Merge tag 'fsverity-for-linus' of git://git.kernel.org/pub/scm/fs/fsverity/linux

Pull fsverity updates from Eric Biggers:
 "Several updates for fs/verity/:

   - Do all hashing with the shash API instead of with the ahash API.

     This simplifies the code and reduces API overhead. It should also
     make things slightly easier for XFS's upcoming support for
     fsverity. It does drop fsverity's support for off-CPU hash
     accelerators, but that support was incomplete and not known to be
     used

   - Update and export fsverity_get_digest() so that it's ready for
     overlayfs's upcoming support for fsverity checking of lowerdata

   - Improve the documentation for builtin signature support

   - Fix a bug in the large folio support"

* tag 'fsverity-for-linus' of git://git.kernel.org/pub/scm/fs/fsverity/linux:
  fsverity: improve documentation for builtin signature support
  fsverity: rework fsverity_get_digest() again
  fsverity: simplify error handling in verify_data_block()
  fsverity: don't use bio_first_page_all() in fsverity_verify_bio()
  fsverity: constify fsverity_hash_alg
  fsverity: use shash API instead of ahash API

9 files changed, 152 insertions, 272 deletions

diff --git a/fs/verity/Kconfig b/fs/verity/Kconfig
index a7ffd718f171..e1036e535352 100644
--- a/fs/verity/Kconfig
+++ b/fs/verity/Kconfig
@@ -39,14 +39,14 @@ config FS_VERITY_BUILTIN_SIGNATURES
 	depends on FS_VERITY
 	select SYSTEM_DATA_VERIFICATION
 	help
-	  Support verifying signatures of verity files against the X.509
-	  certificates that have been loaded into the ".fs-verity"
-	  kernel keyring.
+	  This option adds support for in-kernel verification of
+	  fs-verity builtin signatures.
 
-	  This is meant as a relatively simple mechanism that can be
-	  used to provide an authenticity guarantee for verity files, as
-	  an alternative to IMA appraisal.  Userspace programs still
-	  need to check that the verity bit is set in order to get an
-	  authenticity guarantee.
+	  Please take great care before using this feature.  It is not
+	  the only way to do signatures with fs-verity, and the
+	  alternatives (such as userspace signature verification, and
+	  IMA appraisal) can be much better.  For details about the
+	  limitations of this feature, see
+	  Documentation/filesystems/fsverity.rst.
 
 	  If unsure, say N.
diff --git a/fs/verity/enable.c b/fs/verity/enable.c
index fc4c50e5219d..c284f46d1b53 100644
--- a/fs/verity/enable.c
+++ b/fs/verity/enable.c
@@ -7,6 +7,7 @@
 
 #include "fsverity_private.h"
 
+#include <crypto/hash.h>
 #include <linux/mount.h>
 #include <linux/sched/signal.h>
 #include <linux/uaccess.h>
@@ -20,7 +21,7 @@ struct block_buffer {
 /* Hash a block, writing the result to the next level's pending block buffer. */
 static int hash_one_block(struct inode *inode,
 			  const struct merkle_tree_params *params,
-			  struct ahash_request *req, struct block_buffer *cur)
+			  struct block_buffer *cur)
 {
 	struct block_buffer *next = cur + 1;
 	int err;
@@ -36,8 +37,7 @@ static int hash_one_block(struct inode *inode,
 	/* 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, req, virt_to_page(cur->data),
-				  offset_in_page(cur->data),
+	err = fsverity_hash_block(params, inode, cur->data,
 				  &next->data[next->filled]);
 	if (err)
 		return err;
@@ -76,7 +76,6 @@ static int build_merkle_tree(struct file *filp,
 	struct inode *inode = file_inode(filp);
 	const u64 data_size = inode->i_size;
 	const int num_levels = params->num_levels;
-	struct ahash_request *req;
 	struct block_buffer _buffers[1 + FS_VERITY_MAX_LEVELS + 1] = {};
 	struct block_buffer *buffers = &_buffers[1];
 	unsigned long level_offset[FS_VERITY_MAX_LEVELS];
@@ -90,9 +89,6 @@ 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);
-
 	/*
 	 * Allocate the block buffers.  Buffer "-1" is for data blocks.
 	 * Buffers 0 <= level < num_levels are for the actual tree levels.
@@ -130,7 +126,7 @@ static int build_merkle_tree(struct file *filp,
 			fsverity_err(inode, "Short read of file data");
 			goto out;
 		}
-		err = hash_one_block(inode, params, req, &buffers[-1]);
+		err = hash_one_block(inode, params, &buffers[-1]);
 		if (err)
 			goto out;
 		for (level = 0; level < num_levels; level++) {
@@ -141,8 +137,7 @@ static int build_merkle_tree(struct file *filp,
 			}
 			/* Next block at @level is full */
 
