
200 ahash_request_set_crypt(req, &sg, out, PAGE_SIZE);
201
202 if (params->hashstate) {
203 err = crypto_ahash_import(req, params->hashstate);
204 if (err) {
205 fsverity_err(inode,
206 "Error %d importing hash state", err);
207 return err;
208 }
209 err = crypto_ahash_finup(req);
210 } else {
211 err = crypto_ahash_digest(req);
212 }
213
214 err = crypto_wait_req(err, &wait);
215 if (err)
216 fsverity_err(inode, "Error %d computing page hash", err);
217 return err;
218 }
219
220 /**
221 * fsverity_hash_buffer() - hash some data
222 * @alg: the hash algorithm to use
223 * @data: the data to hash
224 * @size: size of data to hash, in bytes
225 * @out: output digest, size 'alg->digest_size' bytes
226 *
227 * Hash some data which is located in physically contiguous memory (i.e. memory
228 * allocated by kmalloc(), not by vmalloc()). No salt is used.
229 *
230 * Return: 0 on success, -errno on failure
231 */
fsverity_hash_buffer(const struct fsverity_hash_alg * alg,const void * data,size_t size,u8 * out)232 int fsverity_hash_buffer(const struct fsverity_hash_alg *alg,
233 const void *data, size_t size, u8 *out)
234 {
235 struct ahash_request *req;
236 struct scatterlist sg;
237 DECLARE_CRYPTO_WAIT(wait);
238 int err;
239
240 req = ahash_request_alloc(alg->tfm, GFP_KERNEL);
241 if (!req)
242 return -ENOMEM;
243
244 sg_init_one(&sg, data, size);
245 ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
246 CRYPTO_TFM_REQ_MAY_BACKLOG,
247 crypto_req_done, &wait);
248 ahash_request_set_crypt(req, &sg, out, size);
249
250 err = crypto_wait_req(crypto_ahash_digest(req), &wait);
251
252 ahash_request_free(req);
253 return err;
254 }
255
fsverity_check_hash_algs(void)256 void __init fsverity_check_hash_algs(void)
257 {
258 size_t i;
259
260 /*
261 * Sanity check the hash algorithms (could be a build-time check, but
262 * they're in an array)
263 */
264 for (i = 0; i < ARRAY_SIZE(fsverity_hash_algs); i++) {
265 const struct fsverity_hash_alg *alg = &fsverity_hash_algs[i];
266
267 if (!alg->name)
268 continue;
269
270 BUG_ON(alg->digest_size > FS_VERITY_MAX_DIGEST_SIZE);
271
272 /*
273 * For efficiency, the implementation currently assumes the
274 * digest and block sizes are powers of 2. This limitation can
275 * be lifted if the code is updated to handle other values.
276 */
277 BUG_ON(!is_power_of_2(alg->digest_size));
278 BUG_ON(!is_power_of_2(alg->block_size));
279 }
280 }
281