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

Certain internal state is set up, during domain construction, in
preparation for possible pass-through device assignment.  On ARM and
AMD V-i hardware this setup includes memory allocation.  On guest
teardown, cleanup was erroneously only performed when the guest
actually had a pass-through device assigned.

IMPACT
======

A malicious guest may, by frequently rebooting over extended periods
of time, run the system out of memory, resulting in a Denial of
Service (DoS).

The leak is no more than 4kbytes per guest boot.

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

Xen versions 3.3 and later are affected.

ARM systems, and x86 AMD systems, are affected.  Intel systems, and
systems without IOMMU/SMMU hardware, are unaffected.

All guest kinds can exploit this vulnerability.

MITIGATION
==========

Limiting the frequency with which a guest is able to reboot, will
limit the memory leak.

Rebooting each host (after migrating its guests) periodically will
reclaim the leaked space.

External References:

http://xenbits.xen.org/xsa/advisory-207.html

Acknowledgements:

Name: the Xen project