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Subject[PATCH] dm: verity target
Date
The verity target provides transparent integrity checking of block devices
using a cryptographic digest.

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).

dm-verity is part of ChromeOS's verified boot path. It is used to verify
the integrity of the root filesystem on boot. The root filesystem is
mounted on a dm-verity partition which transparently verifies each block
with a bootloader verified hash passed into the kernel at boot.

Signed-off-by: Will Drewry <wad@chromium.org>
Signed-off-by: Elly Jones <ellyjones@chromium.org>
Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
Cc: Alasdair G Kergon <agk@redhat.com>
Cc: Milan Broz <mbroz@redhat.com>
Cc: Olof Johansson <olofj@chromium.org>
Cc: dm-devel@redhat.com
Cc: linux-kernel@vger.kernel.org
---
Documentation/device-mapper/dm-bht.txt | 59 ++
Documentation/device-mapper/dm-verity.txt | 76 +++
drivers/md/Kconfig | 30 +
drivers/md/Makefile | 2 +
drivers/md/dm-bht.c | 542 +++++++++++++++
drivers/md/dm-verity.c | 1043 +++++++++++++++++++++++++++++
drivers/md/dm-verity.h | 45 ++
include/linux/dm-bht.h | 166 +++++
8 files changed, 1963 insertions(+), 0 deletions(-)
create mode 100644 Documentation/device-mapper/dm-bht.txt
create mode 100644 Documentation/device-mapper/dm-verity.txt
create mode 100644 drivers/md/dm-bht.c
create mode 100644 drivers/md/dm-verity.c
create mode 100644 drivers/md/dm-verity.h
create mode 100644 include/linux/dm-bht.h

diff --git a/Documentation/device-mapper/dm-bht.txt b/Documentation/device-mapper/dm-bht.txt
new file mode 100644
index 0000000..21d929f
--- /dev/null
+++ b/Documentation/device-mapper/dm-bht.txt
@@ -0,0 +1,59 @@
+dm-bht
+======
+
+dm-bht provides a block hash tree implementation. The use of dm-bht allows
+for integrity checking of a given block device without reading the entire
+set of blocks into memory before use.
+
+In particular, dm-bht supplies an interface for creating and verifying a tree
+of cryptographic digests with any algorithm supported by the kernel crypto API.
+
+The `verity' target is the motivating example.
+
+
+Theory of operation
+===================
+
+dm-bht is logically comprised of multiple nodes organized in a tree-like
+structure. 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.
+
+dm-bht has a given depth starting at 1 (ignoring the root node). Each level in
+the tree is concretely made up of dm_bht_entry structs. Each entry in the tree
+is a collection of neighboring nodes that fit in one page-sized block. The
+number is determined based on PAGE_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 = 32767
+ [ 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
+
+root is treated independently from the depth and the blocks are expected to
+be hashed and supplied to the dm-bht. hash blocks that make up the entry
+contents are expected to be read from disk.
+
+dm-bht does not handle I/O directly but instead expects the consumer to
+supply callbacks. The read callback will always receive a page-align value
+to pass to the block device layer to read in a hash value.
+
+Usage
+=====
+
+The API provides mechanisms for reading and verifying a tree. When reading, all
+required data for the hash tree should be populated for a block before
+attempting a verify. This can be done by calling dm_bht_populate(). When all
+data is ready, a call to dm_bht_verify_block() with the expected hash value will
+perform both the direct block hash check and the hashes of the parent and
+neighboring nodes where needed to ensure validity up to the root hash. Note,
+dm_bht_set_root_hexdigest() should be called before any verification attempts
+occur.
diff --git a/Documentation/device-mapper/dm-verity.txt b/Documentation/device-mapper/dm-verity.txt
new file mode 100644
index 0000000..f33b984
--- /dev/null
+++ b/Documentation/device-mapper/dm-verity.txt
@@ -0,0 +1,76 @@
+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.
+
+Parameters: payload=<device path> hashtree=<hash device path> alg=<alg> \
+ salt=<salt> root_hexagiest=<root hash> \
+ [ hashstart=<hash start> error_behavior=<error behavior> ]
+
+<device path>
+ This is the device that is going to be integrity checked. It may be
+ a subset of the full device as specified to dmsetup (start sector and count)
+ It may be specified as a path, like /dev/sdaX, or a device number,
+ <major>:<minor>.
+
+<hash device path>
+ This is the device that that supplies the dm-bht hash data. It may be
+ specified similarly to the device path and may be the same device. If the
+ same device is used, the hash offset should be outside of the dm-verity
+ configured device size.
+
+<alg>
+ The cryptographic hash algorithm used for this device. This should
+ be the name of the algorithm, like "sha1".
+
+<salt>
+ Salt value (in hex).
+
+<root hash>
+ The hexadecimal encoding of the cryptographic hash of all of the
+ neighboring nodes at the first level of the tree. This hash should be
+ trusted as there is no other authenticity beyond this point.
+
+<hash start>
+ Start address of hashes (default 0).
+
+<error behavior>
+ 0 = return -EIO. 1 = panic. 2 = none. 3 = call notifier.
+
+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.
+
+For more information on the hashing process, see dm-bht.txt.
+
+
+Example
+=======
+
+Setup a device;
+[[
+ dmsetup create vroot --table \
+ "0 204800 verity payload=/dev/sda1 hashtree=/dev/sda2 alg=sha1 "\
+ "root_hexdigest=9f74809a2ee7607b16fcc70d9399a4de9725a727"
+]]
+
+A command line tool is available to compute the hash tree and return the
+root hash value.
+ http://git.chromium.org/cgi-bin/gitweb.cgi?p=dm-verity.git;a=tree
diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index faa4741..3cdf95c 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -370,4 +370,34 @@ config DM_FLAKEY
---help---
A target that intermittently fails I/O for debugging purposes.

+config DM_BHT
+ tristate "Block hash tree support"
+ select CRYPTO
+ select CRYPTO_HASH
+ ---help---
+ Include support for device-mapper devices to use a block hash
+ tree for managing data integrity checks in a scalable way.
+
+ Targets that use this functionality should include it
+ automatically.
+
+ If unsure, say N.
+
+config DM_VERITY
+ tristate "Verity target support"
+ depends on BLK_DEV_DM
+ select DM_BHT
+ select CRYPTO
+ select CRYPTO_HASH
+ ---help---
+ This device-mapper target allows you to create a device that
+ transparently integrity checks the data on it. 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 046860c..c069953 100644
--- a/drivers/md/Makefile
+++ b/drivers/md/Makefile
@@ -39,6 +39,8 @@ obj-$(CONFIG_DM_SNAPSHOT) += dm-snapshot.o
obj-$(CONFIG_DM_PERSISTENT_DATA) += persistent-data/
obj-$(CONFIG_DM_MIRROR) += dm-mirror.o dm-log.o dm-region-hash.o
obj-$(CONFIG_DM_LOG_USERSPACE) += dm-log-userspace.o
+obj-$(CONFIG_DM_BHT) += dm-bht.o
+obj-$(CONFIG_DM_VERITY) += dm-verity.o
obj-$(CONFIG_DM_ZERO) += dm-zero.o
obj-$(CONFIG_DM_RAID) += dm-raid.o
obj-$(CONFIG_DM_THIN_PROVISIONING) += dm-thin-pool.o
diff --git a/drivers/md/dm-bht.c b/drivers/md/dm-bht.c
new file mode 100644
index 0000000..fd853db
--- /dev/null
+++ b/drivers/md/dm-bht.c
@@ -0,0 +1,542 @@
+ /*
+ * Copyright (C) 2011 The Chromium OS Authors <chromium-os-dev@chromium.org>
+ *
+ * Device-Mapper block hash tree interface.
+ * See Documentation/device-mapper/dm-bht.txt for details.
+ *
+ * This file is released under the GPLv2.
