# SPDX-License-Identifier: GPL-2.0
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config FS_VERITY
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bool "FS Verity (read-only file-based authenticity protection)"
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select CRYPTO
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# SHA-256 is implied as it's intended to be the default hash algorithm.
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# To avoid bloat, other wanted algorithms must be selected explicitly.
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# Note that CRYPTO_SHA256 denotes the generic C implementation, but
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# some architectures provided optimized implementations of the same
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# algorithm that may be used instead. In this case, CRYPTO_SHA256 may
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# be omitted even if SHA-256 is being used.
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imply CRYPTO_SHA256
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help
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This option enables fs-verity. fs-verity is the dm-verity
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mechanism implemented at the file level. On supported
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filesystems (currently EXT4 and F2FS), userspace can use an
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ioctl to enable verity for a file, which causes the filesystem
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to build a Merkle tree for the file. The filesystem will then
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transparently verify any data read from the file against the
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Merkle tree. The file is also made read-only.
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This serves as an integrity check, but the availability of the
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Merkle tree root hash also allows efficiently supporting
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various use cases where normally the whole file would need to
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be hashed at once, such as: (a) auditing (logging the file's
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hash), or (b) authenticity verification (comparing the hash
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against a known good value, e.g. from a digital signature).
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fs-verity is especially useful on large files where not all
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the contents may actually be needed. Also, fs-verity verifies
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data each time it is paged back in, which provides better
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protection against malicious disks vs. an ahead-of-time hash.
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If unsure, say N.
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config FS_VERITY_DEBUG
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bool "FS Verity debugging"
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depends on FS_VERITY
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help
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Enable debugging messages related to fs-verity by default.
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Say N unless you are an fs-verity developer.
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config FS_VERITY_BUILTIN_SIGNATURES
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bool "FS Verity builtin signature support"
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depends on FS_VERITY
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select SYSTEM_DATA_VERIFICATION
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help
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Support verifying signatures of verity files against the X.509
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certificates that have been loaded into the ".fs-verity"
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kernel keyring.
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This is meant as a relatively simple mechanism that can be
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used to provide an authenticity guarantee for verity files, as
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an alternative to IMA appraisal. Userspace programs still
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need to check that the verity bit is set in order to get an
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authenticity guarantee.
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If unsure, say N.
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