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Add support for FS_VERITY_METADATA_TYPE_SIGNATURE to
FS_IOC_READ_VERITY_METADATA. This allows a userspace server program to
retrieve the built-in signature (if present) of a verity file for
serving to a client which implements fs-verity compatible verification.
See the patch which introduced FS_IOC_READ_VERITY_METADATA for more
details.
The ability for userspace to read the built-in signatures is also useful
because it allows a system that is using the in-kernel signature
verification to migrate to userspace signature verification.
This has been tested using a new xfstest which calls this ioctl via a
new subcommand for the 'fsverity' program from fsverity-utils.
Link: https://lore.kernel.org/r/20210115181819.34732-7-ebiggers@kernel.org
Reviewed-by: Victor Hsieh <victorhsieh@google.com>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Add support for FS_VERITY_METADATA_TYPE_DESCRIPTOR to
FS_IOC_READ_VERITY_METADATA. This allows a userspace server program to
retrieve the fs-verity descriptor of a file for serving to a client
which implements fs-verity compatible verification. See the patch which
introduced FS_IOC_READ_VERITY_METADATA for more details.
"fs-verity descriptor" here means only the part that userspace cares
about because it is hashed to produce the file digest. It doesn't
include the signature which ext4 and f2fs append to the
fsverity_descriptor struct when storing it on-disk, since that way of
storing the signature is an implementation detail. The next patch adds
a separate metadata_type value for retrieving the signature separately.
This has been tested using a new xfstest which calls this ioctl via a
new subcommand for the 'fsverity' program from fsverity-utils.
Link: https://lore.kernel.org/r/20210115181819.34732-6-ebiggers@kernel.org
Reviewed-by: Victor Hsieh <victorhsieh@google.com>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Add support for FS_VERITY_METADATA_TYPE_MERKLE_TREE to
FS_IOC_READ_VERITY_METADATA. This allows a userspace server program to
retrieve the Merkle tree of a verity file for serving to a client which
implements fs-verity compatible verification. See the patch which
introduced FS_IOC_READ_VERITY_METADATA for more details.
This has been tested using a new xfstest which calls this ioctl via a
new subcommand for the 'fsverity' program from fsverity-utils.
Link: https://lore.kernel.org/r/20210115181819.34732-5-ebiggers@kernel.org
Reviewed-by: Victor Hsieh <victorhsieh@google.com>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Add an ioctl FS_IOC_READ_VERITY_METADATA which will allow reading verity
metadata from a file that has fs-verity enabled, including:
- The Merkle tree
- The fsverity_descriptor (not including the signature if present)
- The built-in signature, if present
This ioctl has similar semantics to pread(). It is passed the type of
metadata to read (one of the above three), and a buffer, offset, and
size. It returns the number of bytes read or an error.
Separate patches will add support for each of the above metadata types.
This patch just adds the ioctl itself.
This ioctl doesn't make any assumption about where the metadata is
stored on-disk. It does assume the metadata is in a stable format, but
that's basically already the case:
- The Merkle tree and fsverity_descriptor are defined by how fs-verity
file digests are computed; see the "File digest computation" section
of Documentation/filesystems/fsverity.rst. Technically, the way in
which the levels of the tree are ordered relative to each other wasn't
previously specified, but it's logical to put the root level first.
- The built-in signature is the value passed to FS_IOC_ENABLE_VERITY.
This ioctl is useful because it allows writing a server program that
takes a verity file and serves it to a client program, such that the
client can do its own fs-verity compatible verification of the file.
This only makes sense if the client doesn't trust the server and if the
server needs to provide the storage for the client.
More concretely, there is interest in using this ability in Android to
export APK files (which are protected by fs-verity) to "protected VMs".
This would use Protected KVM (https://lwn.net/Articles/836693), which
provides an isolated execution environment without having to trust the
traditional "host". A "guest" VM can boot from a signed image and
perform specific tasks in a minimum trusted environment using files that
have fs-verity enabled on the host, without trusting the host or
requiring that the guest has its own trusted storage.
Technically, it would be possible to duplicate the metadata and store it
in separate files for serving. However, that would be less efficient
and would require extra care in userspace to maintain file consistency.
In addition to the above, the ability to read the built-in signatures is
useful because it allows a system that is using the in-kernel signature
verification to migrate to userspace signature verification.
