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FreeBSD-SA-18:09.l1tf Security Advisory
The FreeBSD Project

Topic: L1 Terminal Fault (L1TF) Kernel Information Disclosure

Category: core
Module: Kernel
Announced: 2018-08-14
Affects: All supported versions of FreeBSD.
Corrected: 2018-08-14 17:51:12 UTC (stable/11, 11.1-STABLE)
2018-08-15 02:30:11 UTC (releng/11.2, 11.2-RELEASE-p2)
2018-08-15 02:30:11 UTC (releng/11.1, 11.1-RELEASE-p13)
CVE Name: CVE-2018-3620, CVE-2018-3646

Special Note: Speculative execution vulnerability mitigation remains a work
in progress. This advisory addresses the issue in FreeBSD
11.1 and later. We expect to update this advisory to include
10.4 at a later time.

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

When a program accesses data in memory via a logical address it is translated
to a physical address in RAM by the CPU. Accessing an unmapped logical
address results in what is known as a terminal fault.

II. Problem Description

On certain Intel 64-bit x86 systems there is a period of time during terminal
fault handling where the CPU may use speculative execution to try to load
data. The CPU may speculatively access the level 1 data cache (L1D). Data
which would otherwise be protected may then be determined by using side
channel methods.

This issue affects bhyve on FreeBSD/amd64 systems.

III. Impact

An attacker executing user code, or kernel code inside of a virtual machine,
may be able to read secret data from the kernel or from another virtual
machine.

IV. Workaround

No workaround is available.

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 +30 “Rebooting for 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 11.2]
# fetch https://security.FreeBSD.org/patches/SA-18:09/l1tf-11.2.patch
# fetch https://security.FreeBSD.org/patches/SA-18:09/l1tf-11.2.patch.asc
# gpg –verify l1tf-11.2.patch.asc

[FreeBSD 11.1]
# fetch https://security.FreeBSD.org/patches/SA-18:09/l1tf-11.1.patch
# fetch https://security.FreeBSD.org/patches/SA-18:09/l1tf-11.1.patch.asc
# gpg –verify l1tf-11.1.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

CVE-2018-3620 (L1 Terminal Fault-OS)
– ————————————
FreeBSD reserves the the memory page at physical address 0, so it will not
contain secret data. FreeBSD zeros the paging data structures for unmapped
addresses, so that speculatively executed L1 Terminal Faults will access only
the reserved, unused page.

CVE-2018-3646 (L1 Terminal Fault-VMM)
– ————————————-
Patched systems flush the L1 data cache prior to guest entry, so that there
is no secret data in cache for a terminal fault (from the the guest) to
access.

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

Branch/path Revision
– ————————————————————————-
stable/11/ r337794
releng/11.1/ r337828
releng/11.2/ r337828
– ————————————————————————-

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

More information on L1 Terminal Fault is available at:

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-3620>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-3646>

<URL:https://software.intel.com/security-software-guidance/software-guidance/l1-terminal-fault>

<URL:https://www.intel.com/content/www/us/en/security-center/advisory/intel-sa-00161.html>

The FreeBSD Security Team thanks Intel for disclosing the issue.

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-18:09.l1tf.asc>
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