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Re: [Xen-devel] x86: PIE support and option to extend KASLR randomization
- To: Pavel Machek <pavel@xxxxxx>
- From: Ingo Molnar <mingo@xxxxxxxxxx>
- Date: Fri, 20 Oct 2017 10:13:20 +0200
- Cc: Nicolas Pitre <nicolas.pitre@xxxxxxxxxx>, Michal Hocko <mhocko@xxxxxxxx>, kvm list <kvm@xxxxxxxxxxxxxxx>, Radim Krčmář <rkrcmar@xxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Catalin Marinas <catalin.marinas@xxxxxxx>, Christopher Li <sparse@xxxxxxxxxxx>, Alexei Starovoitov <ast@xxxxxxxxxx>, David Howells <dhowells@xxxxxxxxxx>, Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>, Peter Foley <pefoley2@xxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Kernel Hardening <kernel-hardening@xxxxxxxxxxxxxxxxxx>, Christoph Lameter <cl@xxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Kees Cook <keescook@xxxxxxxxxxxx>, the arch/x86 maintainers <x86@xxxxxxxxxx>, Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>, Daniel Borkmann <daniel@xxxxxxxxxxxxx>, Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>, Joerg Roedel <joro@xxxxxxxxxx>, "Rafael J . Wysocki" <rafael.j.wysocki@xxxxxxxxx>, Daniel Micay <danielmicay@xxxxxxxxx>, Baoquan He <bhe@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-sparse@xxxxxxxxxxxxxxx, Matthias Kaehlcke <mka@xxxxxxxxxxxx>, linux-arch <linux-arch@xxxxxxxxxxxxxxx>, Waiman Long <longman@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxx>, Markus Trippelsdorf <markus@xxxxxxxxxxxxxxx>, Len Brown <len.brown@xxxxxxxxx>, Rik van Riel <riel@xxxxxxxxxx>, Chris Metcalf <cmetcalf@xxxxxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, Linux PM list <linux-pm@xxxxxxxxxxxxxxx>, Brian Gerst <brgerst@xxxxxxxxx>, "H . J . Lu" <hjl.tools@xxxxxxxxx>, Steven Rostedt <rostedt@xxxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Andy Lutomirski <luto@xxxxxxxxxx>, Josh Poimboeuf <jpoimboe@xxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Dou Liyang <douly.fnst@xxxxxxxxxxxxxx>, Paul Bolle <pebolle@xxxxxxxxxx>, "Paul E . McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>, "Rafael J . Wysocki" <rjw@xxxxxxxxxxxxx>, LKML <linux-kernel@xxxxxxxxxxxxxxx>, "David S . Miller" <davem@xxxxxxxxxxxxx>, Kyle Huey <me@xxxxxxxxxxxx>, Lukas Wunner <lukas@xxxxxxxxx>, linux-crypto@xxxxxxxxxxxxxxx, Rob Landley <rob@xxxxxxxxxxx>, Tejun Heo <tj@xxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Tom Lendacky <thomas.lendacky@xxxxxxx>, Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>, Thomas Garnier <thgarnie@xxxxxxxxxx>, "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
- Delivery-date: Fri, 20 Oct 2017 08:13:30 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
* Pavel Machek <pavel@xxxxxx> wrote:
> On Mon 2017-09-25 09:33:42, Ingo Molnar wrote:
> >
> > * Pavel Machek <pavel@xxxxxx> 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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