The em_syscall function in arch/x86/kvm/emulate.c in the KVM implementation in the Linux kernel before 3.2.14 does not properly handle the 0f05 (aka syscall) opcode, which allows guest OS users to cause a denial of service (guest OS crash) via a crafted application, as demonstrated by an NASM file.
https://github.com/torvalds/linux/commit/c2226fc9e87ba3da060e47333657cd6616652b84
https://euvd.enisa.europa.eu/vulnerability/EUVD-2012-0085
https://bugzilla.redhat.com/show_bug.cgi?id=773370
http://www.openwall.com/lists/oss-security/2012/01/12/2
http://www.kernel.org/pub/linux/kernel/v3.x/ChangeLog-3.2.14
http://lists.opensuse.org/opensuse-security-announce/2012-05/msg00013.html