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![Eric Biggers](/assets/img/avatar_default.png)
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>
328 lines
9.1 KiB
C
328 lines
9.1 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* fs/verity/hash_algs.c: fs-verity hash algorithms
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*
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* Copyright 2019 Google LLC
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*/
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#include "fsverity_private.h"
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#include <crypto/hash.h>
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#include <linux/scatterlist.h>
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/* The hash algorithms supported by fs-verity */
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struct fsverity_hash_alg fsverity_hash_algs[] = {
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[FS_VERITY_HASH_ALG_SHA256] = {
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.name = "sha256",
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.digest_size = SHA256_DIGEST_SIZE,
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.block_size = SHA256_BLOCK_SIZE,
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},
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[FS_VERITY_HASH_ALG_SHA512] = {
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.name = "sha512",
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.digest_size = SHA512_DIGEST_SIZE,
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.block_size = SHA512_BLOCK_SIZE,
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},
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};
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static DEFINE_MUTEX(fsverity_hash_alg_init_mutex);
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/**
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* fsverity_get_hash_alg() - validate and prepare a hash algorithm
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* @inode: optional inode for logging purposes
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* @num: the hash algorithm number
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*
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* Get the struct fsverity_hash_alg for the given hash algorithm number, and
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* ensure it has a hash transform ready to go. The hash transforms are
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* allocated on-demand so that we don't waste resources unnecessarily, and
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* because the crypto modules may be initialized later than fs/verity/.
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*
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* Return: pointer to the hash alg on success, else an ERR_PTR()
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*/
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struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
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unsigned int num)
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{
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struct fsverity_hash_alg *alg;
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struct crypto_ahash *tfm;
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int err;
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if (num >= ARRAY_SIZE(fsverity_hash_algs) ||
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!fsverity_hash_algs[num].name) {
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fsverity_warn(inode, "Unknown hash algorithm number: %u", num);
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return ERR_PTR(-EINVAL);
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}
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alg = &fsverity_hash_algs[num];
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/* pairs with smp_store_release() below */
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if (likely(smp_load_acquire(&alg->tfm) != NULL))
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return alg;
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mutex_lock(&fsverity_hash_alg_init_mutex);
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if (alg->tfm != NULL)
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goto out_unlock;
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/*
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* Using the shash API would make things a bit simpler, but the ahash
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* API is preferable as it allows the use of crypto accelerators.
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*/
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tfm = crypto_alloc_ahash(alg->name, 0, 0);
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if (IS_ERR(tfm)) {
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if (PTR_ERR(tfm) == -ENOENT) {
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fsverity_warn(inode,
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"Missing crypto API support for hash algorithm \"%s\"",
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alg->name);
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alg = ERR_PTR(-ENOPKG);
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goto out_unlock;
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}
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fsverity_err(inode,
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"Error allocating hash algorithm \"%s\": %ld",
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alg->name, PTR_ERR(tfm));
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alg = ERR_CAST(tfm);
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goto out_unlock;
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}
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err = -EINVAL;
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if (WARN_ON(alg->digest_size != crypto_ahash_digestsize(tfm)))
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goto err_free_tfm;
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if (WARN_ON(alg->block_size != crypto_ahash_blocksize(tfm)))
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goto err_free_tfm;
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err = mempool_init_kmalloc_pool(&alg->req_pool, 1,
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sizeof(struct ahash_request) +
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crypto_ahash_reqsize(tfm));
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if (err)
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goto err_free_tfm;
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pr_info("%s using implementation \"%s\"\n",
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alg->name, crypto_ahash_driver_name(tfm));
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/* pairs with smp_load_acquire() above */
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smp_store_release(&alg->tfm, tfm);
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goto out_unlock;
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err_free_tfm:
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crypto_free_ahash(tfm);
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alg = ERR_PTR(err);
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out_unlock:
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mutex_unlock(&fsverity_hash_alg_init_mutex);
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return alg;
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}
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/**
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* fsverity_alloc_hash_request() - allocate a hash request object
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* @alg: the hash algorithm for which to allocate the request
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* @gfp_flags: memory allocation flags
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*
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* This is mempool-backed, so this never fails if __GFP_DIRECT_RECLAIM is set in
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* @gfp_flags. However, in that case this might need to wait for all
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* previously-allocated requests to be freed. So to avoid deadlocks, callers
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* must never need multiple requests at a time to make forward progress.
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*
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* Return: the request object on success; NULL on failure (but see above)
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*/
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struct ahash_request *fsverity_alloc_hash_request(struct fsverity_hash_alg *alg,
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gfp_t gfp_flags)
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{
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struct ahash_request *req = mempool_alloc(&alg->req_pool, gfp_flags);
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if (req)
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ahash_request_set_tfm(req, alg->tfm);
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return req;
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}
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/**
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* fsverity_free_hash_request() - free a hash request object
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* @alg: the hash algorithm
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* @req: the hash request object to free
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*/
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void fsverity_free_hash_request(struct fsverity_hash_alg *alg,
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struct ahash_request *req)
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{
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if (req) {
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ahash_request_zero(req);
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mempool_free(req, &alg->req_pool);
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}
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}
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/**
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* fsverity_prepare_hash_state() - precompute the initial hash state
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* @alg: hash algorithm
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* @salt: a salt which is to be prepended to all data to be hashed
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* @salt_size: salt size in bytes, possibly 0
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*
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* Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed
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* initial hash state on success or an ERR_PTR() on failure.
