From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751505AbWGYJLp (ORCPT ); Tue, 25 Jul 2006 05:11:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751514AbWGYJLp (ORCPT ); Tue, 25 Jul 2006 05:11:45 -0400 Received: from liaag2ag.mx.compuserve.com ([149.174.40.158]:6030 "EHLO liaag2ag.mx.compuserve.com") by vger.kernel.org with ESMTP id S1751505AbWGYJLo (ORCPT ); Tue, 25 Jul 2006 05:11:44 -0400 Date: Tue, 25 Jul 2006 05:06:07 -0400 From: Chuck Ebbert <76306.1226@compuserve.com> Subject: Re: [PATCH for 2.6.18rc2] [1/7] i386/x86-64: Don't randomize stack top when... To: Arjan van de Ven Cc: Ingo Molnar , linux-kernel , Linus Torvalds , Andi Kleen Message-ID: <200607250508_MC3-1-C604-C1C9@compuserve.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org In-Reply-To: <1153815124.8932.15.camel@laptopd505.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: To establish a suitable stack offset for two instances of the same application running on two logical processors in the same physical processor package, the stack pointer can be adjusted in the entry function of the application using the technique shown in Example 7-5. Example 7-5 Adding a Pseudo-random Offset to the Stack Pointer in the Entry Function void main() { char * pPrivate = NULL; long myOffset = GetMod7Krandom128X() // A pseudo-random number that is a multiple // of 128 and less than 7K. // Use runtime library routine to reposition. _alloca(myOffset); // The stack pointer. } IA-32 Intel Architecture Optimization Reference Manual, Ch. 7 June 2005 -- Chuck