Messages in this thread | | | Date | Tue, 10 Apr 2012 02:24:43 +0400 | From | Cyrill Gorcunov <> | Subject | Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree |
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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@openvz.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
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