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

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Date:	Sat, 20 Dec 2014 01:19:32 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Hector Marco <hecmargi@....es>,
	Pavel Emelyanov <xemul@...allels.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Anton Blanchard <anton@...ba.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"H. Peter Anvin" <hpa@...or.com>,
	David Daney <ddaney.cavm@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arun Chandran <achandran@...sta.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Ismael Ripoll <iripoll@...ca.upv.es>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Hanno Böck <hanno@...eck.de>,
	Will Deacon <will.deacon@....com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Kees Cook <keescook@...omium.org>,
	Reno Robert <renorobert@...il.com>
Subject: Re: [PATCH] ASLRv3: randomize_va_space=3 preventing offset2lib attack

On Fri, Dec 19, 2014 at 02:11:37PM -0800, Andy Lutomirski wrote:
...
> >
> > Therefore, I can fix the current implementation (maintaining the
> > randomize_va_space=2) by moving the PIE executable from the mmap base
> > area to another one for x86*, ARM* and MIPS (as s390 and PowerPC do).
> > But we shall agree that this increment in the page table is not a
> > issue. Otherwise, the randomize_va_space=3 shall be considered.
> 
> Wrt the vdso itself, though, there is an extra consideration: CRIU.  I
> *think* that the CRIU vdso proxying scheme will work even if the vdso
> changes sizes and is adjacent to other mappings.  Cyrill and/or Pavel,
> am I right?

At least that was the idea. I've been testing old vdso from rhel5 proxified
to 3.x series where vvar segment is present, worked well.

> I'm not fundamentally opposed to mapping the vdso just like any other
> shared library.  I still think that we should have an extra-strong
> randomization mode in which all the libraries are randomized wrt each
> other, though.  For many applications, the extra page table cost will
> be negligible.
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