[PATCH v7 6/7] dm-verity: reduce scope of real and wanted digests

Eric Biggers
2024-10-01T15:39:22Z

In preparation for supporting multibuffer 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 hash solely for the purpose of immediately checking it.

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

Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
drivers/md/dm-verity-fec.c | 19 +++++++++---------
drivers/md/dm-verity-fec.h | 5 +++--
drivers/md/dm-verity-target.c | 36 ++++++++++++++++++-----------------
drivers/md/dm-verity.h | 1 +
4 files changed, 32 insertions(+), 29 deletions(-)

diff --git a/drivers/md/dm-verity-fec.c b/drivers/md/dm-verity-fec.c
index 62b1a44b8dd2e..79f3794e197e6 100644
--- a/drivers/md/dm-verity-fec.c
+++ b/drivers/md/dm-verity-fec.c
@@ -185,15 +185,14 @@ static int fec_decode_bufs(struct dm_verity *v, struct dm_verity_io *io,
*/
static int fec_is_erasure(struct dm_verity *v, struct dm_verity_io *io,
u8 *want_digest, u8 *data)
{
if (unlikely(verity_hash(v, io, data, 1 << v->data_dev_block_bits,
- verity_io_real_digest(v, io), true)))
+ io->tmp_digest, true)))
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;
}

/*
* Read data blocks that are part of the RS block and deinterleave as much as
* fits into buffers. Check for erasure locations if @neras is non-NULL.
@@ -360,11 +359,11 @@ static void fec_init_bufs(struct dm_verity *v, struct dm_verity_fec_io *fio)
* (indicated by @offset) in fio->output. If @use_erasures is non-zero, uses
* hashes to locate erasures.
*/
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;

r = fec_alloc_bufs(v, fio);
@@ -386,27 +385,27 @@ static int fec_decode_rsb(struct dm_verity *v, struct dm_verity_io *io,
pos += fio->nbufs << DM_VERITY_FEC_BUF_RS_BITS;
}

/* 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), true);
+ io->tmp_digest, true);
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;
}

return 0;
}

/* 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);
u64 offset, res, rsb;

@@ -445,13 +444,13 @@ int verity_fec_decode(struct dm_verity *v, struct dm_verity_io *io,
/*
* Locating erasures is slow, so attempt to recover the block without
* 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;
}

memcpy(dest, fio->output, 1 << v->data_dev_block_bits);
diff --git a/drivers/md/dm-verity-fec.h b/drivers/md/dm-verity-fec.h
index 09123a6129538..a6689cdc489db 100644
--- a/drivers/md/dm-verity-fec.h
+++ b/drivers/md/dm-verity-fec.h
@@ -66,12 +66,12 @@ struct dm_verity_fec_io {
#define DM_VERITY_OPTS_FEC 8

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);

extern void verity_fec_finish_io(struct dm_verity_io *io);
@@ -97,10 +97,11 @@ 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;
}

diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
index 36e4ddfe2d158..e40c5c083a931 100644
--- a/drivers/md/dm-verity-target.c
+++ b/drivers/md/dm-verity-target.c
@@ -286,16 +286,16 @@ 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,
u8 *want_digest)
{
@@ -334,26 +334,26 @@ static int verity_verify_level(struct dm_verity *v, struct dm_verity_io *io,
r = 1;
goto release_ret_r;
}

r = verity_hash(v, io, data, 1 << v->hash_dev_block_bits,
- verity_io_real_digest(v, io), !io->in_bh);
+ io->tmp_digest, !io->in_bh);
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) {
/*
* Error handling code (FEC included) cannot be run in a
* tasklet since it may sleep, so fallback to work-queue.
*/
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,
hash_block)) {
struct bio *bio =
@@ -412,11 +412,12 @@ int verity_hash_for_block(struct dm_verity *v, struct dm_verity_io *io,

return r;
}

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;
int r;
struct dm_io_request io_req;
@@ -436,16 +437,15 @@ static noinline int verity_recheck(struct dm_verity *v, struct dm_verity_io *io,
r = dm_io(&io_req, 1, &io_loc, NULL, IOPRIO_DEFAULT);
if (unlikely(r))
goto free_ret;

r = verity_hash(v, io, buffer, 1 << v->data_dev_block_bits,
- verity_io_real_digest(v, io), true);
+ io->tmp_digest, true);
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;
}

memcpy(dest, buffer, 1 << v->data_dev_block_bits);
@@ -456,28 +456,29 @@ static noinline int verity_recheck(struct dm_verity *v, struct dm_verity_io *io,
return r;
}

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) {
/*
* Error handling code (FEC included) cannot be run in the
* BH workqueue, so fallback to a standard workqueue.
*/
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)
return -EIO; /* Error correction failed; Just return error */

@@ -564,12 +565,13 @@ static int verity_verify_io(struct dm_verity_io *io)
if (v->validated_blocks)
set_bit(cur_block, v->validated_blocks);
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;
}

diff --git a/drivers/md/dm-verity.h b/drivers/md/dm-verity.h
index 754e70bb5fe09..347d3fc4fff4d 100644
--- a/drivers/md/dm-verity.h
+++ b/drivers/md/dm-verity.h
@@ -93,10 +93,11 @@ struct dm_verity_io {
bool in_bh;

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];

/*
* This struct is followed by a variable-sized hash request of size
--
2.46.2