[Ksplice][Debian 9.0 Updates] New Ksplice updates for Debian 9.0 Stretch (DSA-4279)

[Jamie Iles]

Synopsis: DSA-4279 can now be patched using Ksplice
CVEs: CVE-2018-3620 CVE-2018-3646

Systems running Debian 9.0 Stretch can now use Ksplice to patch
against the latest Debian Security Advisory, DSA-4279.

INSTALLING THE UPDATES

We recommend that all users of Ksplice Uptrack running Debian 9.0
Stretch install these updates.

On systems that have "autoinstall = yes" in /etc/uptrack/uptrack.conf,
these updates will be installed automatically and you do not need to
take any action.

Alternatively, you can install these updates by running:

# /usr/sbin/uptrack-upgrade -y


DESCRIPTION

* CVE-2018-3620, CVE-2018-3646: Information leak in Intel CPUs under terminal fault (x86_64 only).

A flaw in terminal fault handling on Intel CPUs could result in
information leaks across privilege boundaries including between
processes on a system or between virtual machines.

Mitigations for these CVEs include disabling SMT (HyperThreading) on
affected Intel CPUs, extra L1 data cache flushing when running virtual
machines when EPT is supported.  Both of these mitigations have workload
dependent performance implications and can be tuned by the
administrator.  This update will immediately enable L1 data cache
flushes on Intel CPUs if KVM is in use.  Where untrusted guests are in
use it is recommended to disable SMT.

NOTE: on non-64 bit systems, this update does not cover page table
transformations and so is not a full mitigation.

SMT disable:

/sys/devices/system/cpu/smt/control: write "on" to enable SMT, "off" to
disable SMT.  Default: on.

L1D flushing:

/sys/module/kvm_intel/parameters/vmentry_l1d_flush, write:
  - "never": disable L1D flushing, leaving CVE-2018-3620 unmitigated but
  no noticeable performance impact
  - "cond": flush only in high risk transfers, mitigates CVE-2018-3620
  with the minimum number of flushes
  - "always": flush on every VM entry, fully mitigates CVE-2018-3620
  with the most overhead.
Default: "always"

SUPPORT

Ksplice support is available at ksplice-support_ww at oracle.com.