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linux/fs/verity/Kconfig

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fs-verity: add Kconfig and the helper functions for hashing Add the beginnings of the fs/verity/ support layer, including the Kconfig option and various helper functions for hashing. To start, only SHA-256 is supported, but other hash algorithms can easily be added. Reviewed-by: Theodore Ts'o <tytso@mit.edu> Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org> Signed-off-by: Eric Biggers <ebiggers@google.com>
2019-07-22 16:26:21 +00:00
# SPDX-License-Identifier: GPL-2.0
config FS_VERITY
bool "FS Verity (read-only file-based authenticity protection)"
select CRYPTO
fs-verity: define a function to return the integrity protected file digest Define a function named fsverity_get_digest() to return the verity file digest and the associated hash algorithm (enum hash_algo). This assumes that before calling fsverity_get_digest() the file must have been opened, which is even true for the IMA measure/appraise on file open policy rule use case (func=FILE_CHECK). do_open() calls vfs_open() immediately prior to ima_file_check(). Acked-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
2021-11-23 18:37:52 +00:00
select CRYPTO_HASH_INFO
fsverity: relax build time dependency on CRYPTO_SHA256 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>
2021-04-21 07:55:11 +00:00
# SHA-256 is implied as it's intended to be the default hash algorithm.
fs-verity: add Kconfig and the helper functions for hashing Add the beginnings of the fs/verity/ support layer, including the Kconfig option and various helper functions for hashing. To start, only SHA-256 is supported, but other hash algorithms can easily be added. Reviewed-by: Theodore Ts'o <tytso@mit.edu> Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org> Signed-off-by: Eric Biggers <ebiggers@google.com>
2019-07-22 16:26:21 +00:00
# To avoid bloat, other wanted algorithms must be selected explicitly.
fsverity: relax build time dependency on CRYPTO_SHA256 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>
2021-04-21 07:55:11 +00:00
# Note that CRYPTO_SHA256 denotes the generic C implementation, but
# some architectures provided optimized implementations of the same
# algorithm that may be used instead. In this case, CRYPTO_SHA256 may
# be omitted even if SHA-256 is being used.
imply CRYPTO_SHA256
fs-verity: add Kconfig and the helper functions for hashing Add the beginnings of the fs/verity/ support layer, including the Kconfig option and various helper functions for hashing. To start, only SHA-256 is supported, but other hash algorithms can easily be added. Reviewed-by: Theodore Ts'o <tytso@mit.edu> Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org> Signed-off-by: Eric Biggers <ebiggers@google.com>
2019-07-22 16:26:21 +00:00
help
This option enables fs-verity. fs-verity is the dm-verity
mechanism implemented at the file level. On supported
fs-verity: mention btrfs support btrfs supports fs-verity since Linux v5.15. Document this. Signed-off-by: Eric Biggers <ebiggers@google.com> Acked-by: David Sterba <dsterba@suse.com> Link: https://lore.kernel.org/r/20220610000616.18225-1-ebiggers@kernel.org
2022-06-10 00:06:16 +00:00
filesystems (currently ext4, f2fs, and btrfs), userspace can
use an ioctl to enable verity for a file, which causes the
filesystem to build a Merkle tree for the file. The filesystem
will then transparently verify any data read from the file
against the Merkle tree. The file is also made read-only.
fs-verity: add Kconfig and the helper functions for hashing Add the beginnings of the fs/verity/ support layer, including the Kconfig option and various helper functions for hashing. To start, only SHA-256 is supported, but other hash algorithms can easily be added. Reviewed-by: Theodore Ts'o <tytso@mit.edu> Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org> Signed-off-by: Eric Biggers <ebiggers@google.com>
2019-07-22 16:26:21 +00:00
This serves as an integrity check, but the availability of the
Merkle tree root hash also allows efficiently supporting
various use cases where normally the whole file would need to
be hashed at once, such as: (a) auditing (logging the file's
hash), or (b) authenticity verification (comparing the hash
against a known good value, e.g. from a digital signature).
fs-verity is especially useful on large files where not all
the contents may actually be needed. Also, fs-verity verifies
data each time it is paged back in, which provides better
protection against malicious disks vs. an ahead-of-time hash.
If unsure, say N.
config FS_VERITY_DEBUG
bool "FS Verity debugging"
depends on FS_VERITY
help
Enable debugging messages related to fs-verity by default.
Say N unless you are an fs-verity developer.
fs-verity: support builtin file signatures To meet some users' needs, add optional support for having fs-verity handle a portion of the authentication policy in the kernel. An ".fs-verity" keyring is created to which X.509 certificates can be added; then a sysctl 'fs.verity.require_signatures' can be set to cause the kernel to enforce that all fs-verity files contain a signature of their file measurement by a key in this keyring. See the "Built-in signature verification" section of Documentation/filesystems/fsverity.rst for the full documentation. Reviewed-by: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Eric Biggers <ebiggers@google.com>
2019-07-22 16:26:23 +00:00
config FS_VERITY_BUILTIN_SIGNATURES
bool "FS Verity builtin signature support"
depends on FS_VERITY
select SYSTEM_DATA_VERIFICATION
help
Support verifying signatures of verity files against the X.509
certificates that have been loaded into the ".fs-verity"
kernel keyring.
This is meant as a relatively simple mechanism that can be
used to provide an authenticity guarantee for verity files, as
an alternative to IMA appraisal. Userspace programs still
need to check that the verity bit is set in order to get an
authenticity guarantee.
If unsure, say N.
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