[linux-block.git] / fs / verity / hash_algs.c

// SPDX-License-Identifier: GPL-2.0
/*
 * fs-verity hash algorithms
 *
 * Copyright 2019 Google LLC
 */

#include "fsverity_private.h"

#include <crypto/hash.h>
#include <linux/scatterlist.h>

/* The hash algorithms supported by fs-verity */
struct fsverity_hash_alg fsverity_hash_algs[] = {
	[FS_VERITY_HASH_ALG_SHA256] = {
		.name = "sha256",
		.digest_size = SHA256_DIGEST_SIZE,
		.block_size = SHA256_BLOCK_SIZE,
		.algo_id = HASH_ALGO_SHA256,
	},
	[FS_VERITY_HASH_ALG_SHA512] = {
		.name = "sha512",
		.digest_size = SHA512_DIGEST_SIZE,
		.block_size = SHA512_BLOCK_SIZE,
		.algo_id = HASH_ALGO_SHA512,
	},
};

static DEFINE_MUTEX(fsverity_hash_alg_init_mutex);

/**
 * fsverity_get_hash_alg() - validate and prepare a hash algorithm
 * @inode: optional inode for logging purposes
 * @num: the hash algorithm number
 *
 * Get the struct fsverity_hash_alg for the given hash algorithm number, and
 * ensure it has a hash transform ready to go.  The hash transforms are
 * allocated on-demand so that we don't waste resources unnecessarily, and
 * because the crypto modules may be initialized later than fs/verity/.
 *
 * Return: pointer to the hash alg on success, else an ERR_PTR()
 */
struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
						unsigned int num)
{
	struct fsverity_hash_alg *alg;
	struct crypto_ahash *tfm;
	int err;

	if (num >= ARRAY_SIZE(fsverity_hash_algs) ||
	    !fsverity_hash_algs[num].name) {
		fsverity_warn(inode, "Unknown hash algorithm number: %u", num);
		return ERR_PTR(-EINVAL);
	}
	alg = &fsverity_hash_algs[num];

	/* pairs with smp_store_release() below */
	if (likely(smp_load_acquire(&alg->tfm) != NULL))
		return alg;

	mutex_lock(&fsverity_hash_alg_init_mutex);

	if (alg->tfm != NULL)
		goto out_unlock;

	/*
	 * Using the shash API would make things a bit simpler, but the ahash
	 * API is preferable as it allows the use of crypto accelerators.
	 */
	tfm = crypto_alloc_ahash(alg->name, 0, 0);
	if (IS_ERR(tfm)) {
		if (PTR_ERR(tfm) == -ENOENT) {
			fsverity_warn(inode,
				      "Missing crypto API support for hash algorithm \"%s\"",
				      alg->name);
			alg = ERR_PTR(-ENOPKG);
			goto out_unlock;
		}
		fsverity_err(inode,
			     "Error allocating hash algorithm \"%s\": %ld",
			     alg->name, PTR_ERR(tfm));
		alg = ERR_CAST(tfm);
		goto out_unlock;
	}

	err = -EINVAL;
	if (WARN_ON_ONCE(alg->digest_size != crypto_ahash_digestsize(tfm)))
		goto err_free_tfm;
	if (WARN_ON_ONCE(alg->block_size != crypto_ahash_blocksize(tfm)))
		goto err_free_tfm;

	err = mempool_init_kmalloc_pool(&alg->req_pool, 1,
					sizeof(struct ahash_request) +
					crypto_ahash_reqsize(tfm));
	if (err)
		goto err_free_tfm;

	pr_info("%s using implementation \"%s\"\n",
		alg->name, crypto_ahash_driver_name(tfm));

	/* pairs with smp_load_acquire() above */
	smp_store_release(&alg->tfm, tfm);
	goto out_unlock;

err_free_tfm:
	crypto_free_ahash(tfm);
	alg = ERR_PTR(err);
out_unlock:
	mutex_unlock(&fsverity_hash_alg_init_mutex);
	return alg;
}

