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Re: [dm-devel] [PATCH] dm: verity target



Mikulas Patocka (mpatocka redhat com) wrote:
> Hi
> 
> This crashes if the device size is 64MiB (and sha256 hash is used).
> 

Hi Mikulas,

Thanks for catching this! Below is a fix:

diff --git a/drivers/md/dm-verity.c b/drivers/md/dm-verity.c
index 263070d..74616b7 100644
--- a/drivers/md/dm-verity.c
+++ b/drivers/md/dm-verity.c
@@ -278,7 +278,7 @@ static int verity_tree_initialize_entries(struct verity_tree *vt)
         * independently from the vt data structures.  Logically, the root is
         * depth=-1 and the block layer level is depth=vt->depth
         */
-       unsigned int last = vt->block_count;
+       unsigned int last = vt->block_count - 1;
        int depth;
 
        /* check that the largest level->count can't result in an int overflow

I'm still working on addressing akpm's feedback so will send out a v5
once that is done.

Regards,
Mandeep

> I tested it with the userspace utility and it doesn't work with device 
> >= 128MiB, it fails to verify the output of the utility.
> 
> I run this (/dev/vg1/verity_long_data has 128MiB size):
> ./verity mode=create alg=sha256 payload=/dev/vg1/verity_long_data 
> hashtree=/dev/vg1/verity_long_hash 
> salt=1234000000000000000000000000000000000000000000000000000000000000
> dm:dm bht[DEBUG] Setting block_count 32768
> dm:dm bht[DEBUG] Setting depth to 3.
> dm:dm bht[DEBUG] depth: 0 entries: 1
> dm:dm bht[DEBUG] depth: 1 entries: 2
> dm:dm bht[DEBUG] depth: 2 entries: 256
> 0 262144 verity payload=ROOT_DEV hashtree=HASH_DEV hashstart=262144 
> alg=sha256 
> root_hexdigest=6e46e106b288812a881a9da3f11180433f90ce264c4f1e8fa191fb40409846fb 
> salt=1234000000000000000000000000000000000000000000000000000000000000
> 
> dmsetup -r create verity --table "0 `blockdev --getsize 
> /dev/vg1/verity_long_data` verity 0 /dev/vg1/verity_long_data 
> /dev/vg1/verity_long_hash 0 4096 sha256 
> 6e46e106b288812a881a9da3f11180433f90ce264c4f1e8fa191fb40409846fb 
> 1234000000000000000000000000000000000000000000000000000000000000"
> 
> and get a lot of log messages "failed to verify hash (d=3,bi=0)"
> 
> If the device is smaller than 128MiB, it works (except for 64MiB device 
> where it crashes).
> 
> Mikulas
> 
> dmsetup -r create verity --table "0 131072 verity 0 
> /dev/vg1/verity_long_data /dev/vg1/verity_long_hash 0 4096 sha256 
> d821fec17e151a6e7b91c4a7a71487760185c25af49a74955a3e7a718c1f97dd 
> 1234000000000000000000000000000000000000000000000000000000000000"
> 
> [14356.819694] ------------[ cut here ]------------
> [14356.819747] kernel BUG at drivers/md/dm-verity2.c:439!
> [14356.819796] invalid opcode: 0000 [#1] PREEMPT SMP
> [14356.819879] CPU 5
> [14356.819897] Modules linked in: dm_verity2 md5 sha1_generic cryptomgr 
> aead sha256_generic dm_zero dm_bufio crypto_hash crypto_algapi crypto 
> dm_loop dm_mod parport_pc parport powernow_k8 mperf cpufreq_stats 
> cpufreq_powersave cpufreq_userspace cpufreq_conservative cpufreq_ondemand 
> freq_table snd_usb_audio snd_pcm_oss snd_mixer_oss snd_pcm snd_timer 
> snd_page_alloc snd_hwdep snd_usbmidi_lib snd_rawmidi snd soundcore fuse 
> raid0 md_mod lm85 hwmon_vid ide_cd_mod cdrom ohci_hcd ehci_hcd sata_svw 
> libata serverworks ide_core usbcore floppy usb_common rtc_cmos e100 tg3 
> mii libphy k10temp skge hwmon button i2c_piix4 processor unix [last 
> unloaded: dm_verity2]
> [14356.820536]
> [14356.820580] Pid: 10909, comm: dmsetup Not tainted 3.2.0 #19 empty 
> empty/S3992-E
> [14356.820680] RIP: 0010:[<ffffffffa0195908>]  [<ffffffffa0195908>] 
> verity_ctr+0x808/0x860 [dm_verity2]
> [14356.820772] RSP: 0018:ffff880141b7bcc8  EFLAGS: 00010202
> [14356.820821] RAX: 0000000000000408 RBX: ffff8802afedcc28 RCX: 
> 0000000000000002[14356.820875] RDX: 0000000000000081 RSI: ffff88044685a540 
> RDI: ffff8802afc4b000[14356.820929] RBP: ffff8802afedcc00 R08: 
> 0000000000000000 R09: ffff8802afc4a000[14356.820987] R10: 0000000000000001 
> R11: ffffff9000000018 R12: ffffffff8147a630[14356.821041] R13: 
> ffff88044685a558 R14: 0000000000004000 R15: 0000000000000002[14356.821114] 
> FS:  00007f1c9ea567a0(0000) GS:ffff880447c80000(0000) 
> knlGS:0000000000000000
> [14356.821199] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> [14356.821257] CR2: 00007f1c9e199f80 CR3: 00000003fe98e000 CR4: 
> 00000000000006e0[14356.821330] DR0: 0000000000000000 DR1: 0000000000000000 
> DR2: 0000000000000000[14356.821394] DR3: 0000000000000000 DR6: 
> 00000000ffff0ff0 DR7: 0000000000000400[14356.821464] Process dmsetup (pid: 
> 10909, threadinfo ffff880141b7a000, task ffff88023d8dec90)
> [14356.821557] Stack:
> [14356.821606]  ffff880141b7bd34 0000000000000007 ffffc90012ac9040 
> ffff880429987340
