[PATCH] fix mmap random address range on x86 (try2)

[PATCH] fix mmap random address range on x86 (try2)

[Ludwig Nussel]

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;
 }
-- 
1.7.3.4

Re: [PATCH] fix mmap random address range on x86 (try2)

[Randy Dunlap]

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?

thanks,
---
~Randy
*** Remember to use Documentation/SubmitChecklist when testing your code ***

Re: [PATCH] fix mmap random address range on x86 (try2)

[Ludwig Nussel]

[-- Attachment #1: Type: Text/Plain, Size: 1635 bytes --]

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)

[-- Attachment #2: mainaddr.c --]
[-- Type: text/x-csrc, Size: 108 bytes --]

#include <stdio.h>

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