linux-kernel - Re: [PATCH v6 07/13] KVM: s390: introduce struct kvm_s390_gisa

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Message-Id: <42befe0d-ad84-5e34-a05a-0ffb4fcadd56@linux.ibm.com>
Date:   Tue, 29 Jan 2019 16:47:10 +0100
From:   Michael Mueller <mimu@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>,
        Halil Pasic <pasic@...ux.ibm.com>
Cc:     KVM Mailing List <kvm@...r.kernel.org>,
        Linux-S390 Mailing List <linux-s390@...r.kernel.org>,
        linux-kernel@...r.kernel.org,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Pierre Morel <pmorel@...ux.ibm.com>
Subject: Re: [PATCH v6 07/13] KVM: s390: introduce struct
 kvm_s390_gisa_interrupt



On 29.01.19 14:22, Cornelia Huck wrote:
> On Mon, 28 Jan 2019 17:50:54 +0100
> Halil Pasic <pasic@...ux.ibm.com> wrote:
> 
>> On Thu, 24 Jan 2019 13:59:33 +0100
>> Michael Mueller <mimu@...ux.ibm.com> wrote:
>>
>>> Use this struct analog to the kvm interruption structs
>>> for kvm emulated floating and local interruptions.
>>> Further fields will be added with this series as
>>> required.
>>>
>>> Signed-off-by: Michael Mueller <mimu@...ux.ibm.com>
>>
>> While looking at this I was asking myself what guards against invalid
>> gisa pointer dereference e.g. when pending_irqs() is called (see below).
>>
>> AFAIU we set up gisa_int.origin only if we have
>> css_general_characteristics.aiv. Opinions?
> 
> I think you're right that this is a (pre-existing) problem.
> 
>>> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
>>> index 942cc7d33766..ee91d1de0036 100644
>>> --- a/arch/s390/kvm/interrupt.c
>>> +++ b/arch/s390/kvm/interrupt.c
>>> @@ -246,7 +246,8 @@ static inline unsigned long pending_irqs_no_gisa(struct kvm_vcpu *vcpu)
>>>   static inline unsigned long pending_irqs(struct kvm_vcpu *vcpu)
>>>   {
>>>   	return pending_irqs_no_gisa(vcpu) |
>>> -		gisa_get_ipm(vcpu->kvm->arch.gisa) << IRQ_PEND_IO_ISC_7;
>>> +		gisa_get_ipm(vcpu->kvm->arch.gisa_int.origin) <<
>>
>> Unconditional call to gisa_get_ipm(), and get ipm just accesses ->ipm.
> 
> All other callers of this function check for gisa != NULL first, so
> either we should check here as well or move the check into the
> gisa_get_ipm() function.

I suggest to use an explicit test like this.

  static inline unsigned long pending_irqs(struct kvm_vcpu *vcpu)
  {
-       return pending_irqs_no_gisa(vcpu) |
-               gisa_get_ipm(vcpu->kvm->arch.gisa_int.origin) <<
-                       IRQ_PEND_IO_ISC_7;
+       struct kvm_s390_gisa_int *gi = &vcpu->kvm->arch.gisa_int;
+       unsigned long pending_mask;
+
+       pending_mask = pending_irqs_no_gisa(vcpu);
+       if (gi->origin)
+               pending_mask |= gisa_get_ipm(gi->origin) << 
IRQ_PEND_IO_ISC_7;
+       return pending_mask;
  }

Michael


> 
>>
>>> +			IRQ_PEND_IO_ISC_7;
>>>   }
>>>     
>