> [14356.821700]  ffffc90012ac41a4 0000000000020000 ffffc90012ac419d 
> ffffc90012ac4162
> [14356.821787]  ffffc90012ac417c ffffc90012ac41e5 0000000000020000 
> 0000000000000000
> [14356.821905] Call Trace:
> [14356.821965]  [<ffffffffa01d2cab>] ? dm_table_add_target+0x19b/0x450 
> [dm_mod] [14356.822034]  [<ffffffffa01d5690>] ? table_clear+0x80/0x80 
> [dm_mod]
> [14356.822090]  [<ffffffffa01d5762>] ? table_load+0xd2/0x330 [dm_mod]
> [14356.822150]  [<ffffffffa01d5690>] ? table_clear+0x80/0x80 [dm_mod]
> [14356.822213]  [<ffffffffa01d6bf9>] ? ctl_ioctl+0x159/0x2a0 [dm_mod]
> [14356.822286]  [<ffffffff8117351d>] ? ipc_addid+0x4d/0xd0
> [14356.822338]  [<ffffffffa01d6d4e>] ? dm_ctl_ioctl+0xe/0x20 [dm_mod]
> [14356.822411]  [<ffffffff81105a9e>] ? do_vfs_ioctl+0x8e/0x4f0
> [14356.822474]  [<ffffffff8110a980>] ? dput+0x20/0x230
> [14356.822533]  [<ffffffff810f6282>] ? fput+0x162/0x220
> [14356.822590]  [<ffffffff81105f49>] ? sys_ioctl+0x49/0x90
> [14356.822652]  [<ffffffff81313abb>] ? system_call_fastpath+0x16/0x1b
> [14356.822702] Code: 38 ce 65 19 a0 e9 61 fb ff ff 48 c7 c7 d8 62 19 a0 31 
> c0 e8 d9 80 17 e1 48 c7 c7 28 63 19 a0 31 c0 e8 cb 80 17 e1 e9 40 fb ff ff 
> <0f> 0b 48 c7 c7 b8 60 19 a0 31 c0 e8 b6 80 17 e1 e9 9b fa ff ff
> [14356.823081] RIP  [<ffffffffa0195908>] verity_ctr+0x808/0x860 
> [dm_verity2]
> [14356.823146]  RSP <ffff880141b7bcc8>
> [14356.823530] ---[ end trace 773c24b9dbd5cfff ]---
> 
> 
> On Tue, 28 Feb 2012, Mandeep Singh Baines wrote:
> 
> > 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.
> > 
> > Changes in V4:
> > * Discussion over phone (Alasdair G Kergon)
> >  * copy _ioctl fix from dm-linear
> >  * verity_status format fixes to match dm conventions
> >  * s/dm-bht/verity_tree
> >  * put everything into dm-verity.c
> >  * ctr changed to dm conventions
> >  * use hex2bin
> >  * use conventional dm names for function
> >   * s/dm_//
> >   * for example: verity_ctr versus dm_verity_ctr
> >  * use per_cpu API
> > Changes in V3:
> > * Discussion over irc (Alasdair G Kergon)
> >   * Implement ioctl hook
> > Changes in V2:
> > * https://lkml.org/lkml/2011/11/10/85 (Steffen Klassert)
> >   * Use shash API instead of older hash API
> > 
> > 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: Steffen Klassert <steffen klassert secunet com>
> > Cc: Andrew Morton <akpm linux-foundation org>
> > Cc: Mikulas Patocka <mpatocka redhat com>
> > Cc: dm-devel redhat com
> > ---
> >  Documentation/device-mapper/verity.txt |  149 ++++
> >  drivers/md/Kconfig                     |   16 +
> >  drivers/md/Makefile                    |    1 +
> >  drivers/md/dm-verity.c                 | 1411 ++++++++++++++++++++++++++++++++
> >  4 files changed, 1577 insertions(+), 0 deletions(-)
> >  create mode 100644 Documentation/device-mapper/verity.txt
> >  create mode 100644 drivers/md/dm-verity.c
> > 
> > diff --git a/Documentation/device-mapper/verity.txt b/Documentation/device-mapper/verity.txt
> > new file mode 100644
> > index 0000000..b631f12
> > --- /dev/null
> > +++ b/Documentation/device-mapper/verity.txt
> > @@ -0,0 +1,149 @@
> > +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:
> > +    <version> <dev> <hash_dev> <hash_start> <block_size> <alg> <digest> <salt>
> > +
> > +<version>
> > +    This is the version number of the on-disk format. Currently, there is
> > +    only version 0.
> > +
> > +<dev>
> > +    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_dev>
> > +    This is the device that that supplies the hash tree data.  It may be
> > +    specified similarly to the device path and may be the same device.  If the
> > +    same device is used, the hash offset should be outside of the dm-verity
> > +    configured device size.
> > +
> > +<hash_start>
> > +    This is the offset, in 512-byte sectors, from the start of hash_dev to
> > +    the root block of the hash tree.
> > +
> > +<block_size>
> > +    The size of a hash block. Also, the size of a block to be hashed.
> > +
> > +<alg>
> > +    The cryptographic hash algorithm used for this device.  This should
> > +    be the name of the algorithm, like "sha1".
> > +
> > +<digest>
> > +    The hexadecimal encoding of the cryptographic hash of 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.
> > +
> > +<salt>
> > +    The hexadecimal encoding of the salt value.
> > +
> > +Theory of operation
> > +===================
> > +
> > +dm-verity is meant to be setup as part of a verified boot path.  This
> > +may be anything ranging from a boot using tboot or trustedgrub to just
> > +booting from a known-good device (like a USB drive or CD).
> > +
> > +When a dm-verity device is configured, it is expected that the caller
> > +has been authenticated in some way (cryptographic signatures, etc).
