From: Eric Biggers <ebiggers@xxxxxxxxxx>
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.
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
---
fs/verity/enable.c | 8 +--
fs/verity/fsverity_private.h | 16 ++++--
fs/verity/hash_algs.c | 98 +++++++++++++++++++++++++++---------
fs/verity/open.c | 4 +-
fs/verity/verify.c | 17 +++----
5 files changed, 97 insertions(+), 46 deletions(-)
diff --git a/fs/verity/enable.c b/fs/verity/enable.c
index 1f3858d88cf3..1645d6326e32 100644
--- a/fs/verity/enable.c
+++ b/fs/verity/enable.c
@@ -165,9 +165,11 @@ static int build_merkle_tree(struct file *filp,
return 0;
}
+ /* This allocation never fails, since it's mempool-backed. */
+ req = fsverity_alloc_hash_request(params->hash_alg, GFP_KERNEL);
+
pending_hashes = kmalloc(params->block_size, GFP_KERNEL);
- req = ahash_request_alloc(params->hash_alg->tfm, GFP_KERNEL);
- if (!pending_hashes || !req)
+ if (!pending_hashes)
goto out;
/*
@@ -189,7 +191,7 @@ static int build_merkle_tree(struct file *filp,
err = 0;
out:
kfree(pending_hashes);
- ahash_request_free(req);
+ fsverity_free_hash_request(params->hash_alg, req);
return err;
}
diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h
index ab9cfdd8f965..74768cf539da 100644
--- a/fs/verity/fsverity_private.h
+++ b/fs/verity/fsverity_private.h
@@ -16,6 +16,7 @@
#include <crypto/sha.h>
#include <linux/fsverity.h>
+#include <linux/mempool.h>
struct ahash_request;
@@ -37,11 +38,12 @@ struct fsverity_hash_alg {
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 */
+ mempool_t req_pool; /* mempool with a preallocated hash request */
};
/* Merkle tree parameters: hash algorithm, initial hash state, and topology */
struct merkle_tree_params {
- const struct fsverity_hash_alg *hash_alg; /* the hash algorithm */
+ struct fsverity_hash_alg *hash_alg; /* the hash algorithm */
const u8 *hashstate; /* initial hash state or NULL */
unsigned int digest_size; /* same as hash_alg->digest_size */
unsigned int block_size; /* size of data and tree blocks */
@@ -115,14 +117,18 @@ struct fsverity_signed_digest {
extern 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,
+struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
+ unsigned int num);
+struct ahash_request *fsverity_alloc_hash_request(struct fsverity_hash_alg *alg,
+ gfp_t gfp_flags);
+void fsverity_free_hash_request(struct fsverity_hash_alg *alg,
+ struct ahash_request *req);
+const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg,
const u8 *salt, size_t salt_size);
int fsverity_hash_page(const struct merkle_tree_params *params,
const struct inode *inode,
struct ahash_request *req, struct page *page, u8 *out);
-int fsverity_hash_buffer(const struct fsverity_hash_alg *alg,
+int fsverity_hash_buffer(struct fsverity_hash_alg *alg,
const void *data, size_t size, u8 *out);
void __init fsverity_check_hash_algs(void);
diff --git a/fs/verity/hash_algs.c b/fs/verity/hash_algs.c
index 31e6d7d2389a..c37e186ebeb6 100644
--- a/fs/verity/hash_algs.c
+++ b/fs/verity/hash_algs.c
@@ -24,6 +24,8 @@ struct fsverity_hash_alg fsverity_hash_algs[] = {
},
};
+static DEFINE_MUTEX(fsverity_hash_alg_init_mutex);
+
/**
* fsverity_get_hash_alg() - validate and prepare a hash algorithm
* @inode: optional inode for logging purposes
@@ -36,8 +38,8 @@ struct fsverity_hash_alg fsverity_hash_algs[] = {
*
* 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 *fsverity_get_hash_alg(const struct inode *inode,
+ unsigned int num)
{
struct fsverity_hash_alg *alg;
struct crypto_ahash *tfm;
@@ -50,10 +52,15 @@ const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
}
alg = &fsverity_hash_algs[num];
- /* pairs with cmpxchg() below */
- tfm = READ_ONCE(alg->tfm);
- if (likely(tfm != NULL))
+ /* 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.
