KVM: x86: hyper-v: Check if guest is allowed to use XMM registers for hypercall input

TLFS states that "Availability of the XMM fast hypercall interface is
indicated via the “Hypervisor Feature Identification” CPUID Leaf
(0x40000003, see section 2.4.4) ... Any attempt to use this interface
when the hypervisor does not indicate availability will result in a #UD
fault."

Implement the check for 'strict' mode (KVM_CAP_HYPERV_ENFORCE_CPUID).
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Siddharth Chandrasekaran <sidcha@amazon.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210730122625.112848-4-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/hyperv.c

@@ -2140,6 +2140,7 @@ static bool hv_check_hypercall_access(struct kvm_vcpu_hv *hv_vcpu, u16 code)
 
 int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
 {
+	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
 	struct kvm_hv_hcall hc;
 	u64 ret = HV_STATUS_SUCCESS;
 
@@ -2177,13 +2178,21 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
 	trace_kvm_hv_hypercall(hc.code, hc.fast, hc.rep_cnt, hc.rep_idx,
 			       hc.ingpa, hc.outgpa);
 
-	if (unlikely(!hv_check_hypercall_access(to_hv_vcpu(vcpu), hc.code))) {
+	if (unlikely(!hv_check_hypercall_access(hv_vcpu, hc.code))) {
 		ret = HV_STATUS_ACCESS_DENIED;
 		goto hypercall_complete;
 	}
 
-	if (hc.fast && is_xmm_fast_hypercall(&hc))
+	if (hc.fast && is_xmm_fast_hypercall(&hc)) {
+		if (unlikely(hv_vcpu->enforce_cpuid &&
+			     !(hv_vcpu->cpuid_cache.features_edx &
+			       HV_X64_HYPERCALL_XMM_INPUT_AVAILABLE))) {
+			kvm_queue_exception(vcpu, UD_VECTOR);
+			return 1;
+		}
+
 		kvm_hv_hypercall_read_xmm(&hc);
+	}
 
 	switch (hc.code) {
 	case HVCALL_NOTIFY_LONG_SPIN_WAIT: