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

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:

quoted

From: Mike Rapoport <redacted>

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.