Re: [PATCH v3] drm/i915/vma: Fix UAF on reopen vs destroy race

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Tue, Apr 16, 2024 at 10:09:46AM +0200, Janusz Krzysztofik wrote:
> Hi Rodrigo,
> 
> On Tuesday, 16 April 2024 03:16:31 CEST Rodrigo Vivi wrote:
> > On Mon, Apr 15, 2024 at 09:53:09PM +0200, Janusz Krzysztofik wrote:
> > > We defer actually closing, unbinding and destroying a VMA until next idle
> > > point, or until the object is freed in the meantime.  By postponing the
> > > unbind, we allow for the VMA to be reopened by the client, avoiding the
> > > work required to rebind the VMA.
> > > 
> > > It was assumed that as long as a GT is held idle, no VMA would be reopened
> > > while we destroy them.  That assumption is no longer true in multi-GT
> > > configurations, where a VMA we reopen may be handled by a GT different
> > > from the one that we already keep active via its engine while we set up
> > > an execbuf request.
> > > 
> > > <4> [260.290809] ------------[ cut here ]------------
> > > <4> [260.290988] list_del corruption. prev->next should be ffff888118c5d990, but was ffff888118c5a510. (prev=ffff888118c5a510)
> > > <4> [260.291004] WARNING: CPU: 2 PID: 1143 at lib/list_debug.c:62 __list_del_entry_valid_or_report+0xb7/0xe0
> > > ..
> > > <4> [260.291055] CPU: 2 PID: 1143 Comm: kms_plane Not tainted 6.9.0-rc2-CI_DRM_14524-ga25d180c6853+ #1
> > > <4> [260.291058] Hardware name: Intel Corporation Meteor Lake Client Platform/MTL-P LP5x T3 RVP, BIOS MTLPFWI1.R00.3471.D91.2401310918 01/31/2024
> > > <4> [260.291060] RIP: 0010:__list_del_entry_valid_or_report+0xb7/0xe0
> > > ...
> > > <4> [260.291087] Call Trace:
> > > <4> [260.291089]  <TASK>
> > > <4> [260.291124]  i915_vma_reopen+0x43/0x80 [i915]
> > > <4> [260.291298]  eb_lookup_vmas+0x9cb/0xcc0 [i915]
> > > <4> [260.291579]  i915_gem_do_execbuffer+0xc9a/0x26d0 [i915]
> > > <4> [260.291883]  i915_gem_execbuffer2_ioctl+0x123/0x2a0 [i915]
> > > ...
> > > <4> [260.292301]  </TASK>
> > > ...
> > > <4> [260.292506] ---[ end trace 0000000000000000 ]---
> > > <4> [260.292782] general protection fault, probably for non-canonical address 0x6b6b6b6b6b6b6ca3: 0000 [#1] PREEMPT SMP NOPTI
> > > <4> [260.303575] CPU: 2 PID: 1143 Comm: kms_plane Tainted: G        W          6.9.0-rc2-CI_DRM_14524-ga25d180c6853+ #1
> > > <4> [260.313851] Hardware name: Intel Corporation Meteor Lake Client Platform/MTL-P LP5x T3 RVP, BIOS MTLPFWI1.R00.3471.D91.2401310918 01/31/2024
> > > <4> [260.326359] RIP: 0010:eb_validate_vmas+0x114/0xd80 [i915]
> > > ...
> > > <4> [260.428756] Call Trace:
> > > <4> [260.431192]  <TASK>
> > > <4> [639.283393]  i915_gem_do_execbuffer+0xd05/0x26d0 [i915]
> > > <4> [639.305245]  i915_gem_execbuffer2_ioctl+0x123/0x2a0 [i915]
> > > ...
> > > <4> [639.411134]  </TASK>
> > > ...
> > > <4> [639.449979] ---[ end trace 0000000000000000 ]---
> > > 
> > > As soon as we start unbinding and destroying a VMA, marked it as parked,
> > > and also keep it marked as closed for the rest of its life.  When a VMA
> > > to be opened occurs closed, reopen it only if not yet parked.
> > > 
> > > v3: Fix misplaced brackets.
> > > v2: Since we no longer re-init the VMA closed list link on VMA park so it
> > >     looks like still on a list, don't try to delete it from the list again
> > >     after the VMA has been marked as parked.
> > > 
> > > Fixes: b0647a5e79b1 ("drm/i915: Avoid live-lock with i915_vma_parked()")
> > 
> > what about reverting that?
> 
> I didn't think of that.  Why you think that might be a better approach?

well, I thought of that mainly because...

