From: Eric Biggers <ebiggers@kernel.org>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>,
aalbersh@redhat.com, linux-xfs@vger.kernel.org, alexl@redhat.com,
walters@verbum.org, fsverity@lists.linux.dev,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 19/26] xfs: don't bother storing merkle tree blocks for zeroed data blocks
Date: Thu, 2 May 2024 00:01:32 +0000 [thread overview]
Message-ID: <20240502000132.GA1853833@google.com> (raw)
In-Reply-To: <20240501224736.GL360919@frogsfrogsfrogs>
On Wed, May 01, 2024 at 03:47:36PM -0700, Darrick J. Wong wrote:
> On Tue, Apr 30, 2024 at 11:47:23PM -0700, Christoph Hellwig wrote:
> > On Mon, Apr 29, 2024 at 08:29:03PM -0700, Darrick J. Wong wrote:
> > > From: Darrick J. Wong <djwong@kernel.org>
> > >
> > > Now that fsverity tells our merkle tree io functions about what a hash
> > > of a data block full of zeroes looks like, we can use this information
> > > to avoid writing out merkle tree blocks for sparse regions of the file.
> > > For verified gold master images this can save quite a bit of overhead.
> >
> > Is this something that fsverity should be doing in a generic way?
>
> I don't think it's all that useful for ext4/f2fs because they always
> write out full merkle tree blocks even if it's the zerohash over and
> over again. Old kernels aren't going to know how to deal with that.
>
> > It feels odd to have XFS behave different from everyone else here,
> > even if this does feel useful. Do we also need any hash validation
> > that no one tampered with the metadata and added a new extent, or
> > is this out of scope for fsverity?
>
> If they wrote a new extent with nonzero contents, then the validation
> will fail, right?
>
> If they added a new unwritten extent (or a written one full of zeroes),
> then the file data hasn't changed and validation would still pass,
> correct?
The point of fsverity is to verify that file data is consistent with the
top-level file digest. It doesn't really matter which type of extent the data
came from, or if the data got synthesized somehow (e.g. zeroes synthesized from
a hole), as long as fsverity still gets invoked to verify the data. If the data
itself passes verification, then it's good. The same applies to Merkle tree
blocks which are an intermediate step in the verification.
In the Merkle tree, ext4 and f2fs currently just use the same concept of
sparsity as the file data, i.e. when a block is unmapped, it is filled in with
all zeroes. As Darrick noticed, this isn't really the right concept of sparsity
for the Merkle tree, as a block full of hashes of zeroed blocks should be used,
not literally a zeroed block. I think it makes sense to fix this in XFS, as
it's newly adding fsverity support, and this is a filesystem-level
implementation detail. It would be difficult to fix this in ext4 and f2fs since
it would be an on-disk format upgrade. (Existing files should not actually have
any sparse Merkle tree blocks, so we probably could redefine what they mean.
But even if so, old kernels would not be able to read the new files.)
