From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751807AbcFUTfS (ORCPT ); Tue, 21 Jun 2016 15:35:18 -0400 Received: from mout.kundenserver.de ([217.72.192.75]:50890 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751677AbcFUTfO (ORCPT ); Tue, 21 Jun 2016 15:35:14 -0400 From: Arnd Bergmann To: y2038@lists.linaro.org Cc: John Stultz , Stephan Mueller , Herbert Xu , Alexander Kuleshov , lkml , linux-crypto@vger.kernel.org, "David S. Miller" , Kees Cook 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> User-Agent: KMail/5.1.3 (Linux/4.4.0-22-generic; KDE/5.18.0; x86_64; ; ) In-Reply-To: References: <8242305.3NQCWfJAlD@positron.chronox.de> <1724645.8YjKaqazLv@positron.chronox.de> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Provags-ID: V03:K0:9V/fFsZJRPmrtaS+t1ehmVmBXGT6FVlXJNGGB3ZVCn1qzPQnZYC DYCy8wSFXf+Nqsxluwla4bJ/M16jCJfkRAwWIUOCrQPe1WcxqzlhN5sUh6wYQAjCdAqAX9a Sd9Cdzy+53n6sJFpR7S0skCIEMK9swE4+jVfFVnKEuSOGhmMRi1ydgmEgjCFsSApTYlIq6i 8UQmJ91PurWFuD2WrS3fg== X-UI-Out-Filterresults: notjunk:1;V01:K0:MMrcE6WMKqU=:YVnq6e+bRWR/pAoIzA7hwB Wma4QH+UwYKat5lWJziYyXPNKvaTRWcDR1Iaj0af3FdYdeC334w55qPSt6TSgZcpbfPy9sOZB v6xoewMEnLC64Noj0fRK8ktm0XZIYYegAc1NwSrh/iQ98G1LQa2wYgFyx5Pk/Fh/7hbol8t7I xQM9rt6AQT+NmJoqXTgf/tA5PB9iR+CBUYmRS8sQ8oiyipEogBu8bfJcAW9y6MoHzt/9VcrFF zvB1zajabcJw6i9JYDzbJYwnFeUJJmimhvVRviuYQJMlg3kRh2SrHTm/U1cZmd92f3HILW9NY ZSBeIYCL5eU7hti/4+V24tA63xqKVlh/7LIueChkcdbHI3GLzbm9A81xZZSojocoln8g7amOd b32J+O7mWD97ACEE9fYo7Uk36FVkugKnOOOAG5IUY+P9J9onUNA177sKuwWFPRwC4fyrsQ8vK tKRqpiLiEIKSy18WcWCfUkMco9VtQxftHPU4rzRKMkNAy8D7Z2OxDne4213OhpbkP7xK0Axta m2WVD75hlPU9am5sKsDBVfzRndzOYQXLB5DzlhQU3H5YXbsfBiUYxVZHSdWoh36I2qbb62gbf jBu7w2gRmSJJBvaUpDPsx92erH4uiXiULsuwDgkirMpzFMkjGckxs/aDq43BMad9rI0m4YAEq rZnTXdCjWJ9o+WgYmhqn0PTbISC2Fa5jnJzPqKYm3w6fxzgF7Ui1dDrkImxoWNFFv8vjugrO+ fmkCZrogfLlBue8v Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@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