linux-kernel - Re: [Intel-gfx] [PATCH] drm/i915/display: Check source height is

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Date:   Wed, 11 Jan 2023 11:47:52 -0700
From:   Drew Davenport <ddavenport@...omium.org>
To:     "Teres Alexis, Alan Previn" <alan.previn.teres.alexis@...el.com>
Cc:     "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "Vivi, Rodrigo" <rodrigo.vivi@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "airlied@...il.com" <airlied@...il.com>,
        "tzimmermann@...e.de" <tzimmermann@...e.de>,
        "Heikkila, Juha-pekka" <juha-pekka.heikkila@...el.com>
Subject: Re: [Intel-gfx] [PATCH] drm/i915/display: Check source height is > 0

On Tue, Dec 27, 2022 at 05:55:17PM +0000, Teres Alexis, Alan Previn wrote:
> Is there a better place for this check higher up the intel specific atomic-check? (so the check won't be skl specific - i notice that intel_adjusted_rate is also called by
> ilk_foo as well and non-backend-specific functions). Else, perhaps intel_adjusted_rate should add a check + WARN? (if we are trying to propagate this slowly across HW).

Would intel_plane_atomic_check_with_state be a more appropriate
place to check that the src width and height are at least 1? This is
where skl_plane_check and other HW's foo_plane_check functions are called
from.

I don't think that the potential divide-by-zero will be hit in the case
where intel_adjusted_rate is called from ilk_pipe_pixel_rate because the
src rect will not have a fractional part to it in this case. I'm assuming
that something earlier on would catch and reject a src with zero
width/height.

Drew

> 
> 
> ...alan 
> 
> On Mon, 2022-12-26 at 22:53 -0700, Drew Davenport wrote:
> > The error message suggests that the height of the src rect must be at
> > least 1. Reject source with height of 0.
> > 
> > Signed-off-by: Drew Davenport <ddavenport@...omium.org>
> > 
> > ---
> > I was investigating some divide-by-zero crash reports on ChromeOS which
> > pointed to the intel_adjusted_rate function. Further prodding showed
> > that I could reproduce this in a simple test program if I made src_h
> > some value less than 1 but greater than 0.
> > 
> > This seemed to be a sensible place to check that the source height is at
> > least 1. I tried to repro this issue on an amd device I had on hand, and
> > the configuration was rejected.
> > 
> > Would it make sense to add a check that source dimensions are at least 1
> > somewhere in core, like in drm_atomic_plane_check? Or is that a valid
> > use case on some devices, and thus any such check should be done on a
> > per-driver basis?
> > 
> > Thanks.
> > 
> >  drivers/gpu/drm/i915/display/skl_universal_plane.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/skl_universal_plane.c b/drivers/gpu/drm/i915/display/skl_universal_plane.c
> > index 4b79c2d2d6177..9b172a1e90deb 100644
> > --- a/drivers/gpu/drm/i915/display/skl_universal_plane.c
> > +++ b/drivers/gpu/drm/i915/display/skl_universal_plane.c
> > @@ -1627,7 +1627,7 @@ static int skl_check_main_surface(struct intel_plane_state *plane_state)
> >  	u32 offset;
> >  	int ret;
> >  
> > -	if (w > max_width || w < min_width || h > max_height) {
> > +	if (w > max_width || w < min_width || h > max_height || h < 1) {
> >  		drm_dbg_kms(&dev_priv->drm,
> >  			    "requested Y/RGB source size %dx%d outside limits (min: %dx1 max: %dx%d)\n",
> >  			    w, h, min_width, max_width, max_height);
> > -- 
> > 2.39.0.314.g84b9a713c41-goog
> > 
>