kernel: kvm: invalid opcode oops on SET_SREGS with OSXSAVE bit set

The KVM subsystem in the Linux kernel before 3.6.9, when running on hosts that use qemu userspace without XSAVE, allows local users to cause a denial of service kernel OOPS by using the KVMSETSREGS ioctl to set the X86CR4OSXSAVE bit in the guest cr4 register, then calling the KVMRUN ioctl...