Fixes for KMSAN reports #12383

markjdb · 2021-07-16T15:46:52Z

Motivation and Context

I've been doing some work to port a KMSAN (kernel memory sanitizer) implementation to FreeBSD. To help test the port, I booted a KMSAN-enabled kernel on a system with a ZFS root and worked through the reports generated while booting to a login prompt. This PR fixes most of the problems I hit. I have not yet tried running any test suites with KMSAN enabled.

Description

The change fixes five bugs:

three are in the transaction logging code and involve writing uninitialized bytes to the ZIL
one fixes a problem where spa_autoreplace can be initialized from uninitialized memory
one fixes a missing initialization in the dnode constructor, likely a false positive

How Has This Been Tested?

Manual testing on a FreeBSD system booting from ZFS.

Types of changes

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Performance enhancement (non-breaking change which improves efficiency)
Code cleanup (non-breaking change which makes code smaller or more readable)
Breaking change (fix or feature that would cause existing functionality to change)
Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
Documentation (a change to man pages or other documentation)

Checklist:

My code follows the OpenZFS code style requirements.
I have updated the documentation accordingly.
I have read the contributing document.
I have added tests to cover my changes.
I have run the ZFS Test Suite with this change applied.
All commit messages are properly formatted and contain Signed-off-by.

module/zfs/spa.c

module/zfs/zil.c

spa_prop_find() may fail to find the specified property, in which case it suppresses ENOENT from zap_lookup(). In this case, the return value is left uninitialized, so spa_autoreplace was being initialized using an uninitialized stack variable. This was found using KMSAN. It appears to be a regression from commit 9eb7b46, which removed the initialization of "autoreplace" from the definition. Signed-off-by: Mark Johnston <markj@FreeBSD.org>

When logging TX_SETATTR, we could otherwise fail to initialize part of the corresponding ZIL record depending on which fields are present in the xvattr. Initialize the creation time and the AV scan timestamp to zero so that uninitialized bytes are not written to the ZIL. This was found using KMSAN. Signed-off-by: Mark Johnston <markj@FreeBSD.org>

When allocating a record, we round up the allocation size to a multiple of 8. In this case, any padding bytes should be zeroed, otherwise the contents of uninitialized memory are written to the ZIL. This was found using KMSAN. Signed-off-by: Mark Johnston <markj@FreeBSD.org>

When logging a TX_WRITE record in the case where file data has to be copied from the DMU, we pad the log record size to a multiple of 8 bytes. In this case, any padding bytes should be zeroed, otherwise the contents of uninitialized memory are written to the ZIL. This was found using KMSAN. Signed-off-by: Mark Johnston <markj@FreeBSD.org>

It seems nothing ensures that this array is zeroed when a dnode is freshly allocated, so in principle it retains the values from the previous allocation. In practice it seems to be the case that the fields should end up zeroed, but we can zero the field anyway for consistency. This was found using KMSAN. Signed-off-by: Mark Johnston <markj@FreeBSD.org>

When logging TX_SETATTR, we could otherwise fail to initialize part of the corresponding ZIL record depending on which fields are present in the xvattr. Initialize the creation time and the AV scan timestamp to zero so that uninitialized bytes are not written to the ZIL. This was found using KMSAN. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Signed-off-by: Mark Johnston <markj@FreeBSD.org> Closes #12383

When allocating a record, we round up the allocation size to a multiple of 8. In this case, any padding bytes should be zeroed, otherwise the contents of uninitialized memory are written to the ZIL. This was found using KMSAN. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Signed-off-by: Mark Johnston <markj@FreeBSD.org> Closes #12383

When logging a TX_WRITE record in the case where file data has to be copied from the DMU, we pad the log record size to a multiple of 8 bytes. In this case, any padding bytes should be zeroed, otherwise the contents of uninitialized memory are written to the ZIL. This was found using KMSAN. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Signed-off-by: Mark Johnston <markj@FreeBSD.org> Closes #12383

It seems nothing ensures that this array is zeroed when a dnode is freshly allocated, so in principle it retains the values from the previous allocation. In practice it seems to be the case that the fields should end up zeroed, but we can zero the field anyway for consistency. This was found using KMSAN. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Signed-off-by: Mark Johnston <markj@FreeBSD.org> Closes #12383

When logging TX_SETATTR, we could otherwise fail to initialize part of the corresponding ZIL record depending on which fields are present in the xvattr. Initialize the creation time and the AV scan timestamp to zero so that uninitialized bytes are not written to the ZIL. This was found using KMSAN. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Signed-off-by: Mark Johnston <markj@FreeBSD.org> Closes openzfs#12383

When allocating a record, we round up the allocation size to a multiple of 8. In this case, any padding bytes should be zeroed, otherwise the contents of uninitialized memory are written to the ZIL. This was found using KMSAN. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Signed-off-by: Mark Johnston <markj@FreeBSD.org> Closes openzfs#12383

When logging a TX_WRITE record in the case where file data has to be copied from the DMU, we pad the log record size to a multiple of 8 bytes. In this case, any padding bytes should be zeroed, otherwise the contents of uninitialized memory are written to the ZIL. This was found using KMSAN. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Signed-off-by: Mark Johnston <markj@FreeBSD.org> Closes openzfs#12383

It seems nothing ensures that this array is zeroed when a dnode is freshly allocated, so in principle it retains the values from the previous allocation. In practice it seems to be the case that the fields should end up zeroed, but we can zero the field anyway for consistency. This was found using KMSAN. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Signed-off-by: Mark Johnston <markj@FreeBSD.org> Closes openzfs#12383

spa_prop_find() may fail to find the specified property, in which case it suppresses ENOENT from zap_lookup(). In this case, the return value is left uninitialized, so spa_autoreplace was being initialized using an uninitialized stack variable. This was found using KMSAN. It appears to be a regression from commit 9eb7b46, which removed the initialization of "autoreplace" from the definition. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Signed-off-by: Mark Johnston <markj@FreeBSD.org> Closes openzfs#12383