Code: static bool nested_vmx_exit_handled(struct kvm_vcpu *vcpu)
{
	u32 intr_info = vmcs_read32(VM_EXIT_INTR_INFO);
	struct vcpu_vmx *vmx = to_vmx(vcpu);
	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
	u32 exit_reason = vmx->exit_reason;

	if (vmx->nested.nested_run_pending)
		return 0;

	if (unlikely(vmx->fail)) {
		pr_info_ratelimited("%s failed vm entry %x\n", __func__,
				    vmcs_read32(VM_INSTRUCTION_ERROR));
		return 1;
	}

	switch (exit_reason) {
	case EXIT_REASON_EXCEPTION_NMI:
		if (!is_exception(intr_info))
			return 0;
		else if (is_page_fault(intr_info))
			return enable_ept;
		return vmcs12->exception_bitmap &
				(1u << (intr_info & INTR_INFO_VECTOR_MASK));
	case EXIT_REASON_EXTERNAL_INTERRUPT:
		return 0;
	case EXIT_REASON_TRIPLE_FAULT:
		return 1;
	case EXIT_REASON_PENDING_INTERRUPT:
		return nested_cpu_has(vmcs12, CPU_BASED_VIRTUAL_INTR_PENDING);
	case EXIT_REASON_NMI_WINDOW:
		return nested_cpu_has(vmcs12, CPU_BASED_VIRTUAL_NMI_PENDING);
	case EXIT_REASON_TASK_SWITCH:
		return 1;
	case EXIT_REASON_CPUID:
		return 1;
	case EXIT_REASON_HLT:
		return nested_cpu_has(vmcs12, CPU_BASED_HLT_EXITING);
	case EXIT_REASON_INVD:
		return 1;
	case EXIT_REASON_INVLPG:
		return nested_cpu_has(vmcs12, CPU_BASED_INVLPG_EXITING);
	case EXIT_REASON_RDPMC:
		return nested_cpu_has(vmcs12, CPU_BASED_RDPMC_EXITING);
	case EXIT_REASON_RDTSC:
		return nested_cpu_has(vmcs12, CPU_BASED_RDTSC_EXITING);
	case EXIT_REASON_VMCALL: case EXIT_REASON_VMCLEAR:
	case EXIT_REASON_VMLAUNCH: case EXIT_REASON_VMPTRLD:
 	case EXIT_REASON_VMPTRST: case EXIT_REASON_VMREAD:
 	case EXIT_REASON_VMRESUME: case EXIT_REASON_VMWRITE:
 	case EXIT_REASON_VMOFF: case EXIT_REASON_VMON:
 		/*
 		 * VMX instructions trap unconditionally. This allows L1 to
 		 * emulate them for its L2 guest, i.e., allows 3-level nesting!
		 */
		return 1;
	case EXIT_REASON_CR_ACCESS:
		return nested_vmx_exit_handled_cr(vcpu, vmcs12);
	case EXIT_REASON_DR_ACCESS:
		return nested_cpu_has(vmcs12, CPU_BASED_MOV_DR_EXITING);
	case EXIT_REASON_IO_INSTRUCTION:
		return nested_vmx_exit_handled_io(vcpu, vmcs12);
	case EXIT_REASON_MSR_READ:
	case EXIT_REASON_MSR_WRITE:
		return nested_vmx_exit_handled_msr(vcpu, vmcs12, exit_reason);
	case EXIT_REASON_INVALID_STATE:
		return 1;
	case EXIT_REASON_MWAIT_INSTRUCTION:
		return nested_cpu_has(vmcs12, CPU_BASED_MWAIT_EXITING);
	case EXIT_REASON_MONITOR_INSTRUCTION:
		return nested_cpu_has(vmcs12, CPU_BASED_MONITOR_EXITING);
	case EXIT_REASON_PAUSE_INSTRUCTION:
		return nested_cpu_has(vmcs12, CPU_BASED_PAUSE_EXITING) ||
			nested_cpu_has2(vmcs12,
				SECONDARY_EXEC_PAUSE_LOOP_EXITING);
	case EXIT_REASON_MCE_DURING_VMENTRY:
		return 0;
	case EXIT_REASON_TPR_BELOW_THRESHOLD:
		return 1;
	case EXIT_REASON_APIC_ACCESS:
		return nested_cpu_has2(vmcs12,
			SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES);
	case EXIT_REASON_EPT_VIOLATION:
	case EXIT_REASON_EPT_MISCONFIG:
		return 0;
	case EXIT_REASON_PREEMPTION_TIMER:
		return vmcs12->pin_based_vm_exec_control &
			PIN_BASED_VMX_PREEMPTION_TIMER;
	case EXIT_REASON_WBINVD:
		return nested_cpu_has2(vmcs12, SECONDARY_EXEC_WBINVD_EXITING);
	case EXIT_REASON_XSETBV:
		return 1;
	default:
		return 1;
	}
}

Vulnerability Type: DoS 
CWE ID: CWE-20
Summary: arch/x86/kvm/vmx.c in the KVM subsystem in the Linux kernel before 3.12 does not have an exit handler for the INVEPT instruction, which allows guest OS users to cause a denial of service (guest OS crash) via a crafted application.
Commit Message: nEPT: Nested INVEPT

If we let L1 use EPT, we should probably also support the INVEPT instruction.

In our current nested EPT implementation, when L1 changes its EPT table
for L2 (i.e., EPT12), L0 modifies the shadow EPT table (EPT02), and in
the course of this modification already calls INVEPT. But if last level
of shadow page is unsync not all L1's changes to EPT12 are intercepted,
which means roots need to be synced when L1 calls INVEPT. Global INVEPT
should not be different since roots are synced by kvm_mmu_load() each
time EPTP02 changes.

Reviewed-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Nadav Har'El <nyh@il.ibm.com>
Signed-off-by: Jun Nakajima <jun.nakajima@intel.com>
Signed-off-by: Xinhao Xu <xinhao.xu@intel.com>
Signed-off-by: Yang Zhang <yang.z.zhang@Intel.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>