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 D736DC3A5A1 for ; Sun, 25 Aug 2019 18:29:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9DC75217F4 for ; Sun, 25 Aug 2019 18:29:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728860AbfHYS33 (ORCPT ); Sun, 25 Aug 2019 14:29:29 -0400 Received: from mx2.suse.de ([195.135.220.15]:37440 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728828AbfHYS33 (ORCPT ); Sun, 25 Aug 2019 14:29:29 -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 E90B9ADAA; Sun, 25 Aug 2019 18:29:27 +0000 (UTC) Date: Sun, 25 Aug 2019 20:29:22 +0200 From: Borislav Petkov To: Linus Torvalds , Pu Wen Cc: Thomas Gleixner , Tom Lendacky , Linux List Kernel Mailing , the arch/x86 maintainers Subject: Re: [GIT pull] x86/urgent for 5.3-rc5 Message-ID: <20190825182922.GC20639@zn.tnic> References: <156672618029.19810.8479315461492191933.tglx@nanos.tec.linutronix.de> <156672618029.19810.9732807383797358917.tglx@nanos.tec.linutronix.de> <20190825173000.GB20639@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 10:37:47AM -0700, Linus Torvalds wrote: > On Sun, Aug 25, 2019 at 10:30 AM Borislav Petkov wrote: > > > > Should we do that somewhere in the early boot code by adding a WARN_ON() > > or so and see who screams? > > It might be a good idea, just to see if it ever happens (again). > > It doesn't even have to be early boot. It's probably more important to > let the user _know_, than it is to then disable the rdrand > instruction. > > Particularly since we might as well just do it in general, and in the > general case we don't even know how to hide it in cpuid. So maybe just > something like "read the rdrand value a few times, make sure it > actually changes" at CPU bring-up (both boot and resume) > > It sounds like a stupid test, but considering that AMD has had this > particular bug now several times over at least three different > generations, maybe it's not a stupid test after all. My lazy, sticky Sunday brain could come up only with this: --- diff --git a/arch/x86/kernel/cpu/rdrand.c b/arch/x86/kernel/cpu/rdrand.c index 5c900f9527ff..0130a4f4f836 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(1, +"RDRAND gives funky smelling output, might consider not using it by booting with \"nordrand\""); + } #endif --- > Who knows what the Chinese CPU's that use the AMD core do? Hygon? > Whatever. Did they get the firmware fixes? Pu Wen? -- Regards/Gruss, Boris. SUSE Software Solutions Germany GmbH, GF: Felix Imendörffer, HRB 247165, AG München