-			err = hash_one_block(inode, params, req,
-					     &buffers[level]);
+			err = hash_one_block(inode, params, &buffers[level]);
 			if (err)
 				goto out;
 			err = write_merkle_tree_block(inode,
@@ -162,8 +157,7 @@ static int build_merkle_tree(struct file *filp,
 	/* Finish all nonempty pending tree blocks. */
 	for (level = 0; level < num_levels; level++) {
 		if (buffers[level].filled != 0) {
-			err = hash_one_block(inode, params, req,
-					     &buffers[level]);
+			err = hash_one_block(inode, params, &buffers[level]);
 			if (err)
 				goto out;
 			err = write_merkle_tree_block(inode,
@@ -183,7 +177,6 @@ static int build_merkle_tree(struct file *filp,
 out:
 	for (level = -1; level < num_levels; level++)
 		kfree(buffers[level].data);
-	fsverity_free_hash_request(params->hash_alg, req);
 	return err;
 }
 
@@ -215,7 +208,7 @@ static int enable_verity(struct file *filp,
 	}
 	desc->salt_size = arg->salt_size;
 
-	/* Get the signature if the user provided one */
+	/* Get the builtin signature if the user provided one */
 	if (arg->sig_size &&
 	    copy_from_user(desc->signature, u64_to_user_ptr(arg->sig_ptr),
 			   arg->sig_size)) {
diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h
index d34dcc033d72..49bf3a1eb2a0 100644
--- a/fs/verity/fsverity_private.h
+++ b/fs/verity/fsverity_private.h
@@ -11,9 +11,6 @@
 #define pr_fmt(fmt) "fs-verity: " fmt
 
 #include <linux/fsverity.h>
-#include <linux/mempool.h>
-
-struct ahash_request;
 
 /*
  * Implementation limit: maximum depth of the Merkle tree.  For now 8 is plenty;
@@ -23,11 +20,10 @@ struct ahash_request;
 
 /* A hash algorithm supported by fs-verity */
 struct fsverity_hash_alg {
-	struct crypto_ahash *tfm; /* hash tfm, allocated on demand */
+	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 */
-	mempool_t req_pool;	  /* mempool with a preallocated hash request */
 	/*
 	 * The HASH_ALGO_* constant for this algorithm.  This is different from
 	 * FS_VERITY_HASH_ALG_*, which uses a different numbering scheme.
@@ -37,7 +33,7 @@ struct fsverity_hash_alg {
 
 /* Merkle tree parameters: hash algorithm, initial hash state, and topology */
 struct merkle_tree_params {
-	struct fsverity_hash_alg *hash_alg; /* the hash algorithm */
+	const 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 */
@@ -83,18 +79,13 @@ struct fsverity_info {
 
 extern struct fsverity_hash_alg fsverity_hash_algs[];
 