> 
> Anyway, that's a 4 years old patch and a few things have changed since then, 
> so simple revert won't work.  Moreover, I've just checked that patch was 
> supposed to fix another patch, 77853186e547 ("drm/i915: Claim vma while under 
> closed_lock in i915_vma_parked()"), which in turn was supposed to fix 
> aa5e4453dc05 ("drm/i915/gem: Try to flush pending unbind events"), and that 
> one also referenced still another, cb6c3d45f948 ("drm/i915/gem: Avoid parking 
> the vma as we unbind") from December 2019, which finally wasn't a fix but an 
> improvement.

... because of histories like that ^ and I was afraid of this patch here now
just put us into a different corner case.

I have a feeling that without locks there we might just hit another
race soon with the the park and only using the atomic checks.

> Then, we would have to consider new fixes alternative to at least 
> some of those three, I guess. 

Indeed.. I didn't think that deep on that...

> I'd rather not dig that deep, unless we invest 
> in a completely new solution (e.g. backport VMA handling from xe if more 
> effective while compatible to some extent?).  Even then, we need a fix for 
> now.

yeap, not sure if that would help. was also not designed to
the park unpark.

> 
> Alternatively, we can try to revert my 1f33dc0c1189 ("drm/i915: Remove extra 
> multi-gt pm-references") which was a manual revert of f56fe3e91787 ("drm/i915: 
> Fix a VMA UAF for multi-gt platform") -- a workaround that was supposed to 
> address some multi-GT related VMA issues.  While it didn't really resolve 
> those issues it was addressing, I think it may help with this one, which 
> started appearing after I reverted that workaround.  However, its 
> effectiveness is limited to MTL topology.

perhaps the safer path for this case indeed. something that could be really
limited to a single platform would be better.

But I confess that I don't have other better suggestions.
If we need to go with this patch as a quick solution, it is apparently
better than leaving the bug there as is.

+Thomas. any good thoughts there or advices?

Thanks,
Rodrigo.

