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FreeBSD-SA-19:07.mds                                        Security Advisory
                                                          The FreeBSD Project

Topic:          Microarchitectural Data Sampling (MDS)

Category:       core
Module:         kernel
Announced:      2019-05-14
Credits:        Refer to Intel's security advisory at the URL below for
                detailed acknowledgements.
Affects:        All supported versions of FreeBSD.
Corrected:      2019-05-14 17:04:00 UTC (stable/12, 12.0-STABLE)
                2019-05-14 23:19:08 UTC (releng/12.0, 12.0-RELEASE-p4)
                2019-05-14 17:05:02 UTC (stable/11, 11.3-PRERELEASE)
                2019-05-14 23:20:16 UTC (releng/11.2, 11.2-RELEASE-p10)
CVE Name:       CVE-2018-12126, CVE-2018-12127, CVE-2018-12130,
    CVE-2019-11091

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

Modern processors make use of speculative execution, an optimization
technique which performs some action in advance of knowing whether the
result will actually be used.

II.  Problem Description

On some Intel processors utilizing speculative execution a local process may
be able to infer stale information from microarchitectural buffers to obtain
a memory disclosure.

III. Impact

An attacker may be able to read secret data from the kernel or from a
process when executing untrusted code (for example, in a web browser).

IV.  Workaround

No workaround is available.

Systems with users or processors in different trust domains should disable
Hyper-Threading by setting the machdep.hyperthreading_allowed tunable to 0:

# echo 'machdep.hyperthreading_allowed=0 >> /boot/loader.conf'
# shutdown

V.   Solution

Perform one of the following:

Update CPU microcode, upgrade your vulnerable system to a supported FreeBSD
stable or release / security branch (releng) dated after the correction date,
evaluate mitigation and Hyper Threading controls, and reboot the system.

New CPU microcode may be available in a BIOS update from your system vendor,
or by installing the devcpu-data package or sysutils/devcpu-data port.
Ensure that the BIOS update or devcpu-data package is dated after 2014-05-14.

If using the package or port the microcode update can be applied at boot time
by adding the following lines to the system's /boot/loader.conf:

cpu_microcode_load="YES"
cpu_microcode_name="/boot/firmware/intel-ucode.bin"

Microcode updates can also be applied while the system is running.  See
cpucontrol(8) for details.

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

Follow additional details under "Mitigation Configuration" below.

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 12.0-STABLE]
# fetch https://security.FreeBSD.org/patches/SA-19:07/mds.12-stable.patch
# fetch https://security.FreeBSD.org/patches/SA-19:07/mds.12-stable.patch.asc
# gpg --verify mds.12-stable.patch.asc

[FreeBSD 12.0-RELEASE]
# fetch https://security.FreeBSD.org/patches/SA-19:07/mds.12.0.patch
# fetch https://security.FreeBSD.org/patches/SA-19:07/mds.12.0.patch.asc
# gpg --verify mds.12.0.patch.asc

[FreeBSD 11.3-PRERELEASE]
# fetch https://security.FreeBSD.org/patches/SA-19:07/mds.11-stable.patch
# fetch https://security.FreeBSD.org/patches/SA-19:07/mds.11-stable.patch.asc
# gpg --verify mds.11-stable.patch.asc

[FreeBSD 11.2-RELEASE]
# fetch https://security.FreeBSD.org/patches/SA-19:07/mds.11.2.patch
# fetch https://security.FreeBSD.org/patches/SA-19:07/mds.11.2.patch.asc
# gpg --verify mds.11.2.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>.

Mitigation Configuration

Systems with users, processes, or virtual machines in different trust
domains should disable Hyper-Threading by setting the
machdep.hyperthreading_allowed tunable to 0:

# echo machdep.hyperthreading_allowed=0 >> /boot/loader.conf

To activate the MDS mitigation set the hw.mds_disable sysctl.  The settings
are:

0 - mitigation disabled
1 - VERW instruction (microcode) mitigation enabled
2 - Software sequence mitigation enabled (not recommended)
3 - Automatic VERW or Software selection

Automatic mode uses the VERW instruction if supported by the CPU / microcode,
or software sequences if not.  To enable automatic mode at boot:

# echo hw.mds_disable=3 >> /etc/sysctl.conf

Reboot the system:

# shutdown -r +10min "Security update"

Check the mitigation status:

# sysctl hw.mds_disable_state
hw.mds_disable_state: software Silvermont

VI.  Correction details

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

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/12/                                                        r347567
releng/12.0/                                                      r346594
stable/11/                                                        r347568
releng/11.2/                                                      r347595
- -------------------------------------------------------------------------

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://www.intel.com/content/www/us/en/security-center/advisory/intel-sa-00233.html>
<URL:https://www.intel.com/content/www/us/en/architecture-and-technology/mds.html>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-19:07.mds.asc>
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