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

[Andrey Konovalov]

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.