linux-kernel - Re: [PATCH] ASLRv3: randomize_va_space=3 preventing offset2lib attack

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Date:	Mon, 08 Dec 2014 21:09:21 +0100
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	Hector Marco <hecmargi@....es>, linux-kernel@...r.kernel.org
CC:	akpm@...ux-foundation.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, linux@....linux.org.uk, catalin.marinas@....com,
	will.deacon@....com, oleg@...hat.com, luto@...capital.net,
	keescook@...omium.org, Heiko Carstens <heiko.carstens@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Anton Blanchard <anton@...ba.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH] ASLRv3: randomize_va_space=3 preventing offset2lib attack

Am 05.12.2014 um 01:07 schrieb Hector Marco:
> [PATCH] ASLRv3: randomize_va_space=3 preventing offset2lib attack
> 
>   The issue appears on PIE linked executables when all memory areas of
>   a process are randomized (randomize_va_space=2). In this case, the
>   attack "offset2lib" de-randomizes all library areas on 64 bit Linux
>   systems in less than one second.
> 
>   Further details of the PoC attack at:
>   http://cybersecurity.upv.es/attacks/offset2lib/offset2lib.html
> 
>   PIE linked applications are loaded side by side with the dynamic
>   libraries, which is exploited by the offset2lib attack. Moving away
>   the executable from the mmap_base area (libraries area) prevents the
>   attack.
> 
>   This patch loads the PIE linked executable in a different area than
>   the libraries when randomize_va_space=3.
> 
>   Patch implementation details:
> 
>    - The ELF_ET_DYN_BASE address is used as the base to load randomly
>      the PIE executable.
> 
>    - The executable image has the same entropy than
>      randomize_va_space=2.
[...]
> --- a/arch/arm/mm/mmap.c
> +++ b/arch/arm/mm/mmap.c
[...]
> --- a/arch/arm64/mm/mmap.c
> +++ b/arch/arm64/mm/mmap.c
[...]

> --- a/arch/x86/mm/mmap.c
> +++ b/arch/x86/mm/mmap.c
[...]

FWIW, please note that s390 and power (maybe others?) also have PIE support done differently, e.g.
commit d2c9dfccbc3 ("[S390] Randomize PIEs") and commit 501cb16d3cfdc ("powerpc: Randomise PIEs")

What I can tell from a quick look both architectures should be fine regarding offsetlib, as they place the executable already in a different section and randomize those differently even with randomize_va_space=2.

Would it make sense to unify the implementations again?

Christian

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