> > +After instantiation, all hashes will be verified on-demand during
> > +disk access.  If they cannot be verified up to the root node of the
> > +tree, the root hash, then the I/O will fail.  This should identify
> > +tampering with any data on the device and the hash data.
> > +
> > +Cryptographic hashes are used to assert the integrity of the device on a
> > +per-block basis.  This allows for a lightweight hash computation on first read
> > +into the page cache.  Block hashes are stored linearly aligned to the nearest
> > +block the size of a page.
> > +
> > +Hash Tree
> > +---------
> > +
> > +Each node in the tree is a cryptographic hash.  If it is a leaf node, the hash
> > +is of some block data on disk.  If it is an intermediary node, then the hash is
> > +of a number of child nodes.
> > +
> > +Each entry in the tree is a collection of neighboring nodes that fit in one
> > +block.  The number is determined based on block_size and the size of the
> > +selected cryptographic digest algorithm.  The hashes are linearly ordered in
> > +this entry and any unaligned trailing space is ignored but included when
> > +calculating the parent node.
> > +
> > +The tree looks something like:
> > +
> > +alg = sha256, num_blocks = 32768, block_size = 4096
> > +
> > +                                 [   root    ]
> > +                                /    . . .    \
> > +                     [entry_0]                 [entry_1]
> > +                    /  . . .  \                 . . .   \
> > +         [entry_0_0]   . . .  [entry_0_127]    . . . .  [entry_1_127]
> > +           / ... \             /   . . .  \             /           \
> > +     blk_0 ... blk_127  blk_16256   blk_16383      blk_32640 . . . blk_32767
> > +
> > +On-disk format
> > +==============
> > +
> > +Below is the recommended on-disk format. The verity kernel code does not
> > +read the on-disk header. It only reads the hash blocks which directly
> > +follow the header. It is expected that a user-space tool will verify the
> > +integrity of the verity_header and then call dm_setup with the correct
> > +parameters. Alternatively, the header can be omitted and the dm_setup
> > +parameters can be passed via the kernel command-line in a rooted chain
> > +of trust where the command-line is verified.
> > +
> > +The on-disk format is especially useful in cases where the hash blocks
> > +are on a separate partition. The magic number allows easy identification
> > +of the partition contents. Alternatively, the hash blocks can be stored
> > +in the same partition as the data to be verified. In such a configuration
> > +the filesystem on the partition would be sized a little smaller than
> > +the full-partition, leaving room for the hash blocks.
> > +
> > +struct verity_header {
> > +       uint64_t magic = 0x7665726974790a00;
> > +       uint32_t version;
> > +       uint32_t block_size;
> > +       char digest[128]; /* in hex-ascii, null-terminated or 128-bytes */
> > +       char salt[128]; /* in hex-ascii, null-terminated or 128-bytes */
> > +}
> > +
> > +struct verity_header_block {
> > +	struct verity_header;
> > +	char unused[block_size - sizeof(struct verity_header) - sizeof(sig)];
> > +	char sig[128]; /* in hex-ascii, null-terminated or 128-bytes */
> > +}
> > +
> > +Directly following the header are the hash blocks which are stored a depth
> > +at a time (starting from the root), sorted in order of increasing index.
> > +
> > +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.
> > +
> > +Example
> > +=======
> > +
> > +Setup a device;
> > +[[
> > +  dmsetup create vroot --table \
> > +    "0 204800 verity /dev/sda1 /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..b8bb690 100644
> > --- a/drivers/md/Kconfig
> > +++ b/drivers/md/Kconfig
> > @@ -370,4 +370,20 @@ config DM_FLAKEY
> >         ---help---
> >           A target that intermittently fails I/O for debugging purposes.
> >  
> > +config DM_VERITY
> > +        tristate "Verity target support"
> > +        depends on BLK_DEV_DM
> > +        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..70a29af 100644
> > --- a/drivers/md/Makefile
> > +++ b/drivers/md/Makefile
> > @@ -39,6 +39,7 @@ 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-$(CONFIG_DM_VERITY)         += dm-verity.o
> >  obj-$(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-verity.c b/drivers/md/dm-verity.c
> > new file mode 100644
> > index 0000000..87b7958
> > --- /dev/null
> > +++ b/drivers/md/dm-verity.c
> > @@ -0,0 +1,1411 @@
> > +/*
> > + * 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) 2012 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 <crypto/hash.h>
> > +#include <linux/atomic.h>
> > +#include <linux/bio.h>
> > +#include <linux/blkdev.h>
> > +#include <linux/genhd.h>
> > +#include <linux/init.h>
> > +#include <linux/kernel.h>
> > +#include <linux/mempool.h>
> > +#include <linux/module.h>
> > +#include <linux/workqueue.h>
> > +#include <linux/device-mapper.h>
> > +
> > +
> > +#define DM_MSG_PREFIX "verity"
> > +
> > +
> > +/* Helper for printing sector_t */
> > +#define ULL(x) ((unsigned long long)(x))
> > +
> > +#define MIN_IOS 32
> > +#define MIN_BIOS (MIN_IOS * 2)
> > +
> > +/* To avoid allocating memory for digest tests, we just setup a
> > + * max to use for now.
> > + */
> > +#define VERITY_MAX_DIGEST_SIZE 64   /* Supports up to 512-bit digests */
> > +#define VERITY_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 VERITY_TREE_ENTRY_VERIFIED 8  /* 'nodes' checked against parent */
> > +#define VERITY_TREE_ENTRY_READY 4  /* 'nodes' is loaded and available */
> > +#define VERITY_TREE_ENTRY_PENDING 2  /* 'nodes' is being loaded */
> > +#define VERITY_TREE_ENTRY_UNALLOCATED 0 /* untouched */
> > +#define VERITY_TREE_ENTRY_ERROR -1 /* entry is unsuitable for use */
> > +#define VERITY_TREE_ENTRY_ERROR_IO -2 /* I/O error on load */
> > +
> > +/* Additional possible return codes */
> > +#define VERITY_TREE_ENTRY_ERROR_MISMATCH -3 /* Digest mismatch */
> > +
> > +
> > +/* verity_tree_entry
> > + * Contains verity_tree->node_count tree nodes at a given tree depth.
