[Intel-gfx] [PATCH] drm/i915: Sanity check mmap length against object size

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-03-14 11:33:43)
> I am only wondering what happens to reads/write to the trailing area? 
> Does shmemfs expands the backing store for this mmap and we just end up 
> with otherwise unused chunk at the end?

My expectation would be that they generate a SIGBUS since the filp
should not be extended to cover the absent pages. So it would be the
equivalent of mmaping a file then calling ftruncate(0).

I admit it's not obvious if shmem_getpage_gfp (backing shmem_fault)
would prevent allocation of fresh backing pages beyond the initial filp
size. Afaict, we would end up at alloc_page_vma() without rejecting an
index beyond the end of the file.
-Chris