The instruction decoder in arch/x86/kvm/emulate.c in the KVM subsystem in the Linux kernel before 3.18-rc2 lacks intended decoder-table flags for certain RIP-relative instructions, which allows guest OS users to cause a denial of service (NULL pointer dereference and host OS crash) via a crafted application.
https://bugzilla.redhat.com/show_bug.cgi?id=1156615
https://github.com/torvalds/linux/commit/3f6f1480d86bf9fc16c160d803ab1d006e3058d5