Subject: [PATCH] drm/sun4i: Check that the plane coordinates are not negative

From: [email-masked] (Ville Syrjälä)
Date: Fri, 30 Sep 2016 19:22:11 +0300

On Fri, Sep 30, 2016 at 06:08:26PM +0200, Boris Brezillon wrote:
> On Fri, 30 Sep 2016 16:33:20 +0200
> Maxime Ripard <[email-masked]> wrote:
> 
> > Our planes cannot be set at negative coordinates. Make sure we reject such
> > configuration.
> > 
> > Reported-by: Boris Brezillon <[email-masked]>
> > Signed-off-by: Maxime Ripard <[email-masked]>
> > ---
> >  drivers/gpu/drm/sun4i/sun4i_layer.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/sun4i/sun4i_layer.c b/drivers/gpu/drm/sun4i/sun4i_layer.c
> > index f0035bf5efea..f5463c4c2cde 100644
> > --- a/drivers/gpu/drm/sun4i/sun4i_layer.c
> > +++ b/drivers/gpu/drm/sun4i/sun4i_layer.c
> > @@ -29,6 +29,9 @@ struct sun4i_plane_desc {
> >  static int sun4i_backend_layer_atomic_check(struct drm_plane *plane,
> >  					    struct drm_plane_state *state)
> >  {
> > +	if ((state->crtc_x < 0) || (state->crtc_y < 0))
> > +		return -EINVAL;
> > +
> 
> Hm, I think it's a perfectly valid use case from the DRM framework and
> DRM user PoV: you may want to place your plane at a negative CRTC
> offset (which means part of the plane will be hidden).
> 
> Maybe I'm wrong, but it seems you can support that by adapting the
> start address of your framebuffer pointer and the layer size.
> 
> Have you tried doing something like that?

You shouldn't even be looking at the user provided coordinates. Also
you can't return an error from the atomic update hook. The void return
value should have been a decent hint ;) The right fix would be
to move all the error handling into the atomic check hook, which
probably should just call the helper to clip the coordinates and
whatnot. Then the update hook can just use at the clipped 
coordinates when programming the hw registers.

> 
> --->8---
> diff --git a/drivers/gpu/drm/sun4i/sun4i_backend.c b/drivers/gpu/drm/sun4i/sun4i_backend.c
> index 3ab560450a82..6b68804f3035 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_backend.c
> +++ b/drivers/gpu/drm/sun4i/sun4i_backend.c
> @@ -110,15 +110,30 @@ int sun4i_backend_update_layer_coord(struct sun4i_backend *backend,
>  {
>         struct drm_plane_state *state = plane->state;
>         struct drm_framebuffer *fb = state->fb;
> +       int crtc_w, crtc_h, crtc_x, crtc_y;
>  
>         DRM_DEBUG_DRIVER("Updating layer %d\n", layer);
>  
> +       crtc_x = state->crtc_x;
> +       crtc_y = state->crtc_y;
> +       crtc_w = state->crtc_w;
> +       crtc_h = state->crtc_h;
> +
> +       if (crtc_x < 0) {
> +               crtc_w += crtx_x;
> +               crtc_x = 0;
> +       }
> +
> +       if (crtc_y < 0) {
> +               crtc_h += crtx_y;
> +               crtc_y = 0;
> +       }
> +
>         if (plane->type == DRM_PLANE_TYPE_PRIMARY) {
>                 DRM_DEBUG_DRIVER("Primary layer, updating global size W: %u H: %u\n",
>                                  state->crtc_w, state->crtc_h);
>                 regmap_write(backend->regs, SUN4I_BACKEND_DISSIZE_REG,
> -                            SUN4I_BACKEND_DISSIZE(state->crtc_w,
> -                                                  state->crtc_h));
> +                            SUN4I_BACKEND_DISSIZE(crtc_w, crtc_h));
>         }
>  
>         /* Set the line width */
> @@ -130,15 +145,13 @@ int sun4i_backend_update_layer_coord(struct sun4i_backend *backend,
>         DRM_DEBUG_DRIVER("Layer size W: %u H: %u\n",
>                          state->crtc_w, state->crtc_h);
>         regmap_write(backend->regs, SUN4I_BACKEND_LAYSIZE_REG(layer),
> -                    SUN4I_BACKEND_LAYSIZE(state->crtc_w,
> -                                          state->crtc_h));
> +                    SUN4I_BACKEND_LAYSIZE(crtc_w, crtc_h));
>  
>         /* Set base coordinates */
>         DRM_DEBUG_DRIVER("Layer coordinates X: %d Y: %d\n",
>                          state->crtc_x, state->crtc_y);
>         regmap_write(backend->regs, SUN4I_BACKEND_LAYCOOR_REG(layer),
> -                    SUN4I_BACKEND_LAYCOOR(state->crtc_x,
> -                                          state->crtc_y));
> +                    SUN4I_BACKEND_LAYCOOR(crtc_x, crtc_y));
>  
>         return 0;
>  }
> @@ -198,6 +211,12 @@ int sun4i_backend_update_layer_buffer(struct sun4i_backend *backend,
>         paddr += (state->src_x >> 16) * bpp;
>         paddr += (state->src_y >> 16) * fb->pitches[0];
>  
> +       if (state->crtc_x < 0)
> +               paddr -= bpp * state->crtc_x;
> +
> +       if (state->crtc_y < 0)
> +               paddr -= fb->pitches[0] * state->crtc_y;
> +
>         DRM_DEBUG_DRIVER("Setting buffer address to %pad\n", &paddr);
>  
>         /* Write the 32 lower bits of the address (in bits) */
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-- 
Ville Syrj?l?
Intel OTC