- Eric
next prev parent reply other threads:[~2024-05-02 0:01 UTC|newest]
Thread overview: 165+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-30 3:11 [PATCHBOMB v5.6] fs-verity support for XFS Darrick J. Wong
2024-04-30 3:18 ` [PATCHSET v5.6 1/2] fs-verity: support merkle tree access by blocks Darrick J. Wong
2024-04-30 3:19 ` [PATCH 01/18] fs: add FS_XFLAG_VERITY for verity files Darrick J. Wong
2024-04-30 3:19 ` [PATCH 02/18] fsverity: pass tree_blocksize to end_enable_verity() Darrick J. Wong
2024-04-30 3:20 ` [PATCH 03/18] fsverity: convert verification to use byte instead of page offsets Darrick J. Wong
2024-05-01 7:33 ` Christoph Hellwig
2024-05-01 22:33 ` Darrick J. Wong
2024-05-02 0:42 ` Eric Biggers
2024-05-08 20:14 ` Darrick J. Wong
2024-04-30 3:20 ` [PATCH 04/18] fsverity: support block-based Merkle tree caching Darrick J. Wong
2024-05-01 7:36 ` Christoph Hellwig
2024-05-01 22:35 ` Darrick J. Wong
2024-05-02 4:42 ` Christoph Hellwig
2024-05-15 2:16 ` Eric Biggers
2024-04-30 3:20 ` [PATCH 05/18] fsverity: pass the merkle tree block level to fsverity_read_merkle_tree_block Darrick J. Wong
2024-04-30 3:20 ` [PATCH 06/18] fsverity: add per-sb workqueue for post read processing Darrick J. Wong
2024-04-30 3:21 ` [PATCH 07/18] fsverity: add tracepoints Darrick J. Wong
2024-04-30 3:21 ` [PATCH 08/18] fsverity: pass the new tree size and block size to ->begin_enable_verity Darrick J. Wong
2024-04-30 3:21 ` [PATCH 09/18] fsverity: expose merkle tree geometry to callers Darrick J. Wong
2024-04-30 3:22 ` [PATCH 10/18] fsverity: box up the write_merkle_tree_block parameters too Darrick J. Wong
2024-04-30 3:22 ` [PATCH 11/18] fsverity: pass the zero-hash value to the implementation Darrick J. Wong
2024-04-30 3:22 ` [PATCH 12/18] fsverity: report validation errors back to the filesystem Darrick J. Wong
2024-04-30 3:22 ` [PATCH 13/18] fsverity: pass super_block to fsverity_enqueue_verify_work Darrick J. Wong
2024-04-30 3:23 ` [PATCH 14/18] ext4: use a per-superblock fsverity workqueue Darrick J. Wong
2024-04-30 3:23 ` [PATCH 15/18] f2fs: " Darrick J. Wong
2024-04-30 3:23 ` [PATCH 16/18] btrfs: " Darrick J. Wong
2024-04-30 3:23 ` [PATCH 17/18] fsverity: remove system-wide workqueue Darrick J. Wong
2024-04-30 3:24 ` [PATCH 18/18] iomap: integrate fs-verity verification into iomap's read path Darrick J. Wong
2024-05-01 7:10 ` Christoph Hellwig
2024-05-01 22:37 ` Darrick J. Wong
2024-04-30 3:18 ` [PATCHSET v5.6 2/2] xfs: fs-verity support Darrick J. Wong
2024-04-30 3:24 ` [PATCH 01/26] xfs: use unsigned ints for non-negative quantities in xfs_attr_remote.c Darrick J. Wong
2024-05-01 6:55 ` Christoph Hellwig
2024-05-01 22:39 ` Darrick J. Wong
2024-05-02 4:56 ` Christoph Hellwig
2024-05-02 5:56 ` Chandan Babu R
2024-05-02 6:34 ` Christoph Hellwig
2024-04-30 3:24 ` [PATCH 02/26] xfs: turn XFS_ATTR3_RMT_BUF_SPACE into a function Darrick J. Wong
2024-05-01 6:55 ` Christoph Hellwig
