kernel: KVM: NULL pointer dereference in kvm_mmu_invpcid_gva

A flaw was found in KVM. With shadow paging enabled if INVPCID is executed with CR0.PG=0, the invlpg callback is not set, and the result is a NULL pointer dereference. This flaw allows a guest user to cause a kernel oops condition on the host, resulting in a denial of service...