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Message-Id: <1446688954-29589-5-git-send-email-samitolvanen@google.com>
Date: Thu, 5 Nov 2015 02:02:34 +0000
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Mikulas Patocka <mpatocka@...hat.com>,
Mandeep Baines <msb@...omium.org>,
Will Drewry <wad@...omium.org>
Cc: Alasdair Kergon <agk@...hat.com>,
Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
Mark Salyzyn <salyzyn@...gle.com>,
Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH 4/4] dm verity: ignore zero blocks
Add ignore_zero_blocks option, which returns zeros for blocks matching a
zero hash without validating the content.
Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
---
Documentation/device-mapper/verity.txt | 5 ++
drivers/md/dm-verity.c | 88 ++++++++++++++++++++++++++++++----
2 files changed, 83 insertions(+), 10 deletions(-)
diff --git a/Documentation/device-mapper/verity.txt b/Documentation/device-mapper/verity.txt
index 3628d28..1b103b0 100644
--- a/Documentation/device-mapper/verity.txt
+++ b/Documentation/device-mapper/verity.txt
@@ -79,6 +79,11 @@ restart_on_corruption
not compatible with ignore_corruption and requires user space support to
avoid restart loops.
+ignore_zero_blocks
+ Do not verify blocks that are expected to contain zeros and always return
+ zeros instead. This may be useful if the partition contains unused blocks
+ that are not guaranteed to contain zeros.
+
use_fec_from_device
Use forward error correction (FEC) to recover from corruption if hash
verification fails. Use encoding data from the specified device. This
diff --git a/drivers/md/dm-verity.c b/drivers/md/dm-verity.c
index 61dec39..485d59e 100644
--- a/drivers/md/dm-verity.c
+++ b/drivers/md/dm-verity.c
@@ -38,6 +38,7 @@
#define DM_VERITY_OPT_LOGGING "ignore_corruption"
#define DM_VERITY_OPT_RESTART "restart_on_corruption"
+#define DM_VERITY_OPT_IGN_ZEROS "ignore_zero_blocks"
#define DM_VERITY_OPT_FEC_DEV "use_fec_from_device"
#define DM_VERITY_OPT_FEC_BLOCKS "fec_blocks"
@@ -45,7 +46,7 @@
#define DM_VERITY_OPT_FEC_ROOTS "fec_roots"
#define DM_VERITY_OPTS_FEC 8
-#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;
@@ -74,6 +75,7 @@ struct dm_verity {
struct crypto_shash *tfm;
u8 *root_digest; /* digest of the root block */
u8 *salt; /* salt: its size is salt_size */
+ u8 *zero_digest; /* digest for a zero block */
unsigned salt_size;
sector_t data_start; /* data offset in 512-byte sectors */
sector_t hash_start; /* hash start in blocks */
@@ -422,9 +424,9 @@ release_ret_r:
* of the hash tree if necessary.
