Zero out the LBR capabilities during PMU refresh to avoid exposing LBRs to the guest against userspace's wishes. If userspace modifies the guest's CPUID model or invokes KVM_CAP_PMU_CAPABILITY to disable vPMU after an initial KVM_SET_CPUID2, but before the first KVM_RUN, KVM will retain the previous LBR info due to bailing before refreshing the LBR descriptor. Note, this is a very theoretical bug, there is no known use case where a VMM would deliberately enable the vPMU via KVM_SET_CPUID2, and then later disable the vPMU. Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> --- arch/x86/kvm/vmx/pmu_intel.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c index e8a3be0b9df9..d889bb2a1de5 100644 --- a/arch/x86/kvm/vmx/pmu_intel.c +++ b/arch/x86/kvm/vmx/pmu_intel.c @@ -531,6 +531,16 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu) pmu->pebs_enable_mask = ~0ull; pmu->pebs_data_cfg_mask = ~0ull; + memset(&lbr_desc->records, 0, sizeof(lbr_desc->records)); + + /* + * Setting passthrough of LBR MSRs is done only in the VM-Entry loop, + * and PMU refresh is disallowed after the vCPU has run, i.e. this code + * should never be reached while KVM is passing through MSRs. + */ + if (KVM_BUG_ON(lbr_desc->msr_passthrough, vcpu->kvm)) + return; + entry = kvm_find_cpuid_entry(vcpu, 0xa); if (!entry || !vcpu->kvm->arch.enable_pmu) return; -- 2.40.0.rc1.284.g88254d51c5-goog
