[Xen-announce] Xen Security Advisory 113 - Guest effectable page reference leak in MMU_MACHPHYS_UPDATE handling

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

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                    Xen Security Advisory XSA-113

  Guest effectable page reference leak in MMU_MACHPHYS_UPDATE handling

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

An error handling path in the processing of MMU_MACHPHYS_UPDATE failed
to drop a page reference which was acquired in an earlier processing
step.

IMPACT
======

Malicious or buggy stub domain kernels or tool stacks otherwise living
outside of Domain0 can mount a denial of service attack which, if
successful, can affect the whole system.

Only domains controlling HVM guests can exploit this vulnerability.
(This includes domains providing hardware emulation services to HVM
guests.)

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

Xen versions from at least 3.2.x onwards are vulnerable on x86 systems.
Older versions have not been inspected.  ARM systems are not vulnerable.

This vulnerability is only applicable to Xen systems using stub domains
or other forms of disaggregation of control domains for HVM guests.

MITIGATION
==========

Running only PV guests will avoid this issue.

(The security of a Xen system using stub domains is still better than
with a qemu-dm running as an unrestricted dom0 process.  Therefore
users with these configurations should not switch to an unrestricted
dom0 qemu-dm.)

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

A draft of this advisory was mistakenly sent to xen-devel.  The Xen
Project Security Team apologises for this error.  We are working to
share best working practices amongst the team to reduce the risks of
recurrance.

CREDITS
=======

This issue was discovered by Andrew Cooper of Citrix.

RESOLUTION
==========

Applying the attached patch resolves this issue.

xsa113.patch        xen-unstable, Xen 4.4.x, Xen 4.3.x, Xen 4.2.x

$ sha256sum xsa113*.patch
a0f2b792a6b4648151f85fe13961b0bf309a568ed03e1b1d4ea01e4eabf1b18e  xsa113.patch
$
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Attachment: xsa113.patch
Description: Binary data

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