> > + * state is used to transactionally assure that data is paged in
> > + * from disk.  Unless verity_tree kept running crypto contexts for each
> > + * level, we need to load in the data for on-demand verification.
> > + */
> > +struct verity_tree_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.
> > +		       */
> > +};
> > +
> > +/* verity_tree_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 verity_tree_level {
> > +	struct verity_tree_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(*verity_tree_callback)(void *,  /* external context */
> > +			      sector_t,  /* start sector */
> > +			      u8 *,  /* destination page */
> > +			      sector_t,  /* num sectors */
> > +			      struct verity_tree_entry *);
> > +/* verity_tree - Device mapper block hash tree
> > + * verity_tree 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.
> > + */
> > +struct verity_tree {
> > +	/* 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];
> > +	u8 salt[VERITY_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.
> > +	 * Access through per_cpu_ptr() only
> > +	 */
> > +	struct shash_desc * __percpu *hash_desc; /* Container for hash alg */
> > +	unsigned int digest_size;
> > +	sector_t sectors;  /* Number of disk sectors used */
> > +
> > +	/* bool verified;  Full tree is verified */
> > +	u8 digest[VERITY_MAX_DIGEST_SIZE];
> > +	struct verity_tree_level *levels;  /* in reverse order */
> > +	/* Callback for reading from the hash device */
> > +	verity_tree_callback read_cb;
> > +};
> > +
> > +/* per-requested-bio private data */
> > +enum verity_io_flags {
> > +	VERITY_IOFLAGS_CLONED = 0x1,	/* original bio has been cloned */
> > +};
> > +
> > +struct 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 verity_tree 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];
> > +};
> > +
> > +
> > +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 verity_io *io);
> > +static void kverityd_io_bht_populate_end(struct bio *, int error);
> > +
> > +
> > +/*
> > + * Utilities
> > + */
> > +
> > +static void bin2hex(char *dst, const u8 *src, size_t count)
> > +{
> > +	while (count-- > 0) {
> > +		sprintf(dst, "%02hhx", (int)*src);
> > +		dst += 2;
> > +		src++;
> > +	}
> > +}
> > +
> > +/*
> > + * Verity Tree
> > + */
> > +
> > +/* Functions for converting indices to nodes. */
> > +
> > +static inline unsigned int verity_tree_get_level_shift(struct verity_tree *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 verity_tree_index_at_level(struct verity_tree *bht,
> > +						      int depth,
> > +						      unsigned int leaf)
> > +{
> > +	return leaf >> verity_tree_get_level_shift(bht, depth);
> > +}
> > +
> > +static inline struct verity_tree_entry *verity_tree_get_entry(
> > +		struct verity_tree *bht,
> > +		int depth,
> > +		unsigned int block)
> > +{
> > +	unsigned int index = verity_tree_index_at_level(bht, depth, block);
> > +	struct verity_tree_level *level = &bht->levels[depth];
> > +
> > +	return &level->entries[index];
> > +}
> > +
> > +static inline void *verity_tree_get_node(struct verity_tree *bht,
> > +					 struct verity_tree_entry *entry,
> > +					 int depth, unsigned int block)
> > +{
> > +	unsigned int index = verity_tree_index_at_level(bht, depth, block);
> > +	unsigned int node_index = index % bht->node_count;
> > +
> > +	return entry->nodes + (node_index * bht->digest_size);
> > +}
> > +/**
> > + * verity_tree_compute_hash: hashes a page of data
> > + */
> > +static int verity_tree_compute_hash(struct verity_tree *vt, struct page *pg,
> > +				    unsigned int offset, u8 *digest)
> > +{
> > +	struct shash_desc *hash_desc;
> > +	void *data;
> > +	int err;
> > +
> > +	hash_desc = *per_cpu_ptr(vt->hash_desc, smp_processor_id());
> > +
> > +	if (crypto_shash_init(hash_desc)) {
> > +		DMCRIT("failed to reinitialize crypto hash (proc:%d)",
> > +			smp_processor_id());
> > +		return -EINVAL;
> > +	}
> > +	data = kmap_atomic(pg);
> > +	err = crypto_shash_update(hash_desc, data + offset, PAGE_SIZE);
> > +	kunmap_atomic(data);
> > +	if (err) {
> > +		DMCRIT("crypto_hash_update failed");
> > +		return -EINVAL;
> > +	}
> > +	if (crypto_shash_update(hash_desc, vt->salt, sizeof(vt->salt))) {
> > +		DMCRIT("crypto_hash_update failed");
> > +		return -EINVAL;
> > +	}
> > +	if (crypto_shash_final(hash_desc, digest)) {
> > +		DMCRIT("crypto_hash_final failed");
> > +		return -EINVAL;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static int verity_tree_initialize_entries(struct verity_tree *vt)
> > +{
> > +	/* 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 vt data structures.  Logically, the root is
> > +	 * depth=-1 and the block layer level is depth=vt->depth
> > +	 */
> > +	unsigned int last = vt->block_count;
> > +	int depth;
> > +
> > +	/* check that the largest level->count can't result in an int overflow
> > +	 * on allocation or sector calculation.
> > +	 */
> > +	if (((last >> vt->node_count_shift) + 1) >
> > +	    UINT_MAX / max((unsigned int)sizeof(struct verity_tree_entry),
> > +			   (unsigned int)to_sector(vt->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.
