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From: Gerd Hoffmann <kraxel@redhat.com>
Date: Tue, 24 Jan 2017 11:48:50 +0100
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Subject: Re: [Qemu-devel] [PATCH] cirrus: fix oob access issue
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To: Laszlo Ersek <lersek@redhat.com>
Cc: Li Qiang <liq3ea@gmail.com>, qemu-devel@nongnu.org, ghoffman@redhat.com, liqiang6-s@360.cn

> > diff --git a/hw/display/cirrus_vga.c b/hw/display/cirrus_vga.c
> > index 379910d..7ddd289 100644
> > --- a/hw/display/cirrus_vga.c
> > +++ b/hw/display/cirrus_vga.c
> > @@ -277,7 +277,8 @@ static bool blit_region_is_unsafe(struct CirrusVGAS=
tate *s,
> >      }
> >      if (pitch < 0) {
> >          int64_t min =3D addr
> > -            + ((int64_t)s->cirrus_blt_height-1) * pitch;
> > +            + ((int64_t)s->cirrus_blt_height-1) * pitch
> > +            - s->cirrus_blt_width;
> >          int32_t max =3D addr
> >              + s->cirrus_blt_width;
> >          if (min < 0 || max > s->vga.vram_size) {
> >=20
>=20
> I believe this is incorrect. In this case (AFAIR), "addr" points to the
> left-most pixel (=3D lowest address) of the bottom line (=3D highest
> address).

If I read the code correctly it is backwards *both* x and y axis, so
addr is the right-most pixel of the bottom line.

cheers,
  Gerd