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Date:   Tue, 25 Sep 2018 14:12:57 +0000
From:   "Stecklina, Julian" <jsteckli@...zon.de>
To:     "jwadams@...gle.com" <jwadams@...gle.com>,
        "bsingharora@...il.com" <bsingharora@...il.com>
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        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
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Subject: Re: Redoing eXclusive Page Frame Ownership (XPFO) with isolated CPUs
 in mind (for KVM to isolate its guests per CPU)

On Sun, 2018-09-23 at 12:33 +1000, Balbir Singh wrote:
> > And in so doing, significantly reduces the amount of non-kernel
> data
> > vulnerable to speculative execution attacks against the kernel.
> > (and reduces what data can be loaded into the L1 data cache while
> > in kernel mode, to be peeked at by the recent L1 Terminal Fault
> > vulnerability).
> 
> I see and there is no way for gadgets to invoke this path from
> user space to make their speculation successful? We still have to
> flush L1, indepenedent of whether XPFO is enabled or not right?

Yes. And even with XPFO and L1 cache flushing enabled, there are more
steps that need to be taken to reliably guard against information leaks
using speculative execution.

Specifically, I'm looking into making certain allocations in the Linux
kernel process-local to hide even more memory from prefetching.

Another puzzle piece is co-scheduling support that is relevant for
systems with enabled hyperthreading: https://lwn.net/Articles/764461/

Julian
Amazon Development Center Germany GmbH
Berlin - Dresden - Aachen
main office: Krausenstr. 38, 10117 Berlin
Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger
Ust-ID: DE289237879
Eingetragen am Amtsgericht Charlottenburg HRB 149173 B

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