-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 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, struct ahash_request *req,
-			struct page *page, unsigned int offset, u8 *out);
-int fsverity_hash_buffer(struct fsverity_hash_alg *alg,
+			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);
 void __init fsverity_check_hash_algs(void);
 
diff --git a/fs/verity/hash_algs.c b/fs/verity/hash_algs.c
index ea00dbedf756..c598d2035476 100644
--- a/fs/verity/hash_algs.c
+++ b/fs/verity/hash_algs.c
@@ -8,7 +8,6 @@
 #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[] = {
@@ -40,11 +39,11 @@ static DEFINE_MUTEX(fsverity_hash_alg_init_mutex);
  *
  * 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)
+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;
+	struct crypto_shash *tfm;
 	int err;
 
 	if (num >= ARRAY_SIZE(fsverity_hash_algs) ||
@@ -63,11 +62,7 @@ struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
 	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);
+	tfm = crypto_alloc_shash(alg->name, 0, 0);
 	if (IS_ERR(tfm)) {
 		if (PTR_ERR(tfm) == -ENOENT) {
 			fsverity_warn(inode,
@@ -84,26 +79,20 @@ struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
 	}
 
 	err = -EINVAL;
-	if (WARN_ON_ONCE(alg->digest_size != crypto_ahash_digestsize(tfm)))
+	if (WARN_ON_ONCE(alg->digest_size != crypto_shash_digestsize(tfm)))
 		goto err_free_tfm;
-	if (WARN_ON_ONCE(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)
+	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_ahash_driver_name(tfm));
+		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_ahash(tfm);
+	crypto_free_shash(tfm);
 	alg = ERR_PTR(err);
 out_unlock:
 	mutex_unlock(&fsverity_hash_alg_init_mutex);
@@ -111,42 +100,6 @@ out_unlock:
 }
 
 /**
- * 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
@@ -155,27 +108,24 @@ void fsverity_free_hash_request(struct fsverity_hash_alg *alg,
  * 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 *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;
+	SHASH_DESC_ON_STACK(desc, alg->tfm);
 	u8 *padded_salt = NULL;
 	size_t padded_salt_size;
-	struct scatterlist sg;
-	DECLARE_CRYPTO_WAIT(wait);
 	int err;
 
+	desc->tfm = alg->tfm;
+
 	if (salt_size == 0)
 		return NULL;
 
-	hashstate = kmalloc(crypto_ahash_statesize(alg->tfm), GFP_KERNEL);
+	hashstate = kmalloc(crypto_shash_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
@@ -190,26 +140,18 @@ const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg,
 		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);
+	err = crypto_shash_init(desc);
 	if (err)
 		goto err_free;
 
-	err = crypto_wait_req(crypto_ahash_update(req), &wait);
+	err = crypto_shash_update(desc, padded_salt, padded_salt_size);
 	if (err)
 		goto err_free;
 
-	err = crypto_ahash_export(req, hashstate);
+	err = crypto_shash_export(desc, hashstate);
 	if (err)
 		goto err_free;
 out:
-	fsverity_free_hash_request(alg, req);
 	kfree(padded_salt);
 	return hashstate;
 
@@ -223,9 +165,7 @@ err_free:
  * fsverity_hash_block() - hash a single data or hash block
  * @params: the Merkle tree's parameters
  * @inode: inode for which the hashing is being done
- * @req: preallocated hash request
- * @page: the page containing the block to hash
- * @offset: the offset of the block within @page
+ * @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
@@ -234,33 +174,24 @@ err_free:
  * Return: 0 on success, -errno on failure
  */
 int fsverity_hash_block(const struct merkle_tree_params *params,
-			const struct inode *inode, struct ahash_request *req,
-			struct page *page, unsigned int offset, u8 *out)
+			const struct inode *inode, const void *data, u8 *out)
 {
-	struct scatterlist sg;
-	DECLARE_CRYPTO_WAIT(wait);
+	SHASH_DESC_ON_STACK(desc, params->hash_alg->tfm);
 	int err;
 
