[PATCH v5 09/15] dm-verity: make real_digest and want_digest fixed-length

Eric Biggers
2024-06-11T03:49:14Z

Change the digest fields in struct dm_verity_io from variable-length to
fixed-length, since their maximum length is fixed at
HASH_MAX_DIGESTSIZE, i.e. 64 bytes, which is not too big. This is
simpler and makes the fields a bit faster to access.

(HASH_MAX_DIGESTSIZE did not exist when this code was written, which may
explain why it wasn't used.)

This makes the verity_io_real_digest() and verity_io_want_digest()
functions trivial, but this patch leaves them in place temporarily since
most of their callers will go away in a later patch anyway.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
drivers/md/dm-verity-target.c | 3 +--
drivers/md/dm-verity.h | 17 +++++++----------
2 files changed, 8 insertions(+), 12 deletions(-)

diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
index 796d85526696..4ef814a7faf4 100644
--- a/drivers/md/dm-verity-target.c
+++ b/drivers/md/dm-verity-target.c
@@ -1527,12 +1527,11 @@ static int verity_ctr(struct dm_target *ti, unsigned int argc, char **argv)
ti->error = "Cannot allocate workqueue";
r = -ENOMEM;
goto bad;
}

- ti->per_io_data_size = sizeof(struct dm_verity_io) +
- v->ahash_reqsize + v->digest_size * 2;
+ ti->per_io_data_size = sizeof(struct dm_verity_io) + v->ahash_reqsize;

r = verity_fec_ctr(v);
if (r)
goto bad;

diff --git a/drivers/md/dm-verity.h b/drivers/md/dm-verity.h
index 20b1bcf03474..5d3da9f5fc95 100644
--- a/drivers/md/dm-verity.h
+++ b/drivers/md/dm-verity.h
@@ -89,19 +89,16 @@ struct dm_verity_io {
struct work_struct work;
struct work_struct bh_work;

char *recheck_buffer;

+ u8 real_digest[HASH_MAX_DIGESTSIZE];
+ u8 want_digest[HASH_MAX_DIGESTSIZE];
+
/*
- * Three variably-size fields follow this struct:
- *
- * u8 hash_req[v->ahash_reqsize];
- * u8 real_digest[v->digest_size];
- * u8 want_digest[v->digest_size];
- *
- * To access them use: verity_io_hash_req(), verity_io_real_digest()
- * and verity_io_want_digest().
+ * This struct is followed by a variable-sized struct ahash_request of
+ * size v->ahash_reqsize. To access it, use verity_io_hash_req().
*/
};

static inline struct ahash_request *verity_io_hash_req(struct dm_verity *v,
struct dm_verity_io *io)
@@ -110,17 +107,17 @@ static inline struct ahash_request *verity_io_hash_req(struct dm_verity *v,
}

static inline u8 *verity_io_real_digest(struct dm_verity *v,
struct dm_verity_io *io)
{
- return (u8 *)(io + 1) + v->ahash_reqsize;
+ return io->real_digest;
}

static inline u8 *verity_io_want_digest(struct dm_verity *v,
struct dm_verity_io *io)
{
- return (u8 *)(io + 1) + v->ahash_reqsize + v->digest_size;
+ return io->want_digest;
}

extern int verity_for_bv_block(struct dm_verity *v, struct dm_verity_io *io,
struct bvec_iter *iter,
int (*process)(struct dm_verity *v,
--
2.45.1