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_BUILTIN_SIGNATURES 38 bool "FS Verity builtin signature support" 39 depends on FS_VERITY 40 select SYSTEM_DATA_VERIFICATION 41 help 42 Support verifying signatures of verity files against the X.509 43 certificates that have been loaded into the ".fs-verity" 44 kernel keyring. 45 46 This is meant as a relatively simple mechanism that can be 47 used to provide an authenticity guarantee for verity files, as 48 an alternative to IMA appraisal. Userspace programs still 49 need to check that the verity bit is set in order to get an 50 authenticity guarantee. 51 52 If unsure, say N. 53