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fsverity fixes for v6.3-rc4

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Fix two significant performance issues with fsverity.
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Merge tag 'fsverity-for-linus' of git://git.kernel.org/pub/scm/fs/fsverity/linux

Pull fsverity fixes from Eric Biggers:
 "Fix two significant performance issues with fsverity"

* tag 'fsverity-for-linus' of git://git.kernel.org/pub/scm/fs/fsverity/linux:
  fsverity: don't drop pagecache at end of FS_IOC_ENABLE_VERITY
  fsverity: Remove WQ_UNBOUND from fsverity read workqueue
This commit is contained in:
Linus Torvalds 2023-03-20 15:20:33 -07:00
commit 17214b70a1
2 changed files with 19 additions and 18 deletions
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25
fs/verity/enable.c
View File

@ -8,7 +8,6 @@
#include "fsverity_private.h"
#include <linux/mount.h>
#include <linux/pagemap.h>
#include <linux/sched/signal.h>
#include <linux/uaccess.h>
@ -367,25 +366,27 @@ int fsverity_ioctl_enable(struct file *filp, const void __user *uarg)
goto out_drop_write;
err = enable_verity(filp, &arg);
if (err)
goto out_allow_write_access;
/*
* Some pages of the file may have been evicted from pagecache after
* being used in the Merkle tree construction, then read into pagecache
* again by another process reading from the file concurrently. Since
* these pages didn't undergo verification against the file digest which
* fs-verity now claims to be enforcing, we have to wipe the pagecache
* to ensure that all future reads are verified.
* We no longer drop the inode's pagecache after enabling verity. This
* used to be done to try to avoid a race condition where pages could be
* evicted after being used in the Merkle tree construction, then
* re-instantiated by a concurrent read. Such pages are unverified, and
* the backing storage could have filled them with different content, so
* they shouldn't be used to fulfill reads once verity is enabled.
*
* But, dropping the pagecache has a big performance impact, and it
* doesn't fully solve the race condition anyway. So for those reasons,
* and also because this race condition isn't very important relatively
* speaking (especially for small-ish files, where the chance of a page
* being used, evicted, *and* re-instantiated all while enabling verity
* is quite small), we no longer drop the inode's pagecache.
*/
filemap_write_and_wait(inode->i_mapping);
invalidate_inode_pages2(inode->i_mapping);
/*
* allow_write_access() is needed to pair with deny_write_access().
* Regardless, the filesystem won't allow writing to verity files.
*/
out_allow_write_access:
allow_write_access(filp);
out_drop_write:
mnt_drop_write_file(filp);

12
fs/verity/verify.c
View File

@ -387,15 +387,15 @@ EXPORT_SYMBOL_GPL(fsverity_enqueue_verify_work);
int __init fsverity_init_workqueue(void)
{
/*
* Use an unbound workqueue to allow bios to be verified in parallel
* even when they happen to complete on the same CPU. This sacrifices
* locality, but it's worthwhile since hashing is CPU-intensive.
* Use a high-priority workqueue to prioritize verification work, which
* blocks reads from completing, over regular application tasks.
*
* Also use a high-priority workqueue to prioritize verification work,
* which blocks reads from completing, over regular application tasks.
* For performance reasons, don't use an unbound workqueue. Using an
* unbound workqueue for crypto operations causes excessive scheduler
* latency on ARM64.
*/
fsverity_read_workqueue = alloc_workqueue("fsverity_read_queue",
WQ_UNBOUND | WQ_HIGHPRI,
WQ_HIGHPRI,
num_online_cpus());
if (!fsverity_read_workqueue)
return -ENOMEM;