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

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Date:	Tue, 24 Jan 2012 00:03:47 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Kees Cook <keescook@...omium.org>, Tejun Heo <tj@...nel.org>,
	Andrew Vagin <avagin@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	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>,
	Matt Helsley <matthltc@...ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Vasiliy Kulikov <segoon@...nwall.com>, Valdis.Kletnieks@...edu
Subject: Re: [patch 2/4] [RFC] syscalls, x86: Add __NR_kcmp syscall v4

On Mon, Jan 23, 2012 at 10:48:57AM -0800, H. Peter Anvin wrote:
> On 01/23/2012 06:20 AM, Cyrill Gorcunov wrote:
> > +
> > +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];
> > +}
> > +
> 
> Arf... when I said to use xor I meant instead of the add, not instead of
> the multiply, so:
> 
> 	return (v ^ cookies[type][0]) * cookies[type][1];
> 
> Otherwise you have absolutely no source of diffusion at all (symmetric
> cryptography is about combinations of diffusion -- spreading the content
> -- and confusion -- scrambling individual bits of content.)
> 
> +	for (i = 0; i < KCMP_TYPES; i++) {
> +		for (j = 0; j < 2; j++) {
> +			get_random_bytes(&cookies[i][j],
> +					 sizeof(cookies[i][j]));
> +			cookies[i][j] |= (~(~0UL >>  1) | 1);
> +		}
> +	}
> 
> Only cookies[1] -- being used as a multiplicative constant -- needs the OR.

OK. Thanks. I'll update.

	Cyrill
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