2024-04-30 3:24 ` [PATCH 03/26] xfs: create a helper to compute the blockcount of a max sized remote value Darrick J. Wong
2024-05-01 6:56 ` Christoph Hellwig
2024-04-30 3:25 ` [PATCH 04/26] xfs: minor cleanups of xfs_attr3_rmt_blocks Darrick J. Wong
2024-05-01 6:56 ` Christoph Hellwig
2024-04-30 3:25 ` [PATCH 05/26] xfs: use an empty transaction to protect xfs_attr_get from deadlocks Darrick J. Wong
2024-05-01 6:57 ` Christoph Hellwig
2024-05-01 22:42 ` Darrick J. Wong
2024-04-30 3:25 ` [PATCH 06/26] xfs: add attribute type for fs-verity Darrick J. Wong
2024-04-30 3:25 ` [PATCH 07/26] xfs: do not use xfs_attr3_rmt_hdr for remote verity value blocks Darrick J. Wong
2024-04-30 3:26 ` [PATCH 08/26] xfs: add fs-verity ro-compat flag Darrick J. Wong
2024-04-30 3:26 ` [PATCH 09/26] xfs: add inode on-disk VERITY flag Darrick J. Wong
2024-04-30 3:26 ` [PATCH 10/26] xfs: initialize fs-verity on file open and cleanup on inode destruction Darrick J. Wong
2024-04-30 3:26 ` [PATCH 11/26] xfs: don't allow to enable DAX on fs-verity sealed inode Darrick J. Wong
2024-04-30 3:27 ` [PATCH 12/26] xfs: disable direct read path for fs-verity files Darrick J. Wong
2024-04-30 3:27 ` [PATCH 13/26] xfs: widen flags argument to the xfs_iflags_* helpers Darrick J. Wong
2024-05-01 6:54 ` Christoph Hellwig
2024-05-01 22:44 ` Darrick J. Wong
2024-04-30 3:27 ` [PATCH 14/26] xfs: add fs-verity support Darrick J. Wong
2024-04-30 3:28 ` [PATCH 15/26] xfs: create a per-mount shrinker for verity inodes merkle tree blocks Darrick J. Wong
2024-04-30 3:28 ` [PATCH 16/26] xfs: shrink verity blob cache Darrick J. Wong
2024-04-30 3:28 ` [PATCH 17/26] xfs: don't store trailing zeroes of merkle tree blocks Darrick J. Wong
2024-04-30 3:28 ` [PATCH 18/26] xfs: use merkle tree offset as attr hash Darrick J. Wong
2024-05-01 6:53 ` Christoph Hellwig
2024-05-01 7:23 ` Christoph Hellwig
2024-05-07 21:24 ` Darrick J. Wong
2024-05-08 11:47 ` Christoph Hellwig
2024-05-08 20:26 ` Darrick J. Wong
2024-05-09 5:02 ` Christoph Hellwig
2024-05-09 20:02 ` Darrick J. Wong
2024-05-10 5:08 ` Christoph Hellwig
2024-05-10 6:20 ` Christoph Hellwig
2024-05-17 17:17 ` Darrick J. Wong
2024-05-20 12:39 ` Christoph Hellwig
2024-05-20 16:02 ` Darrick J. Wong
2024-05-22 14:37 ` Christoph Hellwig
2024-05-22 18:29 ` Eric Biggers
2024-05-31 21:28 ` Darrick J. Wong
2024-05-31 21:45 ` Eric Biggers
2024-05-09 17:46 ` Eric Biggers
2024-05-09 18:04 ` Darrick J. Wong
2024-05-09 18:36 ` Eric Biggers
2024-04-30 3:29 ` [PATCH 19/26] xfs: don't bother storing merkle tree blocks for zeroed data blocks Darrick J. Wong
2024-05-01 6:47 ` Christoph Hellwig
2024-05-01 22:47 ` Darrick J. Wong
2024-05-02 0:01 ` Eric Biggers [this message]
2024-05-08 20:26 ` Darrick J. Wong
2024-04-30 3:29 ` [PATCH 20/26] xfs: add fs-verity ioctls Darrick J. Wong
2024-04-30 3:29 ` [PATCH 21/26] xfs: advertise fs-verity being available on filesystem Darrick J. Wong
