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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 7FF89ECE58D for ; Wed, 9 Oct 2019 09:38:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 642FF21848 for ; Wed, 9 Oct 2019 09:38:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730595AbfJIJiB convert rfc822-to-8bit (ORCPT ); Wed, 9 Oct 2019 05:38:01 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([146.101.78.151]:53045 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729616AbfJIJiA (ORCPT ); Wed, 9 Oct 2019 05:38:00 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-103-VZzcP8GxPMmH4z8lG9RLRA-1; Wed, 09 Oct 2019 10:37:57 +0100 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Wed, 9 Oct 2019 10:37:56 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Wed, 9 Oct 2019 10:37:56 +0100 From: David Laight To: 'Pavel Machek' CC: "Theodore Y. Ts'o" , Linus Torvalds , Thomas Gleixner , "Ahmed S. Darwish" , LKML , Nicholas Mc Guire , the arch/x86 maintainers , Andy Lutomirski , Kees Cook Subject: RE: x86/random: Speculation to the rescue Thread-Topic: x86/random: Speculation to the rescue Thread-Index: AQHVfV0j+0Zbqc/i0UCMngMctaT4AqdQmbewgAFKogCAACVSoA== Date: Wed, 9 Oct 2019 09:37:56 +0000 Message-ID: <0ee565c2378a4abab6b623d6d3e10a7f@AcuMS.aculab.com> References: <20191006114129.GD24605@amd> <20191006173501.GA31243@amd> <20191006182103.GA2394@amd> <20191007114734.GA6104@mit.edu> <20191007221817.GA4027@amd> <4748b43e6b00415fb21c1a127a835e87@AcuMS.aculab.com> <20191009080240.GA11561@amd> In-Reply-To: <20191009080240.GA11561@amd> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-MC-Unique: VZzcP8GxPMmH4z8lG9RLRA-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Pavel Machek > Sent: 09 October 2019 09:03 > > NAND flash requires ECC so is likely to be async. > > But I2C is clocked from the cpu end - so is fixed. > > RTC i2c may be clocked from the CPU end, but the time source needs to > work when machine is off, so that has a separate crystal for > timekeeping. That only helps if the rtc chip lets you read its internal counters. You get one read of a few bits of 'randomness'. > > Also an embedded system could be booting off a large serial EEPROM. > > These have fixed timings and are clocked from the cpu end. > > Have you seen such system running Linux? You can run Linux on the Nios cpu on an Altera/Intel FPGA. The kernel is likely to be loaded from the same serial eeprom as the FPGA image. I've not personally run such a setup, but there are examples for the dev boards so I assume some people do. I'm not sure I'd want to run Linux on a 100MHz cpu with a slow memory interface. Better finding an fpga with an arm core in the corner! (We do use the Nios cpu - but for standalone code that fits in small internal memory blocks.) David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)