1# SPDX-License-Identifier: GPL-2.0
2
3config FS_VERITY
4	bool "FS Verity (read-only file-based authenticity protection)"
5	select CRYPTO
6	select CRYPTO_HASH_INFO
7	# SHA-256 is implied as it's intended to be the default hash algorithm.
8	# To avoid bloat, other wanted algorithms must be selected explicitly.
9	# Note that CRYPTO_SHA256 denotes the generic C implementation, but
10	# some architectures provided optimized implementations of the same
11	# algorithm that may be used instead. In this case, CRYPTO_SHA256 may
12	# be omitted even if SHA-256 is being used.
13	imply CRYPTO_SHA256
14	help
15	  This option enables fs-verity.  fs-verity is the dm-verity
16	  mechanism implemented at the file level.  On supported
17	  filesystems (currently ext4, f2fs, and btrfs), userspace can
18	  use an ioctl to enable verity for a file, which causes the
19	  filesystem to build a Merkle tree for the file.  The filesystem
20	  will then transparently verify any data read from the file
21	  against the Merkle tree.  The file is also made read-only.
22
23	  This serves as an integrity check, but the availability of the
24	  Merkle tree root hash also allows efficiently supporting
25	  various use cases where normally the whole file would need to
26	  be hashed at once, such as: (a) auditing (logging the file's
27	  hash), or (b) authenticity verification (comparing the hash
28	  against a known good value, e.g. from a digital signature).
29
30	  fs-verity is especially useful on large files where not all
31	  the contents may actually be needed.  Also, fs-verity verifies
32	  data each time it is paged back in, which provides better
33	  protection against malicious disks vs. an ahead-of-time hash.
34
35	  If unsure, say N.
36
37config FS_VERITY_DEBUG
38	bool "FS Verity debugging"
39	depends on FS_VERITY
40	help
41	  Enable debugging messages related to fs-verity by default.
42
43	  Say N unless you are an fs-verity developer.
44
45config FS_VERITY_BUILTIN_SIGNATURES
46	bool "FS Verity builtin signature support"
47	depends on FS_VERITY
48	select SYSTEM_DATA_VERIFICATION
49	help
50	  Support verifying signatures of verity files against the X.509
51	  certificates that have been loaded into the ".fs-verity"
52	  kernel keyring.
53
54	  This is meant as a relatively simple mechanism that can be
55	  used to provide an authenticity guarantee for verity files, as
56	  an alternative to IMA appraisal.  Userspace programs still
57	  need to check that the verity bit is set in order to get an
58	  authenticity guarantee.
59
60	  If unsure, say N.
61