linux-kernel - Re: [PATCH] gpu: ttm: fix GPF in ttm_bo

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Message-ID: <55aa8ece-1f1d-76d0-4f2f-951d39e79484@amd.com>
Date:   Thu, 8 Jul 2021 12:56:19 +0200
From:   Christian König <christian.koenig@....com>
To:     Pavel Skripkin <paskripkin@...il.com>, ray.huang@....com,
        airlied@...ux.ie
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] gpu: ttm: fix GPF in ttm_bo_release

Am 08.07.21 um 12:09 schrieb Pavel Skripkin:
> On Thu, 8 Jul 2021 11:37:01 +0300
> Pavel Skripkin <paskripkin@...il.com> wrote:
>
>> On Thu, 8 Jul 2021 08:49:48 +0200
>> Christian König <christian.koenig@....com> wrote:
>>
>>> Am 07.07.21 um 20:51 schrieb Pavel Skripkin:
>>>> My local syzbot instance hit GPF in ttm_bo_release().
>>>> Unfortunately, syzbot didn't produce a reproducer for this, but I
>>>> found out possible scenario:
>>>>
>>>> drm_gem_vram_create()            <-- drm_gem_vram_object kzalloced
>>>> 				     (bo embedded in this object)
>>>>     ttm_bo_init()
>>>>       ttm_bo_init_reserved()
>>>>         ttm_resource_alloc()
>>>>           man->func->alloc()       <-- allocation failure
>>>>         ttm_bo_put()
>>>> 	ttm_bo_release()
>>>> 	  ttm_mem_io_free()      <-- bo->resource == NULL passed
>>>> 				     as second argument
>>>> 	     *GPF*
>>>>
>>>> So, I've added check in ttm_bo_release() to avoid passing
>>>> NULL as second argument to ttm_mem_io_free().
>> Hi, Christian!
>>
>> Thank you for quick feedback :)
>>
>>> There is another ocassion of this a bit down before we call
>>> ttm_bo_move_to_lru_tail() apart from that good catch.
>>>
>> Did you mean, that ttm_bo_move_to_lru_tail() should have NULL check
>> too?

Yes, exactly that.

>>   I checked it's realization, and, I think, NULL check is necessary
>> there, since mem pointer is dereferenced w/o any checking
>>
>>> But I'm wondering if we should make the functions NULL save instead
>>> of the external check.
>>>
>> I tried to find more possible scenarios of GPF in ttm_bo_release(),
>> but I didn't find one. But, yes, moving NULL check inside
>> ttm_mem_io_free() is more general approach and it will defend this
>> function from GPFs in the future.
>>
>>
>>
>> With regards,
>> Pavel Skripkin
>>
> I misclicked and sent this email to Christian privately :(
>
> Added all thread participants back, sorry.

No problem.

Do you want to update your patch or should I take care of this?

Thanks,
Christian.

>
>
>
> With regards,
> Pavel Skripkin