From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759587Ab2DJWiH (ORCPT ); Tue, 10 Apr 2012 18:38:07 -0400 Received: from mail-lb0-f174.google.com ([209.85.217.174]:46934 "EHLO mail-lb0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756121Ab2DJWiF (ORCPT ); Tue, 10 Apr 2012 18:38:05 -0400 Date: Wed, 11 Apr 2012 02:37:58 +0400 From: Cyrill Gorcunov To: "H. Peter Anvin" Cc: Andrew Morton , Oleg Nesterov , "Eric W. Biederman" , Pavel Emelyanov , Andrey Vagin , KOSAKI Motohiro , Ingo Molnar , Thomas Gleixner , Glauber Costa , Andi Kleen , Tejun Heo , Matt Helsley , Pekka Enberg , Eric Dumazet , Vasiliy Kulikov , Alexey Dobriyan , Valdis.Kletnieks@vt.edu, Michal Marek , Frederic Weisbecker , linux-kernel@vger.kernel.org, Jonathan Corbet Subject: Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree Message-ID: <20120410223758.GL24857@moon> References: <20120215143606.GA14037@redhat.com> <20120215160652.GA17680@redhat.com> <20120215162752.GF4533@moon> <20120409151027.7f3e0fa5.akpm@linux-foundation.org> <20120409222443.GW1625@moon> <4F836F3E.9090207@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4F836F3E.9090207@zytor.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 09, 2012 at 04:22:38PM -0700, H. Peter Anvin wrote: > > 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. > OK, Peter, would the following comment bring light on the obfuscation procedure? --- Add a comment on kcmp obfuscation method Signed-off-by: Cyrill Gorcunov --- kernel/kcmp.c | 11 +++++++++++ 1 file changed, 11 insertions(+) Index: linux-2.6.git/kernel/kcmp.c =================================================================== --- linux-2.6.git.orig/kernel/kcmp.c +++ linux-2.6.git/kernel/kcmp.c @@ -17,6 +17,17 @@ * reasons, still the comparison results should be suitable for * sorting. Thus, we obfuscate kernel pointers values and compare * the production instead. + * + * The obfuscation is done in two steps. First -- we use xor on + * kernel pointer with random value, which puts pointer into + * a new position in reordered space. Second -- we multiply + * the xor production with big odd random number to permute + * bits even more (the oddity is important here, it allow + * us to have meaningful production even if multiplicants + * are big numbers). + * + * Note also the obfuscation itself is invisible to user-space + * and if needed it can be changed to any suitable scheme. */ static unsigned long cookies[KCMP_TYPES][2] __read_mostly;