linux-kernel - Re: [PATCH v3] x86: increase MIN_GAP to include randomized stack

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Message-ID: <20090908085328.GD22397@tiehlicka.suse.cz>
Date:	Tue, 8 Sep 2009 10:53:28 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, "H . Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3] x86: increase MIN_GAP to include randomized stack

On Tue 08-09-09 10:47:46, Jiri Kosina wrote:
> On Tue, 8 Sep 2009, Michal Hocko wrote:
> 
> > Currently we are not including randomized stack size when calculating
> > mmap_base address in arch_pick_mmap_layout for topdown case. This might
> > cause that mmap_base starts in the stack reserved area because stack is
> > randomized by 1GB for 64b (8MB for 32b) and the minimum gap is 128MB.
> > 
> > If the stack really grows down to mmap_base then we can get silent mmap
> > region overwrite by the stack values.
> > 
> > Let's include maximum stack randomization size into MIN_GAP which is
> > used as the low bound for the gap in mmap.
> > 
> > Signed-off-by: Michal Hocko <mhocko@...e.cz>
> > ---
> >  arch/x86/mm/mmap.c |   25 +++++++++++++++++++++++--
> >  1 files changed, 23 insertions(+), 2 deletions(-)
> > 
> > I think that this is also stable material and I will repost it to 
> > stable@...nel.org once you ack it.
> > 
> > Changes from v2:
> > STACK_RND_MASK has to be defined for CONFIG_X86_32 as well.
> > 
> > Changes from v1:
> > Fixed unsigned int overflow in MIN_GAP calculation.
> > 
> > 
> > diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> > index 1658296..a4566a8 100644
> > --- a/arch/x86/mm/mmap.c
> > +++ b/arch/x86/mm/mmap.c
> > @@ -30,12 +30,33 @@
> >  #include <linux/limits.h>
> >  #include <linux/sched.h>
> >  
> > +/* 1GB for 64bit, 8MB for 32bit definition taken from arch/x86/include/asm/elf.h */
> > +#ifndef STACK_RND_MASK
> > +#ifdef CONFIG_X86_64
> > +#define STACK_RND_MASK (test_thread_flag(TIF_IA32) ? 0x7ff : 0x3fffff)
> > +#else
> > +#define STACK_RND_MASK (0x7ff)
> > +#endif
> > +#endif
> 
> I'd still prefer all this macro-magic happening in <asm/elf.h> and 
> including this file from arch/x86/mm/mmap.c, otherwise we are duplicating 
> the STACK_RND_MASK definition, which is messy.

I definitely agree. I just wanted to post the complete patch for
reference. The elf variant will follow.

> 
> -- 
> Jiri Kosina
> SUSE Labs

-- 
Michal Hocko
L3 team 
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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