/**
 * fsverity_alloc_hash_request() - allocate a hash request object
 * @alg: the hash algorithm for which to allocate the request
 * @gfp_flags: memory allocation flags
 *
 * This is mempool-backed, so this never fails if __GFP_DIRECT_RECLAIM is set in
 * @gfp_flags.  However, in that case this might need to wait for all
 * previously-allocated requests to be freed.  So to avoid deadlocks, callers
 * must never need multiple requests at a time to make forward progress.
 *
 * Return: the request object on success; NULL on failure (but see above)
 */
struct ahash_request *fsverity_alloc_hash_request(struct fsverity_hash_alg *alg,
						  gfp_t gfp_flags)
{
	struct ahash_request *req = mempool_alloc(&alg->req_pool, gfp_flags);

	if (req)
		ahash_request_set_tfm(req, alg->tfm);
	return req;
}

/**
 * fsverity_free_hash_request() - free a hash request object
 * @alg: the hash algorithm
 * @req: the hash request object to free
 */
void fsverity_free_hash_request(struct fsverity_hash_alg *alg,
				struct ahash_request *req)
{
	if (req) {
		ahash_request_zero(req);
		mempool_free(req, &alg->req_pool);
	}
}

/**
 * fsverity_prepare_hash_state() - precompute the initial hash state
 * @alg: hash algorithm
 * @salt: a salt which is to be prepended to all data to be hashed
 * @salt_size: salt size in bytes, possibly 0
 *
 * Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed
 *	   initial hash state on success or an ERR_PTR() on failure.
 */
const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg,
				      const u8 *salt, size_t salt_size)
{
	u8 *hashstate = NULL;
	struct ahash_request *req = NULL;
	u8 *padded_salt = NULL;
	size_t padded_salt_size;
	struct scatterlist sg;
	DECLARE_CRYPTO_WAIT(wait);
	int err;

	if (salt_size == 0)
		return NULL;

	hashstate = kmalloc(crypto_ahash_statesize(alg->tfm), GFP_KERNEL);
	if (!hashstate)
		return ERR_PTR(-ENOMEM);

	/* This allocation never fails, since it's mempool-backed. */
	req = fsverity_alloc_hash_request(alg, GFP_KERNEL);

	/*
	 * Zero-pad the salt to the next multiple of the input size of the hash
	 * algorithm's compression function, e.g. 64 bytes for SHA-256 or 128
	 * bytes for SHA-512.  This ensures that the hash algorithm won't have
	 * any bytes buffered internally after processing the salt, thus making
	 * salted hashing just as fast as unsalted hashing.
	 */
	padded_salt_size = round_up(salt_size, alg->block_size);
	padded_salt = kzalloc(padded_salt_size, GFP_KERNEL);
	if (!padded_salt) {
		err = -ENOMEM;
		goto err_free;
	}
	memcpy(padded_salt, salt, salt_size);

	sg_init_one(&sg, padded_salt, padded_salt_size);
	ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
					CRYPTO_TFM_REQ_MAY_BACKLOG,
				   crypto_req_done, &wait);
	ahash_request_set_crypt(req, &sg, NULL, padded_salt_size);

	err = crypto_wait_req(crypto_ahash_init(req), &wait);
	if (err)
		goto err_free;

	err = crypto_wait_req(crypto_ahash_update(req), &wait);
	if (err)
		goto err_free;

	err = crypto_ahash_export(req, hashstate);
	if (err)
		goto err_free;
out:
	fsverity_free_hash_request(alg, req);
	kfree(padded_salt);
	return hashstate;

err_free:
	kfree(hashstate);
	hashstate = ERR_PTR(err);
	goto out;
}

/**
 * fsverity_hash_block() - hash a single data or hash block
 * @params: the Merkle tree's parameters
 * @inode: inode for which the hashing is being done
 * @req: preallocated hash request
 * @page: the page containing the block to hash
 * @offset: the offset of the block within @page
 * @out: output digest, size 'params->digest_size' bytes
 *
 * Hash a single data or hash block.  The hash is salted if a salt is specified
 * in the Merkle tree parameters.
 *
 * Return: 0 on success, -errno on failure
 */
int fsverity_hash_block(const struct merkle_tree_params *params,
			const struct inode *inode, struct ahash_request *req,
			struct page *page, unsigned int offset, u8 *out)
{
	struct scatterlist sg;
	DECLARE_CRYPTO_WAIT(wait);
	int err;

