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
--
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