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author | Eric Biggers <ebiggers@google.com> | 2023-01-27 23:15:29 +0100 |
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committer | Eric Biggers <ebiggers@google.com> | 2023-01-27 23:46:31 +0100 |
commit | 5d0f0e57ed900917836385527ce5b122fa1425a3 (patch) | |
tree | 2a9dd0ba1351b2783a4febe87e98754e6b8472fe /Documentation/filesystems | |
parent | fsverity.rst: update git repo URL for fsverity-utils (diff) | |
download | linux-5d0f0e57ed900917836385527ce5b122fa1425a3.tar.xz linux-5d0f0e57ed900917836385527ce5b122fa1425a3.zip |
fsverity: support verifying data from large folios
Try to make fs/verity/verify.c aware of large folios. This includes
making fsverity_verify_bio() support the case where the bio contains
large folios, and adding a function fsverity_verify_folio() which is the
equivalent of fsverity_verify_page().
There's no way to actually test this with large folios yet, but I've
tested that this doesn't cause any regressions.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20230127221529.299560-1-ebiggers@kernel.org
Diffstat (limited to 'Documentation/filesystems')
-rw-r--r-- | Documentation/filesystems/fsverity.rst | 20 |
1 files changed, 10 insertions, 10 deletions
diff --git a/Documentation/filesystems/fsverity.rst b/Documentation/filesystems/fsverity.rst index 2d9ef906aa2a..ede672dedf11 100644 --- a/Documentation/filesystems/fsverity.rst +++ b/Documentation/filesystems/fsverity.rst @@ -568,22 +568,22 @@ Pagecache ~~~~~~~~~ For filesystems using Linux's pagecache, the ``->read_folio()`` and -``->readahead()`` methods must be modified to verify pages before they -are marked Uptodate. Merely hooking ``->read_iter()`` would be +``->readahead()`` methods must be modified to verify folios before +they are marked Uptodate. Merely hooking ``->read_iter()`` would be insufficient, since ``->read_iter()`` is not used for memory maps. Therefore, fs/verity/ provides the function fsverity_verify_blocks() which verifies data that has been read into the pagecache of a verity -inode. The containing page must still be locked and not Uptodate, so +inode. The containing folio must still be locked and not Uptodate, so it's not yet readable by userspace. As needed to do the verification, fsverity_verify_blocks() will call back into the filesystem to read hash blocks via fsverity_operations::read_merkle_tree_page(). fsverity_verify_blocks() returns false if verification failed; in this -case, the filesystem must not set the page Uptodate. Following this, +case, the filesystem must not set the folio Uptodate. Following this, as per the usual Linux pagecache behavior, attempts by userspace to -read() from the part of the file containing the page will fail with -EIO, and accesses to the page within a memory map will raise SIGBUS. +read() from the part of the file containing the folio will fail with +EIO, and accesses to the folio within a memory map will raise SIGBUS. In principle, verifying a data block requires verifying the entire path in the Merkle tree from the data block to the root hash. @@ -624,8 +624,8 @@ each bio and store it in ``->bi_private``:: verity, or both is enabled. After the bio completes, for each needed postprocessing step the filesystem enqueues the bio_post_read_ctx on a 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. +verification. Finally, folios where no decryption or verity error +occurred are marked Uptodate, and the folios are unlocked. On many filesystems, files can contain holes. Normally, ``->readahead()`` simply zeroes hole blocks and considers the @@ -791,9 +791,9 @@ weren't already directly answered in other parts of this document. :A: There are many reasons why this is not possible or would be very difficult, including the following: - - To prevent bypassing verification, pages must not be marked + - To prevent bypassing verification, folios must not be marked Uptodate until they've been verified. Currently, each - filesystem is responsible for marking pages Uptodate via + filesystem is responsible for marking folios Uptodate via ``->readahead()``. Therefore, currently it's not possible for the VFS to do the verification on its own. Changing this would require significant changes to the VFS and all filesystems. |