dm: add verity target

This device-mapper target creates a read-only device that transparently
validates the data on one underlying device against a pre-generated tree
of cryptographic checksums stored on a second device.

Two checksum device formats are supported: version 0 which is already
shipping in Chromium OS and version 1 which incorporates some
improvements.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
Signed-off-by: Will Drewry <wad@chromium.org>
Signed-off-by: Elly Jones <ellyjones@chromium.org>
Cc: Milan Broz <mbroz@redhat.com>
Cc: Olof Johansson <olofj@chromium.org>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

Documentation/device-mapper/verity.txt

+dm-verity
+==========
+
+Device-Mapper's "verity" target provides transparent integrity checking of
+block devices using a cryptographic digest provided by the kernel crypto API.
+This target is read-only.
+
+Construction Parameters
+=======================
+    <version> <dev> <hash_dev> <hash_start>
+    <data_block_size> <hash_block_size>
+    <num_data_blocks> <hash_start_block>
+    <algorithm> <digest> <salt>
+
+<version>
+    This is the version number of the on-disk format.
+
+    0 is the original format used in the Chromium OS.
+	The salt is appended when hashing, digests are stored continuously and
+	the rest of the block is padded with zeros.
+
+    1 is the current format that should be used for new devices.
+	The salt is prepended when hashing and each digest is
+	padded with zeros to the power of two.
+
+<dev>
+    This is the device containing the data the integrity of which needs to be
+    checked.  It may be specified as a path, like /dev/sdaX, or a device number,
+    <major>:<minor>.
+
+<hash_dev>
+    This is the device that that supplies the hash tree data.  It may be
+    specified similarly to the device path and may be the same device.  If the
+    same device is used, the hash_start should be outside of the dm-verity
+    configured device size.
+
+<data_block_size>
+    The block size on a data device.  Each block corresponds to one digest on
+    the hash device.
+
+<hash_block_size>
+    The size of a hash block.
+
+<num_data_blocks>
+    The number of data blocks on the data device.  Additional blocks are
+    inaccessible.  You can place hashes to the same partition as data, in this
+    case hashes are placed after <num_data_blocks>.
+
+<hash_start_block>
+    This is the offset, in <hash_block_size>-blocks, from the start of hash_dev
+    to the root block of the hash tree.
+
+<algorithm>
+    The cryptographic hash algorithm used for this device.  This should
+    be the name of the algorithm, like "sha1".
+
+<digest>
+    The hexadecimal encoding of the cryptographic hash of the root hash block
+    and the salt.  This hash should be trusted as there is no other authenticity
+    beyond this point.
+
+<salt>
+    The hexadecimal encoding of the salt value.
+
+Theory of operation
+===================
+
+dm-verity is meant to be setup as part of a verified boot path.  This
+may be anything ranging from a boot using tboot or trustedgrub to just
+booting from a known-good device (like a USB drive or CD).
+
+When a dm-verity device is configured, it is expected that the caller
+has been authenticated in some way (cryptographic signatures, etc).
+After instantiation, all hashes will be verified on-demand during
+disk access.  If they cannot be verified up to the root node of the
+tree, the root hash, then the I/O will fail.  This should identify
+tampering with any data on the device and the hash data.
+
+Cryptographic hashes are used to assert the integrity of the device on a
+per-block basis.  This allows for a lightweight hash computation on first read
+into the page cache.  Block hashes are stored linearly-aligned to the nearest
+block the size of a page.
+
+Hash Tree
+---------
+
+Each node in the tree is a cryptographic hash.  If it is a leaf node, the hash
+is of some block data on disk.  If it is an intermediary node, then the hash is
+of a number of child nodes.
+
+Each entry in the tree is a collection of neighboring nodes that fit in one
+block.  The number is determined based on block_size and the size of the
+selected cryptographic digest algorithm.  The hashes are linearly-ordered in
+this entry and any unaligned trailing space is ignored but included when
+calculating the parent node.
+
+The tree looks something like:
+
+alg = sha256, num_blocks = 32768, block_size = 4096
+
+                                 [   root    ]
+                                /    . . .    \
+                     [entry_0]                 [entry_1]
+                    /  . . .  \                 . . .   \
+         [entry_0_0]   . . .  [entry_0_127]    . . . .  [entry_1_127]
+           / ... \             /   . . .  \             /           \
+     blk_0 ... blk_127  blk_16256   blk_16383      blk_32640 . . . blk_32767
+
+
+On-disk format
+==============
+
+Below is the recommended on-disk format. The verity kernel code does not
+read the on-disk header. It only reads the hash blocks which directly
+follow the header. It is expected that a user-space tool will verify the
+integrity of the verity_header and then call dmsetup with the correct
+parameters. Alternatively, the header can be omitted and the dmsetup
+parameters can be passed via the kernel command-line in a rooted chain
+of trust where the command-line is verified.
+
+The on-disk format is especially useful in cases where the hash blocks
+are on a separate partition. The magic number allows easy identification
+of the partition contents. Alternatively, the hash blocks can be stored
+in the same partition as the data to be verified. In such a configuration
+the filesystem on the partition would be sized a little smaller than
+the full-partition, leaving room for the hash blocks.
+
+struct superblock {
+	uint8_t signature[8]
+		"verity\0\0";
+
+	uint8_t version;
+		1 - current format
+
+	uint8_t data_block_bits;
+		log2(data block size)
+
+	uint8_t hash_block_bits;
+		log2(hash block size)
+
+	uint8_t pad1[1];
+		zero padding
+
+	uint16_t salt_size;
+		big-endian salt size
+
+	uint8_t pad2[2];
+		zero padding
+
+	uint32_t data_blocks_hi;
+		big-endian high 32 bits of the 64-bit number of data blocks
+
+	uint32_t data_blocks_lo;
+		big-endian low 32 bits of the 64-bit number of data blocks
+
+	uint8_t algorithm[16];
+		cryptographic algorithm
+
+	uint8_t salt[384];
+		salt (the salt size is specified above)
+
+	uint8_t pad3[88];
+		zero padding to 512-byte boundary
+}
+
+Directly following the header (and with sector number padded to the next hash
+block boundary) are the hash blocks which are stored a depth at a time
+(starting from the root), sorted in order of increasing index.
+
+Status
+======
+V (for Valid) is returned if every check performed so far was valid.
+If any check failed, C (for Corruption) is returned.
+
+Example
+=======
+
+Setup a device:
+  dmsetup create vroot --table \
+    "0 2097152 "\
+    "verity 1 /dev/sda1 /dev/sda2 4096 4096 2097152 1 "\
+    "4392712ba01368efdf14b05c76f9e4df0d53664630b5d48632ed17a137f39076 "\
+    "1234000000000000000000000000000000000000000000000000000000000000"
+
+A command line tool veritysetup is available to compute or verify
+the hash tree or activate the kernel driver.  This is available from
+the LVM2 upstream repository and may be supplied as a package called
+device-mapper-verity-tools:
+    git://sources.redhat.com/git/lvm2
+    http://sourceware.org/git/?p=lvm2.git
+    http://sourceware.org/cgi-bin/cvsweb.cgi/LVM2/verity?cvsroot=lvm2
+
+veritysetup -a vroot /dev/sda1 /dev/sda2 \
+	4392712ba01368efdf14b05c76f9e4df0d53664630b5d48632ed17a137f39076

drivers/md/Kconfig

@@ -370,4 +370,24 @@ config DM_FLAKEY
        ---help---
          A target that intermittently fails I/O for debugging purposes.
 
+config DM_VERITY
+	tristate "Verity target support (EXPERIMENTAL)"
+	depends on BLK_DEV_DM && EXPERIMENTAL
+	select CRYPTO
+	select CRYPTO_HASH
+	select DM_BUFIO
+	---help---
+	  This device-mapper target creates a read-only device that
+	  transparently validates the data on one underlying device against
+	  a pre-generated tree of cryptographic checksums stored on a second
+	  device.
+
+	  You'll need to activate the digests you're going to use in the
+	  cryptoapi configuration.
+
+	  To compile this code as a module, choose M here: the module will
+	  be called dm-verity.
+
+	  If unsure, say N.
+
 endif # MD

drivers/md/Makefile

@@ -42,6 +42,7 @@ obj-$(CONFIG_DM_LOG_USERSPACE)	+= dm-log-userspace.o
 obj-$(CONFIG_DM_ZERO)		+= dm-zero.o
 obj-$(CONFIG_DM_RAID)	+= dm-raid.o
 obj-$(CONFIG_DM_THIN_PROVISIONING)	+= dm-thin-pool.o
+obj-$(CONFIG_DM_VERITY)		+= dm-verity.o
 
 ifeq ($(CONFIG_DM_UEVENT),y)
 dm-mod-objs			+= dm-uevent.o

drivers/md/dm-verity.c

+/*
+ * Copyright (C) 2012 Red Hat, Inc.
+ *
+ * Author: Mikulas Patocka <mpatocka@redhat.com>
+ *
+ * Based on Chromium dm-verity driver (C) 2011 The Chromium OS Authors
+ *
+ * This file is released under the GPLv2.
+ *
+ * In the file "/sys/module/dm_verity/parameters/prefetch_cluster" you can set
+ * default prefetch value. Data are read in "prefetch_cluster" chunks from the
+ * hash device. Setting this greatly improves performance when data and hash
+ * are on the same disk on different partitions on devices with poor random
+ * access behavior.