@@ -64,12 +71,14 @@ const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
fsverity_warn(inode,
"Missing crypto API support for hash algorithm \"%s\"",
alg->name);
- return ERR_PTR(-ENOPKG);
+ alg = ERR_PTR(-ENOPKG);
+ goto out_unlock;
}
fsverity_err(inode,
"Error allocating hash algorithm \"%s\": %ld",
alg->name, PTR_ERR(tfm));
- return ERR_CAST(tfm);
+ alg = ERR_CAST(tfm);
+ goto out_unlock;
}
err = -EINVAL;
@@ -78,18 +87,61 @@ const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
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 READ_ONCE() above */
- if (cmpxchg(&alg->tfm, NULL, tfm) != NULL)
- crypto_free_ahash(tfm);
-
- return alg;
+ /* pairs with smp_load_acquire() above */
+ smp_store_release(&alg->tfm, tfm);
+ goto out_unlock;
err_free_tfm:
crypto_free_ahash(tfm);
- return ERR_PTR(err);
+ 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);
+ }
}
/**
@@ -101,7 +153,7 @@ const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
* 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 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg,
const u8 *salt, size_t salt_size)
{
u8 *hashstate = NULL;
@@ -119,11 +171,8 @@ const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,
if (!hashstate)
return ERR_PTR(-ENOMEM);
- req = ahash_request_alloc(alg->tfm, GFP_KERNEL);
- if (!req) {
- err = -ENOMEM;
- goto err_free;
- }
+ /* 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
@@ -158,7 +207,7 @@ const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,
if (err)
goto err_free;
out:
- ahash_request_free(req);
+ fsverity_free_hash_request(alg, req);
kfree(padded_salt);
return hashstate;
@@ -229,7 +278,7 @@ int fsverity_hash_page(const struct merkle_tree_params *params,
*
* Return: 0 on success, -errno on failure
*/
-int fsverity_hash_buffer(const struct fsverity_hash_alg *alg,
+int fsverity_hash_buffer(struct fsverity_hash_alg *alg,
const void *data, size_t size, u8 *out)
{
struct ahash_request *req;
@@ -237,9 +286,8 @@ int fsverity_hash_buffer(const struct fsverity_hash_alg *alg,
DECLARE_CRYPTO_WAIT(wait);
int err;
- req = ahash_request_alloc(alg->tfm, GFP_KERNEL);
- if (!req)
- return -ENOMEM;
+ /* 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 |
@@ -249,7 +297,7 @@ int fsverity_hash_buffer(const struct fsverity_hash_alg *alg,
err = crypto_wait_req(crypto_ahash_digest(req), &wait);
- ahash_request_free(req);
+ fsverity_free_hash_request(alg, req);
return err;
}
diff --git a/fs/verity/open.c b/fs/verity/open.c
index e9cdf7d00ed2..c5fe6948e262 100644
--- a/fs/verity/open.c
+++ b/fs/verity/open.c
@@ -31,7 +31,7 @@ int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
unsigned int log_blocksize,
const u8 *salt, size_t salt_size)
{
- const struct fsverity_hash_alg *hash_alg;
+ struct fsverity_hash_alg *hash_alg;
int err;
u64 blocks;
u64 offset;
@@ -127,7 +127,7 @@ int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
* Compute the file measurement by hashing the fsverity_descriptor excluding the
* signature and with the sig_size field set to 0.
*/
-static int compute_file_measurement(const struct fsverity_hash_alg *hash_alg,
+static int compute_file_measurement(struct fsverity_hash_alg *hash_alg,
struct fsverity_descriptor *desc,
u8 *measurement)
{
diff --git a/fs/verity/verify.c b/fs/verity/verify.c
index 7fa561c343c2..e0cb62da3864 100644
--- a/fs/verity/verify.c
+++ b/fs/verity/verify.c
@@ -192,13 +192,12 @@ bool fsverity_verify_page(struct page *page)
struct ahash_request *req;
bool valid;
- req = ahash_request_alloc(vi->tree_params.hash_alg->tfm, GFP_NOFS);
- if (unlikely(!req))
- return false;
+ /* This allocation never fails, since it's mempool-backed. */
+ req = fsverity_alloc_hash_request(vi->tree_params.hash_alg, GFP_NOFS);
valid = verify_page(inode, vi, req, page, 0);
- ahash_request_free(req);
+ fsverity_free_hash_request(vi->tree_params.hash_alg, req);
return valid;
}
@@ -229,12 +228,8 @@ void fsverity_verify_bio(struct bio *bio)
struct bvec_iter_all iter_all;
unsigned long max_ra_pages = 0;
- req = ahash_request_alloc(params->hash_alg->tfm, GFP_NOFS);
- if (unlikely(!req)) {
- bio_for_each_segment_all(bv, bio, iter_all)
- SetPageError(bv->bv_page);
- return;
- }
+ /* This allocation never fails, since it's mempool-backed. */
+ req = fsverity_alloc_hash_request(params->hash_alg, GFP_NOFS);
if (bio->bi_opf & REQ_RAHEAD) {
/*
@@ -262,7 +257,7 @@ void fsverity_verify_bio(struct bio *bio)
SetPageError(page);
}
- ahash_request_free(req);
+ fsverity_free_hash_request(params->hash_alg, req);
}
EXPORT_SYMBOL_GPL(fsverity_verify_bio);
#endif /* CONFIG_BLOCK */
--
2.24.1
