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 */
 14struct 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 */
 39const 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
 90err_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 */
104const 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;
160out:
161	ahash_request_free(req);
162	kfree(padded_salt);
163	return hashstate;
164
165err_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 */
184int 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 */
232int 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
256void __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}