linux-kernel - Re: [PATCH for 2.6.18rc2] [1/7] i386/x86-64: Don't randomize stack top when...

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Date:	Tue, 25 Jul 2006 13:38:44 +0200
From:	Andi Kleen <ak@...e.de>
To:	Chuck Ebbert <76306.1226@...puserve.com>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...l.org>
Subject: Re: [PATCH for 2.6.18rc2] [1/7] i386/x86-64: Don't randomize stack top when...

On Tuesday 25 July 2006 11:06, Chuck Ebbert wrote:
> In-Reply-To: <1153815124.8932.15.camel@...topd505.fenrus.org>
>
> On Tue, 25 Jul 2006 10:12:04 +0200, Arjan van de Ven wrote:
> > > >  unsigned long arch_align_stack(unsigned long sp)
> > > >  {
> > > > -     if (randomize_va_space)
> > > > +     if (!(current->personality & ADDR_NO_RANDOMIZE) &&
> > > > randomize_va_space) sp -= get_random_int() % 8192;
> > > >       return sp & ~0xf;
> > > >  }
> > >
> > > I think this needs to be done always, at least on P4.  It really isn't
> > > 'randomization' at the same high level as the rest -- more like a small
> > > adjustment.  And the offset should be a multiple of 128 and < 7K (not
> > > 8K.) Something like this:
> >
> > the 8K was what Intel proposed for 2.4 quite a while ago and has been in
> > use in linux for years and years... Can you explain why you are saying
> > 7Kb? throwing away that 1Kb of cache associativity is unfortunate and
> > shouldn't be done unless there's a good reason, so I'm quite interested
> > in finding out your reason ;)
>
> Well that's what the Intel IA-32 optimization manual says:

The reason I allowed to disable it is that it is sometimes very useful
for debugging if you can get 100% reproducible addresses.

-Andi

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