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@xxxxxxxxxx> --- arch/x86/kvm/x86.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) 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: -- 2.46.0.rc2.264.g509ed76dc8-goog