+ */
+
+#include <linux/atomic.h>
+#include <linux/bitops.h>
+#include <linux/bug.h>
+#include <linux/cpumask.h>
+#include <linux/device-mapper.h>
+#include <linux/dm-bht.h>
+#include <linux/err.h>
+#include <linux/errno.h>
+#include <linux/gfp.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mm_types.h>
+#include <linux/scatterlist.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+
+#define DM_MSG_PREFIX "dm bht"
+
+
+/*
+ * Utilities
+ */
+
+static u8 from_hex(u8 ch)
+{
+ if ((ch >= '0') && (ch <= '9'))
+ return ch - '0';
+ if ((ch >= 'a') && (ch <= 'f'))
+ return ch - 'a' + 10;
+ if ((ch >= 'A') && (ch <= 'F'))
+ return ch - 'A' + 10;
+ return -1;
+}
+
+/**
+ * dm_bht_bin_to_hex - converts a binary stream to human-readable hex
+ * @binary: a byte array of length @binary_len
+ * @hex: a byte array of length @binary_len * 2 + 1
+ */
+static void dm_bht_bin_to_hex(u8 *binary, u8 *hex, unsigned int binary_len)
+{
+ while (binary_len-- > 0) {
+ sprintf((char *)hex, "%02hhx", (int)*binary);
+ hex += 2;
+ binary++;
+ }
+}
+
+/**
+ * dm_bht_hex_to_bin - converts a hex stream to binary
+ * @binary: a byte array of length @binary_len
+ * @hex: a byte array of length @binary_len * 2 + 1
+ */
+static void dm_bht_hex_to_bin(u8 *binary, const u8 *hex,
+ unsigned int binary_len)
+{
+ while (binary_len-- > 0) {
+ *binary = from_hex(*(hex++));
+ *binary *= 16;
+ *binary += from_hex(*(hex++));
+ binary++;
+ }
+}
+
+static void dm_bht_log_mismatch(struct dm_bht *bht, u8 *given, u8 *computed)
+{
+ u8 given_hex[DM_BHT_MAX_DIGEST_SIZE * 2 + 1];
+ u8 computed_hex[DM_BHT_MAX_DIGEST_SIZE * 2 + 1];
+
+ dm_bht_bin_to_hex(given, given_hex, bht->digest_size);
+ dm_bht_bin_to_hex(computed, computed_hex, bht->digest_size);
+ DMERR_LIMIT("%s != %s", given_hex, computed_hex);
+}
+
+/**
+ * dm_bht_compute_hash: hashes a page of data
+ */
+static int dm_bht_compute_hash(struct dm_bht *bht, struct page *pg,
+ unsigned int offset, u8 *digest)
+{
+ struct hash_desc *hash_desc = &bht->hash_desc[smp_processor_id()];
+ struct scatterlist sg;
+
+ sg_init_table(&sg, 1);
+ sg_set_page(&sg, pg, bht->block_size, offset);
+ /* Note, this is synchronous. */
+ if (crypto_hash_init(hash_desc)) {
+ DMCRIT("failed to reinitialize crypto hash (proc:%d)",
+ smp_processor_id());
+ return -EINVAL;
+ }
+ if (crypto_hash_update(hash_desc, &sg, bht->block_size)) {
+ DMCRIT("crypto_hash_update failed");
+ return -EINVAL;
+ }
+ sg_set_buf(&sg, bht->salt, sizeof(bht->salt));
+ if (crypto_hash_update(hash_desc, &sg, sizeof(bht->salt))) {
+ DMCRIT("crypto_hash_update failed");
+ return -EINVAL;
+ }
+ if (crypto_hash_final(hash_desc, digest)) {
+ DMCRIT("crypto_hash_final failed");
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
+/*
+ * Implementation functions
+ */
+
+static int dm_bht_initialize_entries(struct dm_bht *bht)
+{
+ /* last represents the index of the last digest store in the tree.
+ * By walking the tree with that index, it is possible to compute the
+ * total number of entries at each level.
+ *
+ * Since each entry will contain up to |node_count| nodes of the tree,
+ * it is possible that the last index may not be at the end of a given
+ * entry->nodes. In that case, it is assumed the value is padded.
+ *
+ * Note, we treat both the tree root (1 hash) and the tree leaves
+ * independently from the bht data structures. Logically, the root is
+ * depth=-1 and the block layer level is depth=bht->depth
+ */
+ unsigned int last = bht->block_count;
+ int depth;
+
+ /* check that the largest level->count can't result in an int overflow
+ * on allocation or sector calculation.
+ */
+ if (((last >> bht->node_count_shift) + 1) >
+ UINT_MAX / max((unsigned int)sizeof(struct dm_bht_entry),
+ (unsigned int)to_sector(bht->block_size))) {
+ DMCRIT("required entries %u is too large", last + 1);
+ return -EINVAL;
+ }
+
+ /* Track the current sector location for each level so we don't have to
+ * compute it during traversals.
+ */
+ bht->sectors = 0;
+ for (depth = 0; depth < bht->depth; ++depth) {
+ struct dm_bht_level *level = &bht->levels[depth];
+
+ level->count = dm_bht_index_at_level(bht, depth, last) + 1;
+ level->entries = (struct dm_bht_entry *)
+ kcalloc(level->count,
+ sizeof(struct dm_bht_entry),
+ GFP_KERNEL);
+ if (!level->entries) {
+ DMERR("failed to allocate entries for depth %d", depth);
+ return -ENOMEM;
+ }
+ level->sector = bht->sectors;
+ bht->sectors += level->count * to_sector(bht->block_size);
+ }
+
+ return 0;
+}
+
+/**
+ * dm_bht_create - prepares @bht for us
+ * @bht: pointer to a dm_bht_create()d bht
+ * @depth: tree depth without the root; including block hashes
+ * @block_count:the number of block hashes / tree leaves
+ * @alg_name: crypto hash algorithm name
+ *
+ * Returns 0 on success.
+ *
+ * Callers can offset into devices by storing the data in the io callbacks.
+ */
+int dm_bht_create(struct dm_bht *bht, unsigned int block_count,
+ unsigned int block_size, const char *alg_name)
+{
+ int cpu, status;
+
+ bht->block_size = block_size;
+ /* Verify that PAGE_SIZE >= block_size >= SECTOR_SIZE. */
+ if ((block_size > PAGE_SIZE) ||
+ (PAGE_SIZE % block_size) ||
+ (to_sector(block_size) == 0))
+ return -EINVAL;
+
+ /* Setup the hash first. Its length determines much of the bht layout */
+ for (cpu = 0; cpu < nr_cpu_ids; ++cpu) {
+ bht->hash_desc[cpu].tfm = crypto_alloc_hash(alg_name, 0, 0);
+ if (IS_ERR(bht->hash_desc[cpu].tfm)) {
+ DMERR("failed to allocate crypto hash '%s'", alg_name);
+ status = -ENOMEM;
+ bht->hash_desc[cpu].tfm = NULL;
+ goto bad_arg;
+ }
+ }
+ bht->digest_size = crypto_hash_digestsize(bht->hash_desc[0].tfm);
+ /* We expect to be able to pack >=2 hashes into a block */
+ if (block_size / bht->digest_size < 2) {
+ DMERR("too few hashes fit in a block");
+ status = -EINVAL;
+ goto bad_arg;
+ }
+
+ if (bht->digest_size > DM_BHT_MAX_DIGEST_SIZE) {
+ DMERR("DM_BHT_MAX_DIGEST_SIZE too small for chosen digest");
+ status = -EINVAL;
+ goto bad_arg;
+ }
+
+ /* Configure the tree */
+ bht->block_count = block_count;
+ if (block_count == 0) {
+ DMERR("block_count must be non-zero");
+ status = -EINVAL;
+ goto bad_arg;
+ }
+
+ /* Each dm_bht_entry->nodes is one block. The node code tracks
+ * how many nodes fit into one entry where a node is a single
+ * hash (message digest).
+ */
+ bht->node_count_shift = fls(block_size / bht->digest_size) - 1;
+ /* Round down to the nearest power of two. This makes indexing
+ * into the tree much less painful.
+ */
+ bht->node_count = 1 << bht->node_count_shift;
+
+ /* This is unlikely to happen, but with 64k pages, who knows. */
+ if (bht->node_count > UINT_MAX / bht->digest_size) {
+ DMERR("node_count * hash_len exceeds UINT_MAX!");
+ status = -EINVAL;
+ goto bad_arg;
+ }
+
+ bht->depth = DIV_ROUND_UP(fls(block_count - 1), bht->node_count_shift);
+
+ /* Ensure that we can safely shift by this value. */
+ if (bht->depth * bht->node_count_shift >= sizeof(unsigned int) * 8) {
+ DMERR("specified depth and node_count_shift is too large");
+ status = -EINVAL;
+ goto bad_arg;
+ }
+
+ /* Allocate levels. Each level of the tree may have an arbitrary number
+ * of dm_bht_entry structs. Each entry contains node_count nodes.
+ * Each node in the tree is a cryptographic digest of either node_count
+ * nodes on the subsequent level or of a specific block on disk.
+ */
+ bht->levels = (struct dm_bht_level *)
+ kcalloc(bht->depth,
+ sizeof(struct dm_bht_level), GFP_KERNEL);
+ if (!bht->levels) {
+ DMERR("failed to allocate tree levels");
+ status = -ENOMEM;
+ goto bad_level_alloc;
+ }
+
+ bht->read_cb = NULL;
+
+ status = dm_bht_initialize_entries(bht);
+ if (status)
+ goto bad_entries_alloc;
+
+ /* We compute depth such that there is only be 1 block at level 0. */
+ BUG_ON(bht->levels[0].count != 1);
+
+ return 0;
+
+bad_entries_alloc:
+ while (bht->depth-- > 0)
+ kfree(bht->levels[bht->depth].entries);
+ kfree(bht->levels);
+bad_level_alloc:
+bad_arg:
+ for (cpu = 0; cpu < nr_cpu_ids; ++cpu)
+ if (bht->hash_desc[cpu].tfm)
+ crypto_free_hash(bht->hash_desc[cpu].tfm);
+ return status;
+}
+EXPORT_SYMBOL(dm_bht_create);
+
+/**
+ * dm_bht_read_completed
+ * @entry: pointer to the entry that's been loaded
+ * @status: I/O status. Non-zero is failure.
