RE: [PATCH] drm/xe/hdcp: Add NULL check for media_gt in intel_hdcp_gsc_check_status()

[Gustavo Sousa <gustavo.sousa@intel.com>]

"Lin, Shuicheng" <shuicheng.lin@intel.com> writes:

> On Mon, Mar 2, 2026 10:19 AM Gustavo Sousa wrote:
>> When media GT is disabled via configfs, there is no allocation for media_gt,
>> which is kept as NULL.  In such scenario,
>> intel_hdcp_gsc_check_status() results in a kernel pagefault error due to &gt-
>> >uc.gsc being evaluated as an invalid memory address.
>> 
>> Fix that by introducing a NULL check on media_gt and bailing out early if so.
>> 
>> Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>
>> ---
>>  drivers/gpu/drm/xe/display/xe_hdcp_gsc.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>> 
>> diff --git a/drivers/gpu/drm/xe/display/xe_hdcp_gsc.c
>> b/drivers/gpu/drm/xe/display/xe_hdcp_gsc.c
>> index 29c72aa4b0d2..1cac00c17d4c 100644
>> --- a/drivers/gpu/drm/xe/display/xe_hdcp_gsc.c
>> +++ b/drivers/gpu/drm/xe/display/xe_hdcp_gsc.c
>> @@ -39,6 +39,12 @@ static bool intel_hdcp_gsc_check_status(struct
>> drm_device *drm)
>>  	struct xe_gt *gt = tile->media_gt;
>>  	struct xe_gsc *gsc = &gt->uc.gsc;
>
> If gt is NULL, this "&gt->uc.gsc" is already undefined behavior.

I don't think so. It just turns out that the offset will be invalid. We are not
dereferencing the gt pointer here.

> I would prefer to move this assignment to after below check.

I think that might be unecessary. Would you agree with keeping it as-is
based on my argument above?

>
>> 
>> +	if (!gt) {
>> +		drm_dbg_kms(&xe->drm,
>> +			    "not checking GSC status for HDCP2.x: media GT not
>> present or disabled\n");
>> +		return false;
>> +	}
>> +
>>  	if (!gsc || !xe_uc_fw_is_available(&gsc->fw)) {
>
> BTW, if gt is not NULL, then gsc cannot be NULL. So this "!gsc" check
> could be dropped.

Yep. Makes sense.

--
Gustavo Sousa

>
> Shuicheng
>
>>  		drm_dbg_kms(&xe->drm,
>>  			    "GSC Components not ready for HDCP2.x\n");
>> 
>> ---
>> base-commit: 40e52ed6c66cef091579dd7fe49ccd2de135f5c5
>> change-id: 20260302-check-for-null-media_gt-in-
>> intel_hdcp_gsc_check_status-071898b8a402
>> 
>> Best regards,
>> --
>> Gustavo Sousa <gustavo.sousa@intel.com>