Return-path: Received: from outbound1.eu.mailhop.org ([52.28.251.132]:32297 "EHLO outbound1.eu.mailhop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932341AbcHNSL1 (ORCPT ); Sun, 14 Aug 2016 14:11:27 -0400 Date: Sun, 14 Aug 2016 18:11:14 +0000 From: Jason Cooper To: Theodore Ts'o , "Pan, Miaoqing" , Stephan Mueller , "Sepehrdad, Pouyan" , "herbert@gondor.apana.org.au" , "linux-kernel@vger.kernel.org" , "linux-crypto@vger.kernel.org" , ath9k-devel , "linux-wireless@vger.kernel.org" , "ath9k-devel@lists.ath9k.org" , Kalle Valo Subject: Re: [PATCH v2] RANDOM: ATH9K RNG delivers zero bits of entropy Message-ID: <20160814181114.GM2013@io.lakedaemon.net> (sfid-20160814_201144_635714_4DB4CD77) References: <34197429.2CvoIfft9B@positron.chronox.de> <1654172.XfclnXhRmn@positron.chronox.de> <657897b90b8344eeab10d7a0f604988d@aptaiexm02f.ap.qualcomm.com> <1830987.VF9l4XmGxv@tauon.atsec.com> <20160808172930.GD4511@io.lakedaemon.net> <99963d34acea47bbacb3ca73b18fed9f@aptaiexm02f.ap.qualcomm.com> <20160809115622.GG9515@thunk.org> <20160809140444.GB2013@io.lakedaemon.net> <20160810234425.GG10523@thunk.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20160810234425.GG10523@thunk.org> Sender: linux-wireless-owner@vger.kernel.org List-ID: Hey Ted, On Wed, Aug 10, 2016 at 07:44:25PM -0400, Theodore Ts'o wrote: > On Tue, Aug 09, 2016 at 02:04:44PM +0000, Jason Cooper wrote: > > iiuc, Ted, you're saying using the hw_random framework would be > > disasterous because despite most drivers having a default quality of 0, > > rngd assumes 1 bit of entropy for every bit read? > > Sorry, what I was trying to say (but failed) was that bypassing the > hwrng framework and injecting entropy directly the entropy pool was > disatrous. Ok, whew. :) > > Thankfully, most hw_random drivers don't set the quality. So unless the > > user sets the default_quality param, it's zero. > > The fact that this is "most" and not "all" does scare me a little. My recent grep showed that only virtio-rng set it to a non-zero value. > As far as I'm concerned *all* hw_random drivers should set quality to > zero, since it should be up to the system administrator. Agreed. Gathering conversation about this from a few related threads, I have one concern. Apparently there is some confusion in userspace consumers of /dev/hwrng data as to the quality of it. Specifically, rngd (spotted by Stephan Mueller) appears to assume 1bit of entropy per 1 bit read. :-/ So, while moving ath9k-rng to the hwrng framework makes complete sense internally, it's not so good for existing userspace assumptions. I'd think that timeriomem-rng falls in this same category. In light of this, do you think it's worth the effort (I'm volunteering) to create a subcategory of hwrng drivers that are 'environemntal' rngs? They can contribute to the kernel entropy pools, but not to /dev/hwrng. thx, Jason.