	sg_init_table(&sg, 1);
	sg_set_page(&sg, page, params->block_size, offset);
	ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
					CRYPTO_TFM_REQ_MAY_BACKLOG,
				   crypto_req_done, &wait);
	ahash_request_set_crypt(req, &sg, out, params->block_size);

	if (params->hashstate) {
		err = crypto_ahash_import(req, params->hashstate);
		if (err) {
			fsverity_err(inode,
				     "Error %d importing hash state", err);
			return err;
		}
		err = crypto_ahash_finup(req);
	} else {
		err = crypto_ahash_digest(req);
	}

	err = crypto_wait_req(err, &wait);
	if (err)
		fsverity_err(inode, "Error %d computing block hash", err);
	return err;
}

/**
 * fsverity_hash_buffer() - hash some data
 * @alg: the hash algorithm to use
 * @data: the data to hash
 * @size: size of data to hash, in bytes
 * @out: output digest, size 'alg->digest_size' bytes
 *
 * Hash some data which is located in physically contiguous memory (i.e. memory
 * allocated by kmalloc(), not by vmalloc()).  No salt is used.
 *
 * Return: 0 on success, -errno on failure
 */
int fsverity_hash_buffer(struct fsverity_hash_alg *alg,
			 const void *data, size_t size, u8 *out)
{
	struct ahash_request *req;
	struct scatterlist sg;
	DECLARE_CRYPTO_WAIT(wait);
	int err;

	/* This allocation never fails, since it's mempool-backed. */
	req = fsverity_alloc_hash_request(alg, GFP_KERNEL);

	sg_init_one(&sg, data, size);
	ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
					CRYPTO_TFM_REQ_MAY_BACKLOG,
				   crypto_req_done, &wait);
	ahash_request_set_crypt(req, &sg, out, size);

	err = crypto_wait_req(crypto_ahash_digest(req), &wait);

	fsverity_free_hash_request(alg, req);
	return err;
}

void __init fsverity_check_hash_algs(void)
{
	size_t i;

	/*
	 * Sanity check the hash algorithms (could be a build-time check, but
	 * they're in an array)
	 */
	for (i = 0; i < ARRAY_SIZE(fsverity_hash_algs); i++) {
		const struct fsverity_hash_alg *alg = &fsverity_hash_algs[i];

		if (!alg->name)
			continue;

		BUG_ON(alg->digest_size > FS_VERITY_MAX_DIGEST_SIZE);

		/*
		 * For efficiency, the implementation currently assumes the
		 * digest and block sizes are powers of 2.  This limitation can
		 * be lifted if the code is updated to handle other values.
		 */
		BUG_ON(!is_power_of_2(alg->digest_size));
		BUG_ON(!is_power_of_2(alg->block_size));

