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             AUSCERT External Security Bulletin Redistribution

                         linux-4.9 security update
                             14 November 2019


        AusCERT Security Bulletin Summary

Product:           linux-4.9
Publisher:         Debian
Operating System:  Debian GNU/Linux 8
                   Debian GNU/Linux 9
Impact/Access:     Root Compromise        -- Existing Account
                   Access Privileged Data -- Existing Account
                   Denial of Service      -- Existing Account
Resolution:        Patch/Upgrade
CVE Names:         CVE-2019-11135 CVE-2019-0155 CVE-2019-0154

Reference:         ASB-2019.0330

Original Bulletin: 

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Package        : linux-4.9
Version        : 4.9.189-3+deb9u2~deb8u1
CVE ID         : CVE-2018-12207 CVE-2019-0154 CVE-2019-0155 CVE-2019-11135

Several vulnerabilities have been discovered in the Linux kernel that
may lead to a privilege escalation, denial of service, or information


    It was discovered that on Intel CPUs supporting hardware
    virtualisation with Extended Page Tables (EPT), a guest VM may
    manipulate the memory management hardware to cause a Machine Check
    Error (MCE) and denial of service (hang or crash).

    The guest triggers this error by changing page tables without a
    TLB flush, so that both 4 KB and 2 MB entries for the same virtual
    address are loaded into the instruction TLB (iTLB).  This update
    implements a mitigation in KVM that prevents guest VMs from
    loading 2 MB entries into the iTLB.  This will reduce performance
    of guest VMs.

    Further information on the mitigation can be found at
    or in the linux-doc-4.9 package.

    Intel's explanation of the issue can be found at


    Intel discovered that on their 8th and 9th generation GPUs,
    reading certain registers while the GPU is in a low-power state
    can cause a system hang.  A local user permitted to use the GPU
    can use this for denial of service.

    This update mitigates the issue through changes to the i915

    The affected chips (gen8 and gen9) are listed at


    Intel discovered that their 9th generation and newer GPUs are
    missing a security check in the Blitter Command Streamer (BCS).  A
    local user permitted to use the GPU could use this to access any
    memory that the GPU has access to, which could result in a denial
    of service (memory corruption or crash), a leak of sensitive
    information, or privilege escalation.

    This update mitigates the issue by adding the security check to
    the i915 driver.

    The affected chips (gen9 onward) are listed at


    It was discovered that on Intel CPUs supporting transactional
    memory (TSX), a transaction that is going to be aborted may
    continue to execute speculatively, reading sensitive data from
    internal buffers and leaking it through dependent operations.
    Intel calls this "TSX Asynchronous Abort" (TAA).

    For CPUs affected by the previously published Microarchitectural
    Data Sampling (MDS) issues (CVE-2018-12126, CVE-2018-12127,
    CVE-2018-12130, CVE-2019-11091), the existing mitigation also
    mitigates this issue.

    For processors that are vulnerable to TAA but not MDS, this update
    disables TSX by default.  This mitigation requires updated CPU
    microcode.  An updated intel-microcode package (only available in
    Debian non-free) will be provided via a future DLA.  The updated
    CPU microcode may also be available as part of a system firmware
    ("BIOS") update.

    Further information on the mitigation can be found at
    or in the linux-doc-4.9 package.

    Intel's explanation of the issue can be found at

For Debian 8 "Jessie", these problems have been fixed in version

We recommend that you upgrade your linux-4.9 packages.

Further information about Debian LTS security advisories, how to apply
these updates to your system and frequently asked questions can be
found at: https://wiki.debian.org/LTS

- --
Ben Hutchings - Debian developer, member of kernel, installer and LTS teams

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