Re: [PATCH v4] drm/i915/userptr: Disallow wrapping GTT into a userptr

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 08/03/2017 21:59, Chris Wilson wrote:
> If we allow the user to convert a GTT mmap address into a userptr, we
> may end up in recursion hell, where currently we hit a mutex deadlock
> but other possibilities include use-after-free during the
> unbind/cancel_userptr.
>
> [  143.203989] gem_userptr_bli D    0   902    898 0x00000000
> [  143.204054] Call Trace:
> [  143.204137]  __schedule+0x511/0x1180
> [  143.204195]  ? pci_mmcfg_check_reserved+0xc0/0xc0
> [  143.204274]  schedule+0x57/0xe0
> [  143.204327]  schedule_timeout+0x383/0x670
> [  143.204374]  ? trace_hardirqs_on_caller+0x187/0x280
> [  143.204457]  ? trace_hardirqs_on_thunk+0x1a/0x1c
> [  143.204507]  ? usleep_range+0x110/0x110
> [  143.204657]  ? irq_exit+0x89/0x100
> [  143.204710]  ? retint_kernel+0x2d/0x2d
> [  143.204794]  ? trace_hardirqs_on_caller+0x187/0x280
> [  143.204857]  ? _raw_spin_unlock_irq+0x33/0x60
> [  143.204944]  wait_for_common+0x1f0/0x2f0
> [  143.205006]  ? out_of_line_wait_on_atomic_t+0x170/0x170
> [  143.205103]  ? wake_up_q+0xa0/0xa0
> [  143.205159]  ? flush_workqueue_prep_pwqs+0x15a/0x2c0
> [  143.205237]  wait_for_completion+0x1d/0x20
> [  143.205292]  flush_workqueue+0x2e9/0xbb0
> [  143.205339]  ? flush_workqueue+0x163/0xbb0
> [  143.205418]  ? __schedule+0x533/0x1180
> [  143.205498]  ? check_flush_dependency+0x1a0/0x1a0
> [  143.205681]  i915_gem_userptr_mn_invalidate_range_start+0x1c7/0x270 [i915]
> [  143.205865]  ? i915_gem_userptr_dmabuf_export+0x40/0x40 [i915]
> [  143.205955]  __mmu_notifier_invalidate_range_start+0xc6/0x120
> [  143.206044]  ? __mmu_notifier_invalidate_range_start+0x51/0x120
> [  143.206123]  zap_page_range_single+0x1c7/0x1f0
> [  143.206171]  ? unmap_single_vma+0x160/0x160
> [  143.206260]  ? unmap_mapping_range+0xa9/0x1b0
> [  143.206308]  ? vma_interval_tree_subtree_search+0x75/0xd0
> [  143.206397]  unmap_mapping_range+0x18f/0x1b0
> [  143.206444]  ? zap_vma_ptes+0x70/0x70
> [  143.206524]  ? __pm_runtime_resume+0x67/0xa0
> [  143.206723]  i915_gem_release_mmap+0x1ba/0x1c0 [i915]
> [  143.206846]  i915_vma_unbind+0x5c2/0x690 [i915]
> [  143.206925]  ? __lock_is_held+0x52/0x100
> [  143.207076]  i915_gem_object_set_tiling+0x1db/0x650 [i915]
> [  143.207236]  i915_gem_set_tiling_ioctl+0x1d3/0x3b0 [i915]
> [  143.207377]  ? i915_gem_set_tiling_ioctl+0x5/0x3b0 [i915]
> [  143.207457]  drm_ioctl+0x36c/0x670
> [  143.207535]  ? debug_lockdep_rcu_enabled.part.0+0x1a/0x30
> [  143.207730]  ? i915_gem_object_set_tiling+0x650/0x650 [i915]
> [  143.207793]  ? drm_getunique+0x120/0x120
> [  143.207875]  ? __handle_mm_fault+0x996/0x14a0
> [  143.207939]  ? vm_insert_page+0x340/0x340
> [  143.208028]  ? up_write+0x28/0x50
> [  143.208086]  ? vm_mmap_pgoff+0x160/0x190
> [  143.208163]  do_vfs_ioctl+0x12c/0xa60
> [  143.208218]  ? debug_lockdep_rcu_enabled+0x35/0x40
> [  143.208267]  ? ioctl_preallocate+0x150/0x150
> [  143.208353]  ? __do_page_fault+0x36a/0x6e0
> [  143.208400]  ? mark_held_locks+0x23/0xc0
> [  143.208479]  ? up_read+0x1f/0x40
> [  143.208526]  ? entry_SYSCALL_64_fastpath+0x5/0xc6
> [  143.208669]  ? __fget_light+0xa7/0xc0
> [  143.208747]  SyS_ioctl+0x41/0x70
>
> To prevent the possibility of a deadlock, we defer scheduling the worker
> until after we have proven that given the current mm, the userptr range
> does not overlap a GGTT mmaping. If another thread tries to remap the
> GGTT over the userptr before the worker is scheduled, it will be stopped
> by its invalidate-range flushing the current work, before the deadlock
> can occur.
>
> v2: Improve discussion of how we end up in the deadlock.
> v3: Don't forget to mark the userptr as active after a successful
> gup_fast. Rename overlaps_ggtt to noncontiguous_or_overlaps_ggtt.
