Re: [PATCH] drm/i915/display: Check source height is > 0

[Juha-Pekka Heikkila]

Hi Drew,

this is good find. I went looking where the problem is in and saw what 
you probably also saw earlier.

I was wondering if diff below would be better fix? I assume this would 
end up with einval or erange in your case but code flow otherwise would 
stay as is while fixing all future callers for same issue:

diff --git a/drivers/gpu/drm/i915/display/intel_atomic_plane.c 
b/drivers/gpu/drm/i915/display/intel_atomic_plane.c
index 10e1fc9d0698..a9948e8d3543 100644
--- a/drivers/gpu/drm/i915/display/intel_atomic_plane.c
+++ b/drivers/gpu/drm/i915/display/intel_atomic_plane.c
@@ -144,7 +144,7 @@ unsigned int intel_adjusted_rate(const struct 
drm_rect *src,
                                 const struct drm_rect *dst,
                                 unsigned int rate)
 {
-       unsigned int src_w, src_h, dst_w, dst_h;
+       unsigned int src_w, src_h, dst_w, dst_h, dst_wh;

        src_w = drm_rect_width(src) >> 16;
        src_h = drm_rect_height(src) >> 16;
@@ -155,8 +155,10 @@ unsigned int intel_adjusted_rate(const struct 
drm_rect *src,
        dst_w = min(src_w, dst_w);
        dst_h = min(src_h, dst_h);

-       return DIV_ROUND_UP_ULL(mul_u32_u32(rate, src_w * src_h),
-                               dst_w * dst_h);
+       /* in case src contained only fractional part */
+       dst_wh = max(dst_w * dst_h, (unsigned) 1);
+
+       return DIV_ROUND_UP_ULL(mul_u32_u32(rate, src_w * src_h), dst_wh);
 }

 unsigned int intel_plane_pixel_rate(const struct intel_crtc_state 
*crtc_state,


What do you think? I'll in any case come up with some test for this in igt.

/Juha-Pekka

On 27.12.2022 7.53, 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@xxxxxxxxxxxx>
>
> ---
> 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);