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  • [FreeBSD-Announce] FreeBSD Security Advisory FreeBSD-SA-18:07.lazyfpu

    From FreeBSD Security Advisories@21:1/5 to All on Thu Jun 21 07:00:00 2018
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    ============================================================================= FreeBSD-SA-18:07.lazyfpu Security Advisory
    The FreeBSD Project

    Topic: Lazy FPU State Restore Information Disclosure

    Category: core
    Module: kernel
    Announced: 2018-06-21
    Credits: Julian Stecklina from Amazon Germany
    Thomas Prescher from Cyberus Technology GmbH
    Zdenek Sojka from SYSGO AG
    Colin Percival
    Affects: All supported version of FreeBSD.
    Corrected: 2018-06-14 18:50:49 UTC (stable/11, 11.2-PRERELEASE)
    2018-06-15 13:21:37 UTC (releng/11.2, 11.2-RC3)
    2018-06-21 05:17:13 UTC (releng/11.1, 11.1-RELEASE-p11)
    CVE Name: CVE-2018-3665

    Special Note: This advisory only addresses this issue for FreeBSD 11.x on
    i386 and amd64. We expect to update this advisory to include
    10.x in the near future.

    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 CPUs have a floating point unit (FPU) which needs to maintain state
    per thread. One technique is to only save and to only restore the FPU state for a thread when a thread attempts to utilize the FPU. This technique is called Lazy FPU state restore.

    II. Problem Description

    A subset of Intel processors can allow a local thread to infer data from another thread through a speculative execution side channel when Lazy FPU
    state restore is used.

    III. Impact

    Any local thread can potentially read FPU state information from other
    threads running on the host. This could include cryptographic keys when the AES-NI CPU feature is present.

    IV. Workaround

    No workaround is available, but non-Intel branded CPUs are not believed
    to be vulnerable.

    V. Solution

    The patch changes from Lazy FPU state restore to Eager FPU state restore.
    This new technique is the recommended practice from Intel and in some cases
    can actually increase performance, depending on workload.

    Perform one of the following:

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

    Afterward, reboot the system.

    2) 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

    Afterward, reboot the system.

    3) 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 11.1]
    # fetch https://security.FreeBSD.org/patches/SA-18:07/lazyfpu-11.patch
    # fetch https://security.FreeBSD.org/patches/SA-18:07/lazyfpu-11.patch.asc
    # gpg --verify lazyfpu-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/11/ r335169 releng/11.2/ r335196 releng/11.1/ r335465
    - -------------------------------------------------------------------------

    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-00145.html>

    <URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-3665>

    The latest revision of this advisory is available at <URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-18:07.lazyfpu.asc> -----BEGIN PGP SIGNATURE-----

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