Messages in this thread | | | From | Ludwig Nussel <> | Subject | Re: [PATCH] fix mmap random address range on x86 (try2) | Date | Tue, 1 Mar 2011 09:21:57 +0100 |
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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; }
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