1 # SPDX-License-Identifier: GPL-2.0
2 
3 config 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 
37 config FS_VERITY_BUILTIN_SIGNATURES
38 	bool "FS Verity builtin signature support"
39 	depends on FS_VERITY
40 	select SYSTEM_DATA_VERIFICATION
41 	help
42 	  This option adds support for in-kernel verification of
43 	  fs-verity builtin signatures.
44 
45 	  Please take great care before using this feature.  It is not
46 	  the only way to do signatures with fs-verity, and the
47 	  alternatives (such as userspace signature verification, and
48 	  IMA appraisal) can be much better.  For details about the
49 	  limitations of this feature, see
50 	  Documentation/filesystems/fsverity.rst.
51 
52 	  If unsure, say N.
53