Xen Security Advisory XSA-174 hugetlbfs use may crash PV Linux guests *** EMBARGOED UNTIL 2016-04-14 12:00 UTC *** ISSUE DESCRIPTION ================= Huge (2Mb) pages are generally unavailable to PV guests. Since x86 Linux pvops-based kernels are generally multi purpose, they would normally be built with hugetlbfs support enabled. Use of that functionality by an application in a PV guest would cause an infinite page fault loop, and an OOPS to occur upon an attempt to terminate the hung application. IMPACT ====== Depending on the guest kernel configuration, the OOPS could result in a kernel crash (guest DoS). VULNERABLE SYSTEMS ================== All upstream x86 Linux versions operating as PV Xen guests are vulnerable. ARM systems are not vulnerable. x86 HVM guests are not vulnerable. x86 Linux versions derived from linux-2.6.18-xen.hg (XenoLinux) are not vulnerable. Oracle Unbreakable Enterprise Kernels are not vulnerable. We believe that non-Linux guests are not vulnerable, as we are not aware of any with an analogous bug. MITIGATION ========== Running only HVM guests will avoid this issue. Not enabling hugetlbfs use, by not altering the boot time default value of zero in /proc/sys/vm/nr_hugepages (which can only be written by the root user) will avoid this issue. It is possible that disabling (or not enabling) the "panic on OOPS" behavior (via use of the "oops=panic" command line option or the "panic_on_oops" sysctl) will also avoid this issue, by limiting the effect to an application crash. We are not currently sure whether this is an effective mitigation, as we are not sure whether any locks or mutexes are held at the point of the crash. RESOLUTION ========== Applying the attached patch resolves this issue. xsa174.patch Linux 4.5.x ... 3.10.x $ sha256sum xsa174* 1d8da3ea221b7d38df8330650f6e455df5431760d695e7dd6384e2725dcf5b25 xsa174.patch $ DEPLOYMENT DURING EMBARGO ========================= Deployment of patches or mitigations is NOT permitted (except where all the affected systems and VMs are administered and used only by organisations which are members of the Xen Project Security Issues Predisclosure List). Specifically, deployment on public cloud systems is NOT permitted. This is because such host configuration changes would be user mode visible, which could lead to the rediscovery of the vulnerability. But: Distribution of updated software is prohibited (except to other members of the predisclosure list). Predisclosure list members who wish to deploy significantly different patches and/or mitigations, please contact the Xen Project Security Team. (Note: this during-embargo deployment notice is retained in post-embargo publicly released Xen Project advisories, even though it is then no longer applicable. This is to enable the community to have oversight of the Xen Project Security Team's decisionmaking.) For more information about permissible uses of embargoed information, consult the Xen Project community's agreed Security Policy: http://www.xenproject.org/security-policy.html
CVE-2016-3961 (http://nvd.nist.gov/nvd.cfm?cvename=CVE-2016-3961): Xen and the Linux kernel through 4.5.x do not properly suppress hugetlbfs support in x86 PV guests, which allows local PV guest users to cause a denial of service (guest OS crash) by attempting to access a hugetlbfs mapped area.
This patch is not for app-emulation/xen. The patch is a kernel patch
Re-Assigning to kernel team.
The patch is already present in >=linux-3.2.81 >=linux-3.16.36 >=linux-3.18.33 >=linux-4.1.24 >=linux-4.4.9 however it is missing from LTS kernels - linux-3.4 - linux-3.10 - linux-3.12 I contacted linux stable mailing list. Patch is already queued for next linux-3.10 kernel. So we should make a progress when the next LTS kernels are out.
Security, can you please close this obsolete one? Thanks
