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

[Janosch Frank]

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 <address@hidden>
>>
>> Fixes tag?
>> Reviewed-by: Janosch Frank <address@hidden>
> 
> 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.

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