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Date: Wed, 21 Jun 2017 14:24:26 -0400
From: Rik van Riel <>
To: Kees Cook <>, Andrew Morton
Cc: Daniel Micay <>, Qualys Security Advisory
 <>, Thomas Gleixner <>, Ingo Molnar
 <>, "H. Peter Anvin" <>,, 
 Alexander Viro <>, Dmitry Safonov
 <>, Andy Lutomirski <>, Grzegorz
 Andrejczuk <>,  Masahiro Yamada
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:
> Signed-off-by: Kees Cook <>

Acked-by: Rik van Riel <>

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