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Date:      Fri, 26 Aug 2016 15:36:39 +0100
From:      David Chisnall <theraven@FreeBSD.org>
To:        Warner Losh <imp@bsdimp.com>
Cc:        Pedro Giffuni <pfg@freebsd.org>, "freebsd-toolchain@FreeBSD.org" <freebsd-toolchain@freebsd.org>
Subject:   Re: Time to enable partial relro
Message-ID:  <0DDF18BF-E867-4275-AC5F-D52E5B543BD7@FreeBSD.org>
In-Reply-To: <CANCZdfqAmhN1owbo_rDt5xjC%2BbboOHrgu2xDHeZi1P02rX7EwQ@mail.gmail.com>
References:  <b75890eb-d8bd-759e-002f-ab0c16db0975@FreeBSD.org> <CANCZdfqAmhN1owbo_rDt5xjC%2BbboOHrgu2xDHeZi1P02rX7EwQ@mail.gmail.com>
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[-- Attachment #1 --]
On 26 Aug 2016, at 15:18, Warner Losh <imp@bsdimp.com> wrote:
> 
> So what's the summary of why we'd want to do that? What benefit does it bring?
> Sure, other folks do it, but why?

It reduce the attack surface for code reuse attacks: non-PLT GOT entries are read-only and so can’t be manipulated by a memory safety bug.  It doesn’t provide much mitigation, but it also doesn’t cost very much - some security for a negligible cost is probably a sensible thing to pick.

When combined with RTLD_NOW, it provides more hardening, but at a much more significant cost (bigger startup times - much bigger for things like OpenOffice or Firefox, some forms of interposition break, and so on).  That’s still probably worth it for some things (sshd, for example).

David


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