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FreeBSD-SA-19:25.mcepsc                                     Security Advisory
                                                          The FreeBSD Project

Topic:          Machine Check Exception on Page Size Change

Category:       core
Module:         kernel
Announced:      2019-11-12
Credits:        Intel
Affects:        All supported versions of FreeBSD.
Corrected:      2019-11-12 18:03:26 UTC (stable/12, 12.1-STABLE)
                2019-11-12 18:13:04 UTC (releng/12.1, 12.1-RELEASE-p1)
                2019-11-12 18:13:04 UTC (releng/12.0, 12.0-RELEASE-p12)
                2019-11-12 18:04:28 UTC (stable/11, 11.3-STABLE)
                2019-11-12 18:13:04 UTC (releng/11.3, 11.3-RELEASE-p5)
CVE Name:       CVE-2018-12207

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

I.   Background

The Intel machine check architecture is a mechanism to detect and report
hardware errors, such as system bus errors, ECC errors, parity errors, and
others.  This allows the processor to signal the detection of a machine
check error to the operating system.

II.  Problem Description

Intel discovered a previously published erratum on some Intel platforms can
be exploited by malicious software to potentially cause a denial of service
by triggering a machine check that will crash or hang the system.

III. Impact

Malicious guest operating systems may be able to crash the host.

IV.  Workaround

No workaround is available.  Systems not running untrusted guest virtual
machines are not impacted.

V.   Solution

Upgrade your vulnerable 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 vulnerable system via a binary patch:

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

# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min "Rebooting for a security update"

2) To update your vulnerable 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.

[FreeBSD 12.1]
# fetch https://security.FreeBSD.org/patches/SA-19:25/mcepsc.12.1.patch
# fetch https://security.FreeBSD.org/patches/SA-19:25/mcepsc.12.1.patch.asc
# gpg --verify mcepsc.12.1.patch.asc

[FreeBSD 12.0]
# fetch https://security.FreeBSD.org/patches/SA-19:25/mcepsc.12.0.patch
# fetch https://security.FreeBSD.org/patches/SA-19:25/mcepsc.12.0.patch.asc
# gpg --verify mcepsc.12.0.patch.asc

[FreeBSD 11.3]
# fetch https://security.FreeBSD.org/patches/SA-19:25/mcepsc.11.patch
# fetch https://security.FreeBSD.org/patches/SA-19:25/mcepsc.11.patch.asc
# gpg --verify mcepsc.11.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

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/12/                                                        r354650
releng/12.1/                                                      r354653
releng/12.0/                                                      r354653
stable/11/                                                        r354651
releng/11.3/                                                      r354653
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# 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://software.intel.com/security-software-guidance/software-guidance/machine-check-error-avoidance-page-size-change>
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-12207>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-19:25.mcepsc.asc>
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