When a guest increases the set of extended state components for a vCPU saved/restored via XSAVE/XRSTOR (to date this can only be the upper halves of YMM registers, or AMD's LWP state) after already having touched other extended registers restored via XRSTOR (e.g. floating point or XMM ones) during its current scheduled CPU quantum, the hypervisor would make those registers accessible without discarding the values an earlier scheduled vCPU may have left in them. A malicious domain may be able to leverage this to obtain sensitive information such as cryptographic keys from another domain. Acknowledgements: Red Hat would like to thank the Xen project for reporting this issue.
Statement: Not vulnerable. This issue did not affect the versions of the kernel-xen package as shipped with Red Hat Enterprise Linux 5. This issue did not affect Red Hat Enterprise Linux 6 and Red Hat Enterprise MRG 2 as we did not have support for Xen hypervisor.
External References: http://xenbits.xen.org/xsa/advisory-62.html
Created xen tracking bugs for this issue: Affects: fedora-all [bug 1012056]