[PATCH 4/6] mm, arm64: untag user addresses in mm/gup.c

[Kirill A. Shutemov]

On Thu, May 03, 2018 at 04:09:56PM +0200, Andrey Konovalov wrote:
> On Wed, May 2, 2018 at 7:25 PM, Andrey Konovalov <andreyknvl at google.com> wrote:
> > On Wed, May 2, 2018 at 5:36 PM, Kirill A. Shutemov
> > <kirill.shutemov at linux.intel.com> wrote:
> >> On Wed, May 02, 2018 at 02:38:42PM +0000, Andrey Konovalov wrote:
> >>> > Does having a tagged address here makes any difference? I couldn't hit a
> >>> > failure with my simple tests (LD_PRELOAD a library that randomly adds
> >>> > tags to pointers returned by malloc).
> >>>
> >>> I think you're right, follow_page_mask is only called from
> >>> __get_user_pages, which already untagged the address. I'll remove
> >>> untagging here.
> >>
> >> It also called from follow_page(). Have you covered all its callers?
> >
> > Oh, missed that, will take a look.
> 
> I wasn't able to find anything that calls follow_page with pointers
> passed from userspace except for the memory subsystem syscalls, and we
> deliberately don't add untagging in those.

I guess I missed this part, but could you elaborate on this? Why?
Not yet or not ever?

Also I wounder if we can find (with sparse?) all places where we cast out
__user. This would give a nice list of places where to pay attention.

-- 
 Kirill A. Shutemov