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

[Cornelia Huck]

On Mon, 11 May 2020 17:02:06 +0200
David Hildenbrand <address@hidden> wrote:

> 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 <address@hidden>  
> >>>
> >>> Fixes tag?

Probably

Fixes: 832be0d8a3bb ("s390x: sclp: Report insufficient SCCB length")

?

> >>> 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.  
> 
> 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 :)

Same here. Sounds plausible, but I have to trust the folks with the
documentation :)