+ */
+
+#include "dm-bufio.h"
+
+#include <linux/module.h>
+#include <linux/device-mapper.h>
+#include <crypto/hash.h>
+
+#define DM_MSG_PREFIX			"verity"
+
+#define DM_VERITY_IO_VEC_INLINE		16
+#define DM_VERITY_MEMPOOL_SIZE		4
+#define DM_VERITY_DEFAULT_PREFETCH_SIZE	262144
+
+#define DM_VERITY_MAX_LEVELS		63
+
+static unsigned dm_verity_prefetch_cluster = DM_VERITY_DEFAULT_PREFETCH_SIZE;
+
+module_param_named(prefetch_cluster, dm_verity_prefetch_cluster, uint, S_IRUGO | S_IWUSR);
+
+struct dm_verity {
+	struct dm_dev *data_dev;
+	struct dm_dev *hash_dev;
+	struct dm_target *ti;
+	struct dm_bufio_client *bufio;
+	char *alg_name;
+	struct crypto_shash *tfm;
+	u8 *root_digest;	/* digest of the root block */
+	u8 *salt;		/* salt: its size is salt_size */
+	unsigned salt_size;
+	sector_t data_start;	/* data offset in 512-byte sectors */
+	sector_t hash_start;	/* hash start in blocks */
+	sector_t data_blocks;	/* the number of data blocks */
+	sector_t hash_blocks;	/* the number of hash blocks */
+	unsigned char data_dev_block_bits;	/* log2(data blocksize) */
+	unsigned char hash_dev_block_bits;	/* log2(hash blocksize) */
+	unsigned char hash_per_block_bits;	/* log2(hashes in hash block) */
+	unsigned char levels;	/* the number of tree levels */
+	unsigned char version;
+	unsigned digest_size;	/* digest size for the current hash algorithm */
+	unsigned shash_descsize;/* the size of temporary space for crypto */
+	int hash_failed;	/* set to 1 if hash of any block failed */
+
+	mempool_t *io_mempool;	/* mempool of struct dm_verity_io */
+	mempool_t *vec_mempool;	/* mempool of bio vector */
+
+	struct workqueue_struct *verify_wq;
+
+	/* starting blocks for each tree level. 0 is the lowest level. */
+	sector_t hash_level_block[DM_VERITY_MAX_LEVELS];
+};
+
+struct dm_verity_io {
+	struct dm_verity *v;
+	struct bio *bio;
+
+	/* original values of bio->bi_end_io and bio->bi_private */
+	bio_end_io_t *orig_bi_end_io;
+	void *orig_bi_private;
+
+	sector_t block;
+	unsigned n_blocks;
+
+	/* saved bio vector */
+	struct bio_vec *io_vec;
+	unsigned io_vec_size;
+
+	struct work_struct work;
+
+	/* A space for short vectors; longer vectors are allocated separately. */
+	struct bio_vec io_vec_inline[DM_VERITY_IO_VEC_INLINE];
+
+	/*
+	 * Three variably-size fields follow this struct:
+	 *
+	 * u8 hash_desc[v->shash_descsize];
+	 * u8 real_digest[v->digest_size];
+	 * u8 want_digest[v->digest_size];
+	 *
+	 * To access them use: io_hash_desc(), io_real_digest() and io_want_digest().
+	 */
+};
+
+static struct shash_desc *io_hash_desc(struct dm_verity *v, struct dm_verity_io *io)
+{
+	return (struct shash_desc *)(io + 1);
+}
+
+static u8 *io_real_digest(struct dm_verity *v, struct dm_verity_io *io)
+{
+	return (u8 *)(io + 1) + v->shash_descsize;
+}
+
+static u8 *io_want_digest(struct dm_verity *v, struct dm_verity_io *io)
+{
+	return (u8 *)(io + 1) + v->shash_descsize + v->digest_size;
+}
+
+/*
+ * Auxiliary structure appended to each dm-bufio buffer. If the value
+ * hash_verified is nonzero, hash of the block has been verified.
+ *
+ * The variable hash_verified is set to 0 when allocating the buffer, then
+ * it can be changed to 1 and it is never reset to 0 again.
+ *
+ * There is no lock around this value, a race condition can at worst cause
+ * that multiple processes verify the hash of the same buffer simultaneously
+ * and write 1 to hash_verified simultaneously.
+ * This condition is harmless, so we don't need locking.
+ */
+struct buffer_aux {
+	int hash_verified;
+};
+
+/*
+ * Initialize struct buffer_aux for a freshly created buffer.
+ */
+static void dm_bufio_alloc_callback(struct dm_buffer *buf)
+{
+	struct buffer_aux *aux = dm_bufio_get_aux_data(buf);
+
+	aux->hash_verified = 0;
+}
+
+/*
+ * Translate input sector number to the sector number on the target device.
+ */
+static sector_t verity_map_sector(struct dm_verity *v, sector_t bi_sector)
+{
+	return v->data_start + dm_target_offset(v->ti, bi_sector);
+}
+
+/*
+ * Return hash position of a specified block at a specified tree level
+ * (0 is the lowest level).
+ * The lowest "hash_per_block_bits"-bits of the result denote hash position
+ * inside a hash block. The remaining bits denote location of the hash block.
+ */
+static sector_t verity_position_at_level(struct dm_verity *v, sector_t block,
+					 int level)
+{
+	return block >> (level * v->hash_per_block_bits);
+}
+
+static void verity_hash_at_level(struct dm_verity *v, sector_t block, int level,
+				 sector_t *hash_block, unsigned *offset)
+{
+	sector_t position = verity_position_at_level(v, block, level);
+	unsigned idx;
+
+	*hash_block = v->hash_level_block[level] + (position >> v->hash_per_block_bits);
+
+	if (!offset)
+		return;
+
+	idx = position & ((1 << v->hash_per_block_bits) - 1);
+	if (!v->version)
+		*offset = idx * v->digest_size;
+	else
+		*offset = idx << (v->hash_dev_block_bits - v->hash_per_block_bits);
+}
+
+/*
+ * Verify hash of a metadata block pertaining to the specified data block
+ * ("block" argument) at a specified level ("level" argument).