+ * MUST always be called after a read_cb completes.
+ */
+void dm_bht_read_completed(struct dm_bht_entry *entry, int status)
+{
+ if (status) {
+ /* TODO(wad) add retry support */
+ DMCRIT("an I/O error occurred while reading entry");
+ atomic_set(&entry->state, DM_BHT_ENTRY_ERROR_IO);
+ /* entry->nodes will be freed later */
+ return;
+ }
+ BUG_ON(atomic_read(&entry->state) != DM_BHT_ENTRY_PENDING);
+ atomic_set(&entry->state, DM_BHT_ENTRY_READY);
+}
+EXPORT_SYMBOL(dm_bht_read_completed);
+
+/**
+ * dm_bht_verify_block - checks that all nodes in the path for @block are valid
+ * @bht: pointer to a dm_bht_create()d bht
+ * @block: specific block data is expected from
+ * @pg: page holding the block data
+ * @offset: offset into the page
+ *
+ * Returns 0 on success, DM_BHT_ENTRY_ERROR_MISMATCH on error.
+ */
+int dm_bht_verify_block(struct dm_bht *bht, unsigned int block,
+ struct page *pg, unsigned int offset)
+{
+ int state, depth = bht->depth;
+ u8 digest[DM_BHT_MAX_DIGEST_SIZE];
+ struct dm_bht_entry *entry;
+ void *node;
+
+ do {
+ /* Need to check that the hash of the current block is accurate
+ * in its parent.
+ */
+ entry = dm_bht_get_entry(bht, depth - 1, block);
+ state = atomic_read(&entry->state);
+ /* This call is only safe if all nodes along the path
+ * are already populated (i.e. READY) via dm_bht_populate.
+ */
+ BUG_ON(state < DM_BHT_ENTRY_READY);
+ node = dm_bht_get_node(bht, entry, depth, block);
+
+ if (dm_bht_compute_hash(bht, pg, offset, digest) ||
+ memcmp(digest, node, bht->digest_size))
+ goto mismatch;
+
+ /* Keep the containing block of hashes to be verified in the
+ * next pass.
+ */
+ pg = virt_to_page(entry->nodes);
+ offset = offset_in_page(entry->nodes);
+ } while (--depth > 0 && state != DM_BHT_ENTRY_VERIFIED);
+
+ if (depth == 0 && state != DM_BHT_ENTRY_VERIFIED) {
+ if (dm_bht_compute_hash(bht, pg, offset, digest) ||
+ memcmp(digest, bht->root_digest, bht->digest_size))
+ goto mismatch;
+ atomic_set(&entry->state, DM_BHT_ENTRY_VERIFIED);
+ }
+
+ /* Mark path to leaf as verified. */
+ for (depth++; depth < bht->depth; depth++) {
+ entry = dm_bht_get_entry(bht, depth, block);
+ /* At this point, entry can only be in VERIFIED or READY state.
+ * So it is safe to use atomic_set instead of atomic_cmpxchg.
+ */
+ atomic_set(&entry->state, DM_BHT_ENTRY_VERIFIED);
+ }
+
+ return 0;
+
+mismatch:
+ DMERR_LIMIT("verify_path: failed to verify hash (d=%d,bi=%u)",
+ depth, block);
+ dm_bht_log_mismatch(bht, node, digest);
+ return DM_BHT_ENTRY_ERROR_MISMATCH;
+}
+EXPORT_SYMBOL(dm_bht_verify_block);
+
+/**
+ * dm_bht_is_populated - check that entries from disk needed to verify a given
+ * block are all ready
+ * @bht: pointer to a dm_bht_create()d bht
+ * @block: specific block data is expected from
+ *
+ * Callers may wish to call dm_bht_is_populated() when checking an io
+ * for which entries were already pending.
+ */
+bool dm_bht_is_populated(struct dm_bht *bht, unsigned int block)
+{
+ int depth;
+
+ for (depth = bht->depth - 1; depth >= 0; depth--) {
+ struct dm_bht_entry *entry = dm_bht_get_entry(bht, depth,
+ block);
+ if (atomic_read(&entry->state) < DM_BHT_ENTRY_READY)
+ return false;
+ }
+
+ return true;
+}
+EXPORT_SYMBOL(dm_bht_is_populated);
+
+/**
+ * dm_bht_populate - reads entries from disk needed to verify a given block
+ * @bht: pointer to a dm_bht_create()d bht
+ * @ctx: context used for all read_cb calls on this request
+ * @block: specific block data is expected from
+ *
+ * Returns negative value on error. Returns 0 on success.
+ */
+int dm_bht_populate(struct dm_bht *bht, void *ctx, unsigned int block)
+{
+ int depth, state;
+
+ BUG_ON(block >= bht->block_count);
+
+ for (depth = bht->depth - 1; depth >= 0; --depth) {
+ unsigned int index = dm_bht_index_at_level(bht, depth, block);
+ struct dm_bht_level *level = &bht->levels[depth];
+ struct dm_bht_entry *entry = dm_bht_get_entry(bht, depth,
+ block);
+ state = atomic_cmpxchg(&entry->state,
+ DM_BHT_ENTRY_UNALLOCATED,
+ DM_BHT_ENTRY_PENDING);
+ if (state == DM_BHT_ENTRY_VERIFIED)
+ break;
+ if (state <= DM_BHT_ENTRY_ERROR)
+ goto error_state;
+ if (state != DM_BHT_ENTRY_UNALLOCATED)
+ continue;
+
+ /* Current entry is claimed for allocation and loading */
+ entry->nodes = kmalloc(bht->block_size, GFP_NOIO);
+ if (!entry->nodes)
+ goto nomem;
+
+ bht->read_cb(ctx,
+ level->sector + to_sector(index * bht->block_size),
+ entry->nodes, to_sector(bht->block_size), entry);
+ }
+
+ return 0;
+
+error_state:
+ DMCRIT("block %u at depth %d is in an error state", block, depth);
+ return -EPERM;
+
+nomem:
+ DMCRIT("failed to allocate memory for entry->nodes");
+ return -ENOMEM;
+}
+EXPORT_SYMBOL(dm_bht_populate);
+
+/**
+ * dm_bht_destroy - cleans up all memory used by @bht
+ * @bht: pointer to a dm_bht_create()d bht
+ */
+void dm_bht_destroy(struct dm_bht *bht)
+{
+ int depth, cpu;
+
+ for (depth = 0; depth < bht->depth; depth++) {
+ struct dm_bht_entry *entry = bht->levels[depth].entries;
+ struct dm_bht_entry *entry_end = entry +
+ bht->levels[depth].count;
+ for (; entry < entry_end; ++entry)
+ kfree(entry->nodes);
+ kfree(bht->levels[depth].entries);
+ }
+ kfree(bht->levels);
+ for (cpu = 0; cpu < nr_cpu_ids; ++cpu)
+ if (bht->hash_desc[cpu].tfm)
+ crypto_free_hash(bht->hash_desc[cpu].tfm);
+}
+EXPORT_SYMBOL(dm_bht_destroy);
+
+/*
+ * Accessors
+ */
+
+/**
+ * dm_bht_set_root_hexdigest - sets an unverified root digest hash from hex
+ * @bht: pointer to a dm_bht_create()d bht
+ * @hexdigest: array of u8s containing the new digest in binary
+ * Returns non-zero on error. hexdigest should be NUL terminated.
+ */
+int dm_bht_set_root_hexdigest(struct dm_bht *bht, const u8 *hexdigest)
+{
+ /* Make sure we have at least the bytes expected */
+ if (strnlen((char *)hexdigest, bht->digest_size * 2) !=
+ bht->digest_size * 2) {
+ DMERR("root digest length does not match hash algorithm");
+ return -1;
+ }
+ dm_bht_hex_to_bin(bht->root_digest, hexdigest, bht->digest_size);
+ return 0;
+}
+EXPORT_SYMBOL(dm_bht_set_root_hexdigest);
+
+/**
+ * dm_bht_root_hexdigest - returns root digest in hex
+ * @bht: pointer to a dm_bht_create()d bht
+ * @hexdigest: u8 array of size @available
+ * @available: must be bht->digest_size * 2 + 1
+ */
+int dm_bht_root_hexdigest(struct dm_bht *bht, u8 *hexdigest, int available)
+{
+ if (available < 0 ||
+ ((unsigned int) available) < bht->digest_size * 2 + 1) {
+ DMERR("hexdigest has too few bytes available");
+ return -EINVAL;
+ }
+ dm_bht_bin_to_hex(bht->root_digest, hexdigest, bht->digest_size);
+ return 0;
+}
+EXPORT_SYMBOL(dm_bht_root_hexdigest);
+
+/**
+ * dm_bht_set_salt - sets the salt used, in hex
+ * @bht: pointer to a dm_bht_create()d bht
+ * @hexsalt: salt string, as hex; will be zero-padded or truncated to
+ * DM_BHT_SALT_SIZE * 2 hex digits.