> 
> Thanks,
> Janusz
> 
> > 
> > > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/10608
> > > Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
> > > Cc: Chris Wilson <chris.p.wilson@linux.intel.com>
> > > Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > > Cc: stable@vger.kernel.org # v6.0+
> > > ---
> > >  .../gpu/drm/i915/gem/i915_gem_execbuffer.c    | 10 ++++--
> > >  drivers/gpu/drm/i915/i915_vma.c               | 32 +++++++++++++++----
> > >  drivers/gpu/drm/i915/i915_vma.h               |  2 +-
> > >  drivers/gpu/drm/i915/i915_vma_types.h         |  3 ++
> > >  4 files changed, 37 insertions(+), 10 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> > > index 42619fc05de48..97e014f94002e 100644
> > > --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> > > @@ -847,9 +847,12 @@ static int __eb_add_lut(struct i915_execbuffer *eb,
> > >  	if (unlikely(!lut))
> > >  		return -ENOMEM;
> > >  
> > > +	if (!i915_vma_open(vma)) {
> > > +		err = -EEXIST;	/* let eb_vma_lookup() retry */
> > > +		goto err_lut_free;
> > > +	}
> > > +
> > >  	i915_vma_get(vma);
> > > -	if (!atomic_fetch_inc(&vma->open_count))
> > > -		i915_vma_reopen(vma);
> > >  	lut->handle = handle;
> > >  	lut->ctx = ctx;
> > >  
> > > @@ -880,8 +883,9 @@ static int __eb_add_lut(struct i915_execbuffer *eb,
> > >  	return 0;
> > >  
> > >  err:
> > > -	i915_vma_close(vma);
> > >  	i915_vma_put(vma);
> > > +	i915_vma_close(vma);
> > > +err_lut_free:
> > >  	i915_lut_handle_free(lut);
> > >  	return err;
> > >  }
> > > diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> > > index d2f064d2525cc..4435c76f28c8c 100644
> > > --- a/drivers/gpu/drm/i915/i915_vma.c
> > > +++ b/drivers/gpu/drm/i915/i915_vma.c
> > > @@ -1735,14 +1735,33 @@ static void __i915_vma_remove_closed(struct i915_vma *vma)
> > >  	list_del_init(&vma->closed_link);
> > >  }
> > >  
> > > -void i915_vma_reopen(struct i915_vma *vma)
> > > +static struct i915_vma *i915_vma_reopen(struct i915_vma *vma)
> > > +{
> > > +	if (atomic_read(&vma->flags) & I915_VMA_PARKED)
> > > +		return NULL;
> > > +
> > > +	__i915_vma_remove_closed(vma);
> > > +	return vma;
> > > +}
> > > +
> > > +struct i915_vma *i915_vma_open(struct i915_vma *vma)
> > >  {
> > >  	struct intel_gt *gt = vma->vm->gt;
> > >  
> > > +	if (atomic_inc_not_zero(&vma->open_count))
> > > +		return vma;
> > > +
> > >  	spin_lock_irq(&gt->closed_lock);
> > > -	if (i915_vma_is_closed(vma))
> > > -		__i915_vma_remove_closed(vma);
> > > +	if (!atomic_inc_not_zero(&vma->open_count)) {
> > > +		if (i915_vma_is_closed(vma))
> > > +			vma = i915_vma_reopen(vma);
> > > +
> > > +		if (vma)
> > > +			atomic_inc(&vma->open_count);
> > > +	}
> > >  	spin_unlock_irq(&gt->closed_lock);
> > > +
> > > +	return vma;
> > >  }
> > >  
> > >  static void force_unbind(struct i915_vma *vma)
> > > @@ -1770,7 +1789,8 @@ static void release_references(struct i915_vma *vma, struct intel_gt *gt,
> > >  	spin_unlock(&obj->vma.lock);
> > >  
> > >  	spin_lock_irq(&gt->closed_lock);
> > > -	__i915_vma_remove_closed(vma);
> > > +	if (!(atomic_read(&vma->flags) & I915_VMA_PARKED))
> > > +		__i915_vma_remove_closed(vma);
> > >  	spin_unlock_irq(&gt->closed_lock);
> > >  
> > >  	if (vm_ddestroy)
> > > @@ -1854,22 +1874,22 @@ void i915_vma_parked(struct intel_gt *gt)
> > >  		}
> > >  
> > >  		list_move(&vma->closed_link, &closed);
> > > +		atomic_or(I915_VMA_PARKED, &vma->flags);
> > >  	}
> > >  	spin_unlock_irq(&gt->closed_lock);
> > >  
> > > -	/* As the GT is held idle, no vma can be reopened as we destroy them */
> > >  	list_for_each_entry_safe(vma, next, &closed, closed_link) {
> > >  		struct drm_i915_gem_object *obj = vma->obj;
> > >  		struct i915_address_space *vm = vma->vm;
> > >  
> > >  		if (i915_gem_object_trylock(obj, NULL)) {
> > > -			INIT_LIST_HEAD(&vma->closed_link);
> > >  			i915_vma_destroy(vma);
> > >  			i915_gem_object_unlock(obj);
> > >  		} else {
> > >  			/* back you go.. */
> > >  			spin_lock_irq(&gt->closed_lock);
> > >  			list_add(&vma->closed_link, &gt->closed_vma);
> > > +			atomic_andnot(I915_VMA_PARKED, &vma->flags);
> > >  			spin_unlock_irq(&gt->closed_lock);
> > >  		}
> > >  
> > > diff --git a/drivers/gpu/drm/i915/i915_vma.h b/drivers/gpu/drm/i915/i915_vma.h
> > > index e356dfb883d34..331d19672c764 100644
> > > --- a/drivers/gpu/drm/i915/i915_vma.h
> > > +++ b/drivers/gpu/drm/i915/i915_vma.h
> > > @@ -268,7 +268,7 @@ int __must_check i915_vma_unbind_async(struct i915_vma *vma, bool trylock_vm);
> > >  int __must_check i915_vma_unbind_unlocked(struct i915_vma *vma);
> > >  void i915_vma_unlink_ctx(struct i915_vma *vma);
> > >  void i915_vma_close(struct i915_vma *vma);
> > > -void i915_vma_reopen(struct i915_vma *vma);
> > > +struct i915_vma *i915_vma_open(struct i915_vma *vma);
> > >  
> > >  void i915_vma_destroy_locked(struct i915_vma *vma);
> > >  void i915_vma_destroy(struct i915_vma *vma);
> > > diff --git a/drivers/gpu/drm/i915/i915_vma_types.h b/drivers/gpu/drm/i915/i915_vma_types.h
> > > index 559de74d0b114..41784c3025349 100644
> > > --- a/drivers/gpu/drm/i915/i915_vma_types.h
> > > +++ b/drivers/gpu/drm/i915/i915_vma_types.h
> > > @@ -263,6 +263,9 @@ struct i915_vma {
> > >  #define I915_VMA_SCANOUT_BIT	17
> > >  #define I915_VMA_SCANOUT	((int)BIT(I915_VMA_SCANOUT_BIT))
> > >  
> > > +#define I915_VMA_PARKED_BIT	18
> > > +#define I915_VMA_PARKED		((int)BIT(I915_VMA_PARKED_BIT))
> > > +
> > >  	struct i915_active active;
> > >  
> > >  #define I915_VMA_PAGES_BIAS 24
> > 
> 
> 
> 
>