[PATCH i-g-t] lib/i915: Avoid non-canonical address dereference in gem_has_relocations()

[Sebastian Brzezinka]

Hi Krzysztof, 

On Wed Jun 18, 2025 at 11:39 AM UTC, Krzysztof Karas wrote:
> Hi Sebastian,
>
>> Fix a general protection fault in igt at gem_exec_big@single caused by
>> passing a non-canonical address via relocs_ptr. The test previously
>> used a stack-allocated relocation entry, which resulted in an invalid
>> pointer being passed to the kernel, triggering a crash.
> Did this happen as a result using freed heap allocated data?

The issue was triggered while attempting to access memory.
Just wrong pointer.

>
>> 
>> This patch replaces the stack-allocated `reloc` with a NULL pointer,
>> ensuring the kernel correctly interprets the absence of relocations and
>> avoids undefined behavior.
>> 
>> A corresponding kernel patch to sanitize user input for relocs_ptr has
>> been submitted to the i915 mailing list to further harden the interface.
> I noticed that the mentioned patch has been met with some
> pushback from the community. If you believe it is required on
> the i915 side and worth mentioning here, then please move this
> note into the section below "---". Otherwise, please remove
> that part.
a

Sure, gonna do this in v2.  

-- 
Best regards,
Sebastian