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Date: Fri, 26 Apr 2013 21:48:46 -0400
From: Rich Felker <dalias@...ifal.cx>
To: owl-dev@...ts.openwall.com
Subject: Re: PIE on x86_64

On Sat, Apr 27, 2013 at 02:14:05AM +0800, Pavel Labushev wrote:
> On Fri, 12 Apr 2013 22:26:58 +0400
> Solar Designer <solar@...nwall.com> wrote:
> 
> > > What are your reasons not to link executables as ET_DYN, even though
> > > the target CPU architecture is PC-relative?
> > 
> > I think we should start doing that, and benchmark to make sure there's
> > no unexpected performance drop.  Vasily?
> 
> And silence was the answer... Is it too much work? You could make -fpie
> and the other hardening flags compiler's built-in defaults, like it is
> done in Hardened Gentoo. It may be simpler and more robust than
> tweaking specs of every package and would set more secure defaults for
> anything that users might compile.

Unfortunately changing the compiler defaults can break things in
subtle ways. The most common breakage I'm aware of from making pie the
default occurs in packages with assembler source files that are
written in non-pic-compatible ways. These will turn into TEXTRELs in
the pie binary, which depending on the arch, may just result in heavy
runtime bloat (e.g. on 32-bit x86) or produce an error at link time
(e.g. on x86_64). I seem to recall a user running into this issue in
OpenSSL...

Rich

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