From patchwork Fri Apr 8 18:21:41 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Jason A. Donenfeld" X-Patchwork-Id: 12807055 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 A0751C43217 for ; Fri, 8 Apr 2022 18:23:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232556AbiDHSZR (ORCPT ); Fri, 8 Apr 2022 14:25:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42030 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238615AbiDHSZK (ORCPT ); Fri, 8 Apr 2022 14:25:10 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 49D8938237B; Fri, 8 Apr 2022 11:23:04 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id D981C621E6; Fri, 8 Apr 2022 18:23:03 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 99E13C385A3; Fri, 8 Apr 2022 18:22:59 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="CLPULdzg" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1649442178; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=QhQ1HwDDQ0VBViTeG0LB+139Jo2Xk5438IuvpR3RiNg=; b=CLPULdzgGXJrwK4uCCHM7+j7CQPO/TnUdFHV8jGVPXt2oRPuFGfQuIGVwrwhQmuAXIEyIK +pMFaA2OsSQLAz2u75tmYrg486K8df6y/V/MHRdhzu90z8Dl9A4EKbCnoFVpvWCWqoNp4p IgJX3Y50X9yQA9wOGJqYKrd+/9+6GG8= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 2adbe4d1 (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Fri, 8 Apr 2022 18:22:58 +0000 (UTC) From: "Jason A. Donenfeld" To: linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, arnd@arndb.de Cc: "Jason A. Donenfeld" , 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 , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H . Peter Anvin" , Chris Zankel , Max Filippov , John Stultz , Stephen Boyd , 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: [PATCH RFC v1 06/10] x86: use sched_clock() for random_get_entropy() instead of zero Date: Fri, 8 Apr 2022 20:21:41 +0200 Message-Id: <20220408182145.142506-7-Jason@zx2c4.com> In-Reply-To: <20220408182145.142506-1-Jason@zx2c4.com> References: <20220408182145.142506-1-Jason@zx2c4.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org 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 sched_clock() would be preferable, because that always needs to return _something_, even falling back to jiffies eventually. It's not as though sched_clock() 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: Arnd Bergmann Cc: x86@kernel.org Signed-off-by: Jason A. Donenfeld --- arch/x86/include/asm/tsc.h | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h index 01a300a9700b..b0c0b2b9e0f7 100644 --- a/arch/x86/include/asm/tsc.h +++ b/arch/x86/include/asm/tsc.h @@ -5,6 +5,7 @@ #ifndef _ASM_X86_TSC_H #define _ASM_X86_TSC_H +#include #include #include @@ -28,6 +29,16 @@ static inline cycles_t get_cycles(void) return rdtsc(); } +static inline unsigned long random_get_entropy(void) +{ +#ifndef CONFIG_X86_TSC + if (!boot_cpu_has(X86_FEATURE_TSC)) + return sched_clock(); +#endif + return rdtsc(); +} +#define random_get_entropy random_get_entropy + extern struct system_counterval_t convert_art_to_tsc(u64 art); extern struct system_counterval_t convert_art_ns_to_tsc(u64 art_ns);