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authorEric Biggers <ebiggers@google.com>2023-01-27 23:15:29 +0100
committerEric Biggers <ebiggers@google.com>2023-01-27 23:46:31 +0100
commit5d0f0e57ed900917836385527ce5b122fa1425a3 (patch)
tree2a9dd0ba1351b2783a4febe87e98754e6b8472fe /Documentation/filesystems
parentfsverity.rst: update git repo URL for fsverity-utils (diff)
downloadlinux-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.rst20
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.