Re: [PATCH v2 1/2] KVM: s390: Disallow invalid bits in kvm_valid_regs and kvm_dirty_regs

[David Hildenbrand]

On 04.09.19 11:11, Christian Borntraeger wrote:
> 
> 
> On 04.09.19 11:05, David Hildenbrand wrote:
>> On 04.09.19 10:51, Thomas Huth wrote:
>>> If unknown bits are set in kvm_valid_regs or kvm_dirty_regs, this
>>> clearly indicates that something went wrong in the KVM userspace
>>> application. The x86 variant of KVM already contains a check for
>>> bad bits, so let's do the same on s390x now, too.
>>>
>>> Reviewed-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
>>> Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
>>> Reviewed-by: Cornelia Huck <cohuck@xxxxxxxxxx>
>>> Signed-off-by: Thomas Huth <thuth@xxxxxxxxxx>
>>> ---
>>>  arch/s390/include/uapi/asm/kvm.h | 6 ++++++
>>>  arch/s390/kvm/kvm-s390.c         | 4 ++++
>>>  2 files changed, 10 insertions(+)
>>>
>>> diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h
>>> index 47104e5b47fd..436ec7636927 100644
>>> --- a/arch/s390/include/uapi/asm/kvm.h
>>> +++ b/arch/s390/include/uapi/asm/kvm.h
>>> @@ -231,6 +231,12 @@ struct kvm_guest_debug_arch {
>>>  #define KVM_SYNC_GSCB   (1UL << 9)
>>>  #define KVM_SYNC_BPBC   (1UL << 10)
>>>  #define KVM_SYNC_ETOKEN (1UL << 11)
>>> +
>>> +#define KVM_SYNC_S390_VALID_FIELDS \
>>> +	(KVM_SYNC_PREFIX | KVM_SYNC_GPRS | KVM_SYNC_ACRS | KVM_SYNC_CRS | \
>>> +	 KVM_SYNC_ARCH0 | KVM_SYNC_PFAULT | KVM_SYNC_VRS | KVM_SYNC_RICCB | \
>>> +	 KVM_SYNC_FPRS | KVM_SYNC_GSCB | KVM_SYNC_BPBC | KVM_SYNC_ETOKEN)
>>> +
>>
>> We didn't care about the S390 for the actual flags, why care now?
> 
> I think it makes sense to have the interface as defined as possible. If for some
> reason userspace sets a wrong bit this would be undetected. If we at a later point
> in time use that bit this would resultin strange problems.

Not arguing about the concept of checking for valid bits. Was just
wondering if the "S390" part in the name makes sense at all. But you
guys seem to have a consent here.

-- 

Thanks,

David / dhildenb