> > +	 */
> > +	vt->sectors = 0;
> > +	for (depth = 0; depth < vt->depth; ++depth) {
> > +		struct verity_tree_level *level = &vt->levels[depth];
> > +
> > +		level->count = verity_tree_index_at_level(vt, depth, last) + 1;
> > +		level->entries = (struct verity_tree_entry *)
> > +				 kcalloc(level->count,
> > +					 sizeof(struct verity_tree_entry),
> > +					 GFP_KERNEL);
> > +		if (!level->entries) {
> > +			DMERR("failed to allocate entries for depth %d", depth);
> > +			return -ENOMEM;
> > +		}
> > +		level->sector = vt->sectors;
> > +		vt->sectors += level->count * to_sector(vt->block_size);
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +/**
> > + * verity_tree_create - prepares @vt for us
> > + * @vt:	          pointer to a verity_tree_create()d vt
> > + * @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.
> > + */
> > +static int verity_tree_create(struct verity_tree *vt, unsigned int block_count,
> > +			      unsigned int block_size, const char *alg_name)
> > +{
> > +	struct crypto_shash *tfm;
> > +	int size, cpu, status = 0;
> > +
> > +	vt->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;
> > +
> > +	tfm = crypto_alloc_shash(alg_name, 0, 0);
> > +	if (IS_ERR(tfm)) {
> > +		DMERR("failed to allocate crypto hash '%s'", alg_name);
> > +		return -ENOMEM;
> > +	}
> > +	size = sizeof(struct shash_desc) + crypto_shash_descsize(tfm);
> > +
> > +	vt->hash_desc = alloc_percpu(struct shash_desc *);
> > +	if (!vt->hash_desc) {
> > +		DMERR("Failed to allocate per cpu hash_desc");
> > +		status = -ENOMEM;
> > +		goto bad_per_cpu;
> > +	}
> > +
> > +	/* Pre-allocate per-cpu crypto contexts to avoid having to
> > +	 * kmalloc/kfree a context for every hash operation.
> > +	 */
> > +	for_each_possible_cpu(cpu) {
> > +		struct shash_desc *hash_desc = kmalloc(size, GFP_KERNEL);
> > +
> > +		*per_cpu_ptr(vt->hash_desc, cpu) = hash_desc;
> > +		if (!hash_desc) {
> > +			DMERR("failed to allocate crypto hash contexts");
> > +			status = -ENOMEM;
> > +			goto bad_hash_alloc;
> > +		}
> > +		hash_desc->tfm = tfm;
> > +		hash_desc->flags = 0x0;
> > +	}
> > +	vt->digest_size = crypto_shash_digestsize(tfm);
> > +	/* We expect to be able to pack >=2 hashes into a block */
> > +	if (block_size / vt->digest_size < 2) {
> > +		DMERR("too few hashes fit in a block");
> > +		status = -EINVAL;
> > +		goto bad_arg;
> > +	}
> > +
> > +	if (vt->digest_size > VERITY_MAX_DIGEST_SIZE) {
> > +		DMERR("VERITY_MAX_DIGEST_SIZE too small for digest");
> > +		status = -EINVAL;
> > +		goto bad_arg;
> > +	}
> > +
> > +	/* Configure the tree */
> > +	vt->block_count = block_count;
> > +	if (block_count == 0) {
> > +		DMERR("block_count must be non-zero");
> > +		status = -EINVAL;
> > +		goto bad_arg;
> > +	}
> > +
> > +	/* Each verity_tree_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).
> > +	 */
> > +	vt->node_count_shift = fls(block_size / vt->digest_size) - 1;
> > +	/* Round down to the nearest power of two.  This makes indexing
> > +	 * into the tree much less painful.
> > +	 */
> > +	vt->node_count = 1 << vt->node_count_shift;
> > +
> > +	/* This is unlikely to happen, but with 64k pages, who knows. */
> > +	if (vt->node_count > UINT_MAX / vt->digest_size) {
> > +		DMERR("node_count * hash_len exceeds UINT_MAX!");
> > +		status = -EINVAL;
> > +		goto bad_arg;
> > +	}
> > +
> > +	vt->depth = DIV_ROUND_UP(fls(block_count - 1), vt->node_count_shift);
> > +
> > +	/* Ensure that we can safely shift by this value. */
> > +	if (vt->depth * vt->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 verity_tree_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.
> > +	 */
> > +	vt->levels = (struct verity_tree_level *)
> > +			kcalloc(vt->depth,
> > +				sizeof(struct verity_tree_level), GFP_KERNEL);
> > +	if (!vt->levels) {
> > +		DMERR("failed to allocate tree levels");
> > +		status = -ENOMEM;
> > +		goto bad_level_alloc;
> > +	}
> > +
> > +	vt->read_cb = NULL;
> > +
> > +	status = verity_tree_initialize_entries(vt);
> > +	if (status)
> > +		goto bad_entries_alloc;
> > +
> > +	/* We compute depth such that there is only be 1 block at level 0. */
> > +	BUG_ON(vt->levels[0].count != 1);
> > +
> > +	return 0;
> > +
> > +bad_entries_alloc:
> > +	while (vt->depth-- > 0)
> > +		kfree(vt->levels[vt->depth].entries);
> > +	kfree(vt->levels);
> > +bad_level_alloc:
> > +bad_arg:
> > +bad_hash_alloc:
> > +	for_each_possible_cpu(cpu)
> > +		if (*per_cpu_ptr(vt->hash_desc, cpu))
> > +			kfree(*per_cpu_ptr(vt->hash_desc, cpu));
> > +	free_percpu(vt->hash_desc);
> > +bad_per_cpu:
> > +	crypto_free_shash(tfm);
> > +	return status;
> > +}
> > +
> > +/**
> > + * verity_tree_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.
