From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [Y2038] [PATCH] crypto: Jitter RNG - use ktime_get_raw_ns as fallback Date: Tue, 21 Jun 2016 21:37:03 +0200 Message-ID: <4528708.L2m6px9Mjb@wuerfel> References: <8242305.3NQCWfJAlD@positron.chronox.de> <1724645.8YjKaqazLv@positron.chronox.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Cc: John Stultz , Stephan Mueller , Herbert Xu , Alexander Kuleshov , lkml , linux-crypto@vger.kernel.org, "David S. Miller" , Kees Cook To: y2038@lists.linaro.org Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-crypto.vger.kernel.org On Tuesday, June 21, 2016 12:05:06 PM CEST John Stultz wrote: > On Tue, Jun 21, 2016 at 11:49 AM, Stephan Mueller wrote: > > Am Dienstag, 21. Juni 2016, 11:11:42 schrieb John Stultz: > > > > Hi John, > > > >> 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. My original patch changed __getnstimeofday() to __getnstimeofday64(), which kept the original semantics of not warning in case the clock source is suspended (which is the only different to the normal getnstimeofday{,64}(). I did the patch a while time ago along with a number of other patches that I never sent out until last week, so I don't remember the reasoning for suggesting ktime_get_raw_fast_ns() over ktime_get_raw_ns(), but I sure wanted to keep the non-warning behavior, and ktime_get_ns() warns on timekeeping_suspended() while the other two don't. If we don't care about the non-warning aspect, ktime_get_ns() makes most sense here, and the original code should probably have used getnstimeofday() as well. Arnd