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>

3 files changed, 934 insertions, 0 deletions

diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index 71000078351a..10f122a3a856 100644
--- a/drivers/md/Kconfig
+++ b/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
diff --git a/drivers/md/Makefile b/drivers/md/Makefile
index 046860c7a166..8b2e0dffe82e 100644
--- a/drivers/md/Makefile
+++ b/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
diff --git a/drivers/md/dm-verity.c b/drivers/md/dm-verity.c
new file mode 100644
index 000000000000..fa365d39b612
--- /dev/null
+++ b/drivers/md/dm-verity.c
@@ -0,0 +1,913 @@
+/*
+ * 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");