From patchwork Fri Apr 8 18:21:36 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: 12807061 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5CCCDC433EF for ; Fri, 8 Apr 2022 18:23:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=NNzsahAyD5JxCMHSmPe/LQnaDP+9BRptXVd0SJWp6/o=; b=amj0qKacBCmAtR 3wfUZiUVsZ1MaePlwW/QygIMgA9MPE56KKVg2IV1vA7ej1qpm6nMpmgntBbSLlV38YDMhWE0c658S TA3q4YrJnQWyB2CIkpOZNHtwwX3Lxr2uQA/qA9uyb3t3EjtaZTWGgv9s/xFgVTRTcmzlRxN/88gjL Yp/5jLK1ulSxqT32/oM60dWS1ySaAYWh8vTVlXV52cylj764arfEQ/zo68Pl1sIcBC3nXilcRHENc MN9UHtMieXuIYEZF8eKb365JrhKr5t6YDRrS6Xw4TaYJDsidnk3h9BxcRrDgLTkIaNCsVP9n63aEp 65zOrqLMRJJ4bOZj9dYw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nctFg-000rZn-Kz; Fri, 08 Apr 2022 18:22:32 +0000 Received: from ams.source.kernel.org ([145.40.68.75]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nctFV-000rWZ-U5; Fri, 08 Apr 2022 18:22:23 +0000 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 ams.source.kernel.org (Postfix) with ESMTPS id 8F473B82A89; Fri, 8 Apr 2022 18:22:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 96822C385BB; Fri, 8 Apr 2022 18:22:15 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="jcpLG88Y" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1649442134; 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=bKnGziADgzlHYNafG897CPxh8A5i6JayWbcFusMVF+o=; b=jcpLG88YHHP6AloS0heU9nwr6NJdw/JKwkHxnAETctCFQ01GcKhEazXCv1l8LYoXkmFxRD ftX1/Z6lNxkT70S7kwuImsr0xpjUDcs5HuIyBEDxSRaDq4wzLA6+sbCA5e6UpziDcyropk fx7n4JcOruZvQmUQLel+8lYi/eG+/LU= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id e268004a (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Fri, 8 Apr 2022 18:22:14 +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 01/10] random: use sched_clock() for random_get_entropy() if no get_cycles() Date: Fri, 8 Apr 2022 20:21:36 +0200 Message-Id: <20220408182145.142506-2-Jason@zx2c4.com> In-Reply-To: <20220408182145.142506-1-Jason@zx2c4.com> References: <20220408182145.142506-1-Jason@zx2c4.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220408_112222_302195_818F4610 X-CRM114-Status: GOOD ( 16.59 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org In the event that a given arch does not define get_cycles(), falling back to the get_cycles() default implementation that returns 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: Thomas Gleixner Cc: Arnd Bergmann Cc: Theodore Ts'o Signed-off-by: Jason A. Donenfeld --- include/linux/timex.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/include/linux/timex.h b/include/linux/timex.h index 5745c90c8800..bd78f784762e 100644 --- a/include/linux/timex.h +++ b/include/linux/timex.h @@ -61,6 +61,7 @@ #include #include #include +#include #include @@ -74,8 +75,13 @@ * * By default we use get_cycles() for this purpose, but individual * architectures may override this in their asm/timex.h header file. + * If a given arch does not have get_cycles(), then we fallback to + * using sched_clock(). */ +#ifdef get_cycles #define random_get_entropy() ((unsigned long)get_cycles()) +#else +#define random_get_entropy() ((unsigned long)sched_clock()) #endif /*