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

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

[Chuck Ebbert]

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

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

[Andi Kleen]

On Tuesday 25 July 2006 11:06, Chuck Ebbert wrote:
> 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:

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

-Andi

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

[Arjan van de Ven]

> > > 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.

that I fully agree with; if you say as user "hey I don't care about
anything but give me no randomization" we should give the user no
randomization.

-- 
if you want to mail me at work (you don't), use arjan (at) linux.intel.com

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

[Chuck Ebbert]

In-Reply-To: <44c514a8.6HlRR82y133O2bd0%ak@suse.de>

On Mon, 24 Jul 2006 20:42:48 +0200, Andi Kleen wrote:
> 
> --- linux.orig/arch/i386/kernel/process.c
> +++ linux/arch/i386/kernel/process.c
> @@ -37,6 +37,7 @@
>  #include <linux/kallsyms.h>
>  #include <linux/ptrace.h>
>  #include <linux/random.h>
> +#include <linux/personality.h>
>  
>  #include <asm/uaccess.h>
>  #include <asm/pgtable.h>
> @@ -905,7 +906,7 @@ asmlinkage int sys_get_thread_area(struc
>  
>  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:

        unsigned int r = get_random_int();
        sp &= ~0x7f;
        sp -= 128 * ((r % 32) + (r / 32 % 16));
        return sp;

-- 
Chuck

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

[Arjan van de Ven]

On Tue, 2006-07-25 at 03:46 -0400, Chuck Ebbert wrote:
> In-Reply-To: <44c514a8.6HlRR82y133O2bd0%ak@suse.de>
> 
> On Mon, 24 Jul 2006 20:42:48 +0200, Andi Kleen wrote:
> > 
> > --- linux.orig/arch/i386/kernel/process.c
> > +++ linux/arch/i386/kernel/process.c
> > @@ -37,6 +37,7 @@
> >  #include <linux/kallsyms.h>
> >  #include <linux/ptrace.h>
> >  #include <linux/random.h>
> > +#include <linux/personality.h>
> >  
> >  #include <asm/uaccess.h>
> >  #include <asm/pgtable.h>
> > @@ -905,7 +906,7 @@ asmlinkage int sys_get_thread_area(struc
> >  
> >  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 ;)

Greetings,
   Arjan van de Ven