-	sg_init_table(&sg, 1);
-	sg_set_page(&sg, page, params->block_size, offset);
-	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, params->block_size);
+	desc->tfm = params->hash_alg->tfm;
 
 	if (params->hashstate) {
-		err = crypto_ahash_import(req, params->hashstate);
+		err = crypto_shash_import(desc, params->hashstate);
 		if (err) {
 			fsverity_err(inode,
 				     "Error %d importing hash state", err);
 			return err;
 		}
-		err = crypto_ahash_finup(req);
+		err = crypto_shash_finup(desc, data, params->block_size, out);
 	} else {
-		err = crypto_ahash_digest(req);
+		err = crypto_shash_digest(desc, data, params->block_size, out);
 	}
-
-	err = crypto_wait_req(err, &wait);
 	if (err)
 		fsverity_err(inode, "Error %d computing block hash", err);
 	return err;
@@ -273,32 +204,12 @@ int fsverity_hash_block(const struct merkle_tree_params *params,
  * @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,
+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;
-
-	/* 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;
+	return crypto_shash_tfm_digest(alg->tfm, data, size, out);
 }
 
 void __init fsverity_check_hash_algs(void)
diff --git a/fs/verity/measure.c b/fs/verity/measure.c
index 5c79ea1b2468..eec5956141da 100644
--- a/fs/verity/measure.c
+++ b/fs/verity/measure.c
@@ -61,27 +61,42 @@ EXPORT_SYMBOL_GPL(fsverity_ioctl_measure);
 /**
  * fsverity_get_digest() - get a verity file's digest
  * @inode: inode to get digest of
- * @digest: (out) pointer to the digest
- * @alg: (out) pointer to the hash algorithm enumeration
+ * @raw_digest: (out) the raw file digest
+ * @alg: (out) the digest's algorithm, as a FS_VERITY_HASH_ALG_* value
+ * @halg: (out) the digest's algorithm, as a HASH_ALGO_* value
  *
- * Return the file hash algorithm and digest of an fsverity protected file.
- * Assumption: before calling this, the file must have been opened.
+ * Retrieves the fsverity digest of the given file.  The file must have been
+ * opened at least once since the inode was last loaded into the inode cache;
+ * otherwise this function will not recognize when fsverity is enabled.
  *
- * Return: 0 on success, -errno on failure
+ * The file's fsverity digest consists of @raw_digest in combination with either
+ * @alg or @halg.  (The caller can choose which one of @alg or @halg to use.)
+ *
+ * IMPORTANT: Callers *must* make use of one of the two algorithm IDs, since
+ * @raw_digest is meaningless without knowing which algorithm it uses!  fsverity
+ * provides no security guarantee for users who ignore the algorithm ID, even if
+ * they use the digest size (since algorithms can share the same digest size).
+ *
+ * Return: The size of the raw digest in bytes, or 0 if the file doesn't have
+ *	   fsverity enabled.
  */
 int fsverity_get_digest(struct inode *inode,
-			u8 digest[FS_VERITY_MAX_DIGEST_SIZE],
-			enum hash_algo *alg)
+			u8 raw_digest[FS_VERITY_MAX_DIGEST_SIZE],
+			u8 *alg, enum hash_algo *halg)
 {
 	const struct fsverity_info *vi;
 	const struct fsverity_hash_alg *hash_alg;
 
 	vi = fsverity_get_info(inode);
 	if (!vi)
-		return -ENODATA; /* not a verity file */
+		return 0; /* not a verity file */
 
 	hash_alg = vi->tree_params.hash_alg;
-	memcpy(digest, vi->file_digest, hash_alg->digest_size);
-	*alg = hash_alg->algo_id;
-	return 0;
+	memcpy(raw_digest, vi->file_digest, hash_alg->digest_size);
+	if (alg)
+		*alg = hash_alg - fsverity_hash_algs;
+	if (halg)
+		*halg = hash_alg->algo_id;
+	return hash_alg->digest_size;
 }
+EXPORT_SYMBOL_GPL(fsverity_get_digest);
diff --git a/fs/verity/open.c b/fs/verity/open.c
index 52048b7630dc..1db5106a9c38 100644
--- a/fs/verity/open.c
+++ b/fs/verity/open.c
@@ -32,7 +32,7 @@ int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
 				     unsigned int log_blocksize,
 				     const u8 *salt, size_t salt_size)
 {
-	struct fsverity_hash_alg *hash_alg;
+	const struct fsverity_hash_alg *hash_alg;
 	int err;
 	u64 blocks;
 	u64 blocks_in_level[FS_VERITY_MAX_LEVELS];
@@ -156,9 +156,9 @@ out_err:
 