> v4: Fix test ordering between invalid GTT mmaping and range completion
> (Tvrtko)
>
> Reported-by: Michał Winiarski <michal.winiarski@intel.com>
> Testcase: igt/gem_userptr_blits/map-fixed-invalidate-gup
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Michał Winiarski <michal.winiarski@intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem_userptr.c | 88 +++++++++++++++++++++++----------
>  1 file changed, 62 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
> index dc9bf5282071..07046fa4c6a9 100644
> --- a/drivers/gpu/drm/i915/i915_gem_userptr.c
> +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
> @@ -488,6 +488,37 @@ __i915_gem_userptr_set_active(struct drm_i915_gem_object *obj,
>  	return ret;
>  }
>
> +static bool noncontiguous_or_overlaps_ggtt(struct drm_i915_gem_object *obj,
> +					   struct mm_struct *mm)
> +{
> +	const struct vm_operations_struct *gem_vm_ops =
> +		obj->base.dev->driver->gem_vm_ops;
> +	unsigned long addr = obj->userptr.ptr;
> +	const unsigned long end = addr + obj->base.size;
> +	struct vm_area_struct *vma;
> +
> +	/* Check for a contiguous set of vma covering the userptr, if any
> +	 * are absent, they will EFAULT. More importantly if any point back
> +	 * to a drm_i915_gem_object GTT mmaping, we may trigger a deadlock
> +	 * between the deferred gup of this userptr and the object being
> +	 * unbound calling invalidate_range -> cancel_userptr.
> +	 */
> +	for (vma = find_vma(mm, addr); vma; vma = vma->vm_next) {
> +		if (vma->vm_start > addr) /* gap */
> +			break;
> +
> +		if (vma->vm_ops == gem_vm_ops) /* GTT mmapping */
> +			break;
> +
> +		if (vma->vm_end >= end)
> +			return false;
> +
> +		addr = vma->vm_end;
> +	}
> +
> +	return true;
> +}
> +
>  static void
>  __i915_gem_userptr_get_pages_worker(struct work_struct *_work)
>  {
> @@ -556,8 +587,7 @@ __i915_gem_userptr_get_pages_worker(struct work_struct *_work)
>  }
>
>  static struct sg_table *
> -__i915_gem_userptr_get_pages_schedule(struct drm_i915_gem_object *obj,
> -				      bool *active)
> +__i915_gem_userptr_get_pages_schedule(struct drm_i915_gem_object *obj)
>  {
>  	struct get_pages_work *work;
>
> @@ -594,7 +624,6 @@ __i915_gem_userptr_get_pages_schedule(struct drm_i915_gem_object *obj,
>  	INIT_WORK(&work->work, __i915_gem_userptr_get_pages_worker);
>  	schedule_work(&work->work);
>
> -	*active = true;
>  	return ERR_PTR(-EAGAIN);
>  }
>
> @@ -602,10 +631,11 @@ static struct sg_table *
>  i915_gem_userptr_get_pages(struct drm_i915_gem_object *obj)
>  {
>  	const int num_pages = obj->base.size >> PAGE_SHIFT;
> +	struct mm_struct *mm = obj->userptr.mm->mm;
>  	struct page **pvec;
>  	struct sg_table *pages;
> -	int pinned, ret;
>  	bool active;
> +	int pinned;
>
>  	/* If userspace should engineer that these pages are replaced in
>  	 * the vma between us binding this page into the GTT and completion
> @@ -632,37 +662,43 @@ i915_gem_userptr_get_pages(struct drm_i915_gem_object *obj)
>  			return ERR_PTR(-EAGAIN);
>  	}
>
> -	/* Let the mmu-notifier know that we have begun and need cancellation */
> -	ret = __i915_gem_userptr_set_active(obj, true);
> -	if (ret)
> -		return ERR_PTR(ret);
> -
>  	pvec = NULL;
>  	pinned = 0;
> -	if (obj->userptr.mm->mm == current->mm) {
> -		pvec = drm_malloc_gfp(num_pages, sizeof(struct page *),
> -				      GFP_TEMPORARY);
> -		if (pvec == NULL) {
> -			__i915_gem_userptr_set_active(obj, false);
> -			return ERR_PTR(-ENOMEM);
> -		}
>
> -		pinned = __get_user_pages_fast(obj->userptr.ptr, num_pages,
> -					       !obj->userptr.read_only, pvec);
> +	down_read(&mm->mmap_sem);
> +	if (unlikely(noncontiguous_or_overlaps_ggtt(obj, mm))) {
> +		pinned = -EFAULT;
> +	} else if (mm == current->mm) {
> +		pvec = drm_malloc_gfp(num_pages, sizeof(struct page *),
> +				      GFP_TEMPORARY |
> +				      __GFP_NORETRY |
> +				      __GFP_NOWARN);
> +		if (pvec) /* defer to worker if malloc fails */
> +			pinned = __get_user_pages_fast(obj->userptr.ptr,
> +						       num_pages,
> +						       !obj->userptr.read_only,
> +						       pvec);
>  	}
>
>  	active = false;
> -	if (pinned < 0)
> -		pages = ERR_PTR(pinned), pinned = 0;
> -	else if (pinned < num_pages)
> -		pages = __i915_gem_userptr_get_pages_schedule(obj, &active);
> -	else
> +	if (pinned < 0) {
> +		pages = ERR_PTR(pinned);
> +		pinned = 0;
> +	} else if (pinned < num_pages) {
> +		pages = __i915_gem_userptr_get_pages_schedule(obj);
> +		active = pages == ERR_PTR(-EAGAIN);
> +	} else {
>  		pages = __i915_gem_userptr_set_pages(obj, pvec, num_pages);
> -	if (IS_ERR(pages)) {
> -		__i915_gem_userptr_set_active(obj, active);
> -		release_pages(pvec, pinned, 0);
> +		active = !IS_ERR(pages);
>  	}
> +	if (active)
> +		__i915_gem_userptr_set_active(obj, true);
> +	up_read(&mm->mmap_sem);
> +
> +	if (IS_ERR(pages))
> +		release_pages(pvec, pinned, 0);
>  	drm_free_large(pvec);
> +
>  	return pages;
>  }
>
>

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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