		/* Verify that there is a valid mapping to HASH_ALGO_*. */
		BUG_ON(alg->algo_id == 0);
		BUG_ON(alg->digest_size != hash_digest_size[alg->algo_id]);
	}
}
Commit	Line	Data
671e67b4 EB	1	// SPDX-License-Identifier: GPL-2.0
671e67b4 EB	2	/*
7bf765dd	3	* fs-verity hash algorithms
671e67b4 EB	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,
a4bbf53d	19	.algo_id = HASH_ALGO_SHA256,
671e67b4	20	},
add890c9 EB	21	[FS_VERITY_HASH_ALG_SHA512] = {
	22	.name = "sha512",
	23	.digest_size = SHA512_DIGEST_SIZE,
	24	.block_size = SHA512_BLOCK_SIZE,
a4bbf53d	25	.algo_id = HASH_ALGO_SHA512,
add890c9	26	},
671e67b4 EB	27	};
671e67b4 EB	28
439bea10 EB	29	static DEFINE_MUTEX(fsverity_hash_alg_init_mutex);
439bea10 EB	30
671e67b4 EB	31	/**
	32	* fsverity_get_hash_alg() - validate and prepare a hash algorithm
	33	* @inode: optional inode for logging purposes
	34	* @num: the hash algorithm number
	35	*
	36	* Get the struct fsverity_hash_alg for the given hash algorithm number, and
	37	* ensure it has a hash transform ready to go. The hash transforms are
	38	* allocated on-demand so that we don't waste resources unnecessarily, and
	39	* because the crypto modules may be initialized later than fs/verity/.
	40	*
	41	* Return: pointer to the hash alg on success, else an ERR_PTR()
	42	*/
439bea10 EB	43	struct fsverity_hash_alg fsverity_get_hash_alg(const struct inode inode,
439bea10 EB	44	unsigned int num)
671e67b4 EB	45	{
	46	struct fsverity_hash_alg *alg;
	47	struct crypto_ahash *tfm;
	48	int err;
	49
	50	if (num >= ARRAY_SIZE(fsverity_hash_algs) \|\|
	51	!fsverity_hash_algs[num].name) {
	52	fsverity_warn(inode, "Unknown hash algorithm number: %u", num);
	53	return ERR_PTR(-EINVAL);
	54	}
	55	alg = &fsverity_hash_algs[num];
	56
439bea10 EB	57	/* pairs with smp_store_release() below */
439bea10 EB	58	if (likely(smp_load_acquire(&alg->tfm) != NULL))
671e67b4	59	return alg;
439bea10 EB	60
	61	mutex_lock(&fsverity_hash_alg_init_mutex);
	62
	63	if (alg->tfm != NULL)
	64	goto out_unlock;
	65
671e67b4 EB	66	/*
	67	* Using the shash API would make things a bit simpler, but the ahash
	68	* API is preferable as it allows the use of crypto accelerators.
	69	*/
	70	tfm = crypto_alloc_ahash(alg->name, 0, 0);
	71	if (IS_ERR(tfm)) {
	72	if (PTR_ERR(tfm) == -ENOENT) {
	73	fsverity_warn(inode,
	74	"Missing crypto API support for hash algorithm \"%s\"",
	75	alg->name);
439bea10 EB	76	alg = ERR_PTR(-ENOPKG);
439bea10 EB	77	goto out_unlock;
671e67b4 EB	78	}
	79	fsverity_err(inode,
	80	"Error allocating hash algorithm \"%s\": %ld",
	81	alg->name, PTR_ERR(tfm));
439bea10 EB	82	alg = ERR_CAST(tfm);
439bea10 EB	83	goto out_unlock;
671e67b4 EB	84	}
	85
	86	err = -EINVAL;
8eb8af4b	87	if (WARN_ON_ONCE(alg->digest_size != crypto_ahash_digestsize(tfm)))
671e67b4	88	goto err_free_tfm;
8eb8af4b	89	if (WARN_ON_ONCE(alg->block_size != crypto_ahash_blocksize(tfm)))
671e67b4 EB	90	goto err_free_tfm;
671e67b4 EB	91
439bea10 EB	92	err = mempool_init_kmalloc_pool(&alg->req_pool, 1,
	93	sizeof(struct ahash_request) +
	94	crypto_ahash_reqsize(tfm));
	95	if (err)
	96	goto err_free_tfm;
	97
671e67b4 EB	98	pr_info("%s using implementation \"%s\"\n",
	99	alg->name, crypto_ahash_driver_name(tfm));
	100
439bea10 EB	101	/* pairs with smp_load_acquire() above */
	102	smp_store_release(&alg->tfm, tfm);
	103	goto out_unlock;
671e67b4 EB	104
	105	err_free_tfm:
	106	crypto_free_ahash(tfm);
439bea10 EB	107	alg = ERR_PTR(err);
	108	out_unlock:
	109	mutex_unlock(&fsverity_hash_alg_init_mutex);
	110	return alg;
	111	}
	112
	113	/**
	114	* fsverity_alloc_hash_request() - allocate a hash request object
	115	* @alg: the hash algorithm for which to allocate the request
	116	* @gfp_flags: memory allocation flags