+ */
+void dm_bht_set_salt(struct dm_bht *bht, const char *hexsalt)
+{
+ size_t saltlen = min(strlen(hexsalt) / 2, sizeof(bht->salt));
+
+ memset(bht->salt, 0, sizeof(bht->salt));
+ dm_bht_hex_to_bin(bht->salt, (const u8 *)hexsalt, saltlen);
+}
+EXPORT_SYMBOL(dm_bht_set_salt);
+
+/**
+ * dm_bht_salt - returns the salt used, in hex
+ * @bht: pointer to a dm_bht_create()d bht
+ * @hexsalt: buffer to put salt into, of length DM_BHT_SALT_SIZE * 2 + 1.
+ */
+int dm_bht_salt(struct dm_bht *bht, char *hexsalt)
+{
+ dm_bht_bin_to_hex(bht->salt, (u8 *)hexsalt, sizeof(bht->salt));
+ return 0;
+}
+EXPORT_SYMBOL(dm_bht_salt);
+
diff --git a/drivers/md/dm-verity.c b/drivers/md/dm-verity.c
new file mode 100644
index 0000000..a9bd0e8
--- /dev/null
+++ b/drivers/md/dm-verity.c
@@ -0,0 +1,1043 @@
+/*
+ * Originally based on dm-crypt.c,
+ * Copyright (C) 2003 Christophe Saout <christophe@saout.de>
+ * Copyright (C) 2004 Clemens Fruhwirth <clemens@endorphin.org>
+ * Copyright (C) 2006-2008 Red Hat, Inc. All rights reserved.
+ * Copyright (C) 2011 The Chromium OS Authors <chromium-os-dev@chromium.org>
+ * All Rights Reserved.
+ *
+ * This file is released under the GPLv2.
+ *
+ * Implements a verifying transparent block device.
+ * See Documentation/device-mapper/dm-verity.txt
+ */
+#include <linux/async.h>
+#include <linux/atomic.h>
+#include <linux/bio.h>
+#include <linux/blkdev.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/genhd.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/mempool.h>
+#include <linux/mm_types.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/workqueue.h>
+#include <linux/device-mapper.h>
+#include <linux/dm-bht.h>
+
+#include "dm-verity.h"
+
+#define DM_MSG_PREFIX "verity"
+
+/* Supports up to 512-bit digests */
+#define VERITY_MAX_DIGEST_SIZE 64
+
+/* TODO(wad) make both of these report the error line/file to a
+ * verity_bug function.
+ */
+#define VERITY_BUG(msg...) BUG()
+#define VERITY_BUG_ON(cond, msg...) BUG_ON(cond)
+
+/* Helper for printing sector_t */
+#define ULL(x) ((unsigned long long)(x))
+
+#define MIN_IOS 32
+#define MIN_BIOS (MIN_IOS * 2)
+#define VERITY_DEFAULT_BLOCK_SIZE 4096
+
+/* Provide a lightweight means of specifying the global default for
+ * error behavior: eio, reboot, or none
+ * Legacy support for 0 = eio, 1 = reboot/panic, 2 = none, 3 = notify.
+ * This is matched to the enum in dm-verity.h.
+ */
+static const char * const allowed_error_behaviors[] = { "eio", "panic", "none",
+ "notify", NULL };
+static char *error_behavior = "eio";
+module_param(error_behavior, charp, 0644);
+MODULE_PARM_DESC(error_behavior, "Behavior on error "
+ "(eio, panic, none, notify)");
+
+/* Controls whether verity_get_device will wait forever for a device. */
+static int dev_wait;
+module_param(dev_wait, bool, 0444);
+MODULE_PARM_DESC(dev_wait, "Wait forever for a backing device");
+
+/* per-requested-bio private data */
+enum verity_io_flags {
+ VERITY_IOFLAGS_CLONED = 0x1, /* original bio has been cloned */
+};
+
+struct dm_verity_io {
+ struct dm_target *target;
+ struct bio *bio;
+ struct delayed_work work;
+ unsigned int flags;
+
+ int error;
+ atomic_t pending;
+
+ u64 block; /* aligned block index */
+ u64 count; /* aligned count in blocks */
+};
+
+struct verity_config {
+ struct dm_dev *dev;
+ sector_t start;
+ sector_t size;
+
+ struct dm_dev *hash_dev;
+ sector_t hash_start;
+
+ struct dm_bht bht;
+
+ /* Pool required for io contexts */
+ mempool_t *io_pool;
+ /* Pool and bios required for making sure that backing device reads are
+ * in PAGE_SIZE increments.
+ */
+ struct bio_set *bs;
+
+ char hash_alg[CRYPTO_MAX_ALG_NAME];
+
+ int error_behavior;
+};
+
+static struct kmem_cache *_verity_io_pool;
+static struct workqueue_struct *kveritydq, *kverityd_ioq;
+
+static void kverityd_verify(struct work_struct *work);
+static void kverityd_io(struct work_struct *work);
+static void kverityd_io_bht_populate(struct dm_verity_io *io);
+static void kverityd_io_bht_populate_end(struct bio *, int error);
+
+static BLOCKING_NOTIFIER_HEAD(verity_error_notifier);
+
+/*
+ * Exported interfaces
+ */
+
+int dm_verity_register_error_notifier(struct notifier_block *nb)
+{
+ return blocking_notifier_chain_register(&verity_error_notifier, nb);
+}
+EXPORT_SYMBOL_GPL(dm_verity_register_error_notifier);
+
+int dm_verity_unregister_error_notifier(struct notifier_block *nb)
+{
+ return blocking_notifier_chain_unregister(&verity_error_notifier, nb);
+}
+EXPORT_SYMBOL_GPL(dm_verity_unregister_error_notifier);
+
+/*
+ * Allocation and utility functions
+ */
+
+static void kverityd_src_io_read_end(struct bio *clone, int error);
+
+/* Shared destructor for all internal bios */
+static void dm_verity_bio_destructor(struct bio *bio)
+{
+ struct dm_verity_io *io = bio->bi_private;
+ struct verity_config *vc = io->target->private;
+ bio_free(bio, vc->bs);
+}
+
+static struct bio *verity_alloc_bioset(struct verity_config *vc, gfp_t gfp_mask,
+ int nr_iovecs)
+{
+ return bio_alloc_bioset(gfp_mask, nr_iovecs, vc->bs);
+}
+
+static struct dm_verity_io *verity_io_alloc(struct dm_target *ti,
+ struct bio *bio)
+{
+ struct verity_config *vc = ti->private;
+ sector_t sector = bio->bi_sector - ti->begin;
+ struct dm_verity_io *io;
+
+ io = mempool_alloc(vc->io_pool, GFP_NOIO);
+ if (unlikely(!io))
+ return NULL;
+ io->flags = 0;
+ io->target = ti;
+ io->bio = bio;
+ io->error = 0;
+
+ /* Adjust the sector by the virtual starting sector */
+ io->block = to_bytes(sector) / vc->bht.block_size;
+ io->count = bio->bi_size / vc->bht.block_size;
+
+ atomic_set(&io->pending, 0);
+
+ return io;
+}
+
+static struct bio *verity_bio_clone(struct dm_verity_io *io)
+{
+ struct verity_config *vc = io->target->private;
+ struct bio *bio = io->bio;
+ struct bio *clone = verity_alloc_bioset(vc, GFP_NOIO, bio->bi_max_vecs);
+
+ if (!clone)
+ return NULL;
+
+ __bio_clone(clone, bio);
+ clone->bi_private = io;
+ clone->bi_end_io = kverityd_src_io_read_end;
+ clone->bi_bdev = vc->dev->bdev;
+ clone->bi_sector += vc->start - io->target->begin;
+ clone->bi_destructor = dm_verity_bio_destructor;
+
+ return clone;
+}
+
+/* If the request is not successful, this handler takes action.
+ * TODO make this call a registered handler.
