[PATCH 2/4] kvm: vmx: Raise #UD on unsupported RDRAND

[Paolo Bonzini]

From: Jim Mattson <jmattson@xxxxxxxxxx>

A guest may not be configured to support RDRAND, even when the host
does. If the guest does not support RDRAND, intercept the instruction
and synthesize #UD. Also clear the "allowed-1" bit for RDRAND exiting
in the IA32_VMX_PROCBASED_CTLS2 MSR.

Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/kvm/vmx.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 08381a5d8879..1f2c69de7872 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2818,7 +2818,7 @@ 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_RDRAND | SECONDARY_EXEC_RDSEED |
+		SECONDARY_EXEC_RDSEED |
 		SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES |
 		SECONDARY_EXEC_DESC |
 		SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE |
@@ -3671,6 +3671,7 @@ 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_RDRAND |
 			SECONDARY_EXEC_ENABLE_PML |
 			SECONDARY_EXEC_TSC_SCALING |
 			SECONDARY_EXEC_ENABLE_VMFUNC;
@@ -5273,6 +5274,12 @@ static u32 vmx_exec_control(struct vcpu_vmx *vmx)
 	return exec_control;
 }
 
+static bool vmx_rdrand_supported(void)
+{
+	return vmcs_config.cpu_based_2nd_exec_ctrl &
+		SECONDARY_EXEC_RDRAND;
+}
+
 static void vmx_compute_secondary_exec_control(struct vcpu_vmx *vmx)
 {
 	struct kvm_vcpu *vcpu = &vmx->vcpu;
@@ -5342,6 +5349,21 @@ static void vmx_compute_secondary_exec_control(struct vcpu_vmx *vmx)
 		}
 	}
 
+	if (vmx_rdrand_supported()) {
+		bool rdrand_enabled = guest_cpuid_has(vcpu, X86_FEATURE_RDRAND);
+		if (rdrand_enabled)
+			exec_control &= ~SECONDARY_EXEC_RDRAND;
+
+		if (nested) {
+			if (rdrand_enabled)
+				vmx->nested.nested_vmx_secondary_ctls_high |=
+					SECONDARY_EXEC_RDRAND;
+			else
+				vmx->nested.nested_vmx_secondary_ctls_high &=
+					~SECONDARY_EXEC_RDRAND;
+		}
+	}
+
 	vmx->secondary_exec_control = exec_control;
 }
 
@@ -6847,6 +6869,12 @@ static int handle_mwait(struct kvm_vcpu *vcpu)
 	return handle_nop(vcpu);
 }
 
+static int handle_invalid_op(struct kvm_vcpu *vcpu)
+{
+	kvm_queue_exception(vcpu, UD_VECTOR);
+	return 1;
+}
+
 static int handle_monitor_trap(struct kvm_vcpu *vcpu)
 {
 	return 1;
@@ -8090,6 +8118,7 @@ static int (*const kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
 	[EXIT_REASON_MONITOR_INSTRUCTION]     = handle_monitor,
 	[EXIT_REASON_INVEPT]                  = handle_invept,
 	[EXIT_REASON_INVVPID]                 = handle_invvpid,
+	[EXIT_REASON_RDRAND]                  = handle_invalid_op,
 	[EXIT_REASON_XSAVES]                  = handle_xsaves,
 	[EXIT_REASON_XRSTORS]                 = handle_xrstors,
 	[EXIT_REASON_PML_FULL]		      = handle_pml_full,
-- 
1.8.3.1