From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH v2 0/5] split ET_DYN ASLR from mmap ASLR
Date: Tue, 3 Mar 2015 08:31:32 +0100
Message-ID: <20150303073132.GA30602@gmail.com>
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Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
	Russell King <linux@arm.linux.org.uk>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Ralf Baechle <ralf@linux-mips.org>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
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	Alexander Viro <viro@zeniv.linux.org.uk>,
	Oleg Nesterov <oleg@redhat.com>,
	Andy Lutomirski <luto@amacapital.net>,
	"David A. Long" <dave.long@linaro.org>,
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	Arun Chandran <achandran@mvista.com>,
	Yann Droneaud <ydroneaud@opteya.com>,
	Min-Hua Chen <orca.chen@gmail.com>,
	Paul Burton <paul.burton@imgtec.com>,
	Alex Smith <alex@alex-smith.me.uk>,
	Markos Chandras <markos.chandras
To: Kees Cook <keescook@chromium.org>
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* Kees Cook <keescook@chromium.org> wrote:

> To address the "offset2lib" ASLR weakness[1], this separates ET_DYN
> ASLR from mmap ASLR, as already done on s390. The architectures
> that are already randomizing mmap (arm, arm64, mips, powerpc, s390,
> and x86), have their various forms of arch_mmap_rnd() made available
> via the new CONFIG_ARCH_HAS_ELF_RANDOMIZE. For these architectures,
> arch_randomize_brk() is collapsed as well.
> 
> This is an alternative to the solutions in:
> https://lkml.org/lkml/2015/2/23/442

Looks good so far:

Reviewed-by: Ingo Molnar <mingo@kernel.org>

While reviewing this series I also noticed that the following code 
could be factored out from architecture mmap code as well:

  - arch_pick_mmap_layout() uses very similar patterns across the 
    platforms, with only few variations. Many architectures use 
    the same duplicated mmap_is_legacy() helper as well. There's 
    usually just trivial differences between mmap_legacy_base() 
    approaches as well.

  - arch_mmap_rnd(): the PF_RANDOMIZE checks are needlessly
    exposed to the arch routine - the arch routine should only 
    concentrate on arch details, not generic flags like
    PF_RANDOMIZE.

In theory the mmap layout could be fully parametrized as well: i.e. no 
callback functions to architectures by default at all: just 
declarations of bits of randomization desired (or, available address 
space bits), and perhaps an arch helper to allow 32-bit vs. 64-bit 
address space distinctions.

'Weird' architectures could provide special routines, but only by 
overriding the default behavior, which should be generic, safe and 
robust.

Thanks,

	Ingo