Re: [PATCH] ati-vga: increment mm_index in ati_mm_read/write

[BALATON Zoltan]

On Wed, 3 Jun 2020, Gerd Hoffmann wrote:
> On Wed, Jun 03, 2020 at 06:17:32PM +0530, P J P wrote:
> > From: Prasad J Pandit <pjp@fedoraproject.org>
> >
> > While accessing VGA registers via ati_mm_read/write routines,
> > a guest may set 's->regs.mm_index' such that it leads to infinite
> > recursion.
>
> Lovely.
>
> > Increment the mm_index value to avoid it.
>
> Hmm, why modify mm_index?  Shouldn't we just check it is non-zero
> before calling ati_mm_read/ati_mm_write?

I haven't found any mention in any docs that say MM_INDEX should auto 
increment so unless this is proven to do that on real hardware I also 
think forbiding indexed access to index registers should be enough.

Regards,
BALATON Zoltan