path: root/man/veritysetup.8

.TH VERITYSETUP "8" "January 2021" "veritysetup" "Maintenance Commands"
.SH NAME
veritysetup - manage dm-verity (block level verification) volumes
.SH SYNOPSIS
.B veritysetup <options> <action> <action args>
.SH DESCRIPTION
.PP
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.

Veritysetup supports these operations:
.PP
\fIformat\fR <data_device> <hash_device>
.IP
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.

\fB<options>\fR can be [\-\-hash, \-\-no-superblock, \-\-format,
\-\-data-block-size, \-\-hash-block-size, \-\-data-blocks, \-\-hash-offset,
\-\-salt, \-\-uuid]
.PP
\fIopen\fR <data_device> <name> <hash_device> <root_hash>
.br
\fIcreate\fR <name> <data_device> <hash_device> <root_hash>  (\fBOBSOLETE syntax\fR)
.IP
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.

\fB<options>\fR 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]

If option \-\-no-superblock is used, you have to use as the same options
as in initial format operation.
.PP
\fIverify\fR <data_device> <hash_device> <root_hash>
.IP
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.

\fB<options>\fR can be [\-\-hash-offset, \-\-no-superblock]

If option \-\-no-superblock is used, you have to use as the same options
as in initial format operation.
.PP
\fIclose\fR <name>
.IP
Removes existing mapping <name>.

For backward compatibility there is \fBremove\fR command alias
for \fBclose\fR command.
.PP
\fIstatus\fR <name>
.IP
Reports status for the active verity mapping <name>.
.PP
\fIdump\fR <hash_device>
.IP
Reports parameters of verity device from on-disk stored superblock.

\fB<options>\fR can be [\-\-no-superblock]
.SH OPTIONS
.TP
.B "\-\-verbose, \-v"
Print more information on command execution.
.TP
.B "\-\-debug"
Run in debug mode with full diagnostic logs. Debug output
lines are always prefixed by '#'.
.TP
.B "\-\-no-superblock"
Create or use dm-verity without permanent on-disk superblock.
.TP
.B "\-\-format=number"
Specifies the hash version type.
Format type 0 is original Chrome OS version. Format type 1 is current version.
.TP
.B "\-\-data-block-size=bytes"
Used block size for the data device.
(Note kernel supports only page-size as maximum here.)
.TP
.B "\-\-hash-block-size=bytes"
Used block size for the hash device.
(Note kernel supports only page-size as maximum here.)
.TP
.B "\-\-data-blocks=blocks"
Size of data device used in verification.
If not specified, the whole device is used.
.TP
.B "\-\-hash-offset=bytes"
Offset of hash area/superblock on hash_device.
Value must be aligned to disk sector offset.
.TP
.B "\-\-salt=hex string"
Salt used for format or verification.
Format is a hexadecimal string.
.TP
.B "\-\-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.
.TP
.B "\-\-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.)

\fBWARNING:\fR Use these options only for very specific cases.
These options are available since Linux kernel version 4.1.
.TP
.B "\-\-ignore-zero-blocks"
Instruct kernel to not verify blocks that are expected to contain zeroes
and always directly return zeroes instead.

\fBWARNING:\fR Use this option only in very specific cases.
This option is available since Linux kernel version 4.5.
.TP
.B "\-\-check-at-most-once"
Instruct kernel to verify blocks only the first time they are read
from the data device, rather than every time.

\fBWARNING:\fR 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.
.TP
.B "\-\-hash=hash"
Hash algorithm for dm-verity. For default see \-\-help option.
.TP
.B "\-\-version"
Show the program version.
.TP
.B "\-\-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.

.TP
.B "\-\-fec-offset=bytes"
This is the offset, in bytes, from the start of the FEC device to the beginning of the encoding data.
.TP
.B "\-\-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).
.TP
.B "\-\-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.
.TP
.SH 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.

.SH EXAMPLES
.B "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).

.B "veritysetup format <data_device> <hash_device>"

Calculates and stores verification data on hash_device for the whole data_device.

.B "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.

.B "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.

.B "veritysetup \-\-data-blocks=256 \-\-hash-offset=1052672 verify <data_device> <hash_device> <root_hash>"

Verifies device without activation (in userspace).

.B "veritysetup \-\-fec-device=<fec_device> \-\-fec-roots=10 format <data_device> <hash_device>"

Calculates and stores verification and encoding data for data_device.

.SH 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
\-\-debug option added.
.SH AUTHORS
The first implementation of veritysetup was written by Chrome OS authors.

This version is based on verification code written by Mikulas Patocka <mpatocka@redhat.com>
and rewritten for libcryptsetup by Milan Broz <gmazyland@gmail.com>.
.SH COPYRIGHT
Copyright \(co 2012-2021 Red Hat, Inc.
.br
Copyright \(co 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.
.SH SEE ALSO
The project website at \fBhttps://gitlab.com/cryptsetup/cryptsetup\fR

The verity on-disk format specification available at
\fBhttps://gitlab.com/cryptsetup/cryptsetup/wikis/DMVerity\fR