Re: [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings

Mike Rapoport
2019-10-28T13:00:29Z

On Mon, Oct 28, 2019 at 03:31:24PM +0300, Kirill A. Shutemov wrote:
> On Sun, Oct 27, 2019 at 12:17:32PM +0200, Mike Rapoport wrote:
> > From: Mike Rapoport <rppt@linux.ibm.com>
> >
> > The mappings created with MAP_EXCLUSIVE are visible only in the context of
> > the owning process and can be used by applications to store secret
> > information that will not be visible not only to other processes but to the
> > kernel as well.
> >
> > The pages in these mappings are removed from the kernel direct map and
> > marked with PG_user_exclusive flag. When the exclusive area is unmapped,
> > the pages are mapped back into the direct map.
>
> I probably blind, but I don't see where you manipulate direct map...

__get_user_pages() calls __set_page_user_exclusive() which in turn calls
set_direct_map_invalid_noflush() that makes the page not present.

> --
> Kirill A. Shutemov

--
Sincerely yours,
Mike.