[PATCH 1/2] drm/ttm: set ttm_buffer_object pointer as null after it's freed

[Huang Rui]

On Mon, Sep 10, 2018 at 05:25:48PM +0800, Koenig, Christian wrote:
> Am 10.09.2018 um 11:23 schrieb Huang Rui:
> > On Mon, Sep 10, 2018 at 11:00:04AM +0200, Christian König wrote:
> >> Hi Ray,
> >>
> >> well those patches doesn't make sense, the pointer is only local to
> >> the function.
> > You're right.
> > I narrowed it with gdb dump from ttm_bo_bulk_move_lru_tail+0x2b, the
> > use-after-free should be in below codes:
> >
> > man = &bulk->tt[i].first->bdev->man[TTM_PL_TT];
> > ttm_bo_bulk_move_helper(&bulk->tt[i], &man->lru[i], false);
> >
> > Is there a case, when orignal bo is destroyed in the bulk pos, but it
> > doesn't update pos->first pointer, then we still use it during the bulk
> > moving?
> 
> Only when a per VM BO is freed or the VM destroyed.
> 
> The first case should now be handled by "drm/amdgpu: set bulk_moveable 
> to false when a per VM is released" and when we use a destroyed VM we 
> would see other problems as well.
> 

If a VM instance is teared down, all BOs which belong that VM should be
removed from LRU. But how can we submit cmd based on a destroyed VM? You
know, we do the bulk move at last step of submission.


Thanks,
Ray

> BTW: Just pushed this commit to the repository, should show up any second.
> 
> Christian.
> 
> >
> > Thanks,
> > Ray
> >
> >> Regards,
> >> Christian.
> >>
> >> Am 10.09.2018 um 10:57 schrieb Huang Rui:
> >>> It avoids to be refered again after freed.
> >>>
> >>> Signed-off-by: Huang Rui <ray.huang at amd.com>
> >>> Cc: Christian König <christian.koenig at amd.com>
> >>> Cc: Tom StDenis <Tom.StDenis at amd.com>
> >>> ---
> >>>   drivers/gpu/drm/ttm/ttm_bo.c | 1 +
> >>>   1 file changed, 1 insertion(+)
> >>>
> >>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> >>> index 138c989..d3ef5f8 100644
> >>> --- a/drivers/gpu/drm/ttm/ttm_bo.c
> >>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> >>> @@ -54,6 +54,7 @@ static struct attribute ttm_bo_count = {
> >>>   static void ttm_bo_default_destroy(struct ttm_buffer_object *bo)
> >>>   {
> >>>   	kfree(bo);
> >>> +	bo = NULL;
> >>>   }
> >>>   static inline int ttm_mem_type_from_place(const struct ttm_place *place,
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>