Re: [PATCH v1 2/8] s390/sclp: check sccb len before filling in data

[David Hildenbrand <david@redhat.com>]

On 11.05.20 16:50, Janosch Frank wrote:
> On 5/11/20 4:44 PM, David Hildenbrand wrote:
>> On 11.05.20 16:36, Janosch Frank wrote:
>>> On 5/9/20 1:08 AM, Collin Walling wrote:
>>>> The SCCB must be checked for a sufficient length before it is filled
>>>> with any data. If the length is insufficient, then the SCLP command
>>>> is suppressed and the proper response code is set in the SCCB header.
>>>>
>>>> Signed-off-by: Collin Walling <walling@linux.ibm.com>
>>>
>>> Fixes tag?
>>> Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
>>
>> This is not a fix AFAIKs.
>> sclp_service_call()/sclp_service_call_protected() always supplies a full
>> SCCB of exactly 4k size.
>>
> 
> We don't check for QEMU's 4k buffer here, but for the length that was
> specified by the guest.
> 
> It's valid for the guest to request cpu info and state that its buffer
> is only 1k. We can't write everything in 1k if we have ~200 cpus, so
> we'll report the insufficient length rc.
> 
> What he fixes here is the time of the length check, it should be done
> before any changes are being done to the work_sccb.

I don't have access to the spec, especially, if the guest can expect
nothing else in the sccb to change in case we report an error code. So
whatever you tell me, I have to trust you :)


-- 
Thanks,

David / dhildenb