2024-04-30 3:29 ` [PATCH 22/26] xfs: check and repair the verity inode flag state Darrick J. Wong
2024-04-30 3:30 ` [PATCH 23/26] xfs: teach online repair to evaluate fsverity xattrs Darrick J. Wong
2024-04-30 3:30 ` [PATCH 24/26] xfs: report verity failures through the health system Darrick J. Wong
2024-04-30 3:30 ` [PATCH 25/26] xfs: make it possible to disable fsverity Darrick J. Wong
2024-05-01 6:48 ` Christoph Hellwig
2024-05-01 22:50 ` Darrick J. Wong
2024-05-02 0:15 ` Eric Biggers
2024-05-08 20:31 ` Darrick J. Wong
2024-05-09 5:04 ` Christoph Hellwig
2024-05-09 14:45 ` Darrick J. Wong
2024-05-09 15:06 ` Christoph Hellwig
2024-05-09 15:09 ` Darrick J. Wong
2024-05-09 15:13 ` Christoph Hellwig
2024-05-09 15:43 ` Darrick J. Wong
2024-05-17 19:36 ` Theodore Ts'o
2024-04-30 3:30 ` [PATCH 26/26] xfs: enable ro-compat fs-verity flag Darrick J. Wong
2024-04-30 3:19 ` [PATCHSET v5.6] xfsprogs: fs-verity support for XFS Darrick J. Wong
2024-04-30 3:31 ` [PATCH 01/38] fs: add FS_XFLAG_VERITY for verity files Darrick J. Wong
2024-04-30 3:31 ` [PATCH 02/38] xfs: use unsigned ints for non-negative quantities in xfs_attr_remote.c Darrick J. Wong
2024-04-30 3:31 ` [PATCH 03/38] xfs: turn XFS_ATTR3_RMT_BUF_SPACE into a function Darrick J. Wong
2024-04-30 3:31 ` [PATCH 04/38] xfs: create a helper to compute the blockcount of a max sized remote value Darrick J. Wong
2024-04-30 3:32 ` [PATCH 05/38] xfs: minor cleanups of xfs_attr3_rmt_blocks Darrick J. Wong
2024-04-30 3:32 ` [PATCH 06/38] xfs: use an empty transaction to protect xfs_attr_get from deadlocks Darrick J. Wong
2024-04-30 3:32 ` [PATCH 07/38] xfs: add attribute type for fs-verity Darrick J. Wong
2024-04-30 3:32 ` [PATCH 08/38] xfs: do not use xfs_attr3_rmt_hdr for remote verity value blocks Darrick J. Wong
2024-04-30 3:33 ` [PATCH 09/38] xfs: add fs-verity ro-compat flag Darrick J. Wong
2024-04-30 3:33 ` [PATCH 10/38] xfs: add inode on-disk VERITY flag Darrick J. Wong
2024-04-30 3:33 ` [PATCH 11/38] xfs: add fs-verity support Darrick J. Wong
2024-04-30 3:34 ` [PATCH 12/38] xfs: use merkle tree offset as attr hash Darrick J. Wong
2024-04-30 3:34 ` [PATCH 13/38] xfs: advertise fs-verity being available on filesystem Darrick J. Wong
2024-04-30 3:34 ` [PATCH 14/38] xfs: report verity failures through the health system Darrick J. Wong
2024-04-30 3:34 ` [PATCH 15/38] xfs: enable ro-compat fs-verity flag Darrick J. Wong
2024-04-30 3:35 ` [PATCH 16/38] libfrog: add fsverity to xfs_report_geom output Darrick J. Wong
2024-04-30 3:35 ` [PATCH 17/38] xfs_db: introduce attr_modify command Darrick J. Wong
2024-04-30 3:35 ` [PATCH 18/38] xfs_db: add ATTR_PARENT support to " Darrick J. Wong
2024-04-30 3:35 ` [PATCH 19/38] xfs_db: make attr_set/remove/modify be able to handle fs-verity attrs Darrick J. Wong
2024-04-30 3:36 ` [PATCH 20/38] man: document attr_modify command Darrick J. Wong
