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 X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=FROM_EXCESS_BASE64, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2FA82C04A6B for ; Fri, 10 May 2019 17:13:05 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 05553208C3 for ; Fri, 10 May 2019 17:13:05 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 05553208C3 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([127.0.0.1]:47219 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hP94y-00006y-B0 for qemu-devel@archiver.kernel.org; Fri, 10 May 2019 13:13:04 -0400 Received: from eggs.gnu.org ([209.51.188.92]:53727) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hP94C-000850-6y for qemu-devel@nongnu.org; Fri, 10 May 2019 13:12:17 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hP948-00028T-4m for qemu-devel@nongnu.org; Fri, 10 May 2019 13:12:16 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53510) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hP946-000249-9f for qemu-devel@nongnu.org; Fri, 10 May 2019 13:12:11 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id EB44B20B02; Fri, 10 May 2019 17:12:06 +0000 (UTC) Received: from redhat.com (ovpn-112-68.ams2.redhat.com [10.36.112.68]) by smtp.corp.redhat.com (Postfix) with ESMTPS id F2F535D6A9; Fri, 10 May 2019 17:11:59 +0000 (UTC) Date: Fri, 10 May 2019 18:11:56 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: "Michael S. Tsirkin" Message-ID: <20190510171156.GR7671@redhat.com> References: <20190510134203.24012-1-lvivier@redhat.com> <20190510134203.24012-2-lvivier@redhat.com> <20190510121135-mutt-send-email-mst@kernel.org> <20190510161644.GP7671@redhat.com> <20190510121939-mutt-send-email-mst@kernel.org> <20190510162554.GQ7671@redhat.com> <20190510125323-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190510125323-mutt-send-email-mst@kernel.org> User-Agent: Mutt/1.11.4 (2019-03-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Fri, 10 May 2019 17:12:07 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v3 1/3] VirtIO-RNG: Update default entropy source to `/dev/urandom` X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Laurent Vivier , Kashyap Chamarthy , Amit Shah , Richard Henderson , qemu-devel@nongnu.org, Markus Armbruster , "Richard W . M . Jones" , Stefan Hajnoczi Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, May 10, 2019 at 12:55:18PM -0400, Michael S. Tsirkin wrote: > On Fri, May 10, 2019 at 05:25:54PM +0100, Daniel P. Berrang=C3=A9 wrote= : > > On Fri, May 10, 2019 at 12:21:19PM -0400, Michael S. Tsirkin wrote: > > > On Fri, May 10, 2019 at 05:16:44PM +0100, Daniel P. Berrang=C3=A9 w= rote: > > > > On Fri, May 10, 2019 at 12:12:41PM -0400, Michael S. Tsirkin wrot= e: > > > > > On Fri, May 10, 2019 at 03:42:01PM +0200, Laurent Vivier wrote: > > > > > > From: Kashyap Chamarthy > > > > > >=20 > > > > > > When QEMU exposes a VirtIO-RNG device to the guest, that devi= ce needs a > > > > > > source of entropy, and that source needs to be "non-blocking"= , like > > > > > > `/dev/urandom`. However, currently QEMU defaults to the prob= lematic > > > > > > `/dev/random`, which is "blocking" (as in, it waits until suf= ficient > > > > > > entropy is available). > > > > > >=20 > > > > > > Why prefer `/dev/urandom` over `/dev/random`? > > > > > > --------------------------------------------- > > > > > >=20 > > > > > > The man pages of urandom(4) and random(4) state: > > > > > >=20 > > > > > > "The /dev/random device is a legacy interface which dates= back to a > > > > > > time where the cryptographic primitives used in the imple= mentation > > > > > > of /dev/urandom were not widely trusted. It will return = random > > > > > > bytes only within the estimated number of bits of fresh n= oise in the > > > > > > entropy pool, blocking if necessary. /dev/random is suit= able for > > > > > > applications that need high quality randomness, and can a= fford > > > > > > indeterminate delays." > > > > > >=20 > > > > > > Further, the "Usage" section of the said man pages state: > > > > > >=20 > > > > > > "The /dev/random interface is considered a legacy interfa= ce, and > > > > > > /dev/urandom is preferred and sufficient in all use cases= , with the > > > > > > exception of applications which require randomness during= early boot > > > > > > time; for these applications, getrandom(2) must be used i= nstead, > > > > > > because it will block until the entropy pool is initializ= ed. > > > > >=20 > > > > > So how about just using getrandom then? > > > >=20 > > > > The 3rd patch in this series addresses that. > > >=20 > > > It seems to use qemu_guest_getrandom which in turn > > > with patch 1 calls /dev/urandom... > > > Did I miss something? > >=20 > > qemu_guest_getrandom will preferentially use the crypto library rando= m > > APIs (gnutls, or gcrypt). If both are compiled out that it will use > > getrandom() if supported by the C library and current kernel. If that > > fails then it will try /dev/urandom if it exists, finally /dev/random= .=20 > > On Windows it uses their native crypto API. See this dependant series= : > >=20 > > https://lists.gnu.org/archive/html/qemu-devel/2019-05/msg02237.html >=20 > In particular >=20 > https://lists.gnu.org/archive/html/qemu-devel/2019-05/msg02238.html >=20 > maybe clarify this is just for systems without getrandom then. I'm not sure I see what the problem is. That patch is implementing the fallback behaviour I describe above, with the crypto library preferred, falling back to getrandom, then /dev/urandom, finally /dev/random. Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| |: https://libvirt.org -o- https://fstop138.berrange.c= om :| |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :|