lkml.org 
[lkml]   [2011]   [Mar]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] fix mmap random address range on x86 (try2)
Date
Randy Dunlap wrote:
> On Mon, 28 Feb 2011 15:53:03 +0100 Ludwig Nussel wrote:
> > On x86 casting the unsigned int result of get_random_int() to long
> > may result in a negative value. On x86 the range of mmap_rnd()
> > therefore was -255 to 255. The 32bit mode on x86_64 used 0 to 255 as
> > intended.
> >
> > The bug was introduced by commit 675a081 in January 2008.
> >
> > Signed-off-by: Ludwig Nussel <ludwig.nussel@suse.de>
> > ---
> > arch/x86/mm/mmap.c | 4 ++--
> > 1 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> > index 1dab519..f927429 100644
> > --- a/arch/x86/mm/mmap.c
> > +++ b/arch/x86/mm/mmap.c
> > @@ -87,9 +87,9 @@ static unsigned long mmap_rnd(void)
> > */
> > if (current->flags & PF_RANDOMIZE) {
> > if (mmap_is_ia32())
> > - rnd = (long)get_random_int() % (1<<8);
> > + rnd = get_random_int() % (1<<8);
> > else
> > - rnd = (long)(get_random_int() % (1<<28));
> > + rnd = get_random_int() % (1<<28);
> > }
> > return rnd << PAGE_SHIFT;
> > }
>
> Is there a test case for this?
> Can it be tested/checked/observed?

Sure. The attached program prints the address of the main function
to stdout. Compile it for i586, run it several times in a loop and
count the number of distinct addresses.

x86_64:
$ gcc -g -O2 -Wall -fpie -pie -m32 -o mainaddr mainaddr.c && for ((i=0;i<5000;++i)); do ./mainaddr; done | sort -u | wc -l
256

On native i586 without the patch the result is 511

cu
Ludwig

--
(o_ Ludwig Nussel
//\
V_/_ http://www.suse.de/
SUSE LINUX Products GmbH, GF: Markus Rex, HRB 16746 (AG Nuernberg)
#include <stdio.h>

int main(int argc, char *argv[])
{
printf("%lu\n", (unsigned long)main);
return 0;
}

\
 
 \ /
  Last update: 2011-03-01 09:25    [W:0.064 / U:12.156 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site