veritysetup
VERITYSETUP(8) Maintenance Commands VERITYSETUP(8)
NAME
veritysetup - manage dm-verity (block level verification) volumes
SYNOPSIS
veritysetup <options> <action> <action args>
DESCRIPTION
Veritysetup is used to configure dm-verity managed device-mapper map-
pings.
Device-mapper verity target provides read-only transparent integrity
checking of block devices using kernel crypto API.
The dm-verity devices are always read-only.
Veritysetup supports these operations:
format <data_device> <hash_device>
Calculates and permanently stores hash verification data for
data_device. Hash area can be located on the same device after
data if specified by --hash-offset option.
Note you need to provide root hash string for device verifica-
tion or activation. Root hash must be trusted.
The data or hash device argument can be block device or file im-
age. If hash device path doesn't exist, it will be created as
file.
<options> can be [--hash, --no-superblock, --format, --data-
block-size, --hash-block-size, --data-blocks, --hash-offset,
--salt, --uuid, --root-hash-file]
If option --root-hash-file is used, the root hash is stored in
hex-encoded text format in <path>.
open <data_device> <name> <hash_device> <root_hash>
open <data_device> <name> <hash_device> --root-hash-file <path>
create <name> <data_device> <hash_device> <root_hash> (OBSOLETE syn-
tax)
Creates a mapping with <name> backed by device <data_device> and
using <hash_device> for in-kernel verification.
The <root_hash> is a hexadecimal string.
<options> can be [--hash-offset, --no-superblock, --ignore-cor-
ruption or --restart-on-corruption, --panic-on-corruption, --ig-
nore-zero-blocks, --check-at-most-once, --root-hash-signature,
--root-hash-file]
If option --root-hash-file is used, the root hash is read from
<path> instead of from the command line parameter. Expects hex-
encoded text, without terminating newline.
If option --no-superblock is used, you have to use as the same
options as in initial format operation.
verify <data_device> <hash_device> <root_hash>
verify <data_device> <hash_device> --root-hash-file <path>
Verifies data on data_device with use of hash blocks stored on
hash_device.
This command performs userspace verification, no kernel device
is created.
The <root_hash> is a hexadecimal string.
If option --root-hash-file is used, the root hash is read from
<path> instead of from the command line parameter. Expects hex-
encoded text, without terminating newline.
<options> can be [--hash-offset, --no-superblock, --root-hash-
file]
If option --no-superblock is used, you have to use as the same
options as in initial format operation.
close <name>
Removes existing mapping <name>.
For backward compatibility there is remove command alias for
close command.
<options> can be [--deferred] or [--cancel-deferred]
status <name>
Reports status for the active verity mapping <name>.
dump <hash_device>
Reports parameters of verity device from on-disk stored su-
perblock.
<options> can be [--hash-offset]
OPTIONS
--verbose, -v
Print more information on command execution.
--debug
Run in debug mode with full diagnostic logs. Debug output lines
are always prefixed by '#'.
--no-superblock
Create or use dm-verity without permanent on-disk superblock.
--format=number
Specifies the hash version type. Format type 0 is original
Chrome OS version. Format type 1 is current version.
--data-block-size=bytes
Used block size for the data device. (Note kernel supports only
page-size as maximum here.)
--hash-block-size=bytes
Used block size for the hash device. (Note kernel supports only
page-size as maximum here.)
--data-blocks=blocks
Size of data device used in verification. If not specified, the
whole device is used.
--hash-offset=bytes
Offset of hash area/superblock on hash_device. Value must be
aligned to disk sector offset.
--salt=hex string
Salt used for format or verification. Format is a hexadecimal
string.
--uuid=UUID
Use the provided UUID for format command instead of generating
new one.
The UUID must be provided in standard UUID format, e.g.
12345678-1234-1234-1234-123456789abc.
--ignore-corruption , --restart-on-corruption , --panic-on-corruption
Defines what to do if data integrity problem is detected (data
corruption).
Without these options kernel fails the IO operation with I/O er-
ror. With --ignore-corruption option the corruption is only
logged. With --restart-on-corruption or --panic-on-corruption
the kernel is restarted (panicked) immediately. (You have to
provide way how to avoid restart loops.)
WARNING: Use these options only for very specific cases. These
options are available since Linux kernel version 4.1.
--ignore-zero-blocks
Instruct kernel to not verify blocks that are expected to con-
tain zeroes and always directly return zeroes instead.
