dm-verity: reduce scope of real and wanted digests

In preparation for supporting interleaved hashing where dm-verity will
need to keep track of the real and wanted digests for multiple data
blocks simultaneously, stop using the want_digest and real_digest fields
of struct dm_verity_io from so many different places.  Specifically:

- Make various functions take want_digest as a parameter rather than
  having it be implicitly passed via the struct dm_verity_io.

- Add a new tmp_digest field, and use this instead of real_digest when
  computing a digest solely for the purpose of immediately checking it.

The result is that real_digest and want_digest are used only by
verity_verify_io().

Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

Author: Eric Biggers

drivers/md/dm-verity-fec.c

@@ -188,14 +188,13 @@ static int fec_decode_bufs(struct dm_verity *v, struct dm_verity_io *io,
  * Locate data block erasures using verity hashes.
  */
 static int fec_is_erasure(struct dm_verity *v, struct dm_verity_io *io,
-			  u8 *want_digest, u8 *data)
+			  const u8 *want_digest, const u8 *data)
 {
 	if (unlikely(verity_hash(v, io, data, 1 << v->data_dev_block_bits,
-				 verity_io_real_digest(v, io))))
+				 io->tmp_digest)))
 		return 0;
 
-	return memcmp(verity_io_real_digest(v, io), want_digest,
-		      v->digest_size) != 0;
+	return memcmp(io->tmp_digest, want_digest, v->digest_size) != 0;
 }
 
 /*
@@ -366,7 +365,7 @@ static void fec_init_bufs(struct dm_verity *v, struct dm_verity_fec_io *fio)
  */
 static int fec_decode_rsb(struct dm_verity *v, struct dm_verity_io *io,
 			  struct dm_verity_fec_io *fio, u64 rsb, u64 offset,
-			  bool use_erasures)
+			  const u8 *want_digest, bool use_erasures)
 {
 	int r, neras = 0;
 	unsigned int pos;
@@ -392,12 +391,11 @@ static int fec_decode_rsb(struct dm_verity *v, struct dm_verity_io *io,
 
 	/* Always re-validate the corrected block against the expected hash */
 	r = verity_hash(v, io, fio->output, 1 << v->data_dev_block_bits,
-			verity_io_real_digest(v, io));
+			io->tmp_digest);
 	if (unlikely(r < 0))
 		return r;
 
-	if (memcmp(verity_io_real_digest(v, io), verity_io_want_digest(v, io),
-		   v->digest_size)) {
+	if (memcmp(io->tmp_digest, want_digest, v->digest_size)) {
 		DMERR_LIMIT("%s: FEC %llu: failed to correct (%d erasures)",
 			    v->data_dev->name, (unsigned long long)rsb, neras);
 		return -EILSEQ;
@@ -408,7 +406,8 @@ static int fec_decode_rsb(struct dm_verity *v, struct dm_verity_io *io,
 
 /* Correct errors in a block. Copies corrected block to dest. */
 int verity_fec_decode(struct dm_verity *v, struct dm_verity_io *io,
-		      enum verity_block_type type, sector_t block, u8 *dest)
+		      enum verity_block_type type, const u8 *want_digest,
+		      sector_t block, u8 *dest)
 {
 	int r;
 	struct dm_verity_fec_io *fio = fec_io(io);
@@ -451,9 +450,9 @@ int verity_fec_decode(struct dm_verity *v, struct dm_verity_io *io,
 	 * them first. Do a second attempt with erasures if the corruption is
 	 * bad enough.
 	 */
-	r = fec_decode_rsb(v, io, fio, rsb, offset, false);
+	r = fec_decode_rsb(v, io, fio, rsb, offset, want_digest, false);
 	if (r < 0) {
-		r = fec_decode_rsb(v, io, fio, rsb, offset, true);
+		r = fec_decode_rsb(v, io, fio, rsb, offset, want_digest, true);
 		if (r < 0)
 			goto done;
 	}

drivers/md/dm-verity-fec.h

@@ -68,8 +68,8 @@ struct dm_verity_fec_io {
 extern bool verity_fec_is_enabled(struct dm_verity *v);
 
 extern int verity_fec_decode(struct dm_verity *v, struct dm_verity_io *io,
-			     enum verity_block_type type, sector_t block,
-			     u8 *dest);
+			     enum verity_block_type type, const u8 *want_digest,
+			     sector_t block, u8 *dest);
 
 extern unsigned int verity_fec_status_table(struct dm_verity *v, unsigned int sz,
 					char *result, unsigned int maxlen);
@@ -99,6 +99,7 @@ static inline bool verity_fec_is_enabled(struct dm_verity *v)
 static inline int verity_fec_decode(struct dm_verity *v,
 				    struct dm_verity_io *io,
 				    enum verity_block_type type,
+				    const u8 *want_digest,
 				    sector_t block, u8 *dest)
 {
 	return -EOPNOTSUPP;

drivers/md/dm-verity-target.c

@@ -229,12 +229,12 @@ static int verity_handle_err(struct dm_verity *v, enum verity_block_type type,
  * Verify hash of a metadata block pertaining to the specified data block
  * ("block" argument) at a specified level ("level" argument).
  *
- * On successful return, verity_io_want_digest(v, io) contains the hash value
- * for a lower tree level or for the data block (if we're at the lowest level).
+ * On successful return, want_digest contains the hash value for a lower tree
+ * level or for the data block (if we're at the lowest level).
  *
  * If "skip_unverified" is true, unverified buffer is skipped and 1 is returned.
  * If "skip_unverified" is false, unverified buffer is hashed and verified
- * against current value of verity_io_want_digest(v, io).
+ * against current value of want_digest.
  */
 static int verity_verify_level(struct dm_verity *v, struct dm_verity_io *io,
 			       sector_t block, int level, bool skip_unverified,
@@ -273,7 +273,7 @@ static int verity_verify_level(struct dm_verity *v, struct dm_verity_io *io,
 		if (IS_ERR(data))
 			return r;
 		if (verity_fec_decode(v, io, DM_VERITY_BLOCK_TYPE_METADATA,
-				      hash_block, data) == 0) {
+				      want_digest, hash_block, data) == 0) {
 			aux = dm_bufio_get_aux_data(buf);
 			aux->hash_verified = 1;
 			goto release_ok;
@@ -293,11 +293,11 @@ static int verity_verify_level(struct dm_verity *v, struct dm_verity_io *io,
 		}
 
 		r = verity_hash(v, io, data, 1 << v->hash_dev_block_bits,
-				verity_io_real_digest(v, io));
+				io->tmp_digest);
 		if (unlikely(r < 0))
 			goto release_ret_r;
 
-		if (likely(memcmp(verity_io_real_digest(v, io), want_digest,
+		if (likely(memcmp(io->tmp_digest, want_digest,
 				  v->digest_size) == 0))
 			aux->hash_verified = 1;
 		else if (static_branch_unlikely(&use_bh_wq_enabled) && io->in_bh) {
@@ -308,7 +308,7 @@ static int verity_verify_level(struct dm_verity *v, struct dm_verity_io *io,
 			r = -EAGAIN;
 			goto release_ret_r;
 		} else if (verity_fec_decode(v, io, DM_VERITY_BLOCK_TYPE_METADATA,
-					     hash_block, data) == 0)
+					     want_digest, hash_block, data) == 0)
 			aux->hash_verified = 1;
 		else if (verity_handle_err(v,
 					   DM_VERITY_BLOCK_TYPE_METADATA,
@@ -372,7 +372,8 @@ int verity_hash_for_block(struct dm_verity *v, struct dm_verity_io *io,
 }
 
 static noinline int verity_recheck(struct dm_verity *v, struct dm_verity_io *io,
-				   sector_t cur_block, u8 *dest)
+				   const u8 *want_digest, sector_t cur_block,
+				   u8 *dest)
 {
 	struct page *page;
 	void *buffer;
@@ -396,12 +397,11 @@ static noinline int verity_recheck(struct dm_verity *v, struct dm_verity_io *io,
 		goto free_ret;
 
 	r = verity_hash(v, io, buffer, 1 << v->data_dev_block_bits,
-			verity_io_real_digest(v, io));
+			io->tmp_digest);
 	if (unlikely(r))
 		goto free_ret;
 
-	if (memcmp(verity_io_real_digest(v, io),
-		   verity_io_want_digest(v, io), v->digest_size)) {
+	if (memcmp(io->tmp_digest, want_digest, v->digest_size)) {
 		r = -EIO;
 		goto free_ret;
 	}
@@ -416,8 +416,9 @@ static noinline int verity_recheck(struct dm_verity *v, struct dm_verity_io *io,
 
 static int verity_handle_data_hash_mismatch(struct dm_verity *v,
 					    struct dm_verity_io *io,
-					    struct bio *bio, sector_t blkno,
-					    u8 *data)
+					    struct bio *bio,
+					    const u8 *want_digest,
+					    sector_t blkno, u8 *data)
 {
 	if (static_branch_unlikely(&use_bh_wq_enabled) && io->in_bh) {
 		/*
@@ -426,14 +427,14 @@ static int verity_handle_data_hash_mismatch(struct dm_verity *v,
 		 */
 		return -EAGAIN;
 	}
-	if (verity_recheck(v, io, blkno, data) == 0) {
+	if (verity_recheck(v, io, want_digest, blkno, data) == 0) {
 		if (v->validated_blocks)
 			set_bit(blkno, v->validated_blocks);
 		return 0;
 	}
 #if defined(CONFIG_DM_VERITY_FEC)
-	if (verity_fec_decode(v, io, DM_VERITY_BLOCK_TYPE_DATA, blkno,
-			      data) == 0)
+	if (verity_fec_decode(v, io, DM_VERITY_BLOCK_TYPE_DATA, want_digest,
+			      blkno, data) == 0)
 		return 0;
 #endif
 	if (bio->bi_status)
@@ -525,8 +526,9 @@ static int verity_verify_io(struct dm_verity_io *io)
 			kunmap_local(data);
 			continue;
 		}
-		r = verity_handle_data_hash_mismatch(v, io, bio, cur_block,
-						     data);
+		r = verity_handle_data_hash_mismatch(v, io, bio,
+						     verity_io_want_digest(v, io),
+						     cur_block, data);
 		kunmap_local(data);
 		if (unlikely(r))
 			return r;

drivers/md/dm-verity.h

@@ -99,6 +99,7 @@ struct dm_verity_io {
 	struct work_struct work;
 	struct work_struct bh_work;
 
+	u8 tmp_digest[HASH_MAX_DIGESTSIZE];
 	u8 real_digest[HASH_MAX_DIGESTSIZE];
 	u8 want_digest[HASH_MAX_DIGESTSIZE];