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

[Catalin Marinas]

On Tue, Feb 26, 2019 at 03:39:08PM +0100, Andrey Konovalov wrote:
> On Sat, Feb 23, 2019 at 12:06 AM Dave Hansen <dave.hansen@xxxxxxxxx> wrote:
> >
> > On 2/22/19 4:53 AM, Andrey Konovalov wrote:
> > > userfaultfd_register() and userfaultfd_unregister() use provided user
> > > pointers for vma lookups, which can only by done with untagged pointers.
> >
> > 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().

-- 
Catalin