Thread (6 messages) flat view 6 messages, 3 authors, 2016-06-21

Re: [PATCH] crypto: Jitter RNG - use ktime_get_raw_ns as fallback

From: John Stultz <hidden>
Date: 2016-06-21 19:12:11
Also in: lkml

On Tue, Jun 21, 2016 at 11:49 AM, Stephan Mueller [off-list ref] wrote:
Am Dienstag, 21. Juni 2016, 11:11:42 schrieb John Stultz:

Hi John,
quoted
I don't see in the above an explanation of *why* you're using
ktime_get_raw_ns() instead of ktime_get_ns().
Could you help me understand what the difference is or point me to some
documentation? I understood that we only talked about the _raw variant.
Using specialized interfaces with subtle semantics w/o understanding
them is sort of my concern here.

There are reasons why you might want to use the ktime_get_raw_ns()
interface over ktime_get_ns(), but they have not been made clear in
the comment. Arnd discussed some potential concerns that the freq
adjustment done by ntp might be somewhat predictable/controlled by
remote parties, which could have some effect in the calculation. That
feels a little overly vague to me, but I'm no crypto expert, so if
that is a reasonable concern, then it should be a conscious and
documented decision.

thanks
-john
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