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=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 3D70EC10F14 for ; Thu, 3 Oct 2019 21:34:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1B4B22086A for ; Thu, 3 Oct 2019 21:34:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733197AbfJCVeD (ORCPT ); Thu, 3 Oct 2019 17:34:03 -0400 Received: from edison.jonmasters.org ([173.255.233.168]:45010 "EHLO edison.jonmasters.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731694AbfJCVeD (ORCPT ); Thu, 3 Oct 2019 17:34:03 -0400 X-Greylist: delayed 1394 seconds by postgrey-1.27 at vger.kernel.org; Thu, 03 Oct 2019 17:34:03 EDT Received: from boston.jonmasters.org ([50.195.43.97] helo=tonnant.bos.jonmasters.org) by edison.jonmasters.org with esmtpsa (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1iG8N4-0002a7-GX; Thu, 03 Oct 2019 21:10:46 +0000 To: "Ahmed S. Darwish" , Theodore Ts'o , Andreas Dilger , Linus Torvalds Cc: Jan Kara , zhangjs , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org References: <20190910042107.GA1517@darwi-home-pc> From: Jon Masters Message-ID: <60fc1d03-314a-6b0a-2c8f-100394b05969@jonmasters.org> Date: Thu, 3 Oct 2019 17:10:45 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20190910042107.GA1517@darwi-home-pc> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 50.195.43.97 X-SA-Exim-Mail-From: jcm@jonmasters.org Subject: Re: Linux 5.3-rc8 X-SA-Exim-Version: 4.2.1 (built Sun, 08 Nov 2009 07:31:22 +0000) X-SA-Exim-Scanned: Yes (on edison.jonmasters.org) Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On 9/10/19 12:21 AM, Ahmed S. Darwish wrote: > Can this even be considered a user-space breakage? I'm honestly not > sure. On my modern RDRAND-capable x86, just running rng-tools rngd(8) > early-on fixes the problem. I'm not sure about the status of older > CPUs though. Tangent: I asked aloud on Twitter last night if anyone had exploited Rowhammer-like effects to generate entropy...and sure enough, the usual suspects have: https://arxiv.org/pdf/1808.04286.pdf While this requires low level access to a memory controller, it's perhaps an example of something a platform designer could look at as a source to introduce boot-time entropy for e.g. EFI_RNG_PROTOCOL even on an existing platform without dedicated hardware for the purpose. Just a thought. Jon.