+ */
+static void verity_error(struct verity_config *vc, struct dm_verity_io *io,
+ int error)
+{
+ const char *message;
+ int error_mode = DM_VERITY_ERROR_BEHAVIOR_PANIC;
+ dev_t devt = 0;
+ u64 block = ~0;
+ int transient = 1;
+ struct dm_verity_error_state error_state;
+
+ if (vc) {
+ devt = vc->dev->bdev->bd_dev;
+ error_mode = vc->error_behavior;
+ }
+
+ if (io) {
+ io->error = -EIO;
+ block = io->block;
+ }
+
+ switch (error) {
+ case -ENOMEM:
+ message = "out of memory";
+ break;
+ case -EBUSY:
+ message = "pending data seen during verify";
+ break;
+ case -EFAULT:
+ message = "crypto operation failure";
+ break;
+ case -EACCES:
+ message = "integrity failure";
+ /* Image is bad. */
+ transient = 0;
+ break;
+ case -EPERM:
+ message = "hash tree population failure";
+ /* Should be dm-bht specific errors */
+ transient = 0;
+ break;
+ case -EINVAL:
+ message = "unexpected missing/invalid data";
+ /* The device was configured incorrectly - fallback. */
+ transient = 0;
+ break;
+ default:
+ /* Other errors can be passed through as IO errors */
+ message = "unknown or I/O error";
+ return;
+ }
+
+ DMERR_LIMIT("verification failure occurred: %s", message);
+
+ if (error_mode == DM_VERITY_ERROR_BEHAVIOR_NOTIFY) {
+ error_state.code = error;
+ error_state.transient = transient;
+ error_state.block = block;
+ error_state.message = message;
+ error_state.dev_start = vc->start;
+ error_state.dev_len = vc->size;
+ error_state.dev = vc->dev->bdev;
+ error_state.hash_dev_start = vc->hash_start;
+ error_state.hash_dev_len = vc->bht.sectors;
+ error_state.hash_dev = vc->hash_dev->bdev;
+
+ /* Set default fallthrough behavior. */
+ error_state.behavior = DM_VERITY_ERROR_BEHAVIOR_PANIC;
+ error_mode = DM_VERITY_ERROR_BEHAVIOR_PANIC;
+
+ if (!blocking_notifier_call_chain(
+ &verity_error_notifier, transient, &error_state)) {
+ error_mode = error_state.behavior;
+ }
+ }
+
+ switch (error_mode) {
+ case DM_VERITY_ERROR_BEHAVIOR_EIO:
+ break;
+ case DM_VERITY_ERROR_BEHAVIOR_NONE:
+ if (error != -EIO && io)
+ io->error = 0;
+ break;
+ default:
+ goto do_panic;
+ }
+ return;
+
+do_panic:
+ panic("dm-verity failure: "
+ "device:%u:%u error:%d block:%llu message:%s",
+ MAJOR(devt), MINOR(devt), error, ULL(block), message);
+}
+
+/**
+ * verity_parse_error_behavior - parse a behavior charp to the enum
+ * @behavior: NUL-terminated char array
+ *
+ * Checks if the behavior is valid either as text or as an index digit
+ * and returns the proper enum value or -1 on error.
+ */
+static int verity_parse_error_behavior(const char *behavior)
+{
+ const char * const *allowed = allowed_error_behaviors;
+ char index = '0';
+
+ for (; *allowed; allowed++, index++)
+ if (!strcmp(*allowed, behavior) || behavior[0] == index)
+ break;
+
+ if (!*allowed)
+ return -1;
+
+ /* Convert to the integer index matching the enum. */
+ return allowed - allowed_error_behaviors;
+}
+
+/*
+ * Reverse flow of requests into the device.
+ *
+ * (Start at the bottom with verity_map and work your way upward).
+ */
+
+static void verity_inc_pending(struct dm_verity_io *io);
+
+static void verity_return_bio_to_caller(struct dm_verity_io *io)
+{
+ struct verity_config *vc = io->target->private;
+
+ if (io->error)
+ verity_error(vc, io, io->error);
+
+ bio_endio(io->bio, io->error);
+ mempool_free(io, vc->io_pool);
+}
+
+/* Check for any missing bht hashes. */
+static bool verity_is_bht_populated(struct dm_verity_io *io)
+{
+ struct verity_config *vc = io->target->private;
+ u64 block;
+
+ for (block = io->block; block < io->block + io->count; ++block)
+ if (!dm_bht_is_populated(&vc->bht, block))
+ return false;
+
+ return true;
+}
+
+/* verity_dec_pending manages the lifetime of all dm_verity_io structs.
+ * Non-bug error handling is centralized through this interface and
+ * all passage from workqueue to workqueue.
+ */
+static void verity_dec_pending(struct dm_verity_io *io)
+{
+ if (!atomic_dec_and_test(&io->pending))
+ goto done;
+
+ if (unlikely(io->error))
+ goto io_error;
+
+ /* I/Os that were pending may now be ready */
+ if (verity_is_bht_populated(io)) {
+ INIT_DELAYED_WORK(&io->work, kverityd_verify);
+ queue_delayed_work(kveritydq, &io->work, 0);
+ } else {
+ INIT_DELAYED_WORK(&io->work, kverityd_io);
+ queue_delayed_work(kverityd_ioq, &io->work, HZ/10);
+ }
+
+done:
+ return;
+
+io_error:
+ verity_return_bio_to_caller(io);
+}
+
+/* Walks the data set and computes the hash of the data read from the
+ * untrusted source device. The computed hash is then passed to dm-bht
+ * for verification.
+ */
+static int verity_verify(struct verity_config *vc,
+ struct dm_verity_io *io)
+{
+ unsigned int block_size = vc->bht.block_size;
+ struct bio *bio = io->bio;
+ u64 block = io->block;
+ unsigned int idx;
+ int r;
+
+ for (idx = bio->bi_idx; idx < bio->bi_vcnt; idx++) {
+ struct bio_vec *bv = bio_iovec_idx(bio, idx);
+ unsigned int offset = bv->bv_offset;
+ unsigned int len = bv->bv_len;
+
+ VERITY_BUG_ON(offset % block_size);
+ VERITY_BUG_ON(len % block_size);
+
+ while (len) {
+ r = dm_bht_verify_block(&vc->bht, block,
+ bv->bv_page, offset);
+ if (r)
+ goto bad_return;
+
+ offset += block_size;
+ len -= block_size;
+ block++;
+ cond_resched();
+ }
+ }
+
+ return 0;
+
+bad_return:
+ /* dm_bht functions aren't expected to return errno friendly
+ * values. They are converted here for uniformity.
+ */
+ if (r > 0) {
+ DMERR("Pending data for block %llu seen at verify", ULL(block));
+ r = -EBUSY;
+ } else {
+ DMERR_LIMIT("Block hash does not match!");
+ r = -EACCES;
+ }
+ return r;
+}
+
+/* Services the verify workqueue */
+static void kverityd_verify(struct work_struct *work)
+{
+ struct delayed_work *dwork = container_of(work, struct delayed_work,
+ work);
+ struct dm_verity_io *io = container_of(dwork, struct dm_verity_io,
+ work);
+ struct verity_config *vc = io->target->private;
+
+ io->error = verity_verify(vc, io);
+
+ /* Free up the bio and tag with the return value */
+ verity_return_bio_to_caller(io);
+}
+
+/* Asynchronously called upon the completion of dm-bht I/O. The status
+ * of the operation is passed back to dm-bht and the next steps are
+ * decided by verity_dec_pending.
+ */
+static void kverityd_io_bht_populate_end(struct bio *bio, int error)
+{
+ struct dm_bht_entry *entry = (struct dm_bht_entry *) bio->bi_private;
+ struct dm_verity_io *io = (struct dm_verity_io *) entry->io_context;
+
+ /* Tell the tree to atomically update now that we've populated
+ * the given entry.
+ */
+ dm_bht_read_completed(entry, error);
+
+ /* Clean up for reuse when reading data to be checked */
+ bio->bi_vcnt = 0;
+ bio->bi_io_vec->bv_offset = 0;
+ bio->bi_io_vec->bv_len = 0;
+ bio->bi_io_vec->bv_page = NULL;
+ /* Restore the private data to I/O so the destructor can be shared. */
+ bio->bi_private = (void *) io;
+ bio_put(bio);
+
+ /* We bail but assume the tree has been marked bad. */
+ if (unlikely(error)) {
+ DMERR("Failed to read for sector %llu (%u)",
+ ULL(io->bio->bi_sector), io->bio->bi_size);
+ io->error = error;
+ /* Pass through the error to verity_dec_pending below */
+ }
+ /* When pending = 0, it will transition to reading real data */
+ verity_dec_pending(io);
+}
+
+/* Called by dm-bht (via dm_bht_populate), this function provides
+ * the message digests to dm-bht that are stored on disk.
+ */
+static int kverityd_bht_read_callback(void *ctx, sector_t start, u8 *dst,
+ sector_t count,
+ struct dm_bht_entry *entry)
+{
+ struct dm_verity_io *io = ctx; /* I/O for this batch */
+ struct verity_config *vc;
+ struct bio *bio;
+
+ vc = io->target->private;
+
+ /* The I/O context is nested inside the entry so that we don't need one
+ * io context per page read.
+ */
+ entry->io_context = ctx;
+
+ /* We should only get page size requests at present. */
+ verity_inc_pending(io);
+ bio = verity_alloc_bioset(vc, GFP_NOIO, 1);
+ if (unlikely(!bio)) {
+ DMCRIT("Out of memory at bio_alloc_bioset");
+ dm_bht_read_completed(entry, -ENOMEM);
+ return -ENOMEM;
+ }
+ bio->bi_private = (void *) entry;
+ bio->bi_idx = 0;
+ bio->bi_size = vc->bht.block_size;
+ bio->bi_sector = vc->hash_start + start;
+ bio->bi_bdev = vc->hash_dev->bdev;
+ bio->bi_end_io = kverityd_io_bht_populate_end;
+ bio->bi_rw = REQ_META;
+ /* Only need to free the bio since the page is managed by bht */
+ bio->bi_destructor = dm_verity_bio_destructor;
+ bio->bi_vcnt = 1;
+ bio->bi_io_vec->bv_offset = offset_in_page(dst);
+ bio->bi_io_vec->bv_len = to_bytes(count);
+ /* dst is guaranteed to be a page_pool allocation */
+ bio->bi_io_vec->bv_page = virt_to_page(dst);
+ /* Track that this I/O is in use. There should be no risk of the io
+ * being removed prior since this is called synchronously.