WARNING: Use this option only in very specific cases. This op-
tion is available since Linux kernel version 4.5.
--check-at-most-once
Instruct kernel to verify blocks only the first time they are
read from the data device, rather than every time.
WARNING: It provides a reduced level of security because only
offline tampering of the data device's content will be detected,
not online tampering. This option is available since Linux ker-
nel version 4.17.
--hash=hash
Hash algorithm for dm-verity. For default see --help option.
--version
Show the program version.
--fec-device=fec_device
Use forward error correction (FEC) to recover from corruption if
hash verification fails. Use encoding data from the specified
device.
The fec device argument can be block device or file image. For
format, if fec device path doesn't exist, it will be created as
file.
Block sizes for data and hash devices must match. Also, if the
verity data_device is encrypted the fec_device should be too.
FEC calculation covers data, hash area, and optional foreign
metadata stored on the same device with the hash tree (addi-
tional space after hash area). Size of this optional additional
area protected by FEC is calculated from image sizes, so you
must be sure that you use the same images for activation.
If the hash device is in a separate image, metadata covers the
whole rest of the image after the hash area.
If hash and FEC device is in the image, metadata ends on the FEC
area offset.
--fec-offset=bytes
This is the offset, in bytes, from the start of the FEC device
to the beginning of the encoding data.
--fec-roots=num
Number of generator roots. This equals to the number of parity
bytes in the encoding data. In RS(M, N) encoding, the number of
roots is M-N. M is 255 and M-N is between 2 and 24 (including).
--root-hash-file=FILE
Path to file with stored root hash in hex-encoded text.
--root-hash-signature=FILE
Path to roothash signature file used to verify the root hash (in
kernel). This feature requires Linux kernel version 5.4 or more
recent.
--deferred
Defers device removal in close command until the last user
closes it.
--cancel-deferred
Removes a previously configured deferred device removal in close
command.
RETURN CODES
Veritysetup returns 0 on success and a non-zero value on error.
Error codes are:
1 wrong parameters
2 no permission
3 out of memory
4 wrong device specified
5 device already exists or device is busy.
EXAMPLES
veritysetup --data-blocks=256 format <data_device> <hash_device>
Calculates and stores verification data on hash_device for the first
256 blocks (of block-size). If hash_device does not exist, it is cre-
ated (as file image).
veritysetup format --root-hash-file <path> <data_device> <hash_device>
Calculates and stores verification data on hash_device for the whole
data_device, and store the root hash as hex-encoded text in <path>.
veritysetup --data-blocks=256 --hash-offset=1052672 format <device>
<device>
Verification data (hashes) is stored on the same device as data (start-
ing at hash-offset). Hash-offset must be greater than number of blocks
in data-area.
veritysetup --data-blocks=256 --hash-offset=1052672 create test-device
<device> <device> <root_hash>
Activates the verity device named test-device. Options --data-blocks
and --hash-offset are the same as in the format command. The
<root_hash> was calculated in format command.
veritysetup --data-blocks=256 --hash-offset=1052672 verify <data_de-
vice> <hash_device> <root_hash>
Verifies device without activation (in userspace).
veritysetup --data-blocks=256 --hash-offset=1052672 --root-hash-file
<path> verify <data_device> <hash_device>
Verifies device without activation (in userspace). Root hash passed via
a file rather than inline.
veritysetup --fec-device=<fec_device> --fec-roots=10 format <data_de-
vice> <hash_device>
Calculates and stores verification and encoding data for data_device.
REPORTING BUGS
Report bugs, including ones in the documentation, on the cryptsetup
mailing list at <dm-crypt@saout.de> or in the 'Issues' section on LUKS
website. Please attach the output of the failed command with the --de-
bug option added.
AUTHORS
The first implementation of veritysetup was written by Chrome OS au-
thors.
This version is based on verification code written by Mikulas Patocka
<mpatocka@redhat.com> and rewritten for libcryptsetup by Milan Broz
<gmazyland@gmail.com>.
COPYRIGHT
Copyright (C) 2012-2021 Red Hat, Inc.
Copyright (C) 2012-2021 Milan Broz
This is free software; see the source for copying conditions. There is
NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE.
SEE ALSO
The project website at https://gitlab.com/cryptsetup/cryptsetup
The verity on-disk format specification available at https://git-
lab.com/cryptsetup/cryptsetup/wikis/DMVerity
veritysetup January 2021 VERITYSETUP(8)
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