Xen 3.x, possibly before 3.1.2, when running on IA64 systems, does not check the RID value for mov_to_rr, which allows a VTi domain to read memory of other domains.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A9471
http://www.securityfocus.com/bid/26716
http://www.redhat.com/support/errata/RHSA-2008-0154.html
http://secunia.com/advisories/29236
http://secunia.com/advisories/27915
http://lists.xensource.com/archives/html/xen-ia64-devel/2007-10/msg00189.html
http://lists.xensource.com/archives/html/xen-announce/2007-11/msg00000.html