KVM: VMX: fix vmx null pointer dereference on debug register access

KVM: VMX: fix vmx null pointer dereference on debug register access

There is a bug in KVM that can be used to crash a host on Intel
machines. If emulator is tricked into emulating mov to/from DR instruction
it causes NULL pointer dereference on VMX since kvm_x86_ops->(set|get)_dr
are not initialized. Recently this is not exploitable from guest
userspace, but malicious guest kernel can trigger it easily.

CVE-2010-0435

On upstream bug was fixed differently around 2.6.34.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>