[kernel-hardening] Re: rowhammer protection [was Re: Getting interrupt every million cache misses]

[Pavel Machek <pavel@ucw.cz>]

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Hi!

> > I agree this needs to be tunable (and with the other suggestions). But
> > this is actually not the most important tunable: the detection
> > threshold (rh_attr.sample_period) should be way more important.
> > 
> > And yes, this will all need to be tunable, somehow. But lets verify
> > that this works, first :-).
> 
> Yeah.
> 
> Btw., a 56 NMI delay is pretty brutal in terms of latencies - it might
> result in a smoother system to detect 100,000 cache misses and do a
> ~5.6 msecs delay instead?
> 
> (Assuming the shorter threshold does not trigger too often, of
> course.)

Yeah, it is brutal workaround for a nasty bug. Slowdown depends on maximum utilization:

+/*
+ * Maximum permitted utilization of DRAM. Setting this to f will mean that
+ * when more than 1/f of maximum cache-miss performance is used, delay will
+ * be inserted, and will have similar effect on rowhammer as refreshing memory
+ * f times more often.
+ *
+ * Setting this to 8 should prevent the rowhammer attack.
+ */
+       int dram_max_utilization_factor = 8;

|                               | no prot. | fact. 1 | fact. 2 | fact. 8 |
| linux-n900$ time ./mkit       | 1m35     | 1m47    | 2m07    | 6m37    |
| rowhammer-test (for 43200000) | 2.86     | 9.75    | 16.7307 | 59.3738 |

(With factor 1 and 2 cpu attacker, we don't guarantee any protection.)

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

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