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Date: Mon, 09 Apr 2012 16:22:38 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Cyrill Gorcunov <gorcunov@openvz.org>
CC: Andrew Morton <akpm@linux-foundation.org>, Oleg Nesterov <oleg@redhat.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Pavel Emelyanov <xemul@parallels.com>,
        Andrey Vagin <avagin@openvz.org>,
        KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
        Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
        Glauber Costa <glommer@parallels.com>,
        Andi Kleen <andi@firstfloor.org>, Tejun Heo <tj@kernel.org>,
        Matt Helsley <matthltc@us.ibm.com>, Pekka Enberg <penberg@kernel.org>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        Vasiliy Kulikov <segoon@openwall.com>,
        Alexey Dobriyan <adobriyan@gmail.com>, Valdis.Kletnieks@vt.edu,
        Michal Marek <mmarek@suse.cz>,
        Frederic Weisbecker <fweisbec@gmail.com>, linux-kernel@vger.kernel.org,
        Jonathan Corbet <corbet@lwn.net>
Subject: Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree
References: <20120215143606.GA14037@redhat.com> <20120215160652.GA17680@redhat.com> <20120215162752.GF4533@moon> <20120409151027.7f3e0fa5.akpm@linux-foundation.org> <20120409222443.GW1625@moon>
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On 04/09/2012 03:24 PM, Cyrill Gorcunov wrote:
>>
>> Having re-read most of the (enormous) email discussion on the kcmp()
>> syscall patch, I'm thinking:
>>
>> - Nobody seems to understand the obfuscation logic.  Jon sounded
>>   confused, Oleg sounds confused and it's rather unclear what it does,
>>   how it does it and why it does it.
> 
> The obfuscation logic was done with great help from hpa@. And the main
> idea was to have ordered results after obfuscation. Per-type noise increase
> randomization of results. So Andrew, I actually dont know what to add
> here. We don't want to provide kernel order back to user-space in
> naked manner.
> 

The obfuscation logic is to provide a 1:1 mapping but which doesn't
preserve ordering, thereby avoid leaking information of kernel pointers
to user space.

	-hpa