linux-kernel - Re: [PATCH 4/5] mm: split ET

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Date:	Wed, 04 Mar 2015 15:16:41 +1100
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Kees Cook <keescook@...omium.org>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Russell King <linux@....linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux390@...ibm.com, x86@...nel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Oleg Nesterov <oleg@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	"David A. Long" <dave.long@...aro.org>,
	Andrey Ryabinin <a.ryabinin@...sung.com>,
	Arun Chandran <achandran@...sta.com>,
	Yann Droneaud <ydroneaud@...eya.com>,
	Min-Hua Chen <orca.chen@...il.com>,
	Paul Burton <paul.burton@...tec.com>,
	Alex Smith <alex@...x-smith.me.uk>,
	Markos Chandras <markos.chandras@...tec.com>,
	Jeff Bailey <jeffbailey@...gle.com>,
	Vineeth Vijayan <vvijayan@...sta.com>,
	Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
	Ben Hutchings <ben@...adent.org.uk>,
	Hector Marco-Gisbert <hecmargi@....es>,
	Borislav Petkov <bp@...e.de>,
	Jan-Simon Möller <dl9pf@....de>,
	linux-arm-kernel@...ts.infradead.org, linux-mips@...ux-mips.org,
	linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 4/5] mm: split ET_DYN ASLR from mmap ASLR

On Mon, 2015-03-02 at 16:19 -0800, Kees Cook wrote:
> This fixes the "offset2lib" weakness in ASLR for arm, arm64, mips,
> powerpc, and x86. The problem is that if there is a leak of ASLR from
> the executable (ET_DYN), it means a leak of shared library offset as
> well (mmap), and vice versa. Further details and a PoC of this attack
> are available here:
> http://cybersecurity.upv.es/attacks/offset2lib/offset2lib.html
> 
> With this patch, a PIE linked executable (ET_DYN) has its own ASLR region:
> 
> $ ./show_mmaps_pie
> 54859ccd6000-54859ccd7000 r-xp  ...  /tmp/show_mmaps_pie
> 54859ced6000-54859ced7000 r--p  ...  /tmp/show_mmaps_pie
> 54859ced7000-54859ced8000 rw-p  ...  /tmp/show_mmaps_pie

Just to be clear, it's the fact that the above vmas are in a different
address range to those below that shows the patch is working, right?

> 7f75be764000-7f75be91f000 r-xp  ...  /lib/x86_64-linux-gnu/libc.so.6
> 7f75be91f000-7f75beb1f000 ---p  ...  /lib/x86_64-linux-gnu/libc.so.6


On powerpc I'm seeing:

# /bin/dash
# cat /proc/$$/maps
524e0000-52510000 r-xp 00000000 08:03 129814                             /bin/dash
52510000-52520000 rw-p 00020000 08:03 129814                             /bin/dash
10034f20000-10034f50000 rw-p 00000000 00:00 0                            [heap]
3fffaeaf0000-3fffaeca0000 r-xp 00000000 08:03 13529                      /lib/powerpc64le-linux-gnu/libc-2.19.so
3fffaeca0000-3fffaecb0000 rw-p 001a0000 08:03 13529                      /lib/powerpc64le-linux-gnu/libc-2.19.so
3fffaecc0000-3fffaecd0000 rw-p 00000000 00:00 0 
3fffaecd0000-3fffaecf0000 r-xp 00000000 00:00 0                          [vdso]
3fffaecf0000-3fffaed20000 r-xp 00000000 08:03 13539                      /lib/powerpc64le-linux-gnu/ld-2.19.so
3fffaed20000-3fffaed30000 rw-p 00020000 08:03 13539                      /lib/powerpc64le-linux-gnu/ld-2.19.so
3fffc7070000-3fffc70a0000 rw-p 00000000 00:00 0                          [stack]


Whereas previously the /bin/dash vmas were up at 3fff..

So looks good to me for powerpc.

Acked-by: Michael Ellerman <mpe@...erman.id.au>

cheers



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