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[v3,1/7] KVM: x86/pmu: Avoid setting BIT_ULL(-1) to pmu->host_cross_mapped_mask

Message ID 20220831085328.45489-2-likexu@tencent.com (mailing list archive)
State New, archived
Headers show
Series x86/pmu: Corner cases fixes and optimization | expand

Commit Message

Like Xu Aug. 31, 2022, 8:53 a.m. UTC 
From: Like Xu <likexu@tencent.com>

In the extreme case of host counters multiplexing and contention, the
perf_event requested by the guest's pebs counter is not allocated to any
actual physical counter, in which case hw.idx is bookkept as -1,
resulting in an out-of-bounds access to host_cross_mapped_mask.

Fixes: 854250329c02 ("KVM: x86/pmu: Disable guest PEBS temporarily in two rare situations")
Signed-off-by: Like Xu <likexu@tencent.com>
---
 arch/x86/kvm/vmx/pmu_intel.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

Comments

Sean Christopherson Sept. 22, 2022, 10:30 p.m. UTC | #1 
On Wed, Aug 31, 2022, Like Xu wrote:
> +		hw_idx = pmc->perf_event->hw.idx;
> +		/* make it a little less dependent on perf's exact behavior */

Reworded this to explain how a negative value can be encountered.

> +		if (hw_idx != pmc->idx && hw_idx > -1)
> +			pmu->host_cross_mapped_mask |= BIT_ULL(hw_idx);
>  	}
>  }
diff mbox series

Patch

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index c399637a3a79..d595ff33d32d 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -776,20 +776,20 @@  static void intel_pmu_cleanup(struct kvm_vcpu *vcpu)
 void intel_pmu_cross_mapped_check(struct kvm_pmu *pmu)
 {
 	struct kvm_pmc *pmc = NULL;
-	int bit;
+	int bit, hw_idx;
 
 	for_each_set_bit(bit, (unsigned long *)&pmu->global_ctrl,
 			 X86_PMC_IDX_MAX) {
 		pmc = intel_pmc_idx_to_pmc(pmu, bit);
 
 		if (!pmc || !pmc_speculative_in_use(pmc) ||
-		    !intel_pmc_is_enabled(pmc))
+		    !intel_pmc_is_enabled(pmc) || !pmc->perf_event)
 			continue;
 
-		if (pmc->perf_event && pmc->idx != pmc->perf_event->hw.idx) {
-			pmu->host_cross_mapped_mask |=
-				BIT_ULL(pmc->perf_event->hw.idx);
-		}
+		hw_idx = pmc->perf_event->hw.idx;
+		/* make it a little less dependent on perf's exact behavior */
+		if (hw_idx != pmc->idx && hw_idx > -1)
+			pmu->host_cross_mapped_mask |= BIT_ULL(hw_idx);
 	}
 }