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@xxxxxxxxx>
---
v2: Rework the patch to fix the underlying bug of not catching nested
VMEntry with invalid guest state and unrestricted guest disabled.
v1: https://patchwork.kernel.org/patch/10259397
arch/x86/kvm/vmx.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 5912148..e4858f6 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -6823,6 +6823,13 @@ 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;
@@ -10945,6 +10952,14 @@ 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))
--
2.7.4
