[PATCH] KVM: arm/arm64: Assign pmc->idx before kvm_pmu_stop_counter()

[PATCH] KVM: arm/arm64: Assign pmc->idx before kvm_pmu_stop_counter()

[Zenghui Yu]

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;
+		kvm_pmu_stop_counter(vcpu, &pmu->pmc[i]);
 	}
 
 	bitmap_zero(vcpu->arch.pmu.chained, ARMV8_PMU_MAX_COUNTER_PAIRS);
-- 
1.8.3.1


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Re: [PATCH] KVM: arm/arm64: Assign pmc->idx before kvm_pmu_stop_counter()

[Julien Thierry]

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).

> +		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,

-- 
Julien Thierry
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Re: [PATCH] KVM: arm/arm64: Assign pmc->idx before kvm_pmu_stop_counter()

[Marc Zyngier]

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?

Thanks,

	M.
-- 
Jazz is not dead, it just smells funny...
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Re: [PATCH] KVM: arm/arm64: Assign pmc->idx before kvm_pmu_stop_counter()

[Zenghui Yu]

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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