[PATCH v6 2/2] kvm: vmx: Raise #UD on unsupported RDRAND

[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>
---
 arch/x86/kvm/vmx.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 9dd8637c3392..1d59806b315b 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3668,6 +3668,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
 			SECONDARY_EXEC_SHADOW_VMCS |
 			SECONDARY_EXEC_XSAVES |
 			SECONDARY_EXEC_RDSEED |
+			SECONDARY_EXEC_RDRAND |
 			SECONDARY_EXEC_ENABLE_PML |
 			SECONDARY_EXEC_TSC_SCALING |
 			SECONDARY_EXEC_ENABLE_VMFUNC;
@@ -5304,6 +5305,9 @@ static u32 vmx_secondary_exec_control(struct vcpu_vmx *vmx)
 	if (guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDSEED))
 		exec_control &= ~SECONDARY_EXEC_RDSEED;
 
+	if (guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDRAND))
+		exec_control &= ~SECONDARY_EXEC_RDRAND;
+
 	return exec_control;
 }
 
@@ -8058,6 +8062,7 @@ static int (*const kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
 	[EXIT_REASON_INVEPT]                  = handle_invept,
 	[EXIT_REASON_INVVPID]                 = handle_invvpid,
 	[EXIT_REASON_RDSEED]                  = handle_invalid_op,
+	[EXIT_REASON_RDRAND]                  = handle_invalid_op,
 	[EXIT_REASON_XSAVES]                  = handle_xsaves,
 	[EXIT_REASON_XRSTORS]                 = handle_xrstors,
 	[EXIT_REASON_PML_FULL]		      = handle_pml_full,
@@ -8992,6 +8997,12 @@ static bool vmx_rdseed_supported(void)
 		SECONDARY_EXEC_RDSEED;
 }
 
+static bool vmx_rdrand_supported(void)
+{
+	return vmcs_config.cpu_based_2nd_exec_ctrl &
+		SECONDARY_EXEC_RDRAND;
+}
+
 static bool vmx_xsaves_supported(void)
 {
 	return vmcs_config.cpu_based_2nd_exec_ctrl &
@@ -9690,6 +9701,12 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
 		secondary_exec_ctl |= SECONDARY_EXEC_RDSEED;
 	}
 
+	if (vmx_rdrand_supported() &&
+	    !guest_cpuid_has(vcpu, X86_FEATURE_RDRAND)) {
+		nested_vmx_secondary_ctrls_clear(vcpu, SECONDARY_EXEC_RDRAND);
+		secondary_exec_ctl |= SECONDARY_EXEC_RDRAND;
+	}
+
 	if (cpu_has_secondary_exec_ctrls())
 		vmcs_set_secondary_exec_control(secondary_exec_ctl);
 
-- 
2.14.1.342.g6490525c54-goog