swh:1:snp:173f8deb0c56c557784b4fd217e7608ac6197844
Tip revision: a99d8080aaf358d5d23581244e5da23b35e340b9 authored by Linus Torvalds on 03 November 2019, 22:07:26 UTC
Linux 5.4-rc6
Linux 5.4-rc6
Tip revision: a99d808
hash_algs.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,
},
};
/**
* 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()
*/
const 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 cmpxchg() below */
tfm = READ_ONCE(alg->tfm);
if (likely(tfm != NULL))
return alg;
/*
* 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);
return ERR_PTR(-ENOPKG);
}
fsverity_err(inode,
"Error allocating hash algorithm \"%s\": %ld",
alg->name, PTR_ERR(tfm));
return ERR_CAST(tfm);
}
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;
pr_info("%s using implementation \"%s\"\n",
alg->name, crypto_ahash_driver_name(tfm));
/* pairs with READ_ONCE() above */
if (cmpxchg(&alg->tfm, NULL, tfm) != NULL)
crypto_free_ahash(tfm);
return alg;
err_free_tfm:
crypto_free_ahash(tfm);
return ERR_PTR(err);
}
/**
* 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(const 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);
req = ahash_request_alloc(alg->tfm, GFP_KERNEL);
if (!req) {
err = -ENOMEM;
goto err_free;
}
/*
* 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:
ahash_request_free(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(const 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;
req = ahash_request_alloc(alg->tfm, GFP_KERNEL);
if (!req)
return -ENOMEM;
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);
ahash_request_free(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));
}
}