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

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Date:   Wed, 30 Oct 2019 09:15:30 +0100
From:   Mike Rapoport <rppt@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        James Bottomley <jejb@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, linux-api@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org,
        Mike Rapoport <rppt@...ux.ibm.com>
Subject: Re: [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user
 mappings

On Tue, Oct 29, 2019 at 12:02:34PM +0100, David Hildenbrand wrote:
> On 27.10.19 11:17, Mike Rapoport wrote:
> >From: Mike Rapoport <rppt@...ux.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.
> >
> 
> Just a thought, the kernel is still able to indirectly read the contents of
> these pages by doing a kdump from kexec environment, right?

Right.

> Also, I wonder
> what would happen if you map such pages via /dev/mem into another user space
> application and e.g., use them along with kvm [1].

Do you mean that one application creates MAP_EXCLUSIVE and another
applications accesses the same physical pages via /dev/mem? 

With /dev/mem all physical memory is visible...
 
> [1] https://lwn.net/Articles/778240/
> 
> -- 
> 
> Thanks,
> 
> David / dhildenb
> 

-- 
Sincerely yours,
Mike.