	117	*
	118	* This is mempool-backed, so this never fails if __GFP_DIRECT_RECLAIM is set in
	119	* @gfp_flags. However, in that case this might need to wait for all
	120	* previously-allocated requests to be freed. So to avoid deadlocks, callers
	121	* must never need multiple requests at a time to make forward progress.
	122	*
	123	* Return: the request object on success; NULL on failure (but see above)
	124	*/
	125	struct ahash_request fsverity_alloc_hash_request(struct fsverity_hash_alg alg,
	126	gfp_t gfp_flags)
	127	{
	128	struct ahash_request *req = mempool_alloc(&alg->req_pool, gfp_flags);
	129
	130	if (req)
	131	ahash_request_set_tfm(req, alg->tfm);
	132	return req;
	133	}
	134
	135	/**
	136	* fsverity_free_hash_request() - free a hash request object
	137	* @alg: the hash algorithm
	138	* @req: the hash request object to free
	139	*/
	140	void fsverity_free_hash_request(struct fsverity_hash_alg *alg,
	141	struct ahash_request *req)
	142	{
	143	if (req) {
	144	ahash_request_zero(req);
	145	mempool_free(req, &alg->req_pool);
	146	}
671e67b4 EB	147	}
	148
	149	/**
	150	* fsverity_prepare_hash_state() - precompute the initial hash state
	151	* @alg: hash algorithm
	152	* @salt: a salt which is to be prepended to all data to be hashed
	153	* @salt_size: salt size in bytes, possibly 0
	154	*
	155	* Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed
	156	* initial hash state on success or an ERR_PTR() on failure.
	157	*/
439bea10	158	const u8 fsverity_prepare_hash_state(struct fsverity_hash_alg alg,
671e67b4 EB	159	const u8 *salt, size_t salt_size)
	160	{
	161	u8 *hashstate = NULL;
	162	struct ahash_request *req = NULL;
	163	u8 *padded_salt = NULL;
	164	size_t padded_salt_size;
	165	struct scatterlist sg;
	166	DECLARE_CRYPTO_WAIT(wait);
	167	int err;
	168
	169	if (salt_size == 0)
	170	return NULL;
	171
	172	hashstate = kmalloc(crypto_ahash_statesize(alg->tfm), GFP_KERNEL);
	173	if (!hashstate)
	174	return ERR_PTR(-ENOMEM);
	175
439bea10 EB	176	/* This allocation never fails, since it's mempool-backed. */
439bea10 EB	177	req = fsverity_alloc_hash_request(alg, GFP_KERNEL);
671e67b4 EB	178
	179	/*
	180	* Zero-pad the salt to the next multiple of the input size of the hash
	181	* algorithm's compression function, e.g. 64 bytes for SHA-256 or 128
	182	* bytes for SHA-512. This ensures that the hash algorithm won't have
	183	* any bytes buffered internally after processing the salt, thus making
	184	* salted hashing just as fast as unsalted hashing.
	185	*/
	186	padded_salt_size = round_up(salt_size, alg->block_size);
	187	padded_salt = kzalloc(padded_salt_size, GFP_KERNEL);
	188	if (!padded_salt) {
	189	err = -ENOMEM;
	190	goto err_free;
	191	}
	192	memcpy(padded_salt, salt, salt_size);
	193
	194	sg_init_one(&sg, padded_salt, padded_salt_size);
	195	ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP \|
	196	CRYPTO_TFM_REQ_MAY_BACKLOG,
	197	crypto_req_done, &wait);
	198	ahash_request_set_crypt(req, &sg, NULL, padded_salt_size);
	199
	200	err = crypto_wait_req(crypto_ahash_init(req), &wait);
	201	if (err)
	202	goto err_free;
	203
	204	err = crypto_wait_req(crypto_ahash_update(req), &wait);
	205	if (err)
	206	goto err_free;
	207
	208	err = crypto_ahash_export(req, hashstate);
	209	if (err)
	210	goto err_free;
	211	out:
439bea10	212	fsverity_free_hash_request(alg, req);
671e67b4 EB	213	kfree(padded_salt);
	214	return hashstate;
	215
	216	err_free:
	217	kfree(hashstate);
	218	hashstate = ERR_PTR(err);
	219	goto out;
	220	}
	221
	222	/**
f45555bf	223	* fsverity_hash_block() - hash a single data or hash block
671e67b4 EB	224	* @params: the Merkle tree's parameters
	225	* @inode: inode for which the hashing is being done