+ */
+ generic_make_request(bio);
+ return 0;
+}
+
+/* Submits an io request for each missing block of block hashes.
+ * The last one to return will then enqueue this on the io workqueue.
+ */
+static void kverityd_io_bht_populate(struct dm_verity_io *io)
+{
+ struct verity_config *vc = io->target->private;
+ u64 block;
+
+ for (block = io->block; block < io->block + io->count; ++block) {
+ int ret = dm_bht_populate(&vc->bht, io, block);
+
+ if (ret < 0) {
+ /* verity_dec_pending will handle the error case. */
+ io->error = ret;
+ break;
+ }
+ }
+}
+
+/* Asynchronously called upon the completion of I/O issued
+ * from kverityd_src_io_read. verity_dec_pending() acts as
+ * the scheduler/flow manager.
+ */
+static void kverityd_src_io_read_end(struct bio *clone, int error)
+{
+ struct dm_verity_io *io = clone->bi_private;
+
+ if (unlikely(!bio_flagged(clone, BIO_UPTODATE) && !error))
+ error = -EIO;
+
+ if (unlikely(error)) {
+ DMERR("Error occurred: %d (%llu, %u)",
+ error, ULL(clone->bi_sector), clone->bi_size);
+ io->error = error;
+ }
+
+ /* Release the clone which just avoids the block layer from
+ * leaving offsets, etc in unexpected states.
+ */
+ bio_put(clone);
+
+ verity_dec_pending(io);
+}
+
+/* If not yet underway, an I/O request will be issued to the vc->dev
+ * device for the data needed. It is cloned to avoid unexpected changes
+ * to the original bio struct.
+ */
+static void kverityd_src_io_read(struct dm_verity_io *io)
+{
+ struct bio *clone;
+
+ /* Check if the read is already issued. */
+ if (io->flags & VERITY_IOFLAGS_CLONED)
+ return;
+
+ io->flags |= VERITY_IOFLAGS_CLONED;
+
+ /* Clone the bio. The block layer may modify the bvec array. */
+ clone = verity_bio_clone(io);
+ if (unlikely(!clone)) {
+ io->error = -ENOMEM;
+ return;
+ }
+
+ verity_inc_pending(io);
+
+ generic_make_request(clone);
+}
+
+/* kverityd_io services the I/O workqueue. For each pass through
+ * the I/O workqueue, a call to populate both the origin drive
+ * data and the hash tree data is made.
+ */
+static void kverityd_io(struct work_struct *work)
+{
+ struct delayed_work *dwork = container_of(work, struct delayed_work,
+ work);
+ struct dm_verity_io *io = container_of(dwork, struct dm_verity_io,
+ work);
+
+ /* Issue requests asynchronously. */
+ verity_inc_pending(io);
+ kverityd_src_io_read(io);
+ kverityd_io_bht_populate(io);
+ verity_dec_pending(io);
+}
+
+/* Paired with verity_dec_pending, the pending value in the io dictate the
+ * lifetime of a request and when it is ready to be processed on the
+ * workqueues.
+ */
+static void verity_inc_pending(struct dm_verity_io *io)
+{
+ atomic_inc(&io->pending);
+}
+
+/* Block-level requests start here. */
+static int verity_map(struct dm_target *ti, struct bio *bio,
+ union map_info *map_context)
+{
+ struct dm_verity_io *io;
+ struct verity_config *vc;
+ struct request_queue *r_queue;
+
+ if (unlikely(!ti)) {
+ DMERR("dm_target was NULL");
+ return -EIO;
+ }
+
+ vc = ti->private;
+ r_queue = bdev_get_queue(vc->dev->bdev);
+
+ if (bio_data_dir(bio) == WRITE) {
+ /* If we silently drop writes, then the VFS layer will cache
+ * the write and persist it in memory. While it doesn't change
+ * the underlying storage, it still may be contrary to the
+ * behavior expected by a verified, read-only device.
+ */
+ DMWARN_LIMIT("write request received. rejecting with -EIO.");
+ verity_error(vc, NULL, -EIO);
+ return -EIO;
+ } else {
+ /* Queue up the request to be verified */
+ io = verity_io_alloc(ti, bio);
+ if (!io) {
+ DMERR_LIMIT("Failed to allocate and init IO data");
+ return DM_MAPIO_REQUEUE;
+ }
+ INIT_DELAYED_WORK(&io->work, kverityd_io);
+ queue_delayed_work(kverityd_ioq, &io->work, 0);
+ }
+
+ return DM_MAPIO_SUBMITTED;
+}
+
+static void splitarg(char *arg, char **key, char **val)
+{
+ *key = strsep(&arg, "=");
+ *val = strsep(&arg, "");
+}
+
+/*
+ * Non-block interfaces and device-mapper specific code
+ */
+
+/**
+ * verity_ctr - Construct a verified mapping
+ * @ti: Target being created
+ * @argc: Number of elements in argv
+ * @argv: Vector of key-value pairs (see below).
+ *
+ * Accepts the following keys:
+ * @payload: hashed device
+ * @hashtree: device hashtree is stored on
+ * @hashstart: start address of hashes (default 0)
+ * @block_size: size of a hash block
+ * @alg: hash algorithm
+ * @root_hexdigest: toplevel hash of the tree
+ * @error_behavior: what to do when verification fails [optional]
+ * @salt: salt, in hex [optional]
+ *
+ * E.g.,
+ * payload=/dev/sda2 hashtree=/dev/sda3 alg=sha256
+ * root_hexdigest=f08aa4a3695290c569eb1b0ac032ae1040150afb527abbeb0a3da33d82fb2c6e
+ *
+ * TODO(wad):
+ * - Boot time addition
+ * - Track block verification to free block_hashes if memory use is a concern
+ * Testing needed:
+ * - Regular slub_debug tracing (on checkins)
+ * - Improper block hash padding
+ * - Improper bundle padding
+ * - Improper hash layout
+ * - Missing padding at end of device
+ * - Improperly sized underlying devices
+ * - Out of memory conditions (make sure this isn't too flaky under high load!)
+ * - Incorrect superhash
+ * - Incorrect block hashes
+ * - Incorrect bundle hashes
+ * - Boot-up read speed; sustained read speeds
+ */
+static int verity_ctr(struct dm_target *ti, unsigned int argc, char **argv)
+{
+ struct verity_config *vc = NULL;
+ int ret = 0;
+ sector_t blocks;
+ unsigned int block_size = VERITY_DEFAULT_BLOCK_SIZE;
+ const char *payload = NULL;
+ const char *hashtree = NULL;
+ unsigned long hashstart = 0;
+ const char *alg = NULL;
+ const char *root_hexdigest = NULL;
+ const char *dev_error_behavior = error_behavior;
+ const char *hexsalt = "";
+ int i;
+
+ for (i = 0; i < argc; ++i) {
+ char *key, *val;
+ DMWARN("Argument %d: '%s'", i, argv[i]);
+ splitarg(argv[i], &key, &val);
+ if (!key) {
+ DMWARN("Bad argument %d: missing key?", i);
+ break;
+ }
+ if (!val) {
+ DMWARN("Bad argument %d='%s': missing value", i, key);
+ break;
+ }
+
+ if (!strcmp(key, "alg")) {
+ alg = val;
+ } else if (!strcmp(key, "payload")) {
+ payload = val;
+ } else if (!strcmp(key, "hashtree")) {
+ hashtree = val;
+ } else if (!strcmp(key, "root_hexdigest")) {
+ root_hexdigest = val;
+ } else if (!strcmp(key, "hashstart")) {
+ if (strict_strtoul(val, 10, &hashstart)) {
+ ti->error = "Invalid hashstart";
+ return -EINVAL;
+ }
+ } else if (!strcmp(key, "block_size")) {
+ unsigned long tmp;
+ if (strict_strtoul(val, 10, &tmp) ||
+ (tmp > UINT_MAX)) {
+ ti->error = "Invalid block_size";
+ return -EINVAL;
+ }
+ block_size = (unsigned int)tmp;
+ } else if (!strcmp(key, "error_behavior")) {
+ dev_error_behavior = val;
+ } else if (!strcmp(key, "salt")) {
+ hexsalt = val;
+ } else if (!strcmp(key, "error_behavior")) {
+ dev_error_behavior = val;
+ }
+ }
+
+#define NEEDARG(n) \
+ if (!(n)) { \
+ ti->error = "Missing argument: " #n; \
+ return -EINVAL; \
+ }
+
+ NEEDARG(alg);
+ NEEDARG(payload);
+ NEEDARG(hashtree);
+ NEEDARG(root_hexdigest);
+
+#undef NEEDARG
+
+ /* The device mapper device should be setup read-only */
+ if ((dm_table_get_mode(ti->table) & ~FMODE_READ) != 0) {
+ ti->error = "Must be created readonly.";
+ return -EINVAL;
+ }
+
+ vc = kzalloc(sizeof(*vc), GFP_KERNEL);
+ if (!vc) {
+ /* TODO(wad) if this is called from the setup helper, then we
+ * catch these errors and do a CrOS specific thing. if not, we
+ * need to have this call the error handler.
