cryptsetup/man/veritysetup.8.adoc

= veritysetup(8)
:doctype: manpage
:manmanual: Maintenance Commands
:mansource: veritysetup {release-version}
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== NAME

veritysetup - manage dm-verity (block level verification) volumes

== SYNOPSIS

*veritysetup <action> [<options>] <action args>*

== DESCRIPTION

Veritysetup is used to configure dm-verity managed device-mapper
mappings.

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.

== BASIC ACTIONS

Veritysetup supports these operations:

=== FORMAT
*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 verification or
activation. Root hash must be trusted.

The data or hash device argument can be block device or file image. 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
*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 syntax*)

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-corruption
or --restart-on-corruption, --panic-on-corruption, --ignore-zero-blocks,
--check-at-most-once, --root-hash-signature, --root-hash-file, --use-tasklets,
--shared].

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
*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
*close <name>* +
remove <name> (*OBSOLETE syntax*)

Removes existing mapping <name>.

*<options>* can be [--deferred] or [--cancel-deferred].

=== STATUS
*status <name>*

Reports status for the active verity mapping <name>.

=== DUMP
*dump <hash_device>*

Reports parameters of verity device from on-disk stored superblock.

*<options>* can be [--hash-offset].

== OPTIONS
*--batch-mode, -q*::
Do not ask for confirmation.

*--cancel-deferred*::
Removes a previously configured deferred device removal in *close*
command.

*--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 kernel version 4.17.

*--data-blocks=blocks*::
Size of data device used in verification. If not specified, the whole
device is used.

*--data-block-size=bytes*::
Used block size for the data device. (Note kernel supports only
page-size as maximum here.)

*--debug*::
Run in debug mode with full diagnostic logs. Debug output lines are
always prefixed by *#*.

*--deferred*::
Defers device removal in *close* command until the last user closes
it.

*--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 (additional 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).

*--format=number*::
Specifies the hash version type. Format type 0 is original Chrome OS
version. Format type 1 is current version.

*--hash=hash*::
Hash algorithm for dm-verity. For default see --help option.

*--hash-block-size=bytes*::
Used block size for the hash device. (Note kernel supports only
page-size as maximum here.)

*--hash-offset=bytes*::
Offset of hash area/superblock on hash_device. Value must be aligned
to disk sector offset.

*--help, -?*::
Show help text and default parameters.

*--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 error. 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 contain
zeroes and always directly return zeroes instead.
+
*WARNING:* Use this option only in very specific cases. This option is
available since Linux kernel version 4.5.

*--no-superblock*::
Create or use dm-verity without permanent on-disk superblock.

*--root-hash-file=FILE*::
Path to file with stored root hash in hex-encoded text.

*--root-hash-signature=FILE*::
Path to root hash signature file used to verify the root hash (in
kernel). This feature requires Linux kernel version 5.4 or more
recent.

*--salt=hex string*::
Salt used for format or verification. Format is a hexadecimal string.

*--shared*::
Allows data device to be used in shared mode. The data device is not checked
for exclusive access in-before the device activation and may be mapped in multiple
verity mappings.

*--usage*::
Show short option help.

*--use-tasklets*::
Try to use kernel tasklets in dm-verity driver for performance reasons.
This option is available since Linux kernel version 6.0.

*--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.

*--verbose, -v*::
Print more information on command execution.

*--version, -V*::
Show the program version.

== 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 created (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
(starting 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_device> <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_device> <hash_device>*

Calculates and stores verification and encoding data for data_device.

== DM-VERITY ON-DISK SPECIFICATION

The on-disk format specification is available at
https://gitlab.com/cryptsetup/cryptsetup/wikis/DMVerity[*DMVerity*] page.

== AUTHORS

The first implementation of veritysetup was written by Chrome OS
authors.

This version is based on verification code written by
mailto:mpatocka@redhat.com[Mikulas Patocka] and rewritten for libcryptsetup
by mailto:gmazyland@gmail.com[Milan Broz].

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