linux-kernel - Re: [PATCH v2 0/5] split ET

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Date:	Tue, 3 Mar 2015 08:31:32 +0100
From:	Ingo Molnar <mingo@...nel.org>
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>,
	Michael Ellerman <mpe@...erman.id.au>,
	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,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 0/5] split ET_DYN ASLR from mmap ASLR


* Kees Cook <keescook@...omium.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@...nel.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
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