*/
static 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 r, i;
+ int r = 0, i;
if (likely(v->levels)) {
/*
@@ -436,7 +438,7 @@ static int verity_hash_for_block(struct dm_verity *v, struct dm_verity_io *io,
*/
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);
@@ -444,10 +446,16 @@ static int verity_hash_for_block(struct dm_verity *v, struct dm_verity_io *io,
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;
}
- return 0;
+out:
+ if (!r && v->zero_digest)
+ *is_zero = !memcmp(v->zero_digest, digest, v->digest_size);
+ else
+ *is_zero = false;
+
+ return r;
}
/*
@@ -496,11 +504,19 @@ static int verity_bv_hash_update(struct dm_verity *v, struct dm_verity_io *io,
return verity_hash_update(v, 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;
@@ -510,10 +526,23 @@ static int verity_verify_io(struct dm_verity_io *io)
struct shash_desc *desc = io_hash_desc(v, io);
r = verity_hash_for_block(v, io, io->block + b,
- io_want_digest(v, io));
+ 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;
@@ -674,6 +703,7 @@ static int verity_fec_is_erasure(struct dm_verity *v, struct dm_verity_io *io,
static int verity_fec_read_buf(struct dm_verity *v, struct dm_verity_io *io,
u64 rsb, u64 target, int *neras)
{
+ bool is_zero;
int i, j, target_index = -1;
struct dm_buffer *buf;
struct dm_bufio_client *bufio;
@@ -713,9 +743,13 @@ static int verity_fec_read_buf(struct dm_verity *v, struct dm_verity_io *io,
}
if (block < v->data_blocks &&
- verity_hash_for_block(v, io, block, want_digest) == 0) {
- if (neras && *neras <= v->fec_roots &&
- verity_fec_is_erasure(v, io, want_digest, bbuf))
+ verity_hash_for_block(v, io, block, want_digest,
+ &is_zero) == 0) {
+ if (is_zero)
+ memset(bbuf, 0, 1 << v->data_dev_block_bits);
+ else if (neras && *neras <= v->fec_roots &&
+ verity_fec_is_erasure(v, io, want_digest,
+ bbuf))
io->erasures[(*neras)++] = i;
}
@@ -1066,6 +1100,8 @@ static void verity_status(struct dm_target *ti, status_type_t type,
DMEMIT("%02x", v->salt[x]);
if (v->mode != DM_VERITY_MODE_EIO)
args++;
+ if (v->zero_digest)
+ args++;
if (v->fec_dev)
args += DM_VERITY_OPTS_FEC;
if (!args)
@@ -1084,6 +1120,8 @@ static void verity_status(struct dm_target *ti, status_type_t type,
BUG();
}
}
+ if (v->zero_digest)
+ DMEMIT(" " DM_VERITY_OPT_IGN_ZEROS);
if (v->fec_dev)
DMEMIT(" " DM_VERITY_OPT_FEC_DEV " %s "
DM_VERITY_OPT_FEC_BLOCKS " %llu "
@@ -1148,6 +1186,7 @@ static void verity_dtr(struct dm_target *ti)
kfree(v->salt);
kfree(v->root_digest);
+ kfree(v->zero_digest);
if (v->tfm)
crypto_free_shash(v->tfm);
@@ -1164,6 +1203,29 @@ static void verity_dtr(struct dm_target *ti)
kfree(v);
}
+static int verity_alloc_zero_digest(struct dm_verity *v)
+{
+ int r;
+ u8 desc[v->shash_descsize];
+ u8 *zero_data;
+
+ v->zero_digest = kmalloc(v->digest_size, GFP_KERNEL);
+
+ if (!v->zero_digest)
+ return -ENOMEM;
+
+ zero_data = kzalloc(1 << v->data_dev_block_bits, GFP_KERNEL);
+
+ if (!zero_data)
+ return -ENOMEM; /* verity_dtr will free zero_digest */
+
+ r = verity_hash(v, (struct shash_desc *)desc, zero_data,
+ 1 << v->data_dev_block_bits, v->zero_digest);
+
+ kfree(zero_data);
+ return r;
+}
+
static int verity_parse_opt_args(struct dm_arg_set *as, struct dm_verity *v,
const char *opt_string)
{
@@ -1178,6 +1240,12 @@ static int verity_parse_opt_args(struct dm_arg_set *as, struct dm_verity *v,
} else if (!strcasecmp(opt_string, DM_VERITY_OPT_RESTART)) {
v->mode = DM_VERITY_MODE_RESTART;
return 0;
+ } else if (!strcasecmp(opt_string, DM_VERITY_OPT_IGN_ZEROS)) {
+ r = verity_alloc_zero_digest(v);
+ if (r)
+ v->ti->error = "Cannot allocate zero digest";
+
+ return r;
}
/* Remaining arguments require a value */
--
2.6.0.rc2.230.g3dd15c0
--
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