diff mbox series

[4/9] KVM: x86: Reject userspace attempts to access PERF_CAPABILITIES w/o PDCM

Message ID 20240802185511.305849-5-seanjc@google.com (mailing list archive)
State New, archived
Headers show
Series KVM: x86: Add a quirk for feature MSR initialization | expand

Commit Message

Sean Christopherson Aug. 2, 2024, 6:55 p.m. UTC 
Reject userspace accesses to PERF_CAPABILITIES if PDCM isn't set in guest
CPUID, i.e. if the vCPU doesn't actually have PERF_CAPABILITIES.  But!  Do
so via KVM_MSR_RET_UNSUPPORTED, so that reads get '0' and writes of '0'
are ignored if KVM advertised support PERF_CAPABILITIES.

KVM's ABI is that userspace must set guest CPUID prior to setting MSRs,
and that setting MSRs that aren't supposed exist is disallowed (modulo the
'0' exemption).

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/x86.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)
diff mbox series

Patch

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9b52d8f3304f..dbb5e06ef264 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3803,8 +3803,10 @@  int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		vcpu->arch.arch_capabilities = data;
 		break;
 	case MSR_IA32_PERF_CAPABILITIES:
-		if (!msr_info->host_initiated)
-			return 1;
+		if (!msr_info->host_initiated ||
+		    !guest_cpuid_has(vcpu, X86_FEATURE_PDCM))
+			return KVM_MSR_RET_UNSUPPORTED;
+
 		if (data & ~kvm_caps.supported_perf_cap)
 			return 1;
 
@@ -4263,9 +4265,8 @@  int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		msr_info->data = vcpu->arch.arch_capabilities;
 		break;
 	case MSR_IA32_PERF_CAPABILITIES:
-		if (!msr_info->host_initiated &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_PDCM))
-			return 1;
+		if (!guest_cpuid_has(vcpu, X86_FEATURE_PDCM))
+			return KVM_MSR_RET_UNSUPPORTED;
 		msr_info->data = vcpu->arch.perf_capabilities;
 		break;
 	case MSR_IA32_POWER_CTL: