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.
https://bugzilla.redhat.com/show_bug.cgi?id=728042
http://www.openwall.com/lists/oss-security/2011/09/02/2
http://security.gentoo.org/glsa/glsa-201309-24.xml