2023-04-18 14:12:56

by Nikita Zhandarovich

Subject: [PATCH] drm/i915/dp: prevent potential div-by-zero

drm_dp_dsc_sink_max_slice_count() may return 0 if something goes
wrong on the part of the DSC sink and its DPCD register. This null
value may be later used as a divisor in intel_dsc_compute_params(),
which will lead to an error.
In the unlikely event that this issue occurs, fix it by testing the
return value of drm_dp_dsc_sink_max_slice_count() against zero.

Found by Linux Verification Center (linuxtesting.org) with static
analysis tool SVACE.

Fixes: a4a157777c80 ("drm/i915/dp: Compute DSC pipe config in atomic check")
Signed-off-by: Nikita Zhandarovich <[email protected]>
---
drivers/gpu/drm/i915/display/intel_dp.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 62cbab7402e9..c1825f8f885c 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -1533,6 +1533,11 @@ int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
pipe_config->dsc.slice_count =
drm_dp_dsc_sink_max_slice_count(intel_dp->dsc_dpcd,
true);
+ if (!pipe_config->dsc.slice_count) {
+ drm_dbg_kms(&dev_priv->drm, "Unsupported Slice Count %d\n",
+ pipe_config->dsc.slice_count);
+ return -EINVAL;
+ }
} else {
u16 dsc_max_output_bpp = 0;
u8 dsc_dp_slice_count;
--
2.25.1

2023-05-05 14:53:37

by Rodrigo Vivi

Subject: Re: [PATCH] drm/i915/dp: prevent potential div-by-zero

On Tue, Apr 18, 2023 at 07:04:30AM -0700, Nikita Zhandarovich wrote:
> drm_dp_dsc_sink_max_slice_count() may return 0 if something goes
> wrong on the part of the DSC sink and its DPCD register. This null
> value may be later used as a divisor in intel_dsc_compute_params(),
> which will lead to an error.
> In the unlikely event that this issue occurs, fix it by testing the
> return value of drm_dp_dsc_sink_max_slice_count() against zero.
>
> Found by Linux Verification Center (linuxtesting.org) with static
> analysis tool SVACE.
>
> Fixes: a4a157777c80 ("drm/i915/dp: Compute DSC pipe config in atomic check")
> Signed-off-by: Nikita Zhandarovich <[email protected]>

Reviewed-by: Rodrigo Vivi <[email protected]>

and pushed.

Thanks for the patch and sorry for the delay.

> ---
> drivers/gpu/drm/i915/display/intel_dp.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 62cbab7402e9..c1825f8f885c 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -1533,6 +1533,11 @@ int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
> pipe_config->dsc.slice_count =
> drm_dp_dsc_sink_max_slice_count(intel_dp->dsc_dpcd,
> true);
> + if (!pipe_config->dsc.slice_count) {
> + drm_dbg_kms(&dev_priv->drm, "Unsupported Slice Count %d\n",
> + pipe_config->dsc.slice_count);
> + return -EINVAL;
> + }
> } else {
> u16 dsc_max_output_bpp = 0;
> u8 dsc_dp_slice_count;
> --
> 2.25.1
>