2024-04-30 3:36 ` [PATCH 21/38] xfs_db: create hex string as a field type Darrick J. Wong
2024-04-30 3:36 ` [PATCH 22/38] xfs_db: dump verity features and metadata Darrick J. Wong
2024-04-30 3:36 ` [PATCH 23/38] xfs_db: dump merkle tree data Darrick J. Wong
2024-04-30 3:37 ` [PATCH 24/38] xfs_db: dump the verity descriptor Darrick J. Wong
2024-04-30 3:37 ` [PATCH 25/38] xfs_db: don't obfuscate verity xattrs Darrick J. Wong
2024-04-30 3:37 ` [PATCH 26/38] xfs_db: dump the inode verity flag Darrick J. Wong
2024-04-30 3:37 ` [PATCH 27/38] xfs_db: compute hashes of merkle tree blocks Darrick J. Wong
2024-04-30 3:38 ` [PATCH 28/38] xfs_repair: junk fsverity xattrs when unnecessary Darrick J. Wong
2024-04-30 3:38 ` [PATCH 29/38] xfs_repair: clear verity iflag when verity isn't supported Darrick J. Wong
2024-04-30 3:38 ` [PATCH 30/38] xfs_repair: handle verity remote attrs Darrick J. Wong
2024-04-30 3:38 ` [PATCH 31/38] xfs_repair: allow upgrading filesystems with verity Darrick J. Wong
2024-04-30 3:39 ` [PATCH 32/38] xfs_scrub: check verity file metadata Darrick J. Wong
2024-04-30 3:39 ` [PATCH 33/38] xfs_scrub: validate verity file contents when doing a media scan Darrick J. Wong
2024-04-30 3:39 ` [PATCH 34/38] xfs_scrub: use MADV_POPULATE_READ to check verity files Darrick J. Wong
2024-04-30 3:40 ` [PATCH 35/38] xfs_spaceman: report data corruption Darrick J. Wong
2024-04-30 3:40 ` [PATCH 36/38] xfs_io: report fsverity status via statx Darrick J. Wong
2024-04-30 3:40 ` [PATCH 37/38] xfs_io: create magic command to disable verity Darrick J. Wong
2024-04-30 3:40 ` [PATCH 38/38] mkfs.xfs: add verity parameter Darrick J. Wong
2024-04-30 3:19 ` [PATCHSET v5.6] fstests: fs-verity support for XFS Darrick J. Wong
2024-04-30 3:41 ` [PATCH 1/6] common/verity: enable fsverity " Darrick J. Wong
2024-04-30 12:39 ` Andrey Albershteyn
2024-04-30 15:35 ` Darrick J. Wong
2024-04-30 3:41 ` [PATCH 2/6] xfs/{021,122}: adapt to fsverity xattrs Darrick J. Wong
2024-04-30 12:46 ` Andrey Albershteyn
2024-04-30 15:36 ` Darrick J. Wong
2024-04-30 3:41 ` [PATCH 3/6] xfs/122: adapt to fsverity Darrick J. Wong
2024-04-30 12:45 ` Andrey Albershteyn
2024-04-30 15:37 ` Darrick J. Wong
2024-04-30 3:41 ` [PATCH 4/6] xfs: test xfs_scrub detection and correction of corrupt fsverity metadata Darrick J. Wong
2024-04-30 12:29 ` Andrey Albershteyn
2024-04-30 15:43 ` Darrick J. Wong
2024-04-30 3:42 ` [PATCH 5/6] xfs: test disabling fsverity Darrick J. Wong
2024-04-30 12:56 ` Andrey Albershteyn
2024-04-30 13:11 ` Andrey Albershteyn
2024-04-30 15:48 ` Darrick J. Wong
2024-04-30 18:06 ` Andrey Albershteyn
2024-04-30 3:42 ` [PATCH 6/6] common/populate: add verity files to populate xfs images Darrick J. Wong
2024-04-30 13:22 ` Andrey Albershteyn
2024-04-30 15:49 ` Darrick J. Wong
2024-05-11 5:01 ` [PATCHSET v5.6] fstests: fs-verity support for XFS Zorro Lang
2024-05-17 15:56 ` Darrick J. Wong
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