[PATCH v2 4/4] KVM: selftests: Check VMPTRLD with active eVMCS

[Vitaly Kuznetsov]

Check that VMPTRLD when eVMCS is active results in #UD. This matches
genuine Hyper-V's behavior.

Use KVM_ASM_SAFE framework to handle #UD from VMPTRLD. Unfortunately, the
same trick cannot be applied to the existing #UD check on VMLAUNCH as
VMLAUNCH clobbers all registers which KVM_ASM_SAFE depends on. Keep
VMLAUNCH handling separately.

Assisted-by: Claude:claude-sonnet-4-6
Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
 tools/testing/selftests/kvm/include/x86/vmx.h | 19 +++++++++++---
 .../testing/selftests/kvm/x86/hyperv_evmcs.c  | 26 +++++++++++++++----
 2 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/x86/vmx.h b/tools/testing/selftests/kvm/include/x86/vmx.h
index 047d02aa9688..e6adde3970d4 100644
--- a/tools/testing/selftests/kvm/include/x86/vmx.h
+++ b/tools/testing/selftests/kvm/include/x86/vmx.h
@@ -325,9 +325,6 @@ static inline int vmptrld(u64 vmcs_pa)
 {
 	u8 ret;
 
-	if (enable_evmcs)
-		return -1;
-
 	__asm__ __volatile__ ("vmptrld %[pa]; setna %[ret]"
 		: [ret]"=rm"(ret)
 		: [pa]"m"(vmcs_pa)
@@ -336,6 +333,22 @@ static inline int vmptrld(u64 vmcs_pa)
 	return ret;
 }
 
+static inline int vmptrld_safe(u64 vmcs_pa)
+{
+	u64 error_code;
+	u8 vector;
+	u8 failed;
+
+	asm volatile(KVM_ASM_SAFE("vmptrld %[pa]")
+		     "\n\tsetna %[failed]"
+		     : KVM_ASM_SAFE_OUTPUTS(vector, error_code),
+		       [failed]"=qm"(failed)
+		     : [pa]"m"(vmcs_pa)
+		     : "cc", "memory", KVM_ASM_SAFE_CLOBBERS);
+
+	return vector ? vector : failed ? -EINVAL : 0;
+}
+
 static inline int vmptrst(u64 *value)
 {
 	u64 tmp;
diff --git a/tools/testing/selftests/kvm/x86/hyperv_evmcs.c b/tools/testing/selftests/kvm/x86/hyperv_evmcs.c
index 88262ddf7fcb..cff27638834b 100644
--- a/tools/testing/selftests/kvm/x86/hyperv_evmcs.c
+++ b/tools/testing/selftests/kvm/x86/hyperv_evmcs.c
@@ -23,7 +23,11 @@ static int ud_count;
 static void guest_ud_handler(struct ex_regs *regs)
 {
 	ud_count++;
-	regs->rip += 3; /* VMLAUNCH */
+	/*
+	 * VMLAUNCH insn can't be easily covered by KVM_ASM_SAFE framework but
+	 * luckily the instruction is always three bytes.
+	 */
+	regs->rip += 3;
 }
 
 static void guest_nmi_handler(struct ex_regs *regs)
@@ -182,7 +186,15 @@ void guest_code(struct vmx_pages *vmx_pages, struct hyperv_test_pages *hv_pages,
 	GUEST_ASSERT(vmreadz(VM_EXIT_REASON) == EXIT_REASON_VMCALL);
 	GUEST_SYNC(11);
 
-	/* Try enlightened vmptrld with an incorrect GPA */
+	/* VMPTRLD instruction causes #UD after enlightened VMLAUNCH */
+	GUEST_ASSERT(vmptrld_safe(hv_pages->enlightened_vmcs_gpa) == UD_VECTOR);
+
+	/*
+	 * Try enlightened vmptrld with an incorrect GPA. GUEST_SYNC(12) signals
+	 * the host to enable guest_ud_handler() which cannot be enabled beforehand
+	 * to not override the default fixup handler from KVM_ASM_SAFE().
+	 */
+	GUEST_SYNC(12);
 	evmcs_vmptrld(0xdeadbeef, hv_pages->enlightened_vmcs);
 	GUEST_ASSERT(vmlaunch());
 	GUEST_ASSERT(ud_count == 1);
@@ -256,7 +268,6 @@ int main(int argc, char *argv[])
 	vcpu_args_set(vcpu, 3, vmx_pages_gva, hv_pages_gva, addr_gva2gpa(vm, hcall_page));
 	vcpu_set_msr(vcpu, HV_X64_MSR_VP_INDEX, vcpu->id);
 
-	vm_install_exception_handler(vm, UD_VECTOR, guest_ud_handler);
 	vm_install_exception_handler(vm, NMI_VECTOR, guest_nmi_handler);
 
 	pr_info("Running L1 which uses EVMCS to run L2\n");
@@ -286,7 +297,7 @@ int main(int argc, char *argv[])
 
 		/* Force immediate L2->L1 exit before resuming */
 		if (stage == 8) {
-			pr_info("Injecting NMI into L1 before L2 had a chance to run after restore\n");
+			pr_debug("Injecting NMI into L1 before L2 had a chance to run after restore\n");
 			inject_nmi(vcpu);
 		}
 
@@ -296,9 +307,14 @@ int main(int argc, char *argv[])
 		 * KVM_STATE_NESTED_EVMCS is not lost.
 		 */
 		if (stage == 9) {
-			pr_info("Trying extra KVM_GET_NESTED_STATE/KVM_SET_NESTED_STATE cycle\n");
+			pr_debug("Trying extra KVM_GET_NESTED_STATE/KVM_SET_NESTED_STATE cycle\n");
 			vcpu = save_restore_vm(vm, vcpu);
 		}
+
+		if (stage == 12) {
+			pr_debug("Trying enlightened VMLAUNCH with an invalid PTR\n");
+			vm_install_exception_handler(vm, UD_VECTOR, guest_ud_handler);
+		}
 	}
 
 done:
-- 
2.55.0