+ */
+ return -EINVAL;
+ }
+
+ /* Calculate the blocks from the given device size */
+ vc->size = ti->len;
+ blocks = to_bytes(vc->size) / block_size;
+ if (dm_bht_create(&vc->bht, blocks, block_size, alg)) {
+ DMERR("failed to create required bht");
+ goto bad_bht;
+ }
+ if (dm_bht_set_root_hexdigest(&vc->bht, root_hexdigest)) {
+ DMERR("root hexdigest error");
+ goto bad_root_hexdigest;
+ }
+ dm_bht_set_salt(&vc->bht, hexsalt);
+ vc->bht.read_cb = kverityd_bht_read_callback;
+
+ /* payload: device to verify */
+ vc->start = 0; /* TODO: should this support a starting offset? */
+ /* We only ever grab the device in read-only mode. */
+ ret = dm_get_device(ti, payload,
+ dm_table_get_mode(ti->table), &vc->dev);
+ if (ret) {
+ DMERR("Failed to acquire device '%s': %d", payload, ret);
+ ti->error = "Device lookup failed";
+ goto bad_verity_dev;
+ }
+
+ if ((to_bytes(vc->start) % block_size) ||
+ (to_bytes(vc->size) % block_size)) {
+ ti->error = "Device must be block_size divisble/aligned";
+ goto bad_hash_start;
+ }
+
+ vc->hash_start = (sector_t)hashstart;
+
+ /* hashtree: device with hashes.
+ * Note, payload == hashtree is okay as long as the size of
+ * ti->len passed to device mapper does not include
+ * the hashes.
+ */
+ if (dm_get_device(ti, hashtree,
+ dm_table_get_mode(ti->table), &vc->hash_dev)) {
+ ti->error = "Hash device lookup failed";
+ goto bad_hash_dev;
+ }
+
+ /* arg4: cryptographic digest algorithm */
+ if (snprintf(vc->hash_alg, CRYPTO_MAX_ALG_NAME, "%s", alg) >=
+ CRYPTO_MAX_ALG_NAME) {
+ ti->error = "Hash algorithm name is too long";
+ goto bad_hash;
+ }
+
+ /* override with optional device-specific error behavior */
+ vc->error_behavior = verity_parse_error_behavior(dev_error_behavior);
+ if (vc->error_behavior == -1) {
+ ti->error = "Bad error_behavior supplied";
+ goto bad_err_behavior;
+ }
+
+ /* TODO: Maybe issues a request on the io queue for block 0? */
+
+ /* Argument processing is done, setup operational data */
+ /* Pool for dm_verity_io objects */
+ vc->io_pool = mempool_create_slab_pool(MIN_IOS, _verity_io_pool);
+ if (!vc->io_pool) {
+ ti->error = "Cannot allocate verity io mempool";
+ goto bad_slab_pool;
+ }
+
+ /* Allocate the bioset used for request padding */
+ /* TODO(wad) allocate a separate bioset for the first verify maybe */
+ vc->bs = bioset_create(MIN_BIOS, 0);
+ if (!vc->bs) {
+ ti->error = "Cannot allocate verity bioset";
+ goto bad_bs;
+ }
+
+ ti->num_flush_requests = 1;
+ ti->private = vc;
+
+ /* TODO(wad) add device and hash device names */
+ {
+ char hashdev[BDEVNAME_SIZE], vdev[BDEVNAME_SIZE];
+ bdevname(vc->hash_dev->bdev, hashdev);
+ bdevname(vc->dev->bdev, vdev);
+ DMINFO("dev:%s hash:%s [sectors:%llu blocks:%llu]", vdev,
+ hashdev, ULL(vc->bht.sectors), ULL(blocks));
+ }
+ return 0;
+
+bad_bs:
+ mempool_destroy(vc->io_pool);
+bad_slab_pool:
+bad_err_behavior:
+bad_hash:
+ dm_put_device(ti, vc->hash_dev);
+bad_hash_dev:
+bad_hash_start:
+ dm_put_device(ti, vc->dev);
+bad_bht:
+bad_root_hexdigest:
+bad_verity_dev:
+ kfree(vc); /* hash is not secret so no need to zero */
+ return -EINVAL;
+}
+
+static void verity_dtr(struct dm_target *ti)
+{
+ struct verity_config *vc = (struct verity_config *) ti->private;
+
+ bioset_free(vc->bs);
+ mempool_destroy(vc->io_pool);
+ dm_bht_destroy(&vc->bht);
+ dm_put_device(ti, vc->hash_dev);
+ dm_put_device(ti, vc->dev);
+ kfree(vc);
+}
+
+static int verity_status(struct dm_target *ti, status_type_t type,
+ char *result, unsigned int maxlen)
+{
+ struct verity_config *vc = (struct verity_config *) ti->private;
+ unsigned int sz = 0;
+ char hashdev[BDEVNAME_SIZE], vdev[BDEVNAME_SIZE];
+ u8 hexdigest[VERITY_MAX_DIGEST_SIZE * 2 + 1] = { 0 };
+
+ dm_bht_root_hexdigest(&vc->bht, hexdigest, sizeof(hexdigest));
+
+ switch (type) {
+ case STATUSTYPE_INFO:
+ break;
+ case STATUSTYPE_TABLE:
+ bdevname(vc->hash_dev->bdev, hashdev);
+ bdevname(vc->dev->bdev, vdev);
+ DMEMIT("/dev/%s /dev/%s %llu %u %s %s",
+ vdev,
+ hashdev,
+ ULL(vc->hash_start),
+ vc->bht.depth,
+ vc->hash_alg,
+ hexdigest);
+ break;
+ }
+ return 0;
+}
+
+static int verity_merge(struct dm_target *ti, struct bvec_merge_data *bvm,
+ struct bio_vec *biovec, int max_size)
+{
+ struct verity_config *vc = ti->private;
+ struct request_queue *q = bdev_get_queue(vc->dev->bdev);
+
+ if (!q->merge_bvec_fn)
+ return max_size;
+
+ bvm->bi_bdev = vc->dev->bdev;
+ bvm->bi_sector = vc->start + bvm->bi_sector - ti->begin;
+
+ /* Optionally, this could just return 0 to stick to single pages. */
+ 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 verity_config *vc = ti->private;
+
+ return fn(ti, vc->dev, vc->start, ti->len, data);
+}
+
+static void verity_io_hints(struct dm_target *ti,
+ struct queue_limits *limits)
+{
+ struct verity_config *vc = ti->private;
+ unsigned int block_size = vc->bht.block_size;
+
+ limits->logical_block_size = block_size;
+ limits->physical_block_size = block_size;
+ blk_limits_io_min(limits, block_size);
+}
+
+static struct target_type verity_target = {
+ .name = "verity",
+ .version = {0, 1, 0},
+ .module = THIS_MODULE,
+ .ctr = verity_ctr,
+ .dtr = verity_dtr,
+ .map = verity_map,
+ .merge = verity_merge,
+ .status = verity_status,
+ .iterate_devices = verity_iterate_devices,
+ .io_hints = verity_io_hints,
+};
+
+#define VERITY_WQ_FLAGS (WQ_CPU_INTENSIVE|WQ_HIGHPRI)
+
+static int __init dm_verity_init(void)
+{
+ int r = -ENOMEM;
+
+ _verity_io_pool = KMEM_CACHE(dm_verity_io, 0);
+ if (!_verity_io_pool) {
+ DMERR("failed to allocate pool dm_verity_io");
+ goto bad_io_pool;
+ }
+
+ kverityd_ioq = alloc_workqueue("kverityd_io", VERITY_WQ_FLAGS, 1);
+ if (!kverityd_ioq) {
+ DMERR("failed to create workqueue kverityd_ioq");
+ goto bad_io_queue;
+ }
+
+ kveritydq = alloc_workqueue("kverityd", VERITY_WQ_FLAGS, 1);
+ if (!kveritydq) {
+ DMERR("failed to create workqueue kveritydq");
+ goto bad_verify_queue;
+ }
+
+ r = dm_register_target(&verity_target);
+ if (r < 0) {
+ DMERR("register failed %d", r);
+ goto register_failed;
+ }
+
+ DMINFO("version %u.%u.%u loaded", verity_target.version[0],
+ verity_target.version[1], verity_target.version[2]);
+
+ return r;
+
+register_failed:
+ destroy_workqueue(kveritydq);
+bad_verify_queue:
+ destroy_workqueue(kverityd_ioq);
+bad_io_queue:
+ kmem_cache_destroy(_verity_io_pool);
+bad_io_pool:
+ return r;
+}
+
+static void __exit dm_verity_exit(void)
+{
+ destroy_workqueue(kveritydq);
+ destroy_workqueue(kverityd_ioq);
+
+ dm_unregister_target(&verity_target);
+ kmem_cache_destroy(_verity_io_pool);
+}
+
+module_init(dm_verity_init);
+module_exit(dm_verity_exit);
+
+MODULE_AUTHOR("The Chromium OS Authors <chromium-os-dev@chromium.org>");
+MODULE_DESCRIPTION(DM_NAME " target for transparent disk integrity checking");
+MODULE_LICENSE("GPL");
diff --git a/drivers/md/dm-verity.h b/drivers/md/dm-verity.h
new file mode 100644
index 0000000..e0664c9
--- /dev/null
+++ b/drivers/md/dm-verity.h
@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) 2011 The Chromium OS Authors <chromium-os-dev@chromium.org>
+ * All Rights Reserved.