 /*
  * Compute the file digest by hashing the fsverity_descriptor excluding the
- * signature and with the sig_size field set to 0.
+ * builtin signature and with the sig_size field set to 0.
  */
-static int compute_file_digest(struct fsverity_hash_alg *hash_alg,
+static int compute_file_digest(const struct fsverity_hash_alg *hash_alg,
 			       struct fsverity_descriptor *desc,
 			       u8 *file_digest)
 {
@@ -174,7 +174,7 @@ static int compute_file_digest(struct fsverity_hash_alg *hash_alg,
 
 /*
  * Create a new fsverity_info from the given fsverity_descriptor (with optional
- * appended signature), and check the signature if present.  The
+ * appended builtin signature), and check the signature if present.  The
  * fsverity_descriptor must have already undergone basic validation.
  */
 struct fsverity_info *fsverity_create_info(const struct inode *inode,
@@ -319,8 +319,8 @@ static bool validate_fsverity_descriptor(struct inode *inode,
 }
 
 /*
- * Read the inode's fsverity_descriptor (with optional appended signature) from
- * the filesystem, and do basic validation of it.
+ * Read the inode's fsverity_descriptor (with optional appended builtin
+ * signature) from the filesystem, and do basic validation of it.
  */
 int fsverity_get_descriptor(struct inode *inode,
 			    struct fsverity_descriptor **desc_ret)
diff --git a/fs/verity/read_metadata.c b/fs/verity/read_metadata.c
index 2aefc5565152..f58432772d9e 100644
--- a/fs/verity/read_metadata.c
+++ b/fs/verity/read_metadata.c
@@ -105,7 +105,7 @@ static int fsverity_read_descriptor(struct inode *inode,
 	if (res)
 		return res;
 
-	/* don't include the signature */
+	/* don't include the builtin signature */
 	desc_size = offsetof(struct fsverity_descriptor, signature);
 	desc->sig_size = 0;
 
@@ -131,7 +131,7 @@ static int fsverity_read_signature(struct inode *inode,
 	}
 
 	/*
-	 * Include only the signature.  Note that fsverity_get_descriptor()
+	 * Include only the builtin signature.  fsverity_get_descriptor()
 	 * already verified that sig_size is in-bounds.
 	 */
 	res = fsverity_read_buffer(buf, offset, length, desc->signature,
diff --git a/fs/verity/signature.c b/fs/verity/signature.c
index b8c51ad40d3a..72034bc71c9d 100644
--- a/fs/verity/signature.c
+++ b/fs/verity/signature.c
@@ -5,6 +5,14 @@
  * Copyright 2019 Google LLC
  */
 
+/*
+ * This file implements verification of fs-verity builtin signatures.  Please
+ * take great care before using this feature.  It is not the only way to do
+ * signatures with fs-verity, and the alternatives (such as userspace signature
+ * verification, and IMA appraisal) can be much better.  For details about the
+ * limitations of this feature, see Documentation/filesystems/fsverity.rst.
+ */
+
 #include "fsverity_private.h"
 
 #include <linux/cred.h>
diff --git a/fs/verity/verify.c b/fs/verity/verify.c
index e2508222750b..433cef51f5f6 100644
--- a/fs/verity/verify.c
+++ b/fs/verity/verify.c
@@ -12,38 +12,6 @@
 
 static struct workqueue_struct *fsverity_read_workqueue;
 
