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    SubjectRe: + 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@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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