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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 77BFDC3A5A1 for ; Sun, 25 Aug 2019 20:17:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 48D42206DD for ; Sun, 25 Aug 2019 20:17:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729134AbfHYURb (ORCPT ); Sun, 25 Aug 2019 16:17:31 -0400 Received: from mx2.suse.de ([195.135.220.15]:51840 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728730AbfHYURa (ORCPT ); Sun, 25 Aug 2019 16:17:30 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 88870AE12; Sun, 25 Aug 2019 20:17:29 +0000 (UTC) Date: Sun, 25 Aug 2019 22:17:23 +0200 From: Borislav Petkov To: Linus Torvalds Cc: Pu Wen , Thomas Gleixner , Tom Lendacky , Linux List Kernel Mailing , the arch/x86 maintainers Subject: Re: [GIT pull] x86/urgent for 5.3-rc5 Message-ID: <20190825201723.GG20639@zn.tnic> References: <156672618029.19810.9732807383797358917.tglx@nanos.tec.linutronix.de> <20190825173000.GB20639@zn.tnic> <20190825182922.GC20639@zn.tnic> <20190825193218.GD20639@zn.tnic> <20190825194912.GF20639@zn.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Aug 25, 2019 at 12:59:25PM -0700, Linus Torvalds wrote: > I think WARN_ONCE() is good. It's big enough that it will show up in > dmesg if anybody looks, and if nobody looks I think distros still have > logging for things like that, don't they? Probably. Lemme research that. > Hopefully this never actually triggers in practice, thanks to rdrand > being turned off on known-bad machines now, and Zen 2 being fixed. Right. Here's v2, will do a proper patch tomorrow: --- diff --git a/arch/x86/kernel/cpu/rdrand.c b/arch/x86/kernel/cpu/rdrand.c index 5c900f9527ff..00a9d13c0a92 100644 --- a/arch/x86/kernel/cpu/rdrand.c +++ b/arch/x86/kernel/cpu/rdrand.c @@ -29,7 +29,8 @@ __setup("nordrand", x86_rdrand_setup); #ifdef CONFIG_ARCH_RANDOM void x86_init_rdrand(struct cpuinfo_x86 *c) { - unsigned long tmp; + unsigned int changed = 0; + unsigned long tmp, prev; int i; if (!cpu_has(c, X86_FEATURE_RDRAND)) @@ -42,5 +43,24 @@ void x86_init_rdrand(struct cpuinfo_x86 *c) return; } } + + /* + * Stupid sanity-check whether RDRAND does *actually* generate + * some at least random-looking data. + */ + prev = tmp; + for (i = 0; i < SANITY_CHECK_LOOPS; i++) { + if (rdrand_long(&tmp)) { + if (prev != tmp) + changed++; + + prev = tmp; + } + } + + if (!changed) + WARN_ONCE(1, +"RDRAND gives funky smelling output, might consider not using it by booting with \"nordrand\""); + } #endif -- Regards/Gruss, Boris. SUSE Software Solutions Germany GmbH, GF: Felix Imendörffer, HRB 247165, AG München