fs/verity/Kconfig

# SPDX-License-Identifier: GPL-2.0

config FS_VERITY
	bool "FS Verity (read-only file-based authenticity protection)"
	select CRYPTO
	select CRYPTO_HASH_INFO
	# SHA-256 is implied as it's intended to be the default hash algorithm.
	# To avoid bloat, other wanted algorithms must be selected explicitly.
	# Note that CRYPTO_SHA256 denotes the generic C implementation, but
	# some architectures provided optimized implementations of the same
	# algorithm that may be used instead. In this case, CRYPTO_SHA256 may
	# be omitted even if SHA-256 is being used.
	imply 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, f2fs, and btrfs), 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_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.