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CONFIG_CRYPTO_SHA256 denotes the generic C implementation of the SHA-256 shash algorithm, which is selected as the default crypto shash provider for fsverity. However, fsverity has no strict link time dependency, and the same shash could be exposed by an optimized implementation, and arm64 has a number of those (scalar, NEON-based and one based on special crypto instructions). In such cases, it makes little sense to require that the generic C implementation is incorporated as well, given that it will never be called. To address this, relax the 'select' clause to 'imply' so that the generic driver can be omitted from the build if desired. Acked-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
59 lines
2.4 KiB
Text
59 lines
2.4 KiB
Text
# 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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