Link: https://lore.kernel.org/r/20210115181819.34732-4-ebiggers@kernel.org
Reviewed-by: Victor Hsieh <victorhsieh@google.com>
Acked-by: Jaegeuk Kim <jaegeuk@kernel.org>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Although it isn't used directly by the ioctls,
"struct fsverity_descriptor" is required by userspace programs that need
to compute fs-verity file digests in a standalone way. Therefore
it's also needed to sign files in a standalone way.
Similarly, "struct fsverity_formatted_digest" (previously called
"struct fsverity_signed_digest" which was misleading) is also needed to
sign files if the built-in signature verification is being used.
Therefore, move these structs to the UAPI header.
While doing this, try to make it clear that the signature-related fields
in fsverity_descriptor aren't used in the file digest computation.
Acked-by: Luca Boccassi <luca.boccassi@microsoft.com>
Link: https://lore.kernel.org/r/20201113211918.71883-5-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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I originally chose the name "file measurement" to refer to the fs-verity
file digest to avoid confusion with traditional full-file digests or
with the bare root hash of the Merkle tree.
But the name "file measurement" hasn't caught on, and usually people are
calling it something else, usually the "file digest". E.g. see
"struct fsverity_digest" and "struct fsverity_formatted_digest", the
libfsverity_compute_digest() and libfsverity_sign_digest() functions in
libfsverity, and the "fsverity digest" command.
Having multiple names for the same thing is always confusing.
So to hopefully avoid confusion in the future, rename
"fs-verity file measurement" to "fs-verity file digest".
This leaves FS_IOC_MEASURE_VERITY as the only reference to "measure" in
the kernel, which makes some amount of sense since the ioctl is actively
"measuring" the file.
I'll be renaming this in fsverity-utils too (though similarly the
'fsverity measure' command, which is a wrapper for
FS_IOC_MEASURE_VERITY, will stay).
Acked-by: Luca Boccassi <luca.boccassi@microsoft.com>
Link: https://lore.kernel.org/r/20201113211918.71883-4-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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The name "struct fsverity_signed_digest" is causing confusion because it
isn't actually a signed digest, but rather it's the way that the digest
is formatted in order to be signed. Rename it to
"struct fsverity_formatted_digest" to prevent this confusion.
Also update the struct's comment to clarify that it's specific to the
built-in signature verification support and isn't a requirement for all
fs-verity users.
I'll be renaming this struct in fsverity-utils too.
Acked-by: Luca Boccassi <luca.boccassi@microsoft.com>
Link: https://lore.kernel.org/r/20201113211918.71883-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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The :c:type:`foo` only works properly with structs before
Sphinx 3.x.
On Sphinx 3.x, structs should now be declared using the
.. c:struct, and referenced via :c:struct tag.
As we now have the automarkup.py macro, that automatically
convert:
struct foo
into cross-references, let's get rid of that, solving
several warnings when building docs with Sphinx 3.x.
Reviewed-by: André Almeida <andrealmeid@collabora.com> # blk-mq.rst
Reviewed-by: Takashi Iwai <tiwai@suse.de> # sound
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
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Drop the doubled word "the".
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Theodore Y. Ts'o <tytso@mit.edu>
Cc: linux-fscrypt@vger.kernel.org
Link: https://lore.kernel.org/r/20200703214325.31036-6-rdunlap@infradead.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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Document that the statx() system call can now be used to check whether a
file is a verity file.
Signed-off-by: Eric Biggers <ebiggers@google.com>
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I had meant to replace these TODOs with the actual version when applying
the patches, but forgot to do so. Do it now.
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Add a documentation file for fs-verity, covering:
- Introduction
- Use cases
- User API
- FS_IOC_ENABLE_VERITY
- FS_IOC_MEASURE_VERITY
- FS_IOC_GETFLAGS
- Accessing verity files
- File measurement computation
- Merkle tree
- fs-verity descriptor
- Built-in signature verification
- Filesystem support
- ext4
- f2fs
- Implementation details
- Verifying data
- Pagecache
- Block device based filesystems
- Userspace utility
- Tests
- FAQ
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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Eric Biggers
Mauro Carvalho Chehab
Randy Dunlap