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Advisory

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             Xen Security Advisory CVE-2013-4551 / XSA-75
                              version 2

           Host crash due to guest VMX instruction execution

UPDATES IN VERSION 2
====================

This issue has been assigned CVE-2013-4551.

ISSUE DESCRIPTION
=================

Permission checks on the emulation paths (intended for guests using
nested virtualization) for VMLAUNCH and VMRESUME were deferred too
much.  The hypervisor would try to use internal state which is not set
up unless nested virtualization is actually enabled for a guest.

IMPACT
======

A malicious or misbehaved HVM guest, including malicious or misbehaved user
mode code run in the guest, might be able to crash the host.

VULNERABLE SYSTEMS
==================

Xen 4.2.x and later are vulnerable.
Xen 4.1.x and earlier are not vulnerable.

Only HVM guests run on VMX capable (e.g. Intel) hardware can take
advantage of this vulnerability.

MITIGATION
==========

Running only PV guests, or running HVM guests on SVM capable
(e.g. AMD) hardware will avoid this issue.

Enabling nested virtualization for a HVM guest running on VMX capable
hardware would also allow avoiding the issue.  However this
functionality is still considered experimental, and is not covered by
security support from the Xen Project security team.  This approach is
therefore not recommended for use in production.

CREDITS
=======

This issue was discovered by Jeff Zimmerman.

NOTE REGARDING LACK OF EMBARGO
==============================

This issue was disclosed publicly on the xen-devel mailing list.

RESOLUTION
==========

Applying the appropriate attached patch resolves this issue.

xsa75-4.3-unstable.patch    Xen 4.3.x, xen-unstable
xsa75-4.2.patch             Xen 4.2.x

$ sha256sum xsa75*.patch
5d7bd39e4077dcdf97abf8cf3ceb662403bedf8642ce7d15840b329bc9e56727  xsa75-4.2.patch
7e61b457c9ad8d7c598d88163d2760041033ddb1631cfe989f853b7c2b5cd0bf  xsa75-4.3-unstable.patch
$
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