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Re: [PATCH v11 0/5] Enabling Ring 3 MONITOR/MWAIT feature for Knights Landing

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  Re: [PATCH v11 0/5] Enabling Ring 3 MONITOR/MWAIT feature for  Knights Landing Pavel Machek <pavel@ucw.cz> - 2017-01-03 23:20 +0100
    Re: [PATCH v11 0/5] Enabling Ring 3 MONITOR/MWAIT feature for Knights  Landing Thomas Gleixner <tglx@linutronix.de> - 2017-01-09 10:10 +0100
      Re: [PATCH v11 0/5] Enabling Ring 3 MONITOR/MWAIT feature for  Knights Landing Pavel Machek <pavel@ucw.cz> - 2017-01-09 10:20 +0100

#1550253 — Re: [PATCH v11 0/5] Enabling Ring 3 MONITOR/MWAIT feature for Knights Landing

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On Tue 2016-12-20 14:48:41, Grzegorz Andrejczuk wrote:
> Following patches enable the use of the feature that allows
> the Intel Xeon Phi x200 devices to use MONITOR/MWAIT instructions
> outside ring 0. It allows userspace applications to use
> more efficient synchronization operations, which improves performance
> and energy efficiency.

What kind of security holes does it bring us?

rdseed can be used for two processes to communicate when they should
not (serious problem for android). Can this be used for something similar?

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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#1554159 — Re: [PATCH v11 0/5] Enabling Ring 3 MONITOR/MWAIT feature for Knights Landing

On Tue, 3 Jan 2017, Pavel Machek wrote:

> On Tue 2016-12-20 14:48:41, Grzegorz Andrejczuk wrote:
> > Following patches enable the use of the feature that allows
> > the Intel Xeon Phi x200 devices to use MONITOR/MWAIT instructions
> > outside ring 0. It allows userspace applications to use
> > more efficient synchronization operations, which improves performance
> > and energy efficiency.
> 
> What kind of security holes does it bring us?
> 
> rdseed can be used for two processes to communicate when they should
> not (serious problem for android). Can this be used for something similar?

No. The monitor address must be in the virtual address space of the
caller, so it's like any other 'read' operation.

Thanks,

	tglx

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#1554166

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On Mon 2017-01-09 09:59:42, Thomas Gleixner wrote:
> On Tue, 3 Jan 2017, Pavel Machek wrote:
> 
> > On Tue 2016-12-20 14:48:41, Grzegorz Andrejczuk wrote:
> > > Following patches enable the use of the feature that allows
> > > the Intel Xeon Phi x200 devices to use MONITOR/MWAIT instructions
> > > outside ring 0. It allows userspace applications to use
> > > more efficient synchronization operations, which improves performance
> > > and energy efficiency.
> > 
> > What kind of security holes does it bring us?
> > 
> > rdseed can be used for two processes to communicate when they should
> > not (serious problem for android). Can this be used for something similar?
> 
> No. The monitor address must be in the virtual address space of the
> caller, so it's like any other 'read' operation.

Hmm. Unlike any other 'read' operation, it allows userland to modulate
CPU frequency with great precision; probably allowing userland to
transmit at radio bands, and allowing sound production without
syscalls (singing capacitors).

But userland can probably do that already, with help of
high-resolution timers, so nothing new theree... that I can think off.

Lets wait for the presentation at 39c3 :-).
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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