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Date: Fri, 20 Oct 2017 10:13:20 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Pavel Machek <pavel@....cz>
Cc: "H. Peter Anvin" <hpa@...or.com>, Peter Zijlstra <peterz@...radead.org>,
	Thomas Garnier <thgarnie@...gle.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S . Miller" <davem@...emloft.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>, Arnd Bergmann <arnd@...db.de>,
	Matthias Kaehlcke <mka@...omium.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Juergen Gross <jgross@...e.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Radim Krčmář <rkrcmar@...hat.com>,
	Joerg Roedel <joro@...tes.org>,
	Tom Lendacky <thomas.lendacky@....com>,
	Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...e.de>,
	Brian Gerst <brgerst@...il.com>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	"Rafael J . Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...ux.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Chris Metcalf <cmetcalf@...lanox.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Christopher Li <sparse@...isli.org>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Lukas Wunner <lukas@...ner.de>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Dou Liyang <douly.fnst@...fujitsu.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Alexei Starovoitov <ast@...nel.org>,
	Masahiro Yamada <yamada.masahiro@...ionext.com>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Kees Cook <keescook@...omium.org>, Rik van Riel <riel@...hat.com>,
	David Howells <dhowells@...hat.com>,
	Waiman Long <longman@...hat.com>, Kyle Huey <me@...ehuey.com>,
	Peter Foley <pefoley2@...oley.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Michal Hocko <mhocko@...e.com>,
	Matthew Wilcox <mawilcox@...rosoft.com>,
	"H . J . Lu" <hjl.tools@...il.com>, Paul Bolle <pebolle@...cali.nl>,
	Rob Landley <rob@...dley.net>, Baoquan He <bhe@...hat.com>,
	Daniel Micay <danielmicay@...il.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	linux-crypto@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	xen-devel@...ts.xenproject.org, kvm list <kvm@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	linux-arch <linux-arch@...r.kernel.org>,
	linux-sparse@...r.kernel.org,
	Kernel Hardening <kernel-hardening@...ts.openwall.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: x86: PIE support and option to extend KASLR randomization


* Pavel Machek <pavel@....cz> wrote:

> On Mon 2017-09-25 09:33:42, Ingo Molnar wrote:
> > 
> > * Pavel Machek <pavel@....cz> wrote:
> > 
> > > > For example, there would be collision with regular user-space mappings, right? 
> > > > Can local unprivileged users use mmap(MAP_FIXED) probing to figure out where 
> > > > the kernel lives?
> > > 
> > > Local unpriviledged users can probably get your secret bits using cache probing 
> > > and jump prediction buffers.
> > > 
> > > Yes, you don't want to leak the information using mmap(MAP_FIXED), but CPU will 
> > > leak it for you, anyway.
> > 
> > Depends on the CPU I think, and CPU vendors are busy trying to mitigate this 
> > angle.
> 
> I believe any x86 CPU running Linux will leak it. And with CPU vendors
> putting "artifical inteligence" into branch prediction, no, I don't
> think it is going to get better.
> 
> That does not mean we shoudl not prevent mmap() info leak, but...

That might or might not be so, but there's a world of a difference between
running a relatively long statistical attack figuring out the kernel's
location, versus being able to programmatically probe the kernel's location
by using large MAP_FIXED user-space mmap()s, within a few dozen microseconds
or so and a 100% guaranteed, non-statistical result.

Thanks,

	Ingo

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