Commit f70744c6 authored Oct 28, 2019 by Robin Murphy Committed by Rob Herring Oct 29, 2019

drm/panfrost: Don't dereference bogus MMU pointers



It seems that killing an application while faults are occurring
(particularly with a GPU in FPGA at a whopping 40MHz) can lead to
handling a lingering page fault after all the address space contexts
have already been freed. In this situation, the LRU list is empty so
addr_to_drm_mm_node() ends up dereferencing the list head as if it were
a struct panfrost_mmu entry; this leaves "mmu->as" actually pointing at
the pfdev->alloc_mask bitmap, which is also empty, and given that the
fault has a high likelihood of being in AS0, hilarity ensues.

Sadly, the cleanest solution seems to involve another goto. Oh well, at
least it's robust...

Fixes: 65e51e30 ("drm/panfrost: Prevent race when handling page fault")
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/9a0b09e6b5851f0d4428b72dd6b8b4c0d0ef4206.1572293305.git.robin.murphy@arm.com

parent 6f39188c

drivers/gpu/drm/panfrost/panfrost_mmu.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -406,11 +406,11 @@ addr_to_drm_mm_node(struct panfrost_device *pfdev, int as, u64 addr)
		spin_lock(&pfdev->as_lock);
		list_for_each_entry(mmu, &pfdev->as_lru_list, list) {
		if (as == mmu->as)
		break;
		goto found_mmu;
		}
		if (as != mmu->as)
		goto out;

		found_mmu:
		priv = container_of(mmu, struct panfrost_file_priv, mmu);

		spin_lock(&priv->mm_lock);

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