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FreeBSD-EN-22:08.i386                                           Errata Notice
                                                          The FreeBSD Project

Topic:          Regression in i386 TLB invalidation logic

Category:       core
Module:         i386
Announced:      2022-02-01
Affects:        FreeBSD 12.2 and 12.3
Corrected:      2022-01-25 10:40:16 UTC (stable/12, 12.3-STABLE)
                2022-02-01 19:13:44 UTC (releng/12.3, 12.3-RELEASE-p2)
                2022-02-01 19:13:24 UTC (releng/12.2, 12.2-RELEASE-p13)

For general information regarding FreeBSD Errata Notices and Security
Advisories, including descriptions of the fields above, security
branches, and the following sections, please visit
<URL:https://security.FreeBSD.org/>.

I.   Background

The FreeBSD/i386 port supports running FreeBSD on 32-bit Intel and AMD CPUs.

On the i386 platform, the operating system kernel is responsible for
invalidating per-CPU TLBs (translation lookaside buffer) when virtual memory
mappings are updated. 

II.  Problem Description

The patch which was released as EN-22:04.pcid introduced a regression
affecting FreeBSD 12.2 and 12.3.  This regression introduced a bug in the i386
platform's TLB invalidation logic.

III. Impact

The regression causes kernel panics under multi-core CPU load.

IV.  Workaround

No workaround is available.  Single-core systems are not affected.

V.   Solution

Upgrade your system to a supported FreeBSD stable or release / security
branch (releng) dated after the correction date and reboot.

Perform one of the following:

1) To update your system via a binary patch:

Systems running a RELEASE version of FreeBSD on the amd64, i386, or
(on FreeBSD 13 and later) arm64 platforms can be updated via the
freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min "Rebooting for an errata update"

2) To update your system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch https://security.FreeBSD.org/patches/EN-22:08/i386.patch
# fetch https://security.FreeBSD.org/patches/EN-22:08/i386.patch.asc
# gpg --verify i386.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

This issue is corrected by the corresponding Git commit hash or Subversion
revision number in the following stable and release branches:

Branch/path                             Hash                     Revision
- -------------------------------------------------------------------------
stable/12/                                                        r371519
releng/12.3/                                                      r371536
releng/12.2/                                                      r371534
- -------------------------------------------------------------------------

Run the following command to see which files were modified by a particular
revision, replacing NNNNNN with the revision number:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=261338>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-22:08.i386.asc>
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