> > + */
> > +static void verity_tree_read_completed(struct verity_tree_entry *entry,
> > +				       int status)
> > +{
> > +	if (status) {
> > +		DMCRIT("an I/O error occurred while reading entry");
> > +		atomic_set(&entry->state, VERITY_TREE_ENTRY_ERROR_IO);
> > +		return;
> > +	}
> > +	BUG_ON(atomic_read(&entry->state) != VERITY_TREE_ENTRY_PENDING);
> > +	atomic_set(&entry->state, VERITY_TREE_ENTRY_READY);
> > +}
> > +
> > +/**
> > + * verity_tree_verify_block - checks that all path nodes for @block are valid
> > + * @vt:	     pointer to a verity_tree_create()d vt
> > + * @block:   specific block data is expected from
> > + * @pg:	     page holding the block data
> > + * @offset:  offset into the page
> > + *
> > + * Returns 0 on success, VERITY_TREE_ENTRY_ERROR_MISMATCH on error.
> > + */
> > +static int verity_tree_verify_block(struct verity_tree *vt, unsigned int block,
> > +				    struct page *pg, unsigned int offset)
> > +{
> > +	int state, depth = vt->depth;
> > +	u8 digest[VERITY_MAX_DIGEST_SIZE];
> > +	struct verity_tree_entry *entry;
> > +	void *node;
> > +
> > +	do {
> > +		/* Need to check that the hash of the current block is accurate
> > +		 * in its parent.
> > +		 */
> > +		entry = verity_tree_get_entry(vt, 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 verity_tree_populate.
> > +		 */
> > +		BUG_ON(state < VERITY_TREE_ENTRY_READY);
> > +		node = verity_tree_get_node(vt, entry, depth, block);
> > +
> > +		if (verity_tree_compute_hash(vt, pg, offset, digest) ||
> > +		    memcmp(digest, node, vt->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 != VERITY_TREE_ENTRY_VERIFIED);
> > +
> > +	if (depth == 0 && state != VERITY_TREE_ENTRY_VERIFIED) {
> > +		if (verity_tree_compute_hash(vt, pg, offset, digest) ||
> > +		    memcmp(digest, vt->digest, vt->digest_size))
> > +			goto mismatch;
> > +		atomic_set(&entry->state, VERITY_TREE_ENTRY_VERIFIED);
> > +	}
> > +
> > +	/* Mark path to leaf as verified. */
> > +	for (depth++; depth < vt->depth; depth++) {
> > +		entry = verity_tree_get_entry(vt, 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, VERITY_TREE_ENTRY_VERIFIED);
> > +	}
> > +
> > +	return 0;
> > +
> > +mismatch:
> > +	DMERR_LIMIT("verify_path: failed to verify hash (d=%d,bi=%u)",
> > +		    depth, block);
> > +	return VERITY_TREE_ENTRY_ERROR_MISMATCH;
> > +}
> > +
> > +/**
> > + * verity_tree_is_populated - check that nodes needed to verify a given
> > + *                            block are all ready
> > + * @vt:	    pointer to a verity_tree_create()d vt
> > + * @block:  specific block data is expected from
> > + *
> > + * Callers may wish to call verity_tree_is_populated() when checking an io
> > + * for which entries were already pending.
> > + */
> > +static bool verity_tree_is_populated(struct verity_tree *vt, unsigned int block)
> > +{
> > +	int depth;
> > +
> > +	for (depth = vt->depth - 1; depth >= 0; depth--) {
> > +		struct verity_tree_entry *entry;
> > +		entry = verity_tree_get_entry(vt, depth, block);
> > +		if (atomic_read(&entry->state) < VERITY_TREE_ENTRY_READY)
> > +			return false;
> > +	}
> > +
> > +	return true;
> > +}
> > +
> > +/**
> > + * verity_tree_populate - reads entries from disk needed to verify a given block
> > + * @vt:     pointer to a verity_tree_create()d vt
> > + * @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.
> > + */
> > +static int verity_tree_populate(struct verity_tree *vt, void *ctx,
> > +				unsigned int block)
> > +{
> > +	int depth, state;
> > +
> > +	BUG_ON(block >= vt->block_count);
> > +
> > +	for (depth = vt->depth - 1; depth >= 0; --depth) {
> > +		unsigned int index;
> > +		struct verity_tree_level *level;
> > +		struct verity_tree_entry *entry;
> > +
> > +		index = verity_tree_index_at_level(vt, depth, block);
> > +		level = &vt->levels[depth];
> > +		entry = verity_tree_get_entry(vt, depth, block);
> > +		state = atomic_cmpxchg(&entry->state,
> > +				       VERITY_TREE_ENTRY_UNALLOCATED,
> > +				       VERITY_TREE_ENTRY_PENDING);
> > +		if (state == VERITY_TREE_ENTRY_VERIFIED)
> > +			break;
> > +		if (state <= VERITY_TREE_ENTRY_ERROR)
> > +			goto error_state;
> > +		if (state != VERITY_TREE_ENTRY_UNALLOCATED)
> > +			continue;
> > +
> > +		/* Current entry is claimed for allocation and loading */
> > +		entry->nodes = kmalloc(vt->block_size, GFP_NOIO);
> > +		if (!entry->nodes)
> > +			goto nomem;
> > +
> > +		vt->read_cb(ctx,
> > +			    level->sector + to_sector(index * vt->block_size),
> > +			    entry->nodes, to_sector(vt->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;
> > +}
> > +
> > +/**
> > + * verity_tree_destroy - cleans up all memory used by @vt
> > + * @vt:	 pointer to a verity_tree_create()d vt
> > + */
> > +static void verity_tree_destroy(struct verity_tree *vt)
> > +{
> > +	int depth, cpu;
> > +
> > +	for (depth = 0; depth < vt->depth; depth++) {
> > +		struct verity_tree_entry *entry = vt->levels[depth].entries;
> > +		struct verity_tree_entry *entry_end = entry +
> > +			vt->levels[depth].count;
> > +		for (; entry < entry_end; ++entry)
> > +			kfree(entry->nodes);
> > +		kfree(vt->levels[depth].entries);
> > +	}
> > +	kfree(vt->levels);
> > +	crypto_free_shash((*per_cpu_ptr(vt->hash_desc, 0))->tfm);
> > +	for_each_possible_cpu(cpu)
> > +		kfree(*per_cpu_ptr(vt->hash_desc, cpu));
> > +}
> > +
> > +/*
> > + * Verity Tree Accessors
> > + */
> > +
> > +/**
> > + * verity_tree_set_digest - sets an unverified root digest hash from hex
> > + * @vt:	     pointer to a verity_tree_create()d vt
> > + * @digest:  string containing the digest in hex
> > + * Returns non-zero on error.
