• [FreeBSD-Announce] FreeBSD Errata Notice FreeBSD-EN-18:17.vm

    From FreeBSD Errata Notices@21:1/5 to All on Wed Dec 19 22:00:00 2018
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    ============================================================================= FreeBSD-EN-18:17.vm Errata Notice
    The FreeBSD Project

    Topic: Kernel panic under load on Intel "Skylake" CPUs

    Category: core
    Module: kernel
    Announced: 2018-12-19
    Credits: Mark Johnston
    Affects: FreeBSD 11.2
    Corrected: 2018-12-02 18:08:27 UTC (stable/11, 11.2-STABLE)
    2018-19-19 18:00:58 UTC (releng/11.2, 11.2-RELEASE-p7)

    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 physical page allocator is a component of the kernel responsible for tracking usage of the system's RAM by the kernel and by userland
    applications. It maintains lists of unused memory pages which may be
    returned by the allocator upon demand. It also maintains an integer
    count of the number of pages stored in these lists.

    II. Problem Description

    The kernel contains handling for an Intel erratum affecting Skylake-X
    CPUs. The erratum description states that a processor may hang when
    performing a certain synchronization operation within a particular 4MB
    region of physical memory. FreeBSD works around the erratum by using
    a blacklisting mechanism to ensure that the physical page allocator
    never returns pages in that region. However, this blacklisting
    mechanism contained a bug such that the removal of pages in the region
    was not reflected in the free page count.

    III. Impact

    The discrepancy between the free page count and the physical page
    allocator's state can trigger a NULL pointer dereference when the
    system is under heavy load, resulting in a panic.

    IV. Workaround

    Only systems using a Skylake-X or Skylake Server CPU are affected.

    Affected systems can work around the problem by setting the
    "hw.skz63_enable" to 0 in /boot/loader.conf, causing the handling for
    the Intel erratum to be disabled upon a reboot of the system. However,
    this raises the possibility of being affected by the erratum if software running on the system makes use of Intel TSX.

    V. Solution

    Perform one of the following:

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

    2) To update your 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
    Reboot the system

    3) 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.

    [FreeBSD 11.2]
    # fetch https://security.FreeBSD.org/patches/EN-18:17/vm.patch
    # fetch https://security.FreeBSD.org/patches/EN-18:17/vm.patch.asc
    # gpg --verify vm.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/ r341401 releng/11.2/ r342225
    - -------------------------------------------------------------------------

    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://bugs.freebsd.org/bugzilla/show_bug.cgi?id=231296>

    The latest revision of this advisory is available at <URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-18:17.vm.asc> -----BEGIN PGP SIGNATURE-----

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