From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 04DCEC433F5 for ; Thu, 24 Feb 2022 15:11:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235732AbiBXPMX (ORCPT ); Thu, 24 Feb 2022 10:12:23 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49494 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231255AbiBXPMU (ORCPT ); Thu, 24 Feb 2022 10:12:20 -0500 Received: from isilmar-4.linta.de (isilmar-4.linta.de [136.243.71.142]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4A1D77E5BC; Thu, 24 Feb 2022 07:11:48 -0800 (PST) X-isilmar-external: YES X-isilmar-external: YES X-isilmar-external: YES X-isilmar-external: YES X-isilmar-external: YES X-isilmar-external: YES X-isilmar-external: YES X-isilmar-external: YES Received: from owl.dominikbrodowski.net (owl.brodo.linta [10.2.0.111]) by isilmar-4.linta.de (Postfix) with ESMTPSA id 3C4C920140A; Thu, 24 Feb 2022 15:11:46 +0000 (UTC) Received: by owl.dominikbrodowski.net (Postfix, from userid 1000) id 931B0801A3; Thu, 24 Feb 2022 16:11:16 +0100 (CET) Date: Thu, 24 Feb 2022 16:11:16 +0100 From: Dominik Brodowski To: "Jason A. Donenfeld" Cc: linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, bigeasy@linutronix.de, Sultan Alsawaf , Thomas Gleixner , Peter Zijlstra , Theodore Ts'o Subject: Re: [PATCH] random: do crng pre-init loading in worker rather than irq Message-ID: References: <20220223185511.628452-1-Jason@zx2c4.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am Thu, Feb 24, 2022 at 10:49:12AM +0100 schrieb Jason A. Donenfeld: > On 2/24/22, Dominik Brodowski wrote: > > Am Wed, Feb 23, 2022 at 07:55:11PM +0100 schrieb Jason A. Donenfeld: > >> Taking spinlocks from IRQ context is problematic for PREEMPT_RT. That > >> is, in part, why we take trylocks instead. But apparently this still > >> trips up various lock dependency analyzers. That seems like a bug in the > >> analyzers that should be fixed, rather than having to change things > >> here. > >> > >> But maybe there's another reason to change things up: by deferring the > >> crng pre-init loading to the worker, we can use the cryptographic hash > >> function rather than xor, which is perhaps a meaningful difference when > >> considering this data has only been through the relatively weak > >> fast_mix() function. > >> > >> The biggest downside of this approach is that the pre-init loading is > >> now deferred until later, which means things that need random numbers > >> after interrupts are enabled, but before workqueues are running -- or > >> before this particular worker manages to run -- are going to get into > >> trouble. Hopefully in the real world, this window is rather small, > >> especially since this code won't run until 64 interrupts had occurred. > >> > >> Cc: Dominik Brodowski > >> Cc: Sebastian Andrzej Siewior > >> Cc: Sultan Alsawaf > >> Cc: Thomas Gleixner > >> Cc: Peter Zijlstra > >> Cc: Theodore Ts'o > >> Signed-off-by: Jason A. Donenfeld > >> --- > >> drivers/char/random.c | 62 ++++++++++++------------------------------- > >> 1 file changed, 17 insertions(+), 45 deletions(-) > >> > >> diff --git a/drivers/char/random.c b/drivers/char/random.c > >> index 536237a0f073..9fb06fc298d3 100644 > >> --- a/drivers/char/random.c > >> +++ b/drivers/char/random.c > >> @@ -1298,7 +1278,12 @@ static void mix_interrupt_randomness(struct > >> work_struct *work) > >> local_irq_enable(); > >> > >> mix_pool_bytes(pool, sizeof(pool)); > >> - credit_entropy_bits(1); > >> + > >> + if (unlikely(crng_init == 0)) > >> + crng_pre_init_inject(pool, sizeof(pool), true); > >> + else > >> + credit_entropy_bits(1); > >> + > >> memzero_explicit(pool, sizeof(pool)); > >> } > > > > Might it make sense to call crng_pre_init_inject() before mix_pool_bytes? > > What exactly is the difference you see mattering in the order? I keep > chasing my tail trying to think about it. We had that order beforehand -- and even if it probably doesn't matter, this means crng_pre_init_inject() gets called a tiny bit earlier. That means there's a chance to progres to crng_init=1 a tiny bit earlier as well. Thanks, Dominik