The get_page_from_gfn hypercall function in Xen 4.2 allows local PV guest OS administrators to cause a denial of service (crash) via a crafted GFN that triggers a buffer over-read.
https://exchange.xforce.ibmcloud.com/vulnerabilities/80480
http://www.securityfocus.com/bid/56805
http://www.openwall.com/lists/oss-security/2012/12/03/6
http://security.gentoo.org/glsa/glsa-201309-24.xml