The Xen Security team recently disclosed a vulnerability, Xen Security Advisory 7 (CVE-2012-0217), which would allow guest administrators to escalate to hypervisor-level privileges. The impact is much wider than Xen; many other operating systems seem to have the same vulnerability, including NetBSD, FreeBSD, some versions of Microsoft Windows (including Windows 7), and possibly Apple OSX.
So what was the vulnerability? It has to do with a subtle difference in the way in which Intel processors implement error handling in their version of AMDâ€™s SYSRET instruction. The SYSRET instruction is part of the x86-64 standard defined by AMD. If an operating system is written according to AMDâ€™s spec, but run on Intel hardware, the difference in implementation can be exploited by an attacker to write to arbitrary addresses in the operating systemâ€™s memory. This blog will explore the technical details of the vulnerability.