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author | Linus Torvalds <torvalds@linux-foundation.org> | 2022-08-02 15:24:36 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2022-08-02 15:24:36 -0700 |
commit | 569bede0cff5e98c0f862d486406b79dcada8eea (patch) | |
tree | 9acb37598e0bc339dc3746f03b82151bd977903a /Documentation | |
parent | 043402495deb5ccc3b3479dc69a03f990c41ea8d (diff) | |
parent | 8da572c52a9be6d006bae290339c629fc6501910 (diff) |
Merge tag 'fsverity-for-linus' of git://git.kernel.org/pub/scm/fs/fscrypt/fscrypt
Pull fsverity update from Eric Biggers:
"Just a small documentation update to mention the btrfs support"
* tag 'fsverity-for-linus' of git://git.kernel.org/pub/scm/fs/fscrypt/fscrypt:
fs-verity: mention btrfs support
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/filesystems/fsverity.rst | 53 |
1 files changed, 30 insertions, 23 deletions
diff --git a/Documentation/filesystems/fsverity.rst b/Documentation/filesystems/fsverity.rst index 756f2c215ba1..cb8e7573882a 100644 --- a/Documentation/filesystems/fsverity.rst +++ b/Documentation/filesystems/fsverity.rst @@ -11,9 +11,9 @@ Introduction fs-verity (``fs/verity/``) is a support layer that filesystems can hook into to support transparent integrity and authenticity protection -of read-only files. Currently, it is supported by the ext4 and f2fs -filesystems. Like fscrypt, not too much filesystem-specific code is -needed to support fs-verity. +of read-only files. Currently, it is supported by the ext4, f2fs, and +btrfs filesystems. Like fscrypt, not too much filesystem-specific +code is needed to support fs-verity. fs-verity is similar to `dm-verity <https://www.kernel.org/doc/Documentation/device-mapper/verity.txt>`_ @@ -473,9 +473,9 @@ files being swapped around. Filesystem support ================== -fs-verity is currently supported by the ext4 and f2fs filesystems. -The CONFIG_FS_VERITY kconfig option must be enabled to use fs-verity -on either filesystem. +fs-verity is supported by several filesystems, described below. The +CONFIG_FS_VERITY kconfig option must be enabled to use fs-verity on +any of these filesystems. ``include/linux/fsverity.h`` declares the interface between the ``fs/verity/`` support layer and filesystems. Briefly, filesystems @@ -544,6 +544,13 @@ Currently, f2fs verity only supports a Merkle tree block size of 4096. Also, f2fs doesn't support enabling verity on files that currently have atomic or volatile writes pending. +btrfs +----- + +btrfs supports fs-verity since Linux v5.15. Verity-enabled inodes are +marked with a RO_COMPAT inode flag, and the verity metadata is stored +in separate btree items. + Implementation details ====================== @@ -622,14 +629,14 @@ workqueue, and then the workqueue work does the decryption or verification. Finally, pages where no decryption or verity error occurred are marked Uptodate, and the pages are unlocked. -Files on ext4 and f2fs may contain holes. Normally, ``->readahead()`` -simply zeroes holes and sets the corresponding pages Uptodate; no bios -are issued. To prevent this case from bypassing fs-verity, these -filesystems use fsverity_verify_page() to verify hole pages. +On many filesystems, files can contain holes. Normally, +``->readahead()`` simply zeroes holes and sets the corresponding pages +Uptodate; no bios are issued. To prevent this case from bypassing +fs-verity, these filesystems use fsverity_verify_page() to verify hole +pages. -ext4 and f2fs disable direct I/O on verity files, since otherwise -direct I/O would bypass fs-verity. (They also do the same for -encrypted files.) +Filesystems also disable direct I/O on verity files, since otherwise +direct I/O would bypass fs-verity. Userspace utility ================= @@ -648,7 +655,7 @@ Tests To test fs-verity, use xfstests. For example, using `kvm-xfstests <https://github.com/tytso/xfstests-bld/blob/master/Documentation/kvm-quickstart.md>`_:: - kvm-xfstests -c ext4,f2fs -g verity + kvm-xfstests -c ext4,f2fs,btrfs -g verity FAQ === @@ -771,15 +778,15 @@ weren't already directly answered in other parts of this document. e.g. magically trigger construction of a Merkle tree. :Q: Does fs-verity support remote filesystems? -:A: Only ext4 and f2fs support is implemented currently, but in - principle any filesystem that can store per-file verity metadata - can support fs-verity, regardless of whether it's local or remote. - Some filesystems may have fewer options of where to store the - verity metadata; one possibility is to store it past the end of - the file and "hide" it from userspace by manipulating i_size. The - data verification functions provided by ``fs/verity/`` also assume - that the filesystem uses the Linux pagecache, but both local and - remote filesystems normally do so. +:A: So far all filesystems that have implemented fs-verity support are + local filesystems, but in principle any filesystem that can store + per-file verity metadata can support fs-verity, regardless of + whether it's local or remote. Some filesystems may have fewer + options of where to store the verity metadata; one possibility is + to store it past the end of the file and "hide" it from userspace + by manipulating i_size. The data verification functions provided + by ``fs/verity/`` also assume that the filesystem uses the Linux + pagecache, but both local and remote filesystems normally do so. :Q: Why is anything filesystem-specific at all? Shouldn't fs-verity be implemented entirely at the VFS level? |