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linux-next/fs/verity/hash_algs.c
Eric Biggers 439bea104c fs-verity: use mempool for hash requests
When initializing an fs-verity hash algorithm, also initialize a mempool
that contains a single preallocated hash request object.  Then replace
the direct calls to ahash_request_alloc() and ahash_request_free() with
allocating and freeing from this mempool.

This eliminates the possibility of the allocation failing, which is
desirable for the I/O path.

This doesn't cause deadlocks because there's no case where multiple hash
requests are needed at a time to make forward progress.

Link: https://lore.kernel.org/r/20191231175545.20709-1-ebiggers@kernel.org
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
2020-01-14 13:28:05 -08:00

329 lines
9.1 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* fs/verity/hash_algs.c: 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,
},
[FS_VERITY_HASH_ALG_SHA512] = {
.name = "sha512",
.digest_size = SHA512_DIGEST_SIZE,
.block_size = SHA512_BLOCK_SIZE,
},
};
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(alg->digest_size != crypto_ahash_digestsize(tfm)))
goto err_free_tfm;
if (WARN_ON(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_page() - hash a single data or hash page
* @params: the Merkle tree's parameters
* @inode: inode for which the hashing is being done
* @req: preallocated hash request
* @page: the page to hash
* @out: output digest, size 'params->digest_size' bytes
*
* Hash a single data or hash block, assuming block_size == PAGE_SIZE.
* The hash is salted if a salt is specified in the Merkle tree parameters.
*
* Return: 0 on success, -errno on failure
*/
int fsverity_hash_page(const struct merkle_tree_params *params,
const struct inode *inode,
struct ahash_request *req, struct page *page, u8 *out)
{
struct scatterlist sg;
DECLARE_CRYPTO_WAIT(wait);
int err;
if (WARN_ON(params->block_size != PAGE_SIZE))
return -EINVAL;
sg_init_table(&sg, 1);
sg_set_page(&sg, page, PAGE_SIZE, 0);
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, PAGE_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 page 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));
}
}