[Xen-devel] Xen Security Advisory 75 - Host crash due to guest VMX instruction execution

[Xen.org security team <security@xxxxxxx>]

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                  Xen Security Advisory XSA-75

           Host crash due to guest VMX instruction execution

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
0b2da4ede6507713c75e313ba468b1fd7110e5696974ab72e2135f41ee393a8b  
xsa75-4.2.patch
91936421279fd2fa5321d9ed5a2b71fe76bc0e1348e67126e8b9cde0cb1d32b2  
xsa75-4.3-unstable.patch
$
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Attachment: xsa75-4.2.patch
Description: Binary data

Attachment: xsa75-4.3-unstable.patch
Description: Binary data

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