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

[Paolo Bonzini]

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: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/kvm/vmx.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 8346fd53a42f..b13370381988 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3661,6 +3661,7 @@ 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_RDSEED |
 			SECONDARY_EXEC_ENABLE_PML |
 			SECONDARY_EXEC_TSC_SCALING |
@@ -5295,6 +5296,9 @@ static u32 vmx_secondary_exec_control(struct vcpu_vmx *vmx)
 	if (!enable_pml)
 		exec_control &= ~SECONDARY_EXEC_ENABLE_PML;
 
+	if (guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDRAND))
+		exec_control &= ~SECONDARY_EXEC_RDRAND;
+
 	if (guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDSEED))
 		exec_control &= ~SECONDARY_EXEC_RDSEED;
 
@@ -8051,6 +8055,7 @@ 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_RDSEED]                  = handle_invalid_op,
 	[EXIT_REASON_XSAVES]                  = handle_xsaves,
 	[EXIT_REASON_XRSTORS]                 = handle_xrstors,
@@ -8980,6 +8985,12 @@ static bool vmx_mpx_supported(void)
 		(vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_BNDCFGS);
 }
 
+static bool vmx_rdrand_supported(void)
+{
+	return vmcs_config.cpu_based_2nd_exec_ctrl &
+		SECONDARY_EXEC_RDRAND;
+}
+
 static bool vmx_rdseed_supported(void)
 {
 	return vmcs_config.cpu_based_2nd_exec_ctrl &
@@ -9735,6 +9746,24 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
 		}
 	}
 
+	if (vmx_rdrand_supported()) {
+		bool rdrand_enabled = guest_cpuid_has(vcpu, X86_FEATURE_RDRAND);
+
+		if (rdrand_enabled)
+			secondary_exec_ctl &= ~SECONDARY_EXEC_RDRAND;
+		else
+			secondary_exec_ctl |= 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;
+		}
+	}
+
 	if (vmx_rdseed_supported()) {
 		bool rdseed_enabled = guest_cpuid_has(vcpu, X86_FEATURE_RDSEED);
 
-- 
1.8.3.1