dm verity: add ignore_zero_blocks feature
If ignore_zero_blocks is enabled dm-verity will return zeroes for blocks
matching a zero hash without validating the content.
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
index 4f90ec2..5c5d30c 100644
--- a/drivers/md/dm-verity-target.c
+++ b/drivers/md/dm-verity-target.c
@@ -31,8 +31,9 @@
#define DM_VERITY_OPT_LOGGING "ignore_corruption"
#define DM_VERITY_OPT_RESTART "restart_on_corruption"
+#define DM_VERITY_OPT_IGN_ZEROES "ignore_zero_blocks"
-#define DM_VERITY_OPTS_MAX (1 + DM_VERITY_OPTS_FEC)
+#define DM_VERITY_OPTS_MAX (2 + DM_VERITY_OPTS_FEC)
static unsigned dm_verity_prefetch_cluster = DM_VERITY_DEFAULT_PREFETCH_SIZE;
@@ -309,10 +310,9 @@
* of the hash tree if necessary.
*/
int verity_hash_for_block(struct dm_verity *v, struct dm_verity_io *io,
- sector_t block, u8 *digest)
+ sector_t block, u8 *digest, bool *is_zero)
{
- int i;
- int r;
+ int r = 0, i;
if (likely(v->levels)) {
/*
@@ -324,7 +324,7 @@
*/
r = verity_verify_level(v, io, block, 0, true, digest);
if (likely(r <= 0))
- return r;
+ goto out;
}
memcpy(digest, v->root_digest, v->digest_size);
@@ -332,10 +332,15 @@
for (i = v->levels - 1; i >= 0; i--) {
r = verity_verify_level(v, io, block, i, false, digest);
if (unlikely(r))
- return r;
+ goto out;
}
+out:
+ if (!r && v->zero_digest)
+ *is_zero = !memcmp(v->zero_digest, digest, v->digest_size);
+ else
+ *is_zero = false;
- return 0;
+ return r;
}
/*
@@ -382,11 +387,19 @@
return verity_hash_update(v, verity_io_hash_desc(v, io), data, len);
}
+static int verity_bv_zero(struct dm_verity *v, struct dm_verity_io *io,
+ u8 *data, size_t len)
+{
+ memset(data, 0, len);
+ return 0;
+}
+
/*
* Verify one "dm_verity_io" structure.
*/
static int verity_verify_io(struct dm_verity_io *io)
{
+ bool is_zero;
struct dm_verity *v = io->v;
struct bvec_iter start;
unsigned b;
@@ -396,10 +409,24 @@
struct shash_desc *desc = verity_io_hash_desc(v, io);
r = verity_hash_for_block(v, io, io->block + b,
- verity_io_want_digest(v, io));
+ verity_io_want_digest(v, io),
+ &is_zero);
if (unlikely(r < 0))
return r;
+ if (is_zero) {
+ /*
+ * If we expect a zero block, don't validate, just
+ * return zeros.
+ */
+ r = verity_for_bv_block(v, io, &io->iter,
+ verity_bv_zero);
+ if (unlikely(r < 0))
+ return r;
+
+ continue;
+ }
+
r = verity_hash_init(v, desc);
if (unlikely(r < 0))
return r;
@@ -604,6 +631,8 @@
args++;
if (verity_fec_is_enabled(v))
args += DM_VERITY_OPTS_FEC;
+ if (v->zero_digest)
+ args++;
if (!args)
return;
DMEMIT(" %u", args);
@@ -620,6 +649,8 @@
BUG();
}
}
+ if (v->zero_digest)
+ DMEMIT(" " DM_VERITY_OPT_IGN_ZEROES);
sz = verity_fec_status_table(v, sz, result, maxlen);
break;
}
@@ -671,6 +702,7 @@
kfree(v->salt);
kfree(v->root_digest);
+ kfree(v->zero_digest);
if (v->tfm)
crypto_free_shash(v->tfm);
@@ -688,6 +720,37 @@
kfree(v);
}
+static int verity_alloc_zero_digest(struct dm_verity *v)
+{
+ int r = -ENOMEM;
+ struct shash_desc *desc;
+ u8 *zero_data;
+
+ v->zero_digest = kmalloc(v->digest_size, GFP_KERNEL);
+
+ if (!v->zero_digest)
+ return r;
+
+ desc = kmalloc(v->shash_descsize, GFP_KERNEL);
+
+ if (!desc)
+ return r; /* verity_dtr will free zero_digest */
+
+ zero_data = kzalloc(1 << v->data_dev_block_bits, GFP_KERNEL);
+
+ if (!zero_data)
+ goto out;
+
+ r = verity_hash(v, desc, zero_data, 1 << v->data_dev_block_bits,
+ v->zero_digest);
+
+out:
+ kfree(desc);
+ kfree(zero_data);
+
+ return r;
+}
+
static int verity_parse_opt_args(struct dm_arg_set *as, struct dm_verity *v)
{
int r;
@@ -718,6 +781,14 @@
v->mode = DM_VERITY_MODE_RESTART;
continue;
+ } else if (!strcasecmp(arg_name, DM_VERITY_OPT_IGN_ZEROES)) {
+ r = verity_alloc_zero_digest(v);
+ if (r) {
+ ti->error = "Cannot allocate zero digest";
+ return r;
+ }
+ continue;
+
} else if (verity_is_fec_opt_arg(arg_name)) {
r = verity_fec_parse_opt_args(as, v, &argc, arg_name);
if (r)