linux-kernel - Re: [PATCH drm-misc-next v3 6/7] drm/gpuvm: generalize dma

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Date:   Mon, 11 Sep 2023 16:45:26 +0200
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Danilo Krummrich <dakr@...hat.com>
Cc:     airlied@...il.com, daniel@...ll.ch, matthew.brost@...el.com,
        thomas.hellstrom@...ux.intel.com, sarah.walker@...tec.com,
        donald.robson@...tec.com, christian.koenig@....com,
        faith.ekstrand@...labora.com, dri-devel@...ts.freedesktop.org,
        nouveau@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH drm-misc-next v3 6/7] drm/gpuvm: generalize
 dma_resv/extobj handling and GEM validation

On Sat,  9 Sep 2023 17:31:13 +0200
Danilo Krummrich <dakr@...hat.com> wrote:

> @@ -807,6 +1262,14 @@ drm_gpuvm_bo_destroy(struct kref *kref)
>  
>  	drm_gem_gpuva_assert_lock_held(vm_bo->obj);
>  
> +	spin_lock(&gpuvm->extobj.lock);
> +	list_del(&vm_bo->list.entry.extobj);
> +	spin_unlock(&gpuvm->extobj.lock);
> +
> +	spin_lock(&gpuvm->evict.lock);
> +	list_del(&vm_bo->list.entry.evict);
> +	spin_unlock(&gpuvm->evict.lock);
> +
>  	list_del(&vm_bo->list.entry.gem);
>  
>  	drm_gem_object_put(obj);

I ran into a UAF situation when the drm_gpuvm_bo object is the last
owner of obj, because the lock that's supposed to be held when calling
this function (drm_gem_gpuva_assert_lock_held() call above), belongs to
obj (either obj->resv, or a driver specific lock that's attached to the
driver-specific GEM object). I worked around it by taking a ref to obj
before calling lock()+drm_gpuvm_bo_put()+unlock(), and releasing it
after I'm node with the lock, but that just feels wrong.