Re: [PATCH v6 07/13] KVM: s390: introduce struct kvm_s390_gisa_interrupt

Michael Mueller
2019-01-29T15:47:10Z

On 29.01.19 14:22, Cornelia Huck wrote:
> On Mon, 28 Jan 2019 17:50:54 +0100
> Halil Pasic <pasic@linux.ibm.com> wrote:
>
>> On Thu, 24 Jan 2019 13:59:33 +0100
>> Michael Mueller <mimu@linux.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@linux.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;
>>> }
>>>
>