-static inline int cmp_hashes(const struct fsverity_info *vi,
-			     const u8 *want_hash, const u8 *real_hash,
-			     u64 data_pos, int level)
-{
-	const unsigned int hsize = vi->tree_params.digest_size;
-
-	if (memcmp(want_hash, real_hash, hsize) == 0)
-		return 0;
-
-	fsverity_err(vi->inode,
-		     "FILE CORRUPTED! pos=%llu, level=%d, want_hash=%s:%*phN, real_hash=%s:%*phN",
-		     data_pos, level,
-		     vi->tree_params.hash_alg->name, hsize, want_hash,
-		     vi->tree_params.hash_alg->name, hsize, real_hash);
-	return -EBADMSG;
-}
-
-static bool data_is_zeroed(struct inode *inode, struct page *page,
-			   unsigned int len, unsigned int offset)
-{
-	void *virt = kmap_local_page(page);
-
-	if (memchr_inv(virt + offset, 0, len)) {
-		kunmap_local(virt);
-		fsverity_err(inode,
-			     "FILE CORRUPTED!  Data past EOF is not zeroed");
-		return false;
-	}
-	kunmap_local(virt);
-	return true;
-}
-
 /*
  * Returns true if the hash block with index @hblock_idx in the tree, located in
  * @hpage, has already been verified.
@@ -122,9 +90,7 @@ static bool is_hash_block_verified(struct fsverity_info *vi, struct page *hpage,
  */
 static bool
 verify_data_block(struct inode *inode, struct fsverity_info *vi,
-		  struct ahash_request *req, struct page *data_page,
-		  u64 data_pos, unsigned int dblock_offset_in_page,
-		  unsigned long max_ra_pages)
+		  const void *data, u64 data_pos, unsigned long max_ra_pages)
 {
 	const struct merkle_tree_params *params = &vi->tree_params;
 	const unsigned int hsize = params->digest_size;
@@ -136,11 +102,11 @@ verify_data_block(struct inode *inode, struct fsverity_info *vi,
 	struct {
 		/* Page containing the hash block */
 		struct page *page;
+		/* Mapped address of the hash block (will be within @page) */
+		const void *addr;
 		/* Index of the hash block in the tree overall */
 		unsigned long index;
-		/* Byte offset of the hash block within @page */
-		unsigned int offset_in_page;
-		/* Byte offset of the wanted hash within @page */
+		/* Byte offset of the wanted hash relative to @addr */
 		unsigned int hoffset;
 	} hblocks[FS_VERITY_MAX_LEVELS];
 	/*
@@ -148,7 +114,9 @@ verify_data_block(struct inode *inode, struct fsverity_info *vi,
 	 * index of that block's hash within the current level.
 	 */
 	u64 hidx = data_pos >> params->log_blocksize;
-	int err;
+
+	/* Up to 1 + FS_VERITY_MAX_LEVELS pages may be mapped at once */
+	BUILD_BUG_ON(1 + FS_VERITY_MAX_LEVELS > KM_MAX_IDX);
 
 	if (unlikely(data_pos >= inode->i_size)) {
 		/*
@@ -159,8 +127,12 @@ verify_data_block(struct inode *inode, struct fsverity_info *vi,
 		 * any part past EOF should be all zeroes.  Therefore, we need
 		 * to verify that any data blocks fully past EOF are all zeroes.
 		 */
-		return data_is_zeroed(inode, data_page, params->block_size,
-				      dblock_offset_in_page);
+		if (memchr_inv(data, 0, params->block_size)) {
+			fsverity_err(inode,
+				     "FILE CORRUPTED!  Data past EOF is not zeroed");
+			return false;
+		}
+		return true;
 	}
 
 	/*
@@ -175,6 +147,7 @@ verify_data_block(struct inode *inode, struct fsverity_info *vi,
 		unsigned int hblock_offset_in_page;
 		unsigned int hoffset;
 		struct page *hpage;
+		const void *haddr;
 
 		/*
 		 * The index of the block in the current level; also the index
@@ -192,30 +165,30 @@ verify_data_block(struct inode *inode, struct fsverity_info *vi,
 		hblock_offset_in_page =
 			(hblock_idx << params->log_blocksize) & ~PAGE_MASK;
 
