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

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Message-ID: <085ed07e-e646-f7a4-0370-06f33a2a4e4a@redhat.com>
Date:   Tue, 29 Oct 2019 12:02:34 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Mike Rapoport <rppt@...nel.org>, linux-kernel@...r.kernel.org
Cc:     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 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?. 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].

[1] https://lwn.net/Articles/778240/

-- 

Thanks,

David / dhildenb