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Message-ID: <20171006103933.GA9497@amd>
Date: Fri, 6 Oct 2017 12:39:33 +0200
From: Pavel Machek <pavel@....cz>
To: Ingo Molnar <mingo@...nel.org>
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>,
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the arch/x86 maintainers <x86@...nel.org>,
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Borislav Petkov <bp@...en8.de>
Subject: Re: x86: PIE support and option to extend KASLR randomization
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...
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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