linux-kernel - Re: [RFC c/r 2/4] [RFC] syscalls, x86: Add __NR

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Date:	Fri, 27 Jan 2012 11:59:18 -0800
From:	"hpanvin@...il.com" <hpa@...or.com>
To:	Vasiliy Kulikov <segoon@...nwall.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.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>,
	Alexey Dobriyan <adobriyan@...il.com>, Valdis.Kletnieks@...edu
Subject: Re: [RFC c/r 2/4] [RFC] syscalls, x86: Add __NR_kcmp syscall v7

No, cookies[1] is always odd.

Vasiliy Kulikov <segoon@...nwall.com> wrote:

>Hi Cyrill,
>
>On Fri, Jan 27, 2012 at 21:53 +0400, Cyrill Gorcunov wrote:
>> +/*
>> + * We don't expose real in-memory order of objects for security
>> + * reasons, still the comparision results should be suitable for
>> + * sorting. Thus, we obfuscate kernel pointers values (using random
>> + * cookies obtaned at early boot stage) and compare the production
>> + * instead.
>> + */
>> +static unsigned long cookies[KCMP_TYPES][2] __read_mostly;
>> +
>> +static long kptr_obfuscate(long v, int type)
>> +{
>> +	return (v ^ cookies[type][0]) * cookies[type][1];
>
>AFACS, cookies is fully random value, is it possible that
>
>((v1 ^ cookies[type][0]) * cookies[type][1] == (v2 ^ cookies[type][0])
>* cookies[type][1]) &&
>(v1 != v2)
>
>for too round cookies[type][1]?
>
>Thanks,
>
>-- 
>Vasiliy Kulikov
>http://www.openwall.com - bringing security into open computing
>environments

-- 
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