+ *
+ * On successful return, 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 leve).
+ *
+ * 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 io_want_digest(v, io).
+ */
+static int verity_verify_level(struct dm_verity_io *io, sector_t block,
+			       int level, bool skip_unverified)
+{
+	struct dm_verity *v = io->v;
+	struct dm_buffer *buf;
+	struct buffer_aux *aux;
+	u8 *data;
+	int r;
+	sector_t hash_block;
+	unsigned offset;
+
+	verity_hash_at_level(v, block, level, &hash_block, &offset);
+
+	data = dm_bufio_read(v->bufio, hash_block, &buf);
+	if (unlikely(IS_ERR(data)))
+		return PTR_ERR(data);
+
+	aux = dm_bufio_get_aux_data(buf);
+
+	if (!aux->hash_verified) {
+		struct shash_desc *desc;
+		u8 *result;
+
+		if (skip_unverified) {
+			r = 1;
+			goto release_ret_r;
+		}
+
+		desc = io_hash_desc(v, io);
+		desc->tfm = v->tfm;
+		desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
+		r = crypto_shash_init(desc);
+		if (r < 0) {
+			DMERR("crypto_shash_init failed: %d", r);
+			goto release_ret_r;
+		}
+
+		if (likely(v->version >= 1)) {
+			r = crypto_shash_update(desc, v->salt, v->salt_size);
+			if (r < 0) {
+				DMERR("crypto_shash_update failed: %d", r);
+				goto release_ret_r;
+			}
+		}
+
+		r = crypto_shash_update(desc, data, 1 << v->hash_dev_block_bits);
+		if (r < 0) {
+			DMERR("crypto_shash_update failed: %d", r);
+			goto release_ret_r;
+		}
+
+		if (!v->version) {
+			r = crypto_shash_update(desc, v->salt, v->salt_size);
+			if (r < 0) {
+				DMERR("crypto_shash_update failed: %d", r);
+				goto release_ret_r;
+			}
+		}
+
+		result = io_real_digest(v, io);
+		r = crypto_shash_final(desc, result);
+		if (r < 0) {
+			DMERR("crypto_shash_final failed: %d", r);
+			goto release_ret_r;
+		}
+		if (unlikely(memcmp(result, io_want_digest(v, io), v->digest_size))) {
+			DMERR_LIMIT("metadata block %llu is corrupted",
+				(unsigned long long)hash_block);
+			v->hash_failed = 1;
+			r = -EIO;
+			goto release_ret_r;
+		} else
+			aux->hash_verified = 1;
+	}
+
+	data += offset;
+
+	memcpy(io_want_digest(v, io), data, v->digest_size);
+
+	dm_bufio_release(buf);
+	return 0;
+
+release_ret_r:
+	dm_bufio_release(buf);
+
+	return r;
+}
+
+/*
+ * Verify one "dm_verity_io" structure.
+ */
+static int verity_verify_io(struct dm_verity_io *io)
+{
+	struct dm_verity *v = io->v;
+	unsigned b;
+	int i;
+	unsigned vector = 0, offset = 0;
+
+	for (b = 0; b < io->n_blocks; b++) {
+		struct shash_desc *desc;
+		u8 *result;
+		int r;
+		unsigned todo;
+
+		if (likely(v->levels)) {
+			/*
+			 * First, we try to get the requested hash for
+			 * the current block. If the hash block itself is
+			 * verified, zero is returned. If it isn't, this
+			 * function returns 0 and we fall back to whole
+			 * chain verification.
