[PATCH 2/2] KVM: selftests: Add regression test for KVM writing but not reporting vmcs12

[Sean Christopherson <seanjc@google.com>]

When saving nested vCPU state, verify that KVM didn't write any more bytes
than it reported, and add a sync+save point in the state test to trigger a
save when L1 is active with a valid shadow VMCS.  Before commit <TBD>, KVM
would incorrectly save the shadow VMCS into the userspace buffer without
accounting for the size of the shadow VMCS.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 .../testing/selftests/kvm/lib/x86/processor.c |  6 +++++
 tools/testing/selftests/kvm/x86/state_test.c  | 24 ++++++++++---------
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/tools/testing/selftests/kvm/lib/x86/processor.c b/tools/testing/selftests/kvm/lib/x86/processor.c
index 8374afd08baf..976d53af6de7 100644
--- a/tools/testing/selftests/kvm/lib/x86/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86/processor.c
@@ -1282,10 +1282,16 @@ struct kvm_x86_state *vcpu_save_state(struct kvm_vcpu *vcpu)
 	if (nested_size) {
 		state->nested.size = sizeof(state->nested_);
 
+		memset(state->nested_, 0xaa, sizeof(state->nested_));
+
 		vcpu_nested_state_get(vcpu, &state->nested);
 		TEST_ASSERT(state->nested.size <= nested_size,
 			    "Nested state size too big, %i (KVM_CHECK_CAP gave %i)",
 			    state->nested.size, nested_size);
+
+		for (i = state->nested.size; i < nested_size; i++)
+			TEST_ASSERT((unsigned char)state->nested_[i] == 0xaa,
+				    "KVM killed the canary at offset %u", i);
 	} else {
 		state->nested.size = 0;
 	}
diff --git a/tools/testing/selftests/kvm/x86/state_test.c b/tools/testing/selftests/kvm/x86/state_test.c
index 500b09762555..5bd9a04a3911 100644
--- a/tools/testing/selftests/kvm/x86/state_test.c
+++ b/tools/testing/selftests/kvm/x86/state_test.c
@@ -60,13 +60,13 @@ void vmx_l2_guest_code(void)
 
 	/* L1 has now set up a shadow VMCS for us.  */
 	GUEST_ASSERT(vmread(GUEST_RIP) == 0xc0ffee);
-	GUEST_SYNC(10);
-	GUEST_ASSERT(vmread(GUEST_RIP) == 0xc0ffee);
-	vmwrite(GUEST_RIP, 0xc0fffee);
 	GUEST_SYNC(11);
+	GUEST_ASSERT(vmread(GUEST_RIP) == 0xc0ffee);
+	vmwrite(GUEST_RIP, 0xc0fffee);
+	GUEST_SYNC(12);
 	GUEST_ASSERT(vmread(GUEST_RIP) == 0xc0fffee);
 	vmwrite(GUEST_RIP, 0xc0ffffee);
-	GUEST_SYNC(12);
+	GUEST_SYNC(13);
 
 	/* Done, exit to L1 and never come back.  */
 	vmcall();
@@ -107,15 +107,17 @@ static void vmx_l1_guest_code(struct vmx_pages *vmx_pages)
 
 	vmwrite(SECONDARY_VM_EXEC_CONTROL, SECONDARY_EXEC_SHADOW_VMCS);
 	vmwrite(VMCS_LINK_POINTER, vmx_pages->shadow_vmcs_gpa);
-
-	vmptrld(vmx_pages->shadow_vmcs_gpa);
-	GUEST_ASSERT(__vmlaunch());
 	GUEST_SYNC(8);
-	GUEST_ASSERT(__vmlaunch());
-	GUEST_ASSERT(__vmresume());
 
-	vmwrite(GUEST_RIP, 0xc0ffee);
+	vmptrld(vmx_pages->shadow_vmcs_gpa);
+	GUEST_ASSERT(__vmlaunch());
 	GUEST_SYNC(9);
+
+	GUEST_ASSERT(__vmlaunch());
+	GUEST_ASSERT(__vmresume());
+
+	vmwrite(GUEST_RIP, 0xc0ffee);
+	GUEST_SYNC(10);
 	GUEST_ASSERT(vmread(GUEST_RIP) == 0xc0ffee);
 
 	vmptrld(vmx_pages->vmcs_gpa);
@@ -126,7 +128,7 @@ static void vmx_l1_guest_code(struct vmx_pages *vmx_pages)
 	GUEST_ASSERT(vmread(GUEST_RIP) == 0xc0ffffee);
 	GUEST_ASSERT(__vmlaunch());
 	GUEST_ASSERT(__vmresume());
-	GUEST_SYNC(13);
+	GUEST_SYNC(14);
 	GUEST_ASSERT(vmread(GUEST_RIP) == 0xc0ffffee);
 	GUEST_ASSERT(__vmlaunch());
 	GUEST_ASSERT(__vmresume());
-- 
2.56.0.218.g1ec904b173-goog