-		/* Byte offset of the hash within the page */
-		hoffset = hblock_offset_in_page +
-			  ((hidx << params->log_digestsize) &
-			   (params->block_size - 1));
+		/* Byte offset of the hash within the block */
+		hoffset = (hidx << params->log_digestsize) &
+			  (params->block_size - 1);
 
 		hpage = inode->i_sb->s_vop->read_merkle_tree_page(inode,
 				hpage_idx, level == 0 ? min(max_ra_pages,
 					params->tree_pages - hpage_idx) : 0);
 		if (IS_ERR(hpage)) {
-			err = PTR_ERR(hpage);
 			fsverity_err(inode,
-				     "Error %d reading Merkle tree page %lu",
-				     err, hpage_idx);
-			goto out;
+				     "Error %ld reading Merkle tree page %lu",
+				     PTR_ERR(hpage), hpage_idx);
+			goto error;
 		}
+		haddr = kmap_local_page(hpage) + hblock_offset_in_page;
 		if (is_hash_block_verified(vi, hpage, hblock_idx)) {
-			memcpy_from_page(_want_hash, hpage, hoffset, hsize);
+			memcpy(_want_hash, haddr + hoffset, hsize);
 			want_hash = _want_hash;
+			kunmap_local(haddr);
 			put_page(hpage);
 			goto descend;
 		}
 		hblocks[level].page = hpage;
+		hblocks[level].addr = haddr;
 		hblocks[level].index = hblock_idx;
-		hblocks[level].offset_in_page = hblock_offset_in_page;
 		hblocks[level].hoffset = hoffset;
 		hidx = next_hidx;
 	}
@@ -225,18 +198,14 @@ descend:
 	/* Descend the tree verifying hash blocks. */
 	for (; level > 0; level--) {
 		struct page *hpage = hblocks[level - 1].page;
+		const void *haddr = hblocks[level - 1].addr;
 		unsigned long hblock_idx = hblocks[level - 1].index;
-		unsigned int hblock_offset_in_page =
-			hblocks[level - 1].offset_in_page;
 		unsigned int hoffset = hblocks[level - 1].hoffset;
 
-		err = fsverity_hash_block(params, inode, req, hpage,
-					  hblock_offset_in_page, real_hash);
-		if (err)
-			goto out;
-		err = cmp_hashes(vi, want_hash, real_hash, data_pos, level - 1);
-		if (err)
-			goto out;
+		if (fsverity_hash_block(params, inode, haddr, real_hash) != 0)
+			goto error;
+		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
@@ -246,29 +215,39 @@ descend:
 			set_bit(hblock_idx, vi->hash_block_verified);
 		else
 			SetPageChecked(hpage);
-		memcpy_from_page(_want_hash, hpage, hoffset, hsize);
+		memcpy(_want_hash, haddr + hoffset, hsize);
 		want_hash = _want_hash;
+		kunmap_local(haddr);
 		put_page(hpage);
 	}
 
 	/* Finally, verify the data block. */
-	err = fsverity_hash_block(params, inode, req, data_page,
-				  dblock_offset_in_page, real_hash);
-	if (err)
-		goto out;
-	err = cmp_hashes(vi, want_hash, real_hash, data_pos, -1);
-out:
-	for (; level > 0; level--)
-		put_page(hblocks[level - 1].page);
+	if (fsverity_hash_block(params, inode, data, real_hash) != 0)
+		goto error;
+	if (memcmp(want_hash, real_hash, hsize) != 0)
+		goto corrupted;
+	return true;
 