+			 */
+			int r = verity_verify_level(io, io->block + b, 0, true);
+			if (likely(!r))
+				goto test_block_hash;
+			if (r < 0)
+				return r;
+		}
+
+		memcpy(io_want_digest(v, io), v->root_digest, v->digest_size);
+
+		for (i = v->levels - 1; i >= 0; i--) {
+			int r = verity_verify_level(io, io->block + b, i, false);
+			if (unlikely(r))
+				return r;
+		}
+
+test_block_hash:
+		desc = io_hash_desc(v, io);
+		desc->tfm = v->tfm;
+		desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
+		r = crypto_shash_init(desc);
+		if (r < 0) {
+			DMERR("crypto_shash_init failed: %d", r);
+			return r;
+		}
+
+		if (likely(v->version >= 1)) {
+			r = crypto_shash_update(desc, v->salt, v->salt_size);
+			if (r < 0) {
+				DMERR("crypto_shash_update failed: %d", r);
+				return r;
+			}
+		}
+
+		todo = 1 << v->data_dev_block_bits;
+		do {
+			struct bio_vec *bv;
+			u8 *page;
+			unsigned len;
+
+			BUG_ON(vector >= io->io_vec_size);
+			bv = &io->io_vec[vector];
+			page = kmap_atomic(bv->bv_page);
+			len = bv->bv_len - offset;
+			if (likely(len >= todo))
+				len = todo;
+			r = crypto_shash_update(desc,
+					page + bv->bv_offset + offset, len);
+			kunmap_atomic(page);
+			if (r < 0) {
+				DMERR("crypto_shash_update failed: %d", r);
+				return r;
+			}
+			offset += len;
+			if (likely(offset == bv->bv_len)) {
+				offset = 0;
+				vector++;
+			}
+			todo -= len;
+		} while (todo);
+
+		if (!v->version) {
+			r = crypto_shash_update(desc, v->salt, v->salt_size);
+			if (r < 0) {
+				DMERR("crypto_shash_update failed: %d", r);
+				return r;
+			}
+		}
+
+		result = io_real_digest(v, io);
+		r = crypto_shash_final(desc, result);
+		if (r < 0) {
+			DMERR("crypto_shash_final failed: %d", r);
+			return r;
+		}
+		if (unlikely(memcmp(result, io_want_digest(v, io), v->digest_size))) {
+			DMERR_LIMIT("data block %llu is corrupted",
+				(unsigned long long)(io->block + b));
+			v->hash_failed = 1;
+			return -EIO;
+		}
+	}
+	BUG_ON(vector != io->io_vec_size);
+	BUG_ON(offset);
+
+	return 0;
+}
+
+/*
+ * End one "io" structure with a given error.
+ */
+static void verity_finish_io(struct dm_verity_io *io, int error)
+{
+	struct bio *bio = io->bio;
+	struct dm_verity *v = io->v;
+
+	bio->bi_end_io = io->orig_bi_end_io;
+	bio->bi_private = io->orig_bi_private;
+
+	if (io->io_vec != io->io_vec_inline)
+		mempool_free(io->io_vec, v->vec_mempool);
+
+	mempool_free(io, v->io_mempool);
+
+	bio_endio(bio, error);
+}
+
+static void verity_work(struct work_struct *w)
+{
+	struct dm_verity_io *io = container_of(w, struct dm_verity_io, work);
+
+	verity_finish_io(io, verity_verify_io(io));
+}
+
+static void verity_end_io(struct bio *bio, int error)
+{
+	struct dm_verity_io *io = bio->bi_private;
+
+	if (error) {
+		verity_finish_io(io, error);
+		return;
+	}
+
+	INIT_WORK(&io->work, verity_work);
+	queue_work(io->v->verify_wq, &io->work);
+}
+
+/*
+ * Prefetch buffers for the specified io.
+ * The root buffer is not prefetched, it is assumed that it will be cached
+ * all the time.
+ */
+static void verity_prefetch_io(struct dm_verity *v, struct dm_verity_io *io)
+{
+	int i;
+
+	for (i = v->levels - 2; i >= 0; i--) {
+		sector_t hash_block_start;
+		sector_t hash_block_end;
+		verity_hash_at_level(v, io->block, i, &hash_block_start, NULL);
+		verity_hash_at_level(v, io->block + io->n_blocks - 1, i, &hash_block_end, NULL);
+		if (!i) {
+			unsigned cluster = *(volatile unsigned *)&dm_verity_prefetch_cluster;
+
+			cluster >>= v->data_dev_block_bits;
+			if (unlikely(!cluster))
+				goto no_prefetch_cluster;
+
+			if (unlikely(cluster & (cluster - 1)))
+				cluster = 1 << (fls(cluster) - 1);
+
+			hash_block_start &= ~(sector_t)(cluster - 1);
+			hash_block_end |= cluster - 1;
+			if (unlikely(hash_block_end >= v->hash_blocks))
+				hash_block_end = v->hash_blocks - 1;
+		}
+no_prefetch_cluster:
+		dm_bufio_prefetch(v->bufio, hash_block_start,
+				  hash_block_end - hash_block_start + 1);
+	}
+}
+
+/*
+ * Bio map function. It allocates dm_verity_io structure and bio vector and
+ * fills them. Then it issues prefetches and the I/O.