> > + */
> > +static int verity_tree_set_digest(struct verity_tree *vt, const char *digest)
> > +{
> > +	/* Make sure we have at least the bytes expected */
> > +	if (strnlen((char *)digest, vt->digest_size * 2) !=
> > +	    vt->digest_size * 2) {
> > +		DMERR("root digest length does not match hash algorithm");
> > +		return -1;
> > +	}
> > +	return hex2bin(vt->digest, digest, vt->digest_size);
> > +}
> > +
> > +/**
> > + * verity_tree_digest - returns root digest in hex
> > + * @vt:	     pointer to a verity_tree_create()d vt
> > + * @digest:  buffer to put into, must be of length VERITY_SALT_SIZE * 2 + 1.
> > + */
> > +int verity_tree_digest(struct verity_tree *vt, char *digest)
> > +{
> > +	bin2hex(digest, vt->digest, vt->digest_size);
> > +	return 0;
> > +}
> > +
> > +/**
> > + * verity_tree_set_salt - sets the salt
> > + * @vt:    pointer to a verity_tree_create()d vt
> > + * @salt:  string containing the salt in hex
> > + * Returns non-zero on error.
> > + */
> > +int verity_tree_set_salt(struct verity_tree *vt, const char *salt)
> > +{
> > +	size_t saltlen = min(strlen(salt) / 2, sizeof(vt->salt));
> > +	memset(vt->salt, 0, sizeof(vt->salt));
> > +	return hex2bin(vt->salt, salt, saltlen);
> > +}
> > +
> > +
> > +/**
> > + * verity_tree_salt - returns the salt in hex
> > + * @vt:    pointer to a verity_tree_create()d vt
> > + * @salt:  buffer to put salt into, of length VERITY_SALT_SIZE * 2 + 1.
> > + */
> > +int verity_tree_salt(struct verity_tree *vt, char *salt)
> > +{
> > +	bin2hex(salt, vt->salt, sizeof(vt->salt));
> > +	return 0;
> > +}
> > +
> > +/*
> > + * Allocation and utility functions
> > + */
> > +
> > +static void kverityd_src_io_read_end(struct bio *clone, int error);
> > +
> > +/* Shared destructor for all internal bios */
> > +static void verity_bio_destructor(struct bio *bio)
> > +{
> > +	struct 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 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 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 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 = verity_bio_destructor;
> > +
> > +	return clone;
> > +}
> > +
> > +/*
> > + * 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 verity_io *io);
> > +
> > +static void verity_return_bio_to_caller(struct verity_io *io)
> > +{
> > +	struct verity_config *vc = io->target->private;
> > +
> > +	if (io->error)
> > +		io->error = -EIO;
> > +
> > +	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 verity_io *io)
> > +{
> > +	struct verity_config *vc = io->target->private;
> > +	u64 block;
> > +
> > +	for (block = io->block; block < io->block + io->count; ++block)
> > +		if (!verity_tree_is_populated(&vc->bht, block))
> > +			return false;
> > +
> > +	return true;
> > +}
> > +
> > +/* verity_dec_pending manages the lifetime of all 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 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 verity-tree
> > + * for verification.
> > + */
> > +static int verity_verify(struct verity_config *vc,
> > +			 struct 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;
> > +
> > +		BUG_ON(offset % block_size);
> > +		BUG_ON(len % block_size);
> > +
> > +		while (len) {
> > +			r = verity_tree_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:
> > +	/* verity_tree 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 verity_io *io = container_of(dwork, struct 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 verity-tree I/O. The status
> > + * of the operation is passed back to verity-tree and the next steps are
> > + * decided by verity_dec_pending.
> > + */
> > +static void kverityd_io_bht_populate_end(struct bio *bio, int error)
> > +{
> > +	struct verity_tree_entry *entry;
> > +	struct verity_io *io;
> > +
> > +	entry = (struct verity_tree_entry *) bio->bi_private;
> > +	io = (struct verity_io *) entry->io_context;
> > +
> > +	/* Tell the tree to atomically update now that we've populated
> > +	 * the given entry.
> > +	 */
> > +	verity_tree_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 verity-tree (via verity_tree_populate), this function provides
> > + * the message digests to verity-tree that are stored on disk.
