KVM: x86: emulate RDPID

CVE-2020-2732

commit fb6d4d34 upstream.

This is encoded as F3 0F C7 /7 with a register argument.  The register
argument is the second array in the group9 GroupDual, while F3 is the
fourth element of a Prefix.
Reviewed-by: Wanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Acked-by: Benjamin M Romer <benjamin.romer@canonical.com>
Acked-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

arch/x86/kvm/cpuid.c

@@ -269,13 +269,18 @@ static int __do_cpuid_ent_emulated(struct kvm_cpuid_entry2 *entry,
 {
 	switch (func) {
 	case 0:
-		entry->eax = 1;		/* only one leaf currently */
+		entry->eax = 7;
 		++*nent;
 		break;
 	case 1:
 		entry->ecx = F(MOVBE);
 		++*nent;
 		break;
+	case 7:
+		entry->flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
+		if (index == 0)
+			entry->ecx = F(RDPID);
+		++*nent;
 	default:
 		break;
 	}

arch/x86/kvm/emulate.c

@@ -3518,6 +3518,16 @@ static int em_cwd(struct x86_emulate_ctxt *ctxt)
 	return X86EMUL_CONTINUE;
 }
 
+static int em_rdpid(struct x86_emulate_ctxt *ctxt)
+{
+	u64 tsc_aux = 0;
+
+	if (ctxt->ops->get_msr(ctxt, MSR_TSC_AUX, &tsc_aux))
+		return emulate_gp(ctxt, 0);
+	ctxt->dst.val = tsc_aux;
+	return X86EMUL_CONTINUE;
+}
+
 static int em_rdtsc(struct x86_emulate_ctxt *ctxt)
 {
 	u64 tsc = 0;
@@ -4378,10 +4388,20 @@ static const struct opcode group8[] = {
 	F(DstMem | SrcImmByte | Lock | PageTable,	em_btc),
 };
 
+/*
+ * The "memory" destination is actually always a register, since we come
+ * from the register case of group9.
+ */
+static const struct gprefix pfx_0f_c7_7 = {
+	N, N, N, II(DstMem | ModRM | Op3264 | EmulateOnUD, em_rdpid, rdtscp),
+};
+
+
 static const struct group_dual group9 = { {
 	N, I(DstMem64 | Lock | PageTable, em_cmpxchg8b), N, N, N, N, N, N,
 }, {
-	N, N, N, N, N, N, N, N,
+	N, N, N, N, N, N, N,
+	GP(0, &pfx_0f_c7_7),
 } };
 
 static const struct opcode group11[] = {

arch/x86/kvm/vmx.c

@@ -11034,6 +11034,21 @@ static int vmx_check_intercept(struct kvm_vcpu *vcpu,
 			       struct x86_instruction_info *info,
 			       enum x86_intercept_stage stage)
 {
+	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
+	struct x86_emulate_ctxt *ctxt = &vcpu->arch.emulate_ctxt;
+
+	/*
+	 * RDPID causes #UD if disabled through secondary execution controls.
+	 * Because it is marked as EmulateOnUD, we need to intercept it here.
+	 */
+	if (info->intercept == x86_intercept_rdtscp &&
+	    !nested_cpu_has2(vmcs12, SECONDARY_EXEC_RDTSCP)) {
+		ctxt->exception.vector = UD_VECTOR;
+		ctxt->exception.error_code_valid = false;
+		return X86EMUL_PROPAGATE_FAULT;
+	}
+
+	/* TODO: check more intercepts... */
 	return X86EMUL_CONTINUE;
 }