Date: Wed, 05 Nov 2014 17:01:31 +0100 From: John Spencer <maillist-musl@...fooze.de> To: musl@...ts.openwall.com Subject: Re: fixing -fPIE + -fstack-protector-all 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. > > One possible way to handle this would be giving up the conditional > linking of ssp init and just always initializing it. The .o file is 78 > bytes on i386 and 70 bytes on x86_64, but there would also be some > savings to offset the cost simply from having the code inline in > __init_libc rather than as an external function. that sounds reasonable. do you intend add this symbol and the mandatory init_ssp code even to archs that don't need it (for example x86_64) ? --JS
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