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# SPDX-License-Identifier: GPL-2.0
config FS_VERITY
bool "FS Verity (read-only file-based authenticity protection)"
select CRYPTO
# SHA-256 is selected as it's intended to be the default hash algorithm.
# To avoid bloat, other wanted algorithms must be selected explicitly.
select CRYPTO_SHA256
help
This option enables fs-verity. fs-verity is the dm-verity
mechanism implemented at the file level. On supported
filesystems (currently EXT4 and F2FS), userspace can use an
ioctl to enable verity for a file, which causes the filesystem
to build a Merkle tree for the file. The filesystem will then
transparently verify any data read from the file against the
Merkle tree. The file is also made read-only.
This serves as an integrity check, but the availability of the
Merkle tree root hash also allows efficiently supporting
various use cases where normally the whole file would need to
be hashed at once, such as: (a) auditing (logging the file's
hash), or (b) authenticity verification (comparing the hash
against a known good value, e.g. from a digital signature).
fs-verity is especially useful on large files where not all
the contents may actually be needed. Also, fs-verity verifies
data each time it is paged back in, which provides better
protection against malicious disks vs. an ahead-of-time hash.
If unsure, say N.
config FS_VERITY_DEBUG
bool "FS Verity debugging"
depends on FS_VERITY
help
Enable debugging messages related to fs-verity by default.
Say N unless you are an fs-verity developer.
config FS_VERITY_BUILTIN_SIGNATURES
bool "FS Verity builtin signature support"
depends on FS_VERITY
select SYSTEM_DATA_VERIFICATION
help
Support verifying signatures of verity files against the X.509
certificates that have been loaded into the ".fs-verity"
kernel keyring.
This is meant as a relatively simple mechanism that can be
used to provide an authenticity guarantee for verity files, as
an alternative to IMA appraisal. Userspace programs still
need to check that the verity bit is set in order to get an
authenticity guarantee.
If unsure, say N.
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