Messages in this thread | | | Subject | Re: [PATCH] KVM: arm/arm64: Assign pmc->idx before kvm_pmu_stop_counter() | From | Zenghui Yu <> | Date | Thu, 18 Jul 2019 09:59:46 +0800 |
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Hi Julien, Marc,
On 2019/7/17 23:00, Marc Zyngier wrote: > On 17/07/2019 14:44, Julien Thierry wrote: >> Hi Zenghui, >> >> On 17/07/2019 13:20, Zenghui Yu wrote: >>> We use "pmc->idx" and the "chained" bitmap to determine if the pmc is >>> chained, in kvm_pmu_pmc_is_chained(). But idx might be uninitialized >>> (and random) when we doing this decision, through a KVM_ARM_VCPU_INIT >>> ioctl -> kvm_pmu_vcpu_reset(). And the test_bit() against this random >>> idx will potentially hit a KASAN BUG [1]. >>> >>> Fix it by moving the assignment of idx before kvm_pmu_stop_counter(). >>> >>> [1] https://www.spinics.net/lists/kvm-arm/msg36700.html >>> >>> Fixes: 80f393a23be6 ("KVM: arm/arm64: Support chained PMU counters") >>> Suggested-by: Andrew Murray <andrew.murray@arm.com> >>> Cc: Marc Zyngier <maz@kernel.org> >>> Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>> --- >>> virt/kvm/arm/pmu.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c >>> index 3dd8238..521bfdd 100644 >>> --- a/virt/kvm/arm/pmu.c >>> +++ b/virt/kvm/arm/pmu.c >>> @@ -225,8 +225,8 @@ void kvm_pmu_vcpu_reset(struct kvm_vcpu *vcpu) >>> struct kvm_pmu *pmu = &vcpu->arch.pmu; >>> >>> for (i = 0; i < ARMV8_PMU_MAX_COUNTERS; i++) { >>> - kvm_pmu_stop_counter(vcpu, &pmu->pmc[i]); >>> pmu->pmc[i].idx = i; >> >> Yes, this is kind of a static property that should really be part of a >> "kvm_pmu_vcpu_init()" or "kvm_pmu_vcpu_create()" and is not expected to >> be modified across resets... >> >> There is no such function at the time and I'm unsure whether this >> warrants creating that separate function (I would still suggest creating >> it to make things clearer). > > Yup, that's pretty bad, now that you mention it. I'd be all for the > introduction of kvm_pmu_vcpu_init(), given that we already have > kvm_pmu_vcpu_destroy(). > >> >>> + kvm_pmu_stop_counter(vcpu, &pmu->pmc[i]); >> >> Whatever other opinions are on splitting pmu_vcpu_init/reset, that >> change makes sense and fixes the issue: >> >> Acked-by: Julien Thierry <julien.thierry@arm.com> >> >>> } >>> >>> bitmap_zero(vcpu->arch.pmu.chained, ARMV8_PMU_MAX_COUNTER_PAIRS); >>> >> >> Cheers, >> > > Zenghui, could you please update your patch to take the above into account?
Sure. I will send a v2 with the new subject (may be "KVM: arm/arm64: Introduce kvm_pmu_vcpu_init() to ...").
Thanks for your suggestions!
zenghui
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