kvm: vmx: Raise #UD on unsupported RDSEED

A guest may not be configured to support RDSEED, even when the host
does. If the guest does not support RDSEED, intercept the instruction
and synthesize #UD. Also clear the "allowed-1" bit for RDSEED exiting
in the IA32_VMX_PROCBASED_CTLS2 MSR.
Signed-off-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx.c

@@ -2818,7 +2818,6 @@ static void nested_vmx_setup_ctls_msrs(struct vcpu_vmx *vmx)
 		vmx->nested.nested_vmx_secondary_ctls_high);
 	vmx->nested.nested_vmx_secondary_ctls_low = 0;
 	vmx->nested.nested_vmx_secondary_ctls_high &=
-		SECONDARY_EXEC_RDSEED |
 		SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES |
 		SECONDARY_EXEC_DESC |
 		SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE |
@@ -3671,6 +3670,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
 			SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY |
 			SECONDARY_EXEC_SHADOW_VMCS |
 			SECONDARY_EXEC_XSAVES |
+			SECONDARY_EXEC_RDSEED |
 			SECONDARY_EXEC_RDRAND |
 			SECONDARY_EXEC_ENABLE_PML |
 			SECONDARY_EXEC_TSC_SCALING |
@@ -5280,6 +5280,12 @@ static bool vmx_rdrand_supported(void)
 		SECONDARY_EXEC_RDRAND;
 }
 
+static bool vmx_rdseed_supported(void)
+{
+	return vmcs_config.cpu_based_2nd_exec_ctrl &
+		SECONDARY_EXEC_RDSEED;
+}
+
 static void vmx_compute_secondary_exec_control(struct vcpu_vmx *vmx)
 {
 	struct kvm_vcpu *vcpu = &vmx->vcpu;
@@ -5364,6 +5370,21 @@ static void vmx_compute_secondary_exec_control(struct vcpu_vmx *vmx)
 		}
 	}
 
+	if (vmx_rdseed_supported()) {
+		bool rdseed_enabled = guest_cpuid_has(vcpu, X86_FEATURE_RDSEED);
+		if (rdseed_enabled)
+			exec_control &= ~SECONDARY_EXEC_RDSEED;
+
+		if (nested) {
+			if (rdseed_enabled)
+				vmx->nested.nested_vmx_secondary_ctls_high |=
+					SECONDARY_EXEC_RDSEED;
+			else
+				vmx->nested.nested_vmx_secondary_ctls_high &=
+					~SECONDARY_EXEC_RDSEED;
+		}
+	}
+
 	vmx->secondary_exec_control = exec_control;
 }
 
@@ -8119,6 +8140,7 @@ static int (*const kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
 	[EXIT_REASON_INVEPT]                  = handle_invept,
 	[EXIT_REASON_INVVPID]                 = handle_invvpid,
 	[EXIT_REASON_RDRAND]                  = handle_invalid_op,
+	[EXIT_REASON_RDSEED]                  = handle_invalid_op,
 	[EXIT_REASON_XSAVES]                  = handle_xsaves,
 	[EXIT_REASON_XRSTORS]                 = handle_xrstors,
 	[EXIT_REASON_PML_FULL]		      = handle_pml_full,