+ */
+static int verity_map(struct dm_target *ti, struct bio *bio,
+		      union map_info *map_context)
+{
+	struct dm_verity *v = ti->private;
+	struct dm_verity_io *io;
+
+	bio->bi_bdev = v->data_dev->bdev;
+	bio->bi_sector = verity_map_sector(v, bio->bi_sector);
+
+	if (((unsigned)bio->bi_sector | bio_sectors(bio)) &
+	    ((1 << (v->data_dev_block_bits - SECTOR_SHIFT)) - 1)) {
+		DMERR_LIMIT("unaligned io");
+		return -EIO;
+	}
+
+	if ((bio->bi_sector + bio_sectors(bio)) >>
+	    (v->data_dev_block_bits - SECTOR_SHIFT) > v->data_blocks) {
+		DMERR_LIMIT("io out of range");
+		return -EIO;
+	}
+
+	if (bio_data_dir(bio) == WRITE)
+		return -EIO;
+
+	io = mempool_alloc(v->io_mempool, GFP_NOIO);
+	io->v = v;
+	io->bio = bio;
+	io->orig_bi_end_io = bio->bi_end_io;
+	io->orig_bi_private = bio->bi_private;
+	io->block = bio->bi_sector >> (v->data_dev_block_bits - SECTOR_SHIFT);
+	io->n_blocks = bio->bi_size >> v->data_dev_block_bits;
+
+	bio->bi_end_io = verity_end_io;
+	bio->bi_private = io;
+	io->io_vec_size = bio->bi_vcnt - bio->bi_idx;
+	if (io->io_vec_size < DM_VERITY_IO_VEC_INLINE)
+		io->io_vec = io->io_vec_inline;
+	else
+		io->io_vec = mempool_alloc(v->vec_mempool, GFP_NOIO);
+	memcpy(io->io_vec, bio_iovec(bio),
+	       io->io_vec_size * sizeof(struct bio_vec));
+
+	verity_prefetch_io(v, io);
+
+	generic_make_request(bio);
+
+	return DM_MAPIO_SUBMITTED;
+}
+
+/*
+ * Status: V (valid) or C (corruption found)
+ */
+static int verity_status(struct dm_target *ti, status_type_t type,
+			 char *result, unsigned maxlen)
+{
+	struct dm_verity *v = ti->private;
+	unsigned sz = 0;
+	unsigned x;
+
+	switch (type) {
+	case STATUSTYPE_INFO:
+		DMEMIT("%c", v->hash_failed ? 'C' : 'V');
+		break;
+	case STATUSTYPE_TABLE:
+		DMEMIT("%u %s %s %u %u %llu %llu %s ",
+			v->version,
+			v->data_dev->name,
+			v->hash_dev->name,
+			1 << v->data_dev_block_bits,
+			1 << v->hash_dev_block_bits,
+			(unsigned long long)v->data_blocks,
+			(unsigned long long)v->hash_start,
+			v->alg_name
+			);
+		for (x = 0; x < v->digest_size; x++)
+			DMEMIT("%02x", v->root_digest[x]);
+		DMEMIT(" ");
+		if (!v->salt_size)
+			DMEMIT("-");
+		else
+			for (x = 0; x < v->salt_size; x++)
+				DMEMIT("%02x", v->salt[x]);
+		break;
+	}
+
+	return 0;
+}
+
+static int verity_ioctl(struct dm_target *ti, unsigned cmd,
+			unsigned long arg)
+{
+	struct dm_verity *v = ti->private;
+	int r = 0;
+
+	if (v->data_start ||
+	    ti->len != i_size_read(v->data_dev->bdev->bd_inode) >> SECTOR_SHIFT)
+		r = scsi_verify_blk_ioctl(NULL, cmd);
+
+	return r ? : __blkdev_driver_ioctl(v->data_dev->bdev, v->data_dev->mode,
+				     cmd, arg);
+}
+
+static int verity_merge(struct dm_target *ti, struct bvec_merge_data *bvm,
+			struct bio_vec *biovec, int max_size)
+{
+	struct dm_verity *v = ti->private;
+	struct request_queue *q = bdev_get_queue(v->data_dev->bdev);
+
+	if (!q->merge_bvec_fn)
+		return max_size;
+
+	bvm->bi_bdev = v->data_dev->bdev;
+	bvm->bi_sector = verity_map_sector(v, bvm->bi_sector);
+
+	return min(max_size, q->merge_bvec_fn(q, bvm, biovec));
+}
+
+static int verity_iterate_devices(struct dm_target *ti,
+				  iterate_devices_callout_fn fn, void *data)
+{
+	struct dm_verity *v = ti->private;
+
+	return fn(ti, v->data_dev, v->data_start, ti->len, data);
+}
+
+static void verity_io_hints(struct dm_target *ti, struct queue_limits *limits)
+{
+	struct dm_verity *v = ti->private;
+
+	if (limits->logical_block_size < 1 << v->data_dev_block_bits)
+		limits->logical_block_size = 1 << v->data_dev_block_bits;
+
+	if (limits->physical_block_size < 1 << v->data_dev_block_bits)
+		limits->physical_block_size = 1 << v->data_dev_block_bits;
+
+	blk_limits_io_min(limits, limits->logical_block_size);
+}
+
+static void verity_dtr(struct dm_target *ti)
+{
+	struct dm_verity *v = ti->private;
+
+	if (v->verify_wq)
+		destroy_workqueue(v->verify_wq);
+
+	if (v->vec_mempool)
+		mempool_destroy(v->vec_mempool);
+
+	if (v->io_mempool)
+		mempool_destroy(v->io_mempool);
+
+	if (v->bufio)
+		dm_bufio_client_destroy(v->bufio);
+
+	kfree(v->salt);
+	kfree(v->root_digest);
+
+	if (v->tfm)
+		crypto_free_shash(v->tfm);
+
+	kfree(v->alg_name);
+
+	if (v->hash_dev)
+		dm_put_device(ti, v->hash_dev);
+
+	if (v->data_dev)
+		dm_put_device(ti, v->data_dev);
+
+	kfree(v);
+}
+
+/*
+ * Target parameters:
+ *	<version>	The current format is version 1.
+ *			Vsn 0 is compatible with original Chromium OS releases.
+ *	<data device>
+ *	<hash device>
+ *	<data block size>
+ *	<hash block size>
+ *	<the number of data blocks>
+ *	<hash start block>
+ *	<algorithm>
+ *	<digest>
+ *	<salt>		Hex string or "-" if no salt.
+ */
+static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
+{
+	struct dm_verity *v;
+	unsigned num;
+	unsigned long long num_ll;
+	int r;
+	int i;
+	sector_t hash_position;
+	char dummy;
+
+	v = kzalloc(sizeof(struct dm_verity), GFP_KERNEL);
+	if (!v) {
+		ti->error = "Cannot allocate verity structure";
+		return -ENOMEM;
+	}
+	ti->private = v;
+	v->ti = ti;
+
+	if ((dm_table_get_mode(ti->table) & ~FMODE_READ)) {
+		ti->error = "Device must be readonly";
+		r = -EINVAL;
+		goto bad;
+	}
+
+	if (argc != 10) {
+		ti->error = "Invalid argument count: exactly 10 arguments required";
+		r = -EINVAL;
+		goto bad;
+	}
+
+	if (sscanf(argv[0], "%d%c", &num, &dummy) != 1 ||
+	    num < 0 || num > 1) {
+		ti->error = "Invalid version";
+		r = -EINVAL;
+		goto bad;
+	}
+	v->version = num;
+
+	r = dm_get_device(ti, argv[1], FMODE_READ, &v->data_dev);
+	if (r) {
+		ti->error = "Data device lookup failed";
+		goto bad;
+	}
+
+	r = dm_get_device(ti, argv[2], FMODE_READ, &v->hash_dev);
+	if (r) {
+		ti->error = "Data device lookup failed";
+		goto bad;
+	}
+
+	if (sscanf(argv[3], "%u%c", &num, &dummy) != 1 ||
+	    !num || (num & (num - 1)) ||
+	    num < bdev_logical_block_size(v->data_dev->bdev) ||
+	    num > PAGE_SIZE) {
+		ti->error = "Invalid data device block size";
+		r = -EINVAL;
+		goto bad;
+	}
+	v->data_dev_block_bits = ffs(num) - 1;
+
+	if (sscanf(argv[4], "%u%c", &num, &dummy) != 1 ||
+	    !num || (num & (num - 1)) ||
+	    num < bdev_logical_block_size(v->hash_dev->bdev) ||
+	    num > INT_MAX) {
+		ti->error = "Invalid hash device block size";
+		r = -EINVAL;
+		goto bad;
+	}
+	v->hash_dev_block_bits = ffs(num) - 1;
+
+	if (sscanf(argv[5], "%llu%c", &num_ll, &dummy) != 1 ||
+	    num_ll << (v->data_dev_block_bits - SECTOR_SHIFT) !=
+	    (sector_t)num_ll << (v->data_dev_block_bits - SECTOR_SHIFT)) {
+		ti->error = "Invalid data blocks";
+		r = -EINVAL;
+		goto bad;
+	}
+	v->data_blocks = num_ll;
+
+	if (ti->len > (v->data_blocks << (v->data_dev_block_bits - SECTOR_SHIFT))) {
+		ti->error = "Data device is too small";
+		r = -EINVAL;
+		goto bad;
+	}
+
+	if (sscanf(argv[6], "%llu%c", &num_ll, &dummy) != 1 ||
+	    num_ll << (v->hash_dev_block_bits - SECTOR_SHIFT) !=
+	    (sector_t)num_ll << (v->hash_dev_block_bits - SECTOR_SHIFT)) {
+		ti->error = "Invalid hash start";
+		r = -EINVAL;
+		goto bad;
+	}
+	v->hash_start = num_ll;
+
+	v->alg_name = kstrdup(argv[7], GFP_KERNEL);
+	if (!v->alg_name) {
+		ti->error = "Cannot allocate algorithm name";
+		r = -ENOMEM;
+		goto bad;
+	}
+
+	v->tfm = crypto_alloc_shash(v->alg_name, 0, 0);
+	if (IS_ERR(v->tfm)) {
+		ti->error = "Cannot initialize hash function";
+		r = PTR_ERR(v->tfm);
+		v->tfm = NULL;
+		goto bad;
+	}
+	v->digest_size = crypto_shash_digestsize(v->tfm);
+	if ((1 << v->hash_dev_block_bits) < v->digest_size * 2) {
+		ti->error = "Digest size too big";
+		r = -EINVAL;
+		goto bad;
+	}
+	v->shash_descsize =
+		sizeof(struct shash_desc) + crypto_shash_descsize(v->tfm);
+
+	v->root_digest = kmalloc(v->digest_size, GFP_KERNEL);
+	if (!v->root_digest) {
+		ti->error = "Cannot allocate root digest";
+		r = -ENOMEM;
+		goto bad;
+	}
+	if (strlen(argv[8]) != v->digest_size * 2 ||
+	    hex2bin(v->root_digest, argv[8], v->digest_size)) {
+		ti->error = "Invalid root digest";
+		r = -EINVAL;
+		goto bad;
+	}
+
+	if (strcmp(argv[9], "-")) {
+		v->salt_size = strlen(argv[9]) / 2;
+		v->salt = kmalloc(v->salt_size, GFP_KERNEL);
+		if (!v->salt) {
+			ti->error = "Cannot allocate salt";
+			r = -ENOMEM;
+			goto bad;
+		}
+		if (strlen(argv[9]) != v->salt_size * 2 ||
+		    hex2bin(v->salt, argv[9], v->salt_size)) {
+			ti->error = "Invalid salt";
+			r = -EINVAL;
+			goto bad;
+		}
+	}
+
+	v->hash_per_block_bits =
+		fls((1 << v->hash_dev_block_bits) / v->digest_size) - 1;
+
+	v->levels = 0;
+	if (v->data_blocks)
+		while (v->hash_per_block_bits * v->levels < 64 &&
+		       (unsigned long long)(v->data_blocks - 1) >>
+		       (v->hash_per_block_bits * v->levels))
+			v->levels++;
+
+	if (v->levels > DM_VERITY_MAX_LEVELS) {
+		ti->error = "Too many tree levels";
+		r = -E2BIG;
+		goto bad;
+	}
+
+	hash_position = v->hash_start;
+	for (i = v->levels - 1; i >= 0; i--) {
+		sector_t s;
+		v->hash_level_block[i] = hash_position;
+		s = verity_position_at_level(v, v->data_blocks, i);
+		s = (s >> v->hash_per_block_bits) +
+		    !!(s & ((1 << v->hash_per_block_bits) - 1));
+		if (hash_position + s < hash_position) {
+			ti->error = "Hash device offset overflow";
+			r = -E2BIG;
+			goto bad;
+		}
+		hash_position += s;
+	}
+	v->hash_blocks = hash_position;
+
+	v->bufio = dm_bufio_client_create(v->hash_dev->bdev,
+		1 << v->hash_dev_block_bits, 1, sizeof(struct buffer_aux),
+		dm_bufio_alloc_callback, NULL);
+	if (IS_ERR(v->bufio)) {
+		ti->error = "Cannot initialize dm-bufio";
+		r = PTR_ERR(v->bufio);
+		v->bufio = NULL;
+		goto bad;
+	}
+
+	if (dm_bufio_get_device_size(v->bufio) < v->hash_blocks) {
+		ti->error = "Hash device is too small";
+		r = -E2BIG;
+		goto bad;
+	}
+
+	v->io_mempool = mempool_create_kmalloc_pool(DM_VERITY_MEMPOOL_SIZE,
+	  sizeof(struct dm_verity_io) + v->shash_descsize + v->digest_size * 2);
+	if (!v->io_mempool) {
+		ti->error = "Cannot allocate io mempool";
+		r = -ENOMEM;
+		goto bad;
+	}
+
+	v->vec_mempool = mempool_create_kmalloc_pool(DM_VERITY_MEMPOOL_SIZE,
+					BIO_MAX_PAGES * sizeof(struct bio_vec));
+	if (!v->vec_mempool) {
+		ti->error = "Cannot allocate vector mempool";
+		r = -ENOMEM;
+		goto bad;
+	}
+
+	/* WQ_UNBOUND greatly improves performance when running on ramdisk */
+	v->verify_wq = alloc_workqueue("kverityd", WQ_CPU_INTENSIVE | WQ_MEM_RECLAIM | WQ_UNBOUND, num_online_cpus());
+	if (!v->verify_wq) {
+		ti->error = "Cannot allocate workqueue";
+		r = -ENOMEM;
+		goto bad;
+	}
+
+	return 0;
+
+bad:
+	verity_dtr(ti);
+
+	return r;
+}
+
+static struct target_type verity_target = {
+	.name		= "verity",
+	.version	= {1, 0, 0},
+	.module		= THIS_MODULE,
+	.ctr		= verity_ctr,
+	.dtr		= verity_dtr,
+	.map		= verity_map,
+	.status		= verity_status,
+	.ioctl		= verity_ioctl,
+	.merge		= verity_merge,
+	.iterate_devices = verity_iterate_devices,
+	.io_hints	= verity_io_hints,
+};
+
+static int __init dm_verity_init(void)
+{
+	int r;
+
+	r = dm_register_target(&verity_target);
+	if (r < 0)
+		DMERR("register failed %d", r);
+
+	return r;
+}
+
+static void __exit dm_verity_exit(void)
+{
+	dm_unregister_target(&verity_target);
+}
+
+module_init(dm_verity_init);
+module_exit(dm_verity_exit);
+
+MODULE_AUTHOR("Mikulas Patocka <mpatocka@redhat.com>");
+MODULE_AUTHOR("Mandeep Baines <msb@chromium.org>");
+MODULE_AUTHOR("Will Drewry <wad@chromium.org>");
+MODULE_DESCRIPTION(DM_NAME " target for transparent disk integrity checking");
+MODULE_LICENSE("GPL");