linux-kernel - Re: [PATCH v2] binfmt_elf: Use ELF_ET_DYN

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Date:   Wed, 21 Jun 2017 14:24:26 -0400
From:   Rik van Riel <riel@...hat.com>
To:     Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Daniel Micay <danielmicay@...il.com>,
        Qualys Security Advisory <qsa@...lys.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Dmitry Safonov <dsafonov@...tuozzo.com>,
        Andy Lutomirski <luto@...capital.net>,
        Grzegorz Andrejczuk <grzegorz.andrejczuk@...el.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v2] binfmt_elf: Use ELF_ET_DYN_BASE only for PIE

On Wed, 2017-06-21 at 10:32 -0700, Kees Cook wrote:

> To allow for a lower ELF_ET_DYN_BASE, loaders (ET_DYN without INTERP)
> are loaded into the mmap region, leaving space available for either
> an
> ET_EXEC binary with a fixed location or PIE being loaded into mmap by
> the
> loader. Only PIE programs are loaded offset from ELF_ET_DYN_BASE,
> which
> means architectures can now safely lower their values without risk of
> loaders colliding with their subsequently loaded programs.
> 
> For 64-bit, ELF_ET_DYN_BASE is best set to 4GB to allow runtimes to
> use
> the entire 32-bit address space for 32-bit pointers.
> 
> Thanks to PaX Team, Daniel Micay, and Rik van Riel for inspiration
> and
> suggestions on how to implement this solution.
> 
> Fixes: d1fd836dcf00 ("mm: split ET_DYN ASLR from mmap ASLR")
> Cc: stable@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>

Acked-by: Rik van Riel <riel@...hat.com>