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.
git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git%3Ba=commit%3Bh=c2226fc9e87ba3da060e47333657cd6616652b84
lists.opensuse.org/opensuse-security-announce/2012-05/msg00013.html
www.kernel.org/pub/linux/kernel/v3.x/ChangeLog-3.2.14
www.openwall.com/lists/oss-security/2012/01/12/2
bugzilla.redhat.com/show_bug.cgi?id=773370
github.com/torvalds/linux/commit/c2226fc9e87ba3da060e47333657cd6616652b84