	226	* @req: preallocated hash request
f45555bf EB	227	* @page: the page containing the block to hash
f45555bf EB	228	* @offset: the offset of the block within @page
671e67b4 EB	229	* @out: output digest, size 'params->digest_size' bytes
671e67b4 EB	230	*
f45555bf EB	231	* Hash a single data or hash block. The hash is salted if a salt is specified
f45555bf EB	232	* in the Merkle tree parameters.
671e67b4 EB	233	*
	234	* Return: 0 on success, -errno on failure
	235	*/
f45555bf EB	236	int fsverity_hash_block(const struct merkle_tree_params *params,
	237	const struct inode inode, struct ahash_request req,
	238	struct page page, unsigned int offset, u8 out)
671e67b4 EB	239	{
	240	struct scatterlist sg;
	241	DECLARE_CRYPTO_WAIT(wait);
	242	int err;
	243
671e67b4	244	sg_init_table(&sg, 1);
f45555bf	245	sg_set_page(&sg, page, params->block_size, offset);
671e67b4 EB	246	ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP \|
	247	CRYPTO_TFM_REQ_MAY_BACKLOG,
	248	crypto_req_done, &wait);
f45555bf	249	ahash_request_set_crypt(req, &sg, out, params->block_size);
671e67b4 EB	250
	251	if (params->hashstate) {
	252	err = crypto_ahash_import(req, params->hashstate);
	253	if (err) {
	254	fsverity_err(inode,
	255	"Error %d importing hash state", err);
	256	return err;
	257	}
	258	err = crypto_ahash_finup(req);
	259	} else {
	260	err = crypto_ahash_digest(req);
	261	}
	262
	263	err = crypto_wait_req(err, &wait);
	264	if (err)
f45555bf	265	fsverity_err(inode, "Error %d computing block hash", err);
671e67b4 EB	266	return err;
	267	}
	268
	269	/**
	270	* fsverity_hash_buffer() - hash some data
	271	* @alg: the hash algorithm to use
	272	* @data: the data to hash
	273	* @size: size of data to hash, in bytes
	274	* @out: output digest, size 'alg->digest_size' bytes
	275	*
	276	* Hash some data which is located in physically contiguous memory (i.e. memory
	277	* allocated by kmalloc(), not by vmalloc()). No salt is used.
	278	*
	279	* Return: 0 on success, -errno on failure
	280	*/
439bea10	281	int fsverity_hash_buffer(struct fsverity_hash_alg *alg,
671e67b4 EB	282	const void data, size_t size, u8 out)
	283	{
	284	struct ahash_request *req;
	285	struct scatterlist sg;
	286	DECLARE_CRYPTO_WAIT(wait);
	287	int err;
	288
439bea10 EB	289	/* This allocation never fails, since it's mempool-backed. */
439bea10 EB	290	req = fsverity_alloc_hash_request(alg, GFP_KERNEL);
671e67b4 EB	291
	292	sg_init_one(&sg, data, size);
	293	ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP \|
	294	CRYPTO_TFM_REQ_MAY_BACKLOG,
	295	crypto_req_done, &wait);
	296	ahash_request_set_crypt(req, &sg, out, size);
	297
	298	err = crypto_wait_req(crypto_ahash_digest(req), &wait);
	299
439bea10	300	fsverity_free_hash_request(alg, req);
671e67b4 EB	301	return err;
	302	}
	303
	304	void __init fsverity_check_hash_algs(void)
	305	{
	306	size_t i;
	307
	308	/*
	309	* Sanity check the hash algorithms (could be a build-time check, but
	310	* they're in an array)
	311	*/
	312	for (i = 0; i < ARRAY_SIZE(fsverity_hash_algs); i++) {
	313	const struct fsverity_hash_alg *alg = &fsverity_hash_algs[i];
	314
	315	if (!alg->name)
	316	continue;
	317
	318	BUG_ON(alg->digest_size > FS_VERITY_MAX_DIGEST_SIZE);
	319
	320	/*
	321	* For efficiency, the implementation currently assumes the
	322	* digest and block sizes are powers of 2. This limitation can
	323	* be lifted if the code is updated to handle other values.
	324	*/
	325	BUG_ON(!is_power_of_2(alg->digest_size));
	326	BUG_ON(!is_power_of_2(alg->block_size));
a4bbf53d EB	327
	328	/* Verify that there is a valid mapping to HASH_ALGO_. /
	329	BUG_ON(alg->algo_id == 0);
	330	BUG_ON(alg->digest_size != hash_digest_size[alg->algo_id]);
671e67b4 EB	331	}
671e67b4 EB	332	}