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Date: Fri, 07 Nov 2014 07:25:31 -0500
From: "Anthony G. Basile" <basile@...nsource.dyc.edu>
To: musl@...ts.openwall.com
Subject: Re: fixing -fPIE + -fstack-protector-all
On 11/06/14 07:36, John Spencer wrote:
> Anthony G. Basile wrote:
>> On 11/05/14 10:43, Rich Felker wrote:
>>> However, this proposed solution breaks one odd corner case: static
>>> linking when all the source files were compiled with -fPIC or -fPIE.
>>> In that case, there would be no references to __stack_chk_fail, only
>>> to __stack_chk_fail_local, and thereby __init_ssp would not get
>>> linked, and a zero canary would be used.
>>
>> I would rather not see this solution.
>>
>
> why ?
I want to save that corner case. In gentoo we compile everything
pic/pie, even our executables:
# readelf -h /bin/bash | grep Type:
Type: DYN (Shared object file)
This randomizes even the address of main. The following
#include <stdio.h>
int main() {
printf("%p\n", main);
}
yields
0x61f64b845
0x33fa0b7845
0x189ab51845
0x58531cd845
on successive runs when compiled with our default gcc specs. Along with
PaX's enhenced aslr this helps against brute forcing addresses. Compare
to when I turn off pie:
0x400605
0x400605
0x400605
Having said that, currently we do not support *static* pic/pie in
Gentoo, but I would really like to, especially with musl. Also, I'm not
as worried about the GOT for reasons I stated elsewhere.
--
Anthony G. Basile, Ph. D.
Chair of Information Technology
D'Youville College
Buffalo, NY 14201
(716) 829-8197
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