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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 72E89C433F5 for ; Tue, 19 Apr 2022 18:23:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345808AbiDSS0Q (ORCPT ); Tue, 19 Apr 2022 14:26:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36770 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1357629AbiDSSXe (ORCPT ); Tue, 19 Apr 2022 14:23:34 -0400 Received: from mail.skyhub.de (mail.skyhub.de [5.9.137.197]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CFCD63F31F for ; Tue, 19 Apr 2022 11:16:42 -0700 (PDT) Received: from zn.tnic (p200300ea971b5839329c23fffea6a903.dip0.t-ipconnect.de [IPv6:2003:ea:971b:5839:329c:23ff:fea6:a903]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 2F71F1EC056A; Tue, 19 Apr 2022 20:16:35 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1650392195; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=UoJkiPpVHwxIF95pounRIe0Bw7VF4LrYgBjTdnaLh4M=; b=TSOc8IYhoBaLvKhqpez3H0jtLDK8Eseo4q06zwIlkbjmkVhCwgTpQznSaGHr4tJI5mPOVm DtWKis1fu5W+gNxL/sbpwYLcLQW53nl+zraOpDLEzLeassVwhpGIPTCrFfe75/3S+78kjs hPtr3FvTE+KH1mPoULDw9muY288aKXQ= Date: Tue, 19 Apr 2022 20:16:32 +0200 From: Borislav Petkov To: "Jason A. Donenfeld" Cc: linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, tglx@linutronix.de, arnd@arndb.de, Theodore Ts'o , Dominik Brodowski , Russell King , Catalin Marinas , Will Deacon , Geert Uytterhoeven , Thomas Bogendoerfer , Paul Walmsley , Palmer Dabbelt , Albert Ou , "David S . Miller" , Richard Weinberger , Anton Ivanov , Johannes Berg , Ingo Molnar , Dave Hansen , "H . Peter Anvin" , Chris Zankel , Max Filippov , Stephen Boyd , Dinh Nguyen , linux-arm-kernel@lists.infradead.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-riscv@lists.infradead.org, sparclinux@vger.kernel.org, linux-um@lists.infradead.org, x86@kernel.org, linux-xtensa@linux-xtensa.org Subject: Re: [PATCH v5 07/11] x86: use fallback for random_get_entropy() instead of zero Message-ID: References: <20220419111650.1582274-1-Jason@zx2c4.com> <20220419111650.1582274-8-Jason@zx2c4.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20220419111650.1582274-8-Jason@zx2c4.com> Precedence: bulk List-ID: X-Mailing-List: linux-m68k@vger.kernel.org On Tue, Apr 19, 2022 at 01:16:46PM +0200, Jason A. Donenfeld wrote: > In the event that random_get_entropy() can't access a cycle counter or > similar, falling back to returning 0 is really not the best we can do. > Instead, at least calling random_get_entropy_fallback() would be > preferable, because that always needs to return _something_, even > falling back to jiffies eventually. It's not as though > random_get_entropy_fallback() is super high precision or guaranteed to > be entropic, but basically anything that's not zero all the time is > better than returning zero all the time. > > If CONFIG_X86_TSC=n, then it's possible that we're running on a 486 with > no RDTSC, so we only need the fallback code for that case. > > Cc: Thomas Gleixner > Cc: Arnd Bergmann > Cc: x86@kernel.org > Signed-off-by: Jason A. Donenfeld > --- > arch/x86/include/asm/timex.h | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/arch/x86/include/asm/timex.h b/arch/x86/include/asm/timex.h > index a4a8b1b16c0c..fac180359693 100644 > --- a/arch/x86/include/asm/timex.h > +++ b/arch/x86/include/asm/timex.h > @@ -5,6 +5,16 @@ > #include > #include > > +static inline unsigned long random_get_entropy(void) > +{ > +#ifndef CONFIG_X86_TSC > + if (!boot_cpu_has(X86_FEATURE_TSC)) cpu_feature_enabled() pls. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette