* [f2fs-dev] [PATCH 2/2] fsverity: Switch from crypto_shash to SHA-2 library
2025-06-30 17:22 [f2fs-dev] [PATCH 0/2] Convert fs/verity/ to use SHA-2 library API Eric Biggers via Linux-f2fs-devel
2025-06-30 17:22 ` [f2fs-dev] [PATCH 1/2] lib/crypto: hash_info: Move hash_info.c into lib/crypto/ Eric Biggers via Linux-f2fs-devel
@ 2025-06-30 17:22 ` Eric Biggers via Linux-f2fs-devel
2025-07-04 13:25 ` [f2fs-dev] [PATCH 0/2] Convert fs/verity/ to use SHA-2 library API Ard Biesheuvel via Linux-f2fs-devel
2025-07-09 19:26 ` Eric Biggers via Linux-f2fs-devel
3 siblings, 0 replies; 6+ messages in thread
From: Eric Biggers via Linux-f2fs-devel @ 2025-06-30 17:22 UTC (permalink / raw)
To: fsverity
Cc: Jason A . Donenfeld, Theodore Ts'o, linux-kernel,
linux-f2fs-devel, Eric Biggers, linux-crypto, linux-ext4,
Ard Biesheuvel, linux-btrfs
fsverity supports two hash algorithms: SHA-256 and SHA-512. Since both
of these have a library API now, just use the library API instead of
crypto_shash. Even with multiple algorithms, the library-based code
still ends up being quite a bit simpler, due to how clumsy the
old-school crypto API is. The library-based code is also more
efficient, since it avoids overheads such as indirect calls.
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
---
Documentation/filesystems/fsverity.rst | 3 +-
fs/verity/Kconfig | 6 +-
fs/verity/enable.c | 8 +-
fs/verity/fsverity_private.h | 24 +--
fs/verity/hash_algs.c | 194 +++++++++----------------
fs/verity/open.c | 36 ++---
fs/verity/verify.c | 7 +-
7 files changed, 102 insertions(+), 176 deletions(-)
diff --git a/Documentation/filesystems/fsverity.rst b/Documentation/filesystems/fsverity.rst
index dacdbc1149e67..412cf11e32985 100644
--- a/Documentation/filesystems/fsverity.rst
+++ b/Documentation/filesystems/fsverity.rst
@@ -183,12 +183,11 @@ FS_IOC_ENABLE_VERITY can fail with the following errors:
- ``EKEYREJECTED``: the builtin signature doesn't match the file
- ``EMSGSIZE``: the salt or builtin signature is too long
- ``ENOKEY``: the ".fs-verity" keyring doesn't contain the certificate
needed to verify the builtin signature
- ``ENOPKG``: fs-verity recognizes the hash algorithm, but it's not
- available in the kernel's crypto API as currently configured (e.g.
- for SHA-512, missing CONFIG_CRYPTO_SHA512).
+ available in the kernel as currently configured
- ``ENOTTY``: this type of filesystem does not implement fs-verity
- ``EOPNOTSUPP``: the kernel was not configured with fs-verity
support; or the filesystem superblock has not had the 'verity'
feature enabled on it; or the filesystem does not support fs-verity
on this file. (See `Filesystem support`_.)
diff --git a/fs/verity/Kconfig b/fs/verity/Kconfig
index 40569d3527a71..76d1c5971b826 100644
--- a/fs/verity/Kconfig
+++ b/fs/verity/Kconfig
@@ -1,14 +1,12 @@
# SPDX-License-Identifier: GPL-2.0
config FS_VERITY
bool "FS Verity (read-only file-based authenticity protection)"
- select CRYPTO
select CRYPTO_HASH_INFO
- # SHA-256 is selected as it's intended to be the default hash algorithm.
- # To avoid bloat, other wanted algorithms must be selected explicitly.
- select CRYPTO_SHA256
+ select CRYPTO_LIB_SHA256
+ select CRYPTO_LIB_SHA512
help
This option enables fs-verity. fs-verity is the dm-verity
mechanism implemented at the file level. On supported
filesystems (currently ext4, f2fs, and btrfs), userspace can
use an ioctl to enable verity for a file, which causes the
diff --git a/fs/verity/enable.c b/fs/verity/enable.c
index c284f46d1b535..0816ec295c380 100644
--- a/fs/verity/enable.c
+++ b/fs/verity/enable.c
@@ -5,11 +5,10 @@
* Copyright 2019 Google LLC
*/
#include "fsverity_private.h"
-#include <crypto/hash.h>
#include <linux/mount.h>
#include <linux/sched/signal.h>
#include <linux/uaccess.h>
struct block_buffer {
@@ -22,11 +21,10 @@ struct block_buffer {
static int hash_one_block(struct inode *inode,
const struct merkle_tree_params *params,
struct block_buffer *cur)
{
struct block_buffer *next = cur + 1;
- int err;
/*
* Safety check to prevent a buffer overflow in case of a filesystem bug
* that allows the file size to change despite deny_write_access(), or a
* bug in the Merkle tree logic itself
@@ -35,14 +33,12 @@ static int hash_one_block(struct inode *inode,
return -EINVAL;
/* Zero-pad the block if it's shorter than the block size. */
memset(&cur->data[cur->filled], 0, params->block_size - cur->filled);
- err = fsverity_hash_block(params, inode, cur->data,
- &next->data[next->filled]);
- if (err)
- return err;
+ fsverity_hash_block(params, inode, cur->data,
+ &next->data[next->filled]);
next->filled += params->digest_size;
cur->filled = 0;
return 0;
}
diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h
index b3506f56e180b..5fe854a5b9ad3 100644
--- a/fs/verity/fsverity_private.h
+++ b/fs/verity/fsverity_private.h
@@ -18,25 +18,30 @@
*/
#define FS_VERITY_MAX_LEVELS 8
/* A hash algorithm supported by fs-verity */
struct fsverity_hash_alg {
- struct crypto_shash *tfm; /* hash tfm, allocated on demand */
const char *name; /* crypto API name, e.g. sha256 */
unsigned int digest_size; /* digest size in bytes, e.g. 32 for SHA-256 */
unsigned int block_size; /* block size in bytes, e.g. 64 for SHA-256 */
/*
* The HASH_ALGO_* constant for this algorithm. This is different from
* FS_VERITY_HASH_ALG_*, which uses a different numbering scheme.
*/
enum hash_algo algo_id;
};
+union fsverity_hash_ctx {
+ struct sha256_ctx sha256;
+ struct sha512_ctx sha512;
+};
+
/* Merkle tree parameters: hash algorithm, initial hash state, and topology */
struct merkle_tree_params {
const struct fsverity_hash_alg *hash_alg; /* the hash algorithm */
- const u8 *hashstate; /* initial hash state or NULL */
+ /* initial hash state if salted, NULL if unsalted */
+ const union fsverity_hash_ctx *hashstate;
unsigned int digest_size; /* same as hash_alg->digest_size */
unsigned int block_size; /* size of data and tree blocks */
unsigned int hashes_per_block; /* number of hashes per tree block */
unsigned int blocks_per_page; /* PAGE_SIZE / block_size */
u8 log_digestsize; /* log2(digest_size) */
@@ -74,20 +79,21 @@ struct fsverity_info {
#define FS_VERITY_MAX_SIGNATURE_SIZE (FS_VERITY_MAX_DESCRIPTOR_SIZE - \
sizeof(struct fsverity_descriptor))
/* hash_algs.c */
-extern struct fsverity_hash_alg fsverity_hash_algs[];
+extern const struct fsverity_hash_alg fsverity_hash_algs[];
const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
unsigned int num);
-const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,
- const u8 *salt, size_t salt_size);
-int fsverity_hash_block(const struct merkle_tree_params *params,
- const struct inode *inode, const void *data, u8 *out);
-int fsverity_hash_buffer(const struct fsverity_hash_alg *alg,
- const void *data, size_t size, u8 *out);
+union fsverity_hash_ctx *
+fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,
+ const u8 *salt, size_t salt_size);
+void fsverity_hash_block(const struct merkle_tree_params *params,
+ const struct inode *inode, const void *data, u8 *out);
+void fsverity_hash_buffer(const struct fsverity_hash_alg *alg,
+ const void *data, size_t size, u8 *out);
void __init fsverity_check_hash_algs(void);
/* init.c */
void __printf(3, 4) __cold
diff --git a/fs/verity/hash_algs.c b/fs/verity/hash_algs.c
index 6b08b1d9a7d7c..9bb3c6344907e 100644
--- a/fs/verity/hash_algs.c
+++ b/fs/verity/hash_algs.c
@@ -5,14 +5,12 @@
* Copyright 2019 Google LLC
*/
#include "fsverity_private.h"
-#include <crypto/hash.h>
-
/* The hash algorithms supported by fs-verity */
-struct fsverity_hash_alg fsverity_hash_algs[] = {
+const 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,
@@ -23,144 +21,76 @@ struct fsverity_hash_alg fsverity_hash_algs[] = {
.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
+ * fsverity_get_hash_alg() - get a hash algorithm by number
* @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/.
+ * Get the struct fsverity_hash_alg for the given hash algorithm number.
*
- * Return: pointer to the hash alg on success, else an ERR_PTR()
+ * Return: pointer to the hash alg if it's known, otherwise NULL.
*/
const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
unsigned int num)
{
- struct fsverity_hash_alg *alg;
- struct crypto_shash *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;
-
- tfm = crypto_alloc_shash(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;
+ return NULL;
}
-
- err = -EINVAL;
- if (WARN_ON_ONCE(alg->digest_size != crypto_shash_digestsize(tfm)))
- goto err_free_tfm;
- if (WARN_ON_ONCE(alg->block_size != crypto_shash_blocksize(tfm)))
- goto err_free_tfm;
-
- pr_info("%s using implementation \"%s\"\n",
- alg->name, crypto_shash_driver_name(tfm));
-
- /* pairs with smp_load_acquire() above */
- smp_store_release(&alg->tfm, tfm);
- goto out_unlock;
-
-err_free_tfm:
- crypto_free_shash(tfm);
- alg = ERR_PTR(err);
-out_unlock:
- mutex_unlock(&fsverity_hash_alg_init_mutex);
- return alg;
+ return &fsverity_hash_algs[num];
}
/**
* 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
+ * @salt_size: salt size in bytes
*
- * Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed
- * initial hash state on success or an ERR_PTR() on failure.
+ * Return: the kmalloc()'ed initial hash state, or NULL if out of memory.
*/
-const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,
- const u8 *salt, size_t salt_size)
+union fsverity_hash_ctx *
+fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,
+ const u8 *salt, size_t salt_size)
{
- u8 *hashstate = NULL;
- SHASH_DESC_ON_STACK(desc, alg->tfm);
u8 *padded_salt = NULL;
size_t padded_salt_size;
- int err;
-
- desc->tfm = alg->tfm;
-
- if (salt_size == 0)
- return NULL;
-
- hashstate = kmalloc(crypto_shash_statesize(alg->tfm), GFP_KERNEL);
- if (!hashstate)
- return ERR_PTR(-ENOMEM);
+ union fsverity_hash_ctx ctx;
+ void *res = NULL;
/*
* 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;
- }
+ if (!padded_salt)
+ return NULL;
memcpy(padded_salt, salt, salt_size);
- err = crypto_shash_init(desc);
- if (err)
- goto err_free;
-
- err = crypto_shash_update(desc, padded_salt, padded_salt_size);
- if (err)
- goto err_free;
-
- err = crypto_shash_export(desc, hashstate);
- if (err)
- goto err_free;
-out:
- kfree(padded_salt);
- return hashstate;
-err_free:
- kfree(hashstate);
- hashstate = ERR_PTR(err);
- goto out;
+ switch (alg->algo_id) {
+ case HASH_ALGO_SHA256:
+ sha256_init(&ctx.sha256);
+ sha256_update(&ctx.sha256, padded_salt, padded_salt_size);
+ res = kmemdup(&ctx.sha256, sizeof(ctx.sha256), GFP_KERNEL);
+ break;
+ case HASH_ALGO_SHA512:
+ sha512_init(&ctx.sha512);
+ sha512_update(&ctx.sha512, padded_salt, padded_salt_size);
+ res = kmemdup(&ctx.sha512, sizeof(ctx.sha512), GFP_KERNEL);
+ break;
+ default:
+ WARN_ON_ONCE(1);
+ }
+ kfree(padded_salt);
+ return res;
}
/**
* fsverity_hash_block() - hash a single data or hash block
* @params: the Merkle tree's parameters
@@ -168,50 +98,58 @@ const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,
* @data: virtual address of a buffer containing the block to hash
* @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, const void *data, u8 *out)
+void fsverity_hash_block(const struct merkle_tree_params *params,
+ const struct inode *inode, const void *data, u8 *out)
{
- SHASH_DESC_ON_STACK(desc, params->hash_alg->tfm);
- int err;
-
- desc->tfm = params->hash_alg->tfm;
-
- if (params->hashstate) {
- err = crypto_shash_import(desc, params->hashstate);
- if (err) {
- fsverity_err(inode,
- "Error %d importing hash state", err);
- return err;
- }
- err = crypto_shash_finup(desc, data, params->block_size, out);
- } else {
- err = crypto_shash_digest(desc, data, params->block_size, out);
+ union fsverity_hash_ctx ctx;
+
+ if (!params->hashstate) {
+ fsverity_hash_buffer(params->hash_alg, data, params->block_size,
+ out);
+ return;
+ }
+
+ switch (params->hash_alg->algo_id) {
+ case HASH_ALGO_SHA256:
+ ctx.sha256 = params->hashstate->sha256;
+ sha256_update(&ctx.sha256, data, params->block_size);
+ sha256_final(&ctx.sha256, out);
+ return;
+ case HASH_ALGO_SHA512:
+ ctx.sha512 = params->hashstate->sha512;
+ sha512_update(&ctx.sha512, data, params->block_size);
+ sha512_final(&ctx.sha512, out);
+ return;
+ default:
+ BUG();
}
- 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
- *
- * 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)
+void fsverity_hash_buffer(const struct fsverity_hash_alg *alg,
+ const void *data, size_t size, u8 *out)
{
- return crypto_shash_tfm_digest(alg->tfm, data, size, out);
+ switch (alg->algo_id) {
+ case HASH_ALGO_SHA256:
+ sha256(data, size, out);
+ return;
+ case HASH_ALGO_SHA512:
+ sha512(data, size, out);
+ return;
+ default:
+ BUG();
+ }
}
void __init fsverity_check_hash_algs(void)
{
size_t i;
diff --git a/fs/verity/open.c b/fs/verity/open.c
index fdeb95eca3af3..0604cebe194cd 100644
--- a/fs/verity/open.c
+++ b/fs/verity/open.c
@@ -40,22 +40,22 @@ int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
int level;
memset(params, 0, sizeof(*params));
hash_alg = fsverity_get_hash_alg(inode, hash_algorithm);
- if (IS_ERR(hash_alg))
- return PTR_ERR(hash_alg);
+ if (!hash_alg)
+ return -EINVAL;
params->hash_alg = hash_alg;
params->digest_size = hash_alg->digest_size;
- params->hashstate = fsverity_prepare_hash_state(hash_alg, salt,
- salt_size);
- if (IS_ERR(params->hashstate)) {
- err = PTR_ERR(params->hashstate);
- params->hashstate = NULL;
- fsverity_err(inode, "Error %d preparing hash state", err);
- goto out_err;
+ if (salt_size) {
+ params->hashstate =
+ fsverity_prepare_hash_state(hash_alg, salt, salt_size);
+ if (!params->hashstate) {
+ err = -ENOMEM;
+ goto out_err;
+ }
}
/*
* fs/verity/ directly assumes that the Merkle tree block size is a
* power of 2 less than or equal to PAGE_SIZE. Another restriction
@@ -156,22 +156,19 @@ int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
/*
* Compute the file digest by hashing the fsverity_descriptor excluding the
* builtin signature and with the sig_size field set to 0.
