Re: [PATCH v10 07/12] fs, arm64: untag user pointers in fs/userfaultfd.c

[Dave Hansen]

On 3/1/19 8:59 AM, Catalin Marinas wrote:
>>> So, we have to patch all these sites before the tagged values get to the
>>> point of hitting the vma lookup functions.  Dumb question: Why don't we
>>> just patch the vma lookup functions themselves instead of all of these
>>> callers?
>> That might be a working approach as well. We'll still need to fix up
>> places where the vma fields are accessed directly. Catalin, what do
>> you think?
> Most callers of find_vma*() always follow it by a check of
> vma->vma_start against some tagged address ('end' in the
> userfaultfd_(un)register()) case. So it's not sufficient to untag it in
> find_vma().

If that's truly the common case, sounds like we should have a find_vma()
that does the vma_end checking as well.  Then at least the common case
would not have to worry about tagging.