[PATCH] drm/i915/edp: Check supported link rates DPCD read

[PATCH] drm/i915/edp: Check supported link rates DPCD read

[Nikita Zhandarovich]

intel_edp_set_sink_rates() reads DP_SUPPORTED_LINK_RATES into a local
stack array and then parses the array unconditionally. If the read
fails or returns less data than requested, the array contents are not
valid and may result in bogus sink link rates being used.

Check that the full DPCD block was read before parsing it. If not, fall
back to the default sink rate handling.

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

Fixes: 68f357cb7347 ("drm/i915/dp: generate and cache sink rate array for all DP, not just eDP 1.4")
Signed-off-by: Nikita Zhandarovich <n.zhandarovich@fintech.ru>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 6ef2a0043cda..b6650a12ca54 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -4678,10 +4678,16 @@ intel_edp_set_sink_rates(struct intel_dp *intel_dp)
 
 	if (intel_dp->edp_dpcd[0] >= DP_EDP_14) {
 		__le16 sink_rates[DP_MAX_SUPPORTED_RATES];
+		ssize_t ret;
 		int i;
 
-		drm_dp_dpcd_read(&intel_dp->aux, DP_SUPPORTED_LINK_RATES,
-				 sink_rates, sizeof(sink_rates));
+		ret = drm_dp_dpcd_read(&intel_dp->aux, DP_SUPPORTED_LINK_RATES,
+				       sink_rates, sizeof(sink_rates));
+		if (ret != sizeof(sink_rates)) {
+			drm_dbg_kms(display->drm,
+				    "Unable to read eDP supported link rates, using default rates\n");
+			goto use_default_rates;
+		}
 
 		for (i = 0; i < ARRAY_SIZE(sink_rates); i++) {
 			int rate;
@@ -4715,6 +4721,7 @@ intel_edp_set_sink_rates(struct intel_dp *intel_dp)
 	 * Use DP_LINK_RATE_SET if DP_SUPPORTED_LINK_RATES are available,
 	 * default to DP_MAX_LINK_RATE and DP_LINK_BW_SET otherwise.
 	 */
+use_default_rates:
 	if (intel_dp->num_sink_rates)
 		intel_dp->use_rate_select = true;
 	else

Re: [PATCH] drm/i915/edp: Check supported link rates DPCD read

[Jani Nikula]

On Fri, 29 May 2026, Nikita Zhandarovich <n.zhandarovich@fintech.ru> wrote:
> intel_edp_set_sink_rates() reads DP_SUPPORTED_LINK_RATES into a local
> stack array and then parses the array unconditionally. If the read
> fails or returns less data than requested, the array contents are not
> valid and may result in bogus sink link rates being used.
>
> Check that the full DPCD block was read before parsing it. If not, fall
> back to the default sink rate handling.
>
> Found by Linux Verification Center (linuxtesting.org) with static
> analysis tool SVACE.

Thanks for the patch.

>
> Fixes: 68f357cb7347 ("drm/i915/dp: generate and cache sink rate array for all DP, not just eDP 1.4")
> Signed-off-by: Nikita Zhandarovich <n.zhandarovich@fintech.ru>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 6ef2a0043cda..b6650a12ca54 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -4678,10 +4678,16 @@ intel_edp_set_sink_rates(struct intel_dp *intel_dp)
>  
>  	if (intel_dp->edp_dpcd[0] >= DP_EDP_14) {
>  		__le16 sink_rates[DP_MAX_SUPPORTED_RATES];
> +		ssize_t ret;
>  		int i;
>  
> -		drm_dp_dpcd_read(&intel_dp->aux, DP_SUPPORTED_LINK_RATES,
> -				 sink_rates, sizeof(sink_rates));
> +		ret = drm_dp_dpcd_read(&intel_dp->aux, DP_SUPPORTED_LINK_RATES,
> +				       sink_rates, sizeof(sink_rates));

Please switch to drm_dp_dpcd_read_data(). It'll return < 0 for errors,
and is easier to deal with.

> +		if (ret != sizeof(sink_rates)) {
> +			drm_dbg_kms(display->drm,
> +				    "Unable to read eDP supported link rates, using default rates\n");
> +			goto use_default_rates;

I think I'd avoid the goto and use:

	memset(sink_rates, 0, sizeof(sink_rates));

BR,
Jani.

> +		}
>  
>  		for (i = 0; i < ARRAY_SIZE(sink_rates); i++) {
>  			int rate;
> @@ -4715,6 +4721,7 @@ intel_edp_set_sink_rates(struct intel_dp *intel_dp)
>  	 * Use DP_LINK_RATE_SET if DP_SUPPORTED_LINK_RATES are available,
>  	 * default to DP_MAX_LINK_RATE and DP_LINK_BW_SET otherwise.
>  	 */
> +use_default_rates:
>  	if (intel_dp->num_sink_rates)
>  		intel_dp->use_rate_select = true;
>  	else

-- 
Jani Nikula, Intel