Off-by-one error in the __addr_ok macro in Xen 3.3 and earlier allows local 64 bit PV guest administrators to cause a denial of service (host crash) via unspecified hypercalls that ignore virtual-address bits.
http://rhn.redhat.com/errata/RHSA-2011-1212.html
http://secunia.com/advisories/55082
http://security.gentoo.org/glsa/glsa-201309-24.xml