Code: static int handle_vmptrst(struct kvm_vcpu *vcpu)
{
	unsigned long exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
	u32 vmx_instruction_info = vmcs_read32(VMX_INSTRUCTION_INFO);
	gva_t vmcs_gva;
	struct x86_exception e;

	if (!nested_vmx_check_permission(vcpu))
		return 1;

 	if (get_vmx_mem_address(vcpu, exit_qualification,
 			vmx_instruction_info, true, &vmcs_gva))
 		return 1;
	/* ok to use *_system, as hardware has verified cpl=0 */
 	if (kvm_write_guest_virt_system(&vcpu->arch.emulate_ctxt, vmcs_gva,
 				 (void *)&to_vmx(vcpu)->nested.current_vmptr,
 				 sizeof(u64), &e)) {
		kvm_inject_page_fault(vcpu, &e);
		return 1;
	}
	nested_vmx_succeed(vcpu);
	return kvm_skip_emulated_instruction(vcpu);
}

Vulnerability Type: DoS 
CWE ID: 
Summary: In arch/x86/kvm/vmx.c in the Linux kernel before 4.17.2, when nested virtualization is used, local attackers could cause L1 KVM guests to VMEXIT, potentially allowing privilege escalations and denial of service attacks due to lack of checking of CPL.
Commit Message: kvm: nVMX: Enforce cpl=0 for VMX instructions

VMX instructions executed inside a L1 VM will always trigger a VM exit
even when executed with cpl 3. This means we must perform the
privilege check in software.

Fixes: 70f3aac964ae("kvm: nVMX: Remove superfluous VMX instruction fault checks")
Cc: stable@vger.kernel.org
Signed-off-by: Felix Wilhelm <fwilhelm@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>