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*/
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const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg,
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const u8 *salt, size_t salt_size)
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{
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u8 *hashstate = NULL;
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struct ahash_request *req = NULL;
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u8 *padded_salt = NULL;
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size_t padded_salt_size;
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struct scatterlist sg;
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DECLARE_CRYPTO_WAIT(wait);
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int err;
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if (salt_size == 0)
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return NULL;
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hashstate = kmalloc(crypto_ahash_statesize(alg->tfm), GFP_KERNEL);
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if (!hashstate)
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return ERR_PTR(-ENOMEM);
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/* This allocation never fails, since it's mempool-backed. */
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req = fsverity_alloc_hash_request(alg, GFP_KERNEL);
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/*
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* Zero-pad the salt to the next multiple of the input size of the hash
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* algorithm's compression function, e.g. 64 bytes for SHA-256 or 128
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* bytes for SHA-512. This ensures that the hash algorithm won't have
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* any bytes buffered internally after processing the salt, thus making
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* salted hashing just as fast as unsalted hashing.
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*/
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padded_salt_size = round_up(salt_size, alg->block_size);
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padded_salt = kzalloc(padded_salt_size, GFP_KERNEL);
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if (!padded_salt) {
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err = -ENOMEM;
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goto err_free;
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}
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memcpy(padded_salt, salt, salt_size);
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sg_init_one(&sg, padded_salt, padded_salt_size);
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ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
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CRYPTO_TFM_REQ_MAY_BACKLOG,
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crypto_req_done, &wait);
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ahash_request_set_crypt(req, &sg, NULL, padded_salt_size);
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err = crypto_wait_req(crypto_ahash_init(req), &wait);
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if (err)
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goto err_free;
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err = crypto_wait_req(crypto_ahash_update(req), &wait);
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if (err)
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goto err_free;
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err = crypto_ahash_export(req, hashstate);
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if (err)
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goto err_free;
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out:
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fsverity_free_hash_request(alg, req);
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kfree(padded_salt);
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return hashstate;
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err_free:
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kfree(hashstate);
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hashstate = ERR_PTR(err);
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goto out;
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}
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/**
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* fsverity_hash_page() - hash a single data or hash page
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* @params: the Merkle tree's parameters
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* @inode: inode for which the hashing is being done
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* @req: preallocated hash request
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* @page: the page to hash
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* @out: output digest, size 'params->digest_size' bytes
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*
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* Hash a single data or hash block, assuming block_size == PAGE_SIZE.
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* The hash is salted if a salt is specified in the Merkle tree parameters.
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*
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* Return: 0 on success, -errno on failure
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*/
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int fsverity_hash_page(const struct merkle_tree_params *params,
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const struct inode *inode,
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struct ahash_request *req, struct page *page, u8 *out)
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{
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struct scatterlist sg;
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DECLARE_CRYPTO_WAIT(wait);
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int err;
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if (WARN_ON(params->block_size != PAGE_SIZE))
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return -EINVAL;
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sg_init_table(&sg, 1);
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sg_set_page(&sg, page, PAGE_SIZE, 0);
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ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
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CRYPTO_TFM_REQ_MAY_BACKLOG,
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crypto_req_done, &wait);
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ahash_request_set_crypt(req, &sg, out, PAGE_SIZE);
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if (params->hashstate) {
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err = crypto_ahash_import(req, params->hashstate);
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if (err) {
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fsverity_err(inode,
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"Error %d importing hash state", err);
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return err;
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}
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err = crypto_ahash_finup(req);
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} else {
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err = crypto_ahash_digest(req);
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}
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err = crypto_wait_req(err, &wait);
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if (err)
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fsverity_err(inode, "Error %d computing page hash", err);
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return err;
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}
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/**
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* fsverity_hash_buffer() - hash some data
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* @alg: the hash algorithm to use
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* @data: the data to hash
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* @size: size of data to hash, in bytes
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* @out: output digest, size 'alg->digest_size' bytes
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*
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* Hash some data which is located in physically contiguous memory (i.e. memory
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* allocated by kmalloc(), not by vmalloc()). No salt is used.
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*
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* Return: 0 on success, -errno on failure
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*/
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int fsverity_hash_buffer(struct fsverity_hash_alg *alg,
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const void *data, size_t size, u8 *out)
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{
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struct ahash_request *req;
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struct scatterlist sg;
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DECLARE_CRYPTO_WAIT(wait);
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int err;
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/* This allocation never fails, since it's mempool-backed. */
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req = fsverity_alloc_hash_request(alg, GFP_KERNEL);
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sg_init_one(&sg, data, size);
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ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
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CRYPTO_TFM_REQ_MAY_BACKLOG,
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crypto_req_done, &wait);
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ahash_request_set_crypt(req, &sg, out, size);
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err = crypto_wait_req(crypto_ahash_digest(req), &wait);
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fsverity_free_hash_request(alg, req);
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return err;
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}
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void __init fsverity_check_hash_algs(void)
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{
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size_t i;
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/*
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* Sanity check the hash algorithms (could be a build-time check, but
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* they're in an array)
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*/
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for (i = 0; i < ARRAY_SIZE(fsverity_hash_algs); i++) {
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const struct fsverity_hash_alg *alg = &fsverity_hash_algs[i];
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if (!alg->name)
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continue;
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BUG_ON(alg->digest_size > FS_VERITY_MAX_DIGEST_SIZE);
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/*
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* For efficiency, the implementation currently assumes the
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* digest and block sizes are powers of 2. This limitation can
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* be lifted if the code is updated to handle other values.
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*/
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BUG_ON(!is_power_of_2(alg->digest_size));
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BUG_ON(!is_power_of_2(alg->block_size));
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}
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}
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