linux-kernel - Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree

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Date:	Mon, 09 Apr 2012 16:22:38 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Andrey Vagin <avagin@...nvz.org>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Glauber Costa <glommer@...allels.com>,
	Andi Kleen <andi@...stfloor.org>, Tejun Heo <tj@...nel.org>,
	Matt Helsley <matthltc@...ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Alexey Dobriyan <adobriyan@...il.com>, Valdis.Kletnieks@...edu,
	Michal Marek <mmarek@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>
Subject: Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree

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

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