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Currently, all filesystems that support fsverity (ext4, f2fs, and btrfs)
cache the Merkle tree in the pagecache at a 64K aligned offset after the
end of the file data. This offset needs to be a multiple of the page
size, which is guaranteed only when the page size is 64K or smaller.
64K was chosen to be the "largest reasonable page size". But it isn't
the largest *possible* page size: the hexagon and powerpc ports of Linux
support 256K pages, though that configuration is rarely used.
For now, just disable support for FS_VERITY in these odd configurations
to ensure it isn't used in cases where it would have incorrect behavior.
Fixes: 671e67b47e9f ("fs-verity: add Kconfig and the helper functions for hashing")
Reported-by: Christoph Hellwig <hch@lst.de>
Closes: https://lore.kernel.org/r/20260119063349.GA643@lst.de
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Link: https://lore.kernel.org/r/20260221204525.30426-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
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fsverity supports two hash algorithms: SHA-256 and SHA-512. Since both
of these have a library API now, just use the library API instead of
crypto_shash. Even with multiple algorithms, the library-based code
still ends up being quite a bit simpler, due to how clumsy the
old-school crypto API is. The library-based code is also more
efficient, since it avoids overheads such as indirect calls.
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250630172224.46909-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
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This reverts commit e3a606f2c544b231f6079c8c5fea451e772e1139 because it
allows people to create broken configurations that enable FS_VERITY but
not SHA-256 support.
The commit did allow people to disable the generic SHA-256
implementation when it's not needed. But that at best allowed saving a
bit of code. In the real world people are unlikely to intentionally and
correctly make such a tweak anyway, as they tend to just be confused by
what all the different crypto kconfig options mean.
Of course we really need the crypto API to enable the correct
implementations automatically, but that's for a later fix.
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Link: https://lore.kernel.org/r/20250217185105.26751-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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fsverity builtin signatures (CONFIG_FS_VERITY_BUILTIN_SIGNATURES) aren't
the only way to do signatures with fsverity, and they have some major
limitations. Yet, more users have tried to use them, e.g. recently by
https://github.com/ostreedev/ostree/pull/2640. In most cases this seems
to be because users aren't sufficiently familiar with the limitations of
this feature and what the alternatives are.
Therefore, make some updates to the documentation to try to clarify the
properties of this feature and nudge users in the right direction.
Note that the Integrity Policy Enforcement (IPE) LSM, which is not yet
upstream, is planned to use the builtin signatures. (This differs from
IMA, which uses its own signature mechanism.) For that reason, my
earlier patch "fsverity: mark builtin signatures as deprecated"
(https://lore.kernel.org/r/20221208033548.122704-1-ebiggers@kernel.org),
which marked builtin signatures as "deprecated", was controversial.
This patch therefore stops short of marking the feature as deprecated.
I've also revised the language to focus on better explaining the feature
and what its alternatives are.
Link: https://lore.kernel.org/r/20230620041937.5809-1-ebiggers@kernel.org
Reviewed-by: Colin Walters <walters@verbum.org>
Reviewed-by: Luca Boccassi <bluca@debian.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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I've gotten very little use out of these debug messages, and I'm not
aware of anyone else having used them.
Indeed, sprinkling pr_debug around is not really a best practice these
days, especially for filesystem code. Tracepoints are used instead.
Let's just remove these and start from a clean slate.
This change does not affect info, warning, and error messages.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20221215060420.60692-1-ebiggers@kernel.org
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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
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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>
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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>
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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>
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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>
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