> > + */
> > +static int kverityd_bht_read_callback(void *ctx, sector_t start, u8 *dst,
> > +				      sector_t count,
> > +				      struct verity_tree_entry *entry)
> > +{
> > +	struct 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");
> > +		verity_tree_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 = 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 verity_io *io)
> > +{
> > +	struct verity_config *vc = io->target->private;
> > +	u64 block;
> > +
> > +	for (block = io->block; block < io->block + io->count; ++block) {
> > +		int ret = verity_tree_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 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 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 verity_io *io = container_of(dwork, struct 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 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 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.");
> > +		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;
> > +}
> > +
> > +/*
> > + * Non-block interfaces and device-mapper specific code
> > + */
> > +
> > +/*
> > + * Verity target parameters:
> > + *
> > + * <dev> <hash_dev> <hash_start> <block_size> <alg> <digest> <salt>
> > + *
> > + * version:        version of the hash tree on-disk format
> > + * dev:            device to verify
> > + * hash_dev:       device hashtree is stored on
> > + * hash_start:     start address of hashes
> > + * block_size:     size of a hash block
> > + * alg:            hash algorithm
> > + * digest:         toplevel hash of the tree
> > + * salt:           salt
> > + */
> > +static int verity_ctr(struct dm_target *ti, unsigned int argc, char **argv)
> > +{
> > +	struct verity_config *vc = NULL;
> > +	const char *dev, *hash_dev, *alg, *digest, *salt;
> > +	unsigned long hash_start, block_size, version;
> > +	sector_t blocks;
> > +	int ret;
> > +
> > +	if (argc != 8) {
> > +		ti->error = "Invalid argument count";
> > +		return -EINVAL;
> > +	}
> > +
> > +	if (strict_strtoul(argv[0], 10, &version) ||
> > +	    (version != 0)) {
> > +		ti->error = "Invalid version";
> > +		return -EINVAL;
> > +	}
> > +	dev = argv[1];
> > +	hash_dev = argv[2];
> > +	if (strict_strtoul(argv[3], 10, &hash_start)) {
> > +		ti->error = "Invalid hash_start";
> > +		return -EINVAL;
> > +	}
> > +	if (strict_strtoul(argv[4], 10, &block_size) ||
> > +	    (block_size > UINT_MAX)) {
> > +		ti->error = "Invalid block_size";
> > +		return -EINVAL;
> > +	}
> > +	alg = argv[5];
> > +	digest = argv[6];
> > +	salt = argv[7];
> > +
> > +	/* 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) {
> > +		return -EINVAL;
> > +	}
> > +
> > +	/* Calculate the blocks from the given device size */
> > +	vc->size = ti->len;
> > +	blocks = to_bytes(vc->size) / block_size;
> > +	if (verity_tree_create(&vc->bht, blocks, block_size, alg)) {
> > +		DMERR("failed to create required bht");
> > +		goto bad_bht;
> > +	}
> > +	if (verity_tree_set_digest(&vc->bht, digest)) {
> > +		DMERR("digest error");
> > +		goto bad_digest;
> > +	}
> > +	verity_tree_set_salt(&vc->bht, salt);
> > +	vc->bht.read_cb = kverityd_bht_read_callback;
> > +
> > +	vc->start = 0;
> > +	/* We only ever grab the device in read-only mode. */
> > +	ret = dm_get_device(ti, dev, dm_table_get_mode(ti->table), &vc->dev);
> > +	if (ret) {
> > +		DMERR("Failed to acquire device '%s': %d", dev, 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)hash_start;
> > +
> > +	/*
> > +	 * Note, dev == hash_dev is okay as long as the size of
> > +	 *       ti->len passed to device mapper does not include
> > +	 *       the hashes.
> > +	 */
> > +	if (dm_get_device(ti, hash_dev,
> > +			  dm_table_get_mode(ti->table), &vc->hash_dev)) {
> > +		ti->error = "Hash device lookup failed";
> > +		goto bad_hash_dev;
> > +	}
> > +
> > +	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;
> > +	}
> > +
> > +	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;
> > +	}
> > +
> > +	vc->bs = bioset_create(MIN_BIOS, 0);
> > +	if (!vc->bs) {
> > +		ti->error = "Cannot allocate verity bioset";
> > +		goto bad_bs;
> > +	}
> > +
> > +	ti->private = vc;
> > +
> > +	return 0;
> > +
> > +bad_bs:
> > +	mempool_destroy(vc->io_pool);
> > +bad_slab_pool:
> > +bad_hash:
> > +	dm_put_device(ti, vc->hash_dev);
> > +bad_hash_dev:
> > +bad_hash_start:
> > +	dm_put_device(ti, vc->dev);
> > +bad_bht:
> > +bad_digest:
> > +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);
> > +	verity_tree_destroy(&vc->bht);
> > +	dm_put_device(ti, vc->hash_dev);
> > +	dm_put_device(ti, vc->dev);
> > +	kfree(vc);
> > +}
> > +
> > +static int verity_ioctl(struct dm_target *ti, unsigned int cmd,
> > +			unsigned long arg)
> > +{
> > +	struct verity_config *vc = (struct verity_config *) ti->private;
> > +	struct dm_dev *dev = vc->dev;
> > +	int r = 0;
> > +
> > +	/*
> > +	 * Only pass ioctls through if the device sizes match exactly.
> > +	 */
> > +	if (vc->start ||
> > +	    ti->len != i_size_read(dev->bdev->bd_inode) >> SECTOR_SHIFT)
> > +		r = scsi_verify_blk_ioctl(NULL, cmd);
> > +
> > +	return r ? : __blkdev_driver_ioctl(dev->bdev, dev->mode, cmd, arg);
> > +}
> > +
> > +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 digest[VERITY_MAX_DIGEST_SIZE * 2 + 1] = { 0 };
> > +	char salt[VERITY_SALT_SIZE * 2 + 1] = { 0 };
> > +
> > +	verity_tree_digest(&vc->bht, digest);
> > +	verity_tree_salt(&vc->bht, salt);
> > +
> > +	switch (type) {
> > +	case STATUSTYPE_INFO:
> > +		result[0] = '\0';
> > +		break;
> > +	case STATUSTYPE_TABLE:
> > +		DMEMIT("%s %s %llu %llu %s %s %s",
> > +		       vc->dev->name,
> > +		       vc->hash_dev->name,
> > +		       ULL(vc->hash_start),
> > +		       ULL(vc->bht.block_size),
> > +		       vc->hash_alg,
> > +		       digest,
> > +		       salt);
> > +		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,
> > +	.ioctl  = verity_ioctl,
> > +	.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 verity_init(void)
> > +{
> > +	int r = -ENOMEM;
> > +
> > +	_verity_io_pool = KMEM_CACHE(verity_io, 0);
> > +	if (!_verity_io_pool) {
> > +		DMERR("failed to allocate pool 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 verity_exit(void)
> > +{
> > +	destroy_workqueue(kveritydq);
> > +	destroy_workqueue(kverityd_ioq);
> > +
> > +	dm_unregister_target(&verity_target);
> > +	kmem_cache_destroy(_verity_io_pool);
> > +}
> > +
> > +module_init(verity_init);
> > +module_exit(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");
> > -- 
> > 1.7.7.3
> > 


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