*/
-static int compute_file_digest(const struct fsverity_hash_alg *hash_alg,
- struct fsverity_descriptor *desc,
- u8 *file_digest)
+static void compute_file_digest(const struct fsverity_hash_alg *hash_alg,
+ struct fsverity_descriptor *desc,
+ u8 *file_digest)
{
__le32 sig_size = desc->sig_size;
- int err;
desc->sig_size = 0;
- err = fsverity_hash_buffer(hash_alg, desc, sizeof(*desc), file_digest);
+ fsverity_hash_buffer(hash_alg, desc, sizeof(*desc), file_digest);
desc->sig_size = sig_size;
-
- return err;
}
/*
* Create a new fsverity_info from the given fsverity_descriptor (with optional
* appended builtin signature), and check the signature if present. The
@@ -199,16 +196,11 @@ struct fsverity_info *fsverity_create_info(const struct inode *inode,
goto fail;
}
memcpy(vi->root_hash, desc->root_hash, vi->tree_params.digest_size);
- err = compute_file_digest(vi->tree_params.hash_alg, desc,
- vi->file_digest);
- if (err) {
- fsverity_err(inode, "Error %d computing file digest", err);
- goto fail;
- }
+ compute_file_digest(vi->tree_params.hash_alg, desc, vi->file_digest);
err = fsverity_verify_signature(vi, desc->signature,
le32_to_cpu(desc->sig_size));
if (err)
goto fail;
diff --git a/fs/verity/verify.c b/fs/verity/verify.c
index 4fcad0825a120..481a381128cb9 100644
--- a/fs/verity/verify.c
+++ b/fs/verity/verify.c
@@ -5,11 +5,10 @@
* Copyright 2019 Google LLC
*/
#include "fsverity_private.h"
-#include <crypto/hash.h>
#include <linux/bio.h>
static struct workqueue_struct *fsverity_read_workqueue;
/*
@@ -200,12 +199,11 @@ verify_data_block(struct inode *inode, struct fsverity_info *vi,
struct page *hpage = hblocks[level - 1].page;
const void *haddr = hblocks[level - 1].addr;
unsigned long hblock_idx = hblocks[level - 1].index;
unsigned int hoffset = hblocks[level - 1].hoffset;
- if (fsverity_hash_block(params, inode, haddr, real_hash) != 0)
- goto error;
+ fsverity_hash_block(params, inode, haddr, real_hash);
if (memcmp(want_hash, real_hash, hsize) != 0)
goto corrupted;
/*
* Mark the hash block as verified. This must be atomic and
* idempotent, as the same hash block might be verified by
@@ -220,12 +218,11 @@ verify_data_block(struct inode *inode, struct fsverity_info *vi,
kunmap_local(haddr);
put_page(hpage);
}
/* Finally, verify the data block. */
- if (fsverity_hash_block(params, inode, data, real_hash) != 0)
- goto error;
+ fsverity_hash_block(params, inode, data, real_hash);
if (memcmp(want_hash, real_hash, hsize) != 0)
goto corrupted;
return true;
corrupted:
--
2.50.0
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