KVM: vVMX: signal failure for nested VMEntry if emulation_required

Fail a nested VMEntry with EXIT_REASON_INVALID_STATE if L2 guest state
is invalid, i.e. vmcs12 contained invalid guest state, and unrestricted
guest is disabled in L0 (and by extension disabled in L1).

WARN_ON_ONCE in handle_invalid_guest_state() if we're attempting to
emulate L2, i.e. nested_run_pending is true, to aid debug in the
(hopefully unlikely) scenario that we somehow skip the nested VMEntry
consistency check, e.g. due to a L0 bug.

Note: KVM relies on hardware to detect the scenario where unrestricted
guest is enabled in L0 but disabled in L1 and vmcs12 contains invalid
guest state, i.e. checking emulation_required in prepare_vmcs02 is
required only to handle the case were unrestricted guest is disabled
in L0 since L0 never actually attempts VMLAUNCH/VMRESUME with vmcs02.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 6cefd7b3ff7fc451a9e01875459ce2579043aadc..5d67a15b51160c8d072c57f320f2ba546da07afc 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -6865,6 +6865,13 @@ static int handle_invalid_guest_state(struct kvm_vcpu *vcpu)
        bool intr_window_requested;
        unsigned count = 130;
 
+       /*
+        * We should never reach the point where we are emulating L2
+        * due to invalid guest state as that means we incorrectly
+        * allowed a nested VMEntry with an invalid vmcs12.
+        */
+       WARN_ON_ONCE(vmx->emulation_required && vmx->nested.nested_run_pending);
+
        cpu_exec_ctrl = vmcs_read32(CPU_BASED_VM_EXEC_CONTROL);
        intr_window_requested = cpu_exec_ctrl & CPU_BASED_VIRTUAL_INTR_PENDING;
 
@@ -10990,6 +10997,14 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
                vmx->nested.dirty_vmcs12 = false;
        }
 
+       /*
+        * Guest state is invalid and unrestricted guest is disabled,
+        * which means L1 attempted VMEntry to L2 with invalid state.
+        * Fail the VMEntry.
+        */
+       if (vmx->emulation_required)
+               return 1;
+
        /* Shadow page tables on either EPT or shadow page tables. */
        if (nested_vmx_load_cr3(vcpu, vmcs12->guest_cr3, nested_cpu_has_ept(vmcs12),
                                entry_failure_code))