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Date: Tue, 10 Apr 2012 02:24:43 +0400 From: Cyrill Gorcunov <gorcunov@...nvz.org> To: Andrew Morton <akpm@...ux-foundation.org> Cc: 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>, "H. Peter Anvin" <hpa@...or.com>, 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 Mon, Apr 09, 2012 at 03:10:27PM -0700, Andrew Morton wrote: > Back on to kcmp. > > On Wed, 15 Feb 2012 20:27:52 +0400 > Cyrill Gorcunov <gorcunov@...nvz.org> wrote: > > > On Wed, Feb 15, 2012 at 05:06:52PM +0100, Oleg Nesterov wrote: > > > Not a comment, but the question. I am just curious... > > > > > > > +/* > > > > + * We don't expose real in-memory order of objects for security > > > > + * reasons, still the comparison results should be suitable for > > > > + * sorting. Thus, we obfuscate kernel pointers values 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]; > > > > +} > > > > > > OK, but why do we need this per type? Just to add more obfuscation > > > or there is another reason? > > > > Just to add more obfuscation. > > 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. > > - Lots of people have looked at the code and made comments and there > have been lots of changes. But we presently have zero Acked-by's and > Reviewed-by's. > I guess I can ask hpa@ and Eric for Reviewed-by or Acked-by tag? > I guess this means that at present nobody is aware of any issues with > the proposal, btu nobody is terribly excisted about it either? > I would rather say not much people yet use it. > So what do people think? Any issues? Any nacks? Should I sneak it > into Linus this week or do we need to go another round with it all? > > I'd like to at least have a fighting chance of understnading what's > going on with that obfuscation code. Cyrill -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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