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Date: Wed, 05 Nov 2014 17:34:49 -0800
From: Andy Lutomirski <luto@...capital.net>
To: musl@...ts.openwall.com
Subject: Re: fixing -fPIE + -fstack-protector-all
On 11/05/2014 07:43 AM, Rich Felker wrote:
> On Wed, Nov 05, 2014 at 04:25:03PM +0100, John Spencer wrote:
>> using -fPIE + -fstack-protector-all is currently broken for a number
>> of architectures (most notably i386) in the default gcc setup
>> (including the musl-cross patches), as it depends on a
>> libssp_nonshared.a which provides __stack_chk_fail_local().
>
> As discussed on IRC, I would _like_ to be able to simply add the
> following to crt/i386/crti.s:
>
> __stack_chk_fail_local: hlt
>
> and equivalent for other archs. This has the added benefit of
> effecting a crash without going through the PLT (whereas
> libssp_nonshared.a's __stack_chk_fail_local calls __stack_chk_fail via
> the PLT) so it's not vulnerable to attacks that have overwritten the
> GOT with malicious pointers.
>
> 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.
Can you do something like:
__stack_chk_fail_local:
hlt
.pushsection .discard
call __init_ssp
.popsection
and stick it in either its own object or its own group? Or is ld too
clever for that?
--Andy
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