+ *
+ * This file is released under the GPLv2.
+ *
+ * Provide error types for use when creating a custom error handler.
+ * See Documentation/device-mapper/dm-verity.txt
+ */
+#ifndef DM_VERITY_H
+#define DM_VERITY_H
+
+#include <linux/notifier.h>
+
+struct dm_verity_error_state {
+ int code;
+ int transient; /* Likely to not happen after a reboot */
+ u64 block;
+ const char *message;
+
+ sector_t dev_start;
+ sector_t dev_len;
+ struct block_device *dev;
+
+ sector_t hash_dev_start;
+ sector_t hash_dev_len;
+ struct block_device *hash_dev;
+
+ /* Final behavior after all notifications are completed. */
+ int behavior;
+};
+
+/* This enum must be matched to allowed_error_behaviors in dm-verity.c */
+enum dm_verity_error_behavior {
+ DM_VERITY_ERROR_BEHAVIOR_EIO = 0,
+ DM_VERITY_ERROR_BEHAVIOR_PANIC,
+ DM_VERITY_ERROR_BEHAVIOR_NONE,
+ DM_VERITY_ERROR_BEHAVIOR_NOTIFY
+};
+
+
+int dm_verity_register_error_notifier(struct notifier_block *nb);
+int dm_verity_unregister_error_notifier(struct notifier_block *nb);
+
+#endif /* DM_VERITY_H */
diff --git a/include/linux/dm-bht.h b/include/linux/dm-bht.h
new file mode 100644
index 0000000..0595911
--- /dev/null
+++ b/include/linux/dm-bht.h
@@ -0,0 +1,166 @@
+/*
+ * Copyright (C) 2011 The Chromium OS Authors <chromium-os-dev@chromium.org>
+ *
+ * Device-Mapper block hash tree interface.
+ * See Documentation/device-mapper/dm-bht.txt for details.
+ *
+ * This file is released under the GPLv2.
+ */
+#ifndef __LINUX_DM_BHT_H
+#define __LINUX_DM_BHT_H
+
+#include <linux/compiler.h>
+#include <linux/crypto.h>
+#include <linux/types.h>
+
+/* To avoid allocating memory for digest tests, we just setup a
+ * max to use for now.
+ */
+#define DM_BHT_MAX_DIGEST_SIZE 128 /* 1k hashes are unlikely for now */
+#define DM_BHT_SALT_SIZE 32 /* 256 bits of salt is a lot */
+
+/* UNALLOCATED, PENDING, READY, and VERIFIED are valid states. All other
+ * values are entry-related return codes.
+ */
+#define DM_BHT_ENTRY_VERIFIED 8 /* 'nodes' has been checked against parent */
+#define DM_BHT_ENTRY_READY 4 /* 'nodes' is loaded and available */
+#define DM_BHT_ENTRY_PENDING 2 /* 'nodes' is being loaded */
+#define DM_BHT_ENTRY_UNALLOCATED 0 /* untouched */
+#define DM_BHT_ENTRY_ERROR -1 /* entry is unsuitable for use */
+#define DM_BHT_ENTRY_ERROR_IO -2 /* I/O error on load */
+
+/* Additional possible return codes */
+#define DM_BHT_ENTRY_ERROR_MISMATCH -3 /* Digest mismatch */
+
+/* dm_bht_entry
+ * Contains dm_bht->node_count tree nodes at a given tree depth.
+ * state is used to transactionally assure that data is paged in
+ * from disk. Unless dm_bht kept running crypto contexts for each
+ * level, we need to load in the data for on-demand verification.
+ */
+struct dm_bht_entry {
+ atomic_t state; /* see defines */
+ /* Keeping an extra pointer per entry wastes up to ~33k of
+ * memory if a 1m blocks are used (or 66 on 64-bit arch)
+ */
+ void *io_context; /* Reserve a pointer for use during io */
+ /* data should only be non-NULL if fully populated. */
+ void *nodes; /* The hash data used to verify the children.
+ * Guaranteed to be page-aligned.
+ */
+};
+
+/* dm_bht_level
+ * Contains an array of entries which represent a page of hashes where
+ * each hash is a node in the tree at the given tree depth/level.
+ */
+struct dm_bht_level {
+ struct dm_bht_entry *entries; /* array of entries of tree nodes */
+ unsigned int count; /* number of entries at this level */
+ sector_t sector; /* starting sector for this level */
+};
+
+/* opaque context, start, databuf, sector_count */
+typedef int(*dm_bht_callback)(void *, /* external context */
+ sector_t, /* start sector */
+ u8 *, /* destination page */
+ sector_t, /* num sectors */
+ struct dm_bht_entry *);
+/* dm_bht - Device mapper block hash tree
+ * dm_bht provides a fixed interface for comparing data blocks
+ * against a cryptographic hashes stored in a hash tree. It
+ * optimizes the tree structure for storage on disk.
+ *
+ * The tree is built from the bottom up. A collection of data,
+ * external to the tree, is hashed and these hashes are stored
+ * as the blocks in the tree. For some number of these hashes,
+ * a parent node is created by hashing them. These steps are
+ * repeated.
+ *
+ * TODO(wad): All hash storage memory is pre-allocated and freed once an
+ * entire branch has been verified.
+ */
+struct dm_bht {
+ /* Configured values */
+ int depth; /* Depth of the tree including the root */
+ unsigned int block_count; /* Number of blocks hashed */
+ unsigned int block_size; /* Size of a hash block */
+ char hash_alg[CRYPTO_MAX_ALG_NAME];
+ unsigned char salt[DM_BHT_SALT_SIZE];
+
+ /* Computed values */
+ unsigned int node_count; /* Data size (in hashes) for each entry */
+ unsigned int node_count_shift; /* first bit set - 1 */
+ /* There is one per CPU so that verified can be simultaneous. */
+ struct hash_desc hash_desc[NR_CPUS]; /* Container for the hash alg */
+ unsigned int digest_size;
+ sector_t sectors; /* Number of disk sectors used */
+
+ /* bool verified; Full tree is verified */
+ u8 root_digest[DM_BHT_MAX_DIGEST_SIZE];
+ struct dm_bht_level *levels; /* in reverse order */
+ /* Callback for reading from the hash device */
+ dm_bht_callback read_cb;
+};
+
+/* Constructor for struct dm_bht instances. */
+int dm_bht_create(struct dm_bht *bht,
+ unsigned int block_count,
+ unsigned int block_size,
+ const char *alg_name);
+/* Destructor for struct dm_bht instances. Does not free @bht */
+void dm_bht_destroy(struct dm_bht *bht);
+
+/* Basic accessors for struct dm_bht */
+int dm_bht_set_root_hexdigest(struct dm_bht *bht, const u8 *hexdigest);
+int dm_bht_root_hexdigest(struct dm_bht *bht, u8 *hexdigest, int available);
+void dm_bht_set_salt(struct dm_bht *bht, const char *hexsalt);
+int dm_bht_salt(struct dm_bht *bht, char *hexsalt);
+
+/* Functions for loading in data from disk for verification */
+bool dm_bht_is_populated(struct dm_bht *bht, unsigned int block);
+int dm_bht_populate(struct dm_bht *bht, void *read_cb_ctx,
+ unsigned int block);
+int dm_bht_verify_block(struct dm_bht *bht, unsigned int block,
+ struct page *pg, unsigned int offset);
+void dm_bht_read_completed(struct dm_bht_entry *entry, int status);
+
+/* Functions for converting indices to nodes. */
+
+static inline unsigned int dm_bht_get_level_shift(struct dm_bht *bht,
+ int depth)
+{
+ return (bht->depth - depth) * bht->node_count_shift;
+}
+
+/* For the given depth, this is the entry index. At depth+1 it is the node
+ * index for depth.
+ */
+static inline unsigned int dm_bht_index_at_level(struct dm_bht *bht,
+ int depth,
+ unsigned int leaf)
+{
+ return leaf >> dm_bht_get_level_shift(bht, depth);
+}
+
+static inline struct dm_bht_entry *dm_bht_get_entry(struct dm_bht *bht,
+ int depth,
+ unsigned int block)
+{
+ unsigned int index = dm_bht_index_at_level(bht, depth, block);
+ struct dm_bht_level *level = &bht->levels[depth];
+
+ return &level->entries[index];
+}
+
+static inline void *dm_bht_get_node(struct dm_bht *bht,
+ struct dm_bht_entry *entry,
+ int depth,
+ unsigned int block)
+{
+ unsigned int index = dm_bht_index_at_level(bht, depth, block);
+ unsigned int node_index = index % bht->node_count;
+
+ return entry->nodes + (node_index * bht->digest_size);
+}
+#endif /* __LINUX_DM_BHT_H */
--
1.7.3.1


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