From patchwork Fri Apr 8 18:21:40 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: 12807049 X-Patchwork-Delegate: herbert@gondor.apana.org.au 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 60C08C433EF for ; Fri, 8 Apr 2022 18:23:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238619AbiDHSZO (ORCPT ); Fri, 8 Apr 2022 14:25:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42498 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238611AbiDHSZI (ORCPT ); Fri, 8 Apr 2022 14:25:08 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 484FE37F902; Fri, 8 Apr 2022 11:22:56 -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 D984162213; Fri, 8 Apr 2022 18:22:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A3572C385A1; Fri, 8 Apr 2022 18:22:51 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="G6BU8Ywm" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1649442170; 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=jfm/+0nZe/a0gZ1BVOi1xoOTd0LXu2XtqvwNu5ICWks=; b=G6BU8YwmryDS1gmWE+VsSKq/CaivlVVRO+4FBmjCGpVgAiTEzz4rBGY2zrzrcC6JvcSxxJ QBlo+NeO6cN98+dyhw52GgoZFCETJXKA3Zs612fg5YoJ6Q03UdzN8+K83P/PaMf7MKK1nJ Bi7Y4m7JizYUQvonoKB619aaE5aOiKI= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id c108eea7 (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Fri, 8 Apr 2022 18:22:50 +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 05/10] arm: use sched_clock() for random_get_entropy() instead of zero Date: Fri, 8 Apr 2022 20:21:40 +0200 Message-Id: <20220408182145.142506-6-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-crypto@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. Cc: Arnd Bergmann Cc: Russell King Signed-off-by: Jason A. Donenfeld --- arch/arm/include/asm/timex.h | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/arch/arm/include/asm/timex.h b/arch/arm/include/asm/timex.h index 7c3b3671d6c2..1c51580ee55d 100644 --- a/arch/arm/include/asm/timex.h +++ b/arch/arm/include/asm/timex.h @@ -9,7 +9,18 @@ #ifndef _ASMARM_TIMEX_H #define _ASMARM_TIMEX_H +#include + typedef unsigned long cycles_t; #define get_cycles() ({ cycles_t c; read_current_timer(&c) ? 0 : c; }) +static inline unsigned long random_get_entropy(void) +{ + unsigned long ret = get_cycles(); + if (ret) + return ret; + return sched_clock(); +} +#define random_get_entropy random_get_entropy + #endif