|Public release ||2016-12-21 12:00|
|Updated ||2016-12-21 12:01|
|Title ||x86: missing NULL pointer check in VMFUNC emulation|
Filesadvisory-203.txt (signed advisory file)
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Xen Security Advisory CVE-2016-10025 / XSA-203
x86: missing NULL pointer check in VMFUNC emulation
UPDATES IN VERSION 3
When support for the Intel VMX VMFUNC leaf 0 was added, a new optional
function pointer hvmemul_vmfunc was added to the hvm_emulate_ops
table. As is intended, that new function pointer is NULL on non-VMX
hardware, including AMD SVM hardware. However at a call site, the
necessary NULL check was omitted before the indirect function call.
Malicious guests may cause a hypervisor crash, resulting in a Denial
of Service (DoS).
Xen versions 4.6 and newer are vulnerable. Xen versions 4.5 and earlier
are not vulnerable.
Only HVM guests can exploit the vulnerability. PV guests cannot exploit
Only x86 systems using SVM (AMD virtualisation extensions) rather than
VMX (Intel virtualisation extensions) are vulnerable. This applies to
HVM guests on AMD x86 CPUs. Therefore AMD x86 hardware is vulnerable;
Intel hardware is not vulnerable.
ARM systems are not vulnerable.
Running only PV guests will avoid this vulnerability.
Running HVM guests on only VMX capable hardware will also avoid this
This issue was discovered by Jan Beulich of SUSE.
Applying the appropriate attached patch resolves this issue.
xsa203-4.8.patch Xen 4.8.x
xsa203-4.7.patch Xen 4.7.x, Xen 4.6.x
$ sha256sum xsa203*
DEPLOYMENT DURING EMBARGO
Deployment of the patches and/or mitigations described above (or
others which are substantially similar) is permitted during the
embargo, even on public-facing systems with untrusted guest users and
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
(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is then no longer applicable.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:
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Xenproject.org Security Team