-	return err == 0;
+corrupted:
+	fsverity_err(inode,
+		     "FILE CORRUPTED! pos=%llu, level=%d, want_hash=%s:%*phN, real_hash=%s:%*phN",
+		     data_pos, level - 1,
+		     params->hash_alg->name, hsize, want_hash,
+		     params->hash_alg->name, hsize, real_hash);
+error:
+	for (; level > 0; level--) {
+		kunmap_local(hblocks[level - 1].addr);
+		put_page(hblocks[level - 1].page);
+	}
+	return false;
 }
 
 static bool
-verify_data_blocks(struct inode *inode, struct fsverity_info *vi,
-		   struct ahash_request *req, struct folio *data_folio,
-		   size_t len, size_t offset, unsigned long max_ra_pages)
+verify_data_blocks(struct folio *data_folio, size_t len, size_t offset,
+		   unsigned long max_ra_pages)
 {
+	struct inode *inode = data_folio->mapping->host;
+	struct fsverity_info *vi = inode->i_verity_info;
 	const unsigned int block_size = vi->tree_params.block_size;
 	u64 pos = (u64)data_folio->index << PAGE_SHIFT;
 
@@ -278,11 +257,14 @@ verify_data_blocks(struct inode *inode, struct fsverity_info *vi,
 			 folio_test_uptodate(data_folio)))
 		return false;
 	do {
-		struct page *data_page =
-			folio_page(data_folio, offset >> PAGE_SHIFT);
-
-		if (!verify_data_block(inode, vi, req, data_page, pos + offset,
-				       offset & ~PAGE_MASK, max_ra_pages))
+		void *data;
+		bool valid;
+
+		data = kmap_local_folio(data_folio, offset);
+		valid = verify_data_block(inode, vi, data, pos + offset,
+					  max_ra_pages);
+		kunmap_local(data);
+		if (!valid)
 			return false;
 		offset += block_size;
 		len -= block_size;
@@ -304,19 +286,7 @@ verify_data_blocks(struct inode *inode, struct fsverity_info *vi,
  */
 bool fsverity_verify_blocks(struct folio *folio, size_t len, size_t offset)
 {
-	struct inode *inode = folio->mapping->host;
-	struct fsverity_info *vi = inode->i_verity_info;
-	struct ahash_request *req;
-	bool valid;
-
-	/* This allocation never fails, since it's mempool-backed. */
-	req = fsverity_alloc_hash_request(vi->tree_params.hash_alg, GFP_NOFS);
-
-	valid = verify_data_blocks(inode, vi, req, folio, len, offset, 0);
-
-	fsverity_free_hash_request(vi->tree_params.hash_alg, req);
-
-	return valid;
+	return verify_data_blocks(folio, len, offset, 0);
 }
 EXPORT_SYMBOL_GPL(fsverity_verify_blocks);
 
@@ -337,15 +307,9 @@ EXPORT_SYMBOL_GPL(fsverity_verify_blocks);
  */
 void fsverity_verify_bio(struct bio *bio)
 {
-	struct inode *inode = bio_first_page_all(bio)->mapping->host;
-	struct fsverity_info *vi = inode->i_verity_info;
-	struct ahash_request *req;
 	struct folio_iter fi;
 	unsigned long max_ra_pages = 0;
 
-	/* This allocation never fails, since it's mempool-backed. */
-	req = fsverity_alloc_hash_request(vi->tree_params.hash_alg, GFP_NOFS);
-
 	if (bio->bi_opf & REQ_RAHEAD) {
 		/*
 		 * If this bio is for data readahead, then we also do readahead
@@ -360,14 +324,12 @@ void fsverity_verify_bio(struct bio *bio)
 	}
 
 	bio_for_each_folio_all(fi, bio) {
-		if (!verify_data_blocks(inode, vi, req, fi.folio, fi.length,
-					fi.offset, max_ra_pages)) {
+		if (!verify_data_blocks(fi.folio, fi.length, fi.offset,
+					max_ra_pages)) {
 			bio->bi_status = BLK_STS_IOERR;
 			break;
 		}
 	}
-
-	fsverity_free_hash_request(vi->tree_params.hash_alg, req);
 }
 EXPORT_SYMBOL_GPL(fsverity_verify_bio);
 #endif /* CONFIG_BLOCK */