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Message-ID: <1502131556.1803.10.camel@gmail.com>
Subject: Re: binfmt_elf: use ELF_ET_DYN_BASE only for PIE breaks asan
From: Daniel Micay <danielmicay@gmail.com>
Date: Mon, 07 Aug 2017 14:45:56 -0400
In-Reply-To: <1502131092.1803.8.camel@gmail.com>
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To: Kostya Serebryany <kcc@google.com>, Kees Cook <keescook@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>, Michal Hocko <mhocko@kernel.org>, Andrew Morton <akpm@linux-foundation.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, Rik van Riel <riel@redhat.com>, Reid Kleckner <rnk@google.com>, Peter Collingbourne <pcc@google.com>, eugenis@google.com

> There are currently other issues. Try:
> 
> sysctl vm.mmap_rnd_bits=32
> sysctl vm.mmap_rnd_compat_bits=16
> 
> IIRC that breaks some sanitizers at least for 32-bit executables.

Also, stack mapping rand isn't yet tied to that sysctl but is rather
hard-wired to 11 bits on 32-bit and 20 bits (IIRC) on 64-bit. Once it's
tied to the sysctl (or a different sysctl, if keeping the same defaults
is desired) that will be able to use significantly more address space.

It might be setting it to the maximum + better stack rand that breaks
sanitizers, rather than just setting the entropy higher.

If anyone wants to test some other changes though...

https://github.com/copperhead/linux-hardened/commit/31ebed471d31a437cc551b1bfae03c9e7f58117d.patch
https://github.com/copperhead/linux-hardened/commit/073329e7b541b89172833f61fb84d81f32389d6e.patch

They haven't been submitted for inclusion upstream, but that's the plan:
reaching parity with the ASLR PaX has provided for years when the
entropy values are set to max.

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