From: Zenghui Yu <yuzenghui@huawei.com>
To: Marc Zyngier <maz@kernel.org>,
Julien Thierry <julien.thierry@arm.com>,
<kvmarm@lists.cs.columbia.edu>,
<linux-arm-kernel@lists.infradead.org>
Cc: marc.zyngier@arm.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] KVM: arm/arm64: Assign pmc->idx before kvm_pmu_stop_counter()
Date: Thu, 18 Jul 2019 09:59:46 +0800 [thread overview]
Message-ID: <ae65afd1-fd9a-280f-285f-543b1fa246f3@huawei.com> (raw)
In-Reply-To: <26b64d48-5ff9-7d62-bc44-601fdcc43223@kernel.org>
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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prev parent reply other threads:[~2019-07-18 2:02 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-17 12:20 [PATCH] KVM: arm/arm64: Assign pmc->idx before kvm_pmu_stop_counter() Zenghui Yu
2019-07-17 13:44 ` Julien Thierry
2019-07-17 15:00 ` Marc Zyngier
2019-07-18 1:59 ` Zenghui Yu [this message]
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