1 # SPDX-License-Identifier: GPL-2.0 1 # SPDX-License-Identifier: GPL-2.0
2 2
3 config FS_VERITY 3 config FS_VERITY
4 bool "FS Verity (read-only file-based 4 bool "FS Verity (read-only file-based authenticity protection)"
5 select CRYPTO 5 select CRYPTO
6 select CRYPTO_HASH_INFO !! 6 # SHA-256 is selected as it's intended to be the default hash algorithm.
7 # SHA-256 is implied as it's intended <<
8 # To avoid bloat, other wanted algorit 7 # To avoid bloat, other wanted algorithms must be selected explicitly.
9 # Note that CRYPTO_SHA256 denotes the !! 8 select CRYPTO_SHA256
10 # some architectures provided optimize <<
11 # algorithm that may be used instead. <<
12 # be omitted even if SHA-256 is being <<
13 imply CRYPTO_SHA256 <<
14 help 9 help
15 This option enables fs-verity. fs-v 10 This option enables fs-verity. fs-verity is the dm-verity
16 mechanism implemented at the file le 11 mechanism implemented at the file level. On supported
17 filesystems (currently ext4, f2fs, a !! 12 filesystems (currently EXT4 and F2FS), userspace can use an
18 use an ioctl to enable verity for a !! 13 ioctl to enable verity for a file, which causes the filesystem
19 filesystem to build a Merkle tree fo !! 14 to build a Merkle tree for the file. The filesystem will then
20 will then transparently verify any d !! 15 transparently verify any data read from the file against the
21 against the Merkle tree. The file i !! 16 Merkle tree. The file is also made read-only.
22 17
23 This serves as an integrity check, b 18 This serves as an integrity check, but the availability of the
24 Merkle tree root hash also allows ef 19 Merkle tree root hash also allows efficiently supporting
25 various use cases where normally the 20 various use cases where normally the whole file would need to
26 be hashed at once, such as: (a) audi 21 be hashed at once, such as: (a) auditing (logging the file's
27 hash), or (b) authenticity verificat 22 hash), or (b) authenticity verification (comparing the hash
28 against a known good value, e.g. fro 23 against a known good value, e.g. from a digital signature).
29 24
30 fs-verity is especially useful on la 25 fs-verity is especially useful on large files where not all
31 the contents may actually be needed. 26 the contents may actually be needed. Also, fs-verity verifies
32 data each time it is paged back in, 27 data each time it is paged back in, which provides better
33 protection against malicious disks v 28 protection against malicious disks vs. an ahead-of-time hash.
34 29
35 If unsure, say N. 30 If unsure, say N.
36 31
>> 32 config FS_VERITY_DEBUG
>> 33 bool "FS Verity debugging"
>> 34 depends on FS_VERITY
>> 35 help
>> 36 Enable debugging messages related to fs-verity by default.
>> 37
>> 38 Say N unless you are an fs-verity developer.
>> 39
37 config FS_VERITY_BUILTIN_SIGNATURES 40 config FS_VERITY_BUILTIN_SIGNATURES
38 bool "FS Verity builtin signature supp 41 bool "FS Verity builtin signature support"
39 depends on FS_VERITY 42 depends on FS_VERITY
40 select SYSTEM_DATA_VERIFICATION 43 select SYSTEM_DATA_VERIFICATION
41 help 44 help
42 This option adds support for in-kern !! 45 Support verifying signatures of verity files against the X.509
43 fs-verity builtin signatures. !! 46 certificates that have been loaded into the ".fs-verity"
>> 47 kernel keyring.
44 48
45 Please take great care before using !! 49 This is meant as a relatively simple mechanism that can be
46 the only way to do signatures with f !! 50 used to provide an authenticity guarantee for verity files, as
47 alternatives (such as userspace sign !! 51 an alternative to IMA appraisal. Userspace programs still
48 IMA appraisal) can be much better. !! 52 need to check that the verity bit is set in order to get an
49 limitations of this feature, see !! 53 authenticity guarantee.
50 Documentation/filesystems/fsverity.r <<
51 54
52 If unsure, say N. 55 If unsure, say N.
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