From patchwork Sun Apr 10 21:49:42 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: 12808291 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 CA1E8C4332F for ; Sun, 10 Apr 2022 21:50:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243998AbiDJVw4 (ORCPT ); Sun, 10 Apr 2022 17:52:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41242 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242933AbiDJVwx (ORCPT ); Sun, 10 Apr 2022 17:52:53 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 76A191A064; Sun, 10 Apr 2022 14:50:27 -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 ams.source.kernel.org (Postfix) with ESMTPS id 38289B80CD2; Sun, 10 Apr 2022 21:50:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id BA2B4C385A1; Sun, 10 Apr 2022 21:50:21 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="mljTD4lD" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1649627421; 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=JyQJDqG7G7qoM6gKahWfWcpxoWg/Hr8hXOQQlij0UbM=; b=mljTD4lDHrPCpdKRHHsPWTFR14XiiWdhvN87TPRANPmZWfc+MO66VyuX/rXcSG22A4eyEP dnVOLtFaU6Sq0fucK3TI1wZEKw8xT1SKDR6YeAoPoyixF1BUW3rFAxNA+gC8iEtzcWxwSM 5HC0l2Iwg27gXOb6sTJlPKYcF+fyEVo= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 2f5fc337 (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Sun, 10 Apr 2022 21:50:20 +0000 (UTC) From: "Jason A. Donenfeld" To: linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, tglx@linutronix.de, 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 , Ingo Molnar , Borislav Petkov , Dave Hansen , "H . Peter Anvin" , Chris Zankel , Max Filippov , John Stultz , 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: [PATCH v2 02/11] timekeeping: use ktime_read_raw_clock() for random_get_entropy() if no get_cycles() Date: Sun, 10 Apr 2022 23:49:42 +0200 Message-Id: <20220410214951.55294-3-Jason@zx2c4.com> In-Reply-To: <20220410214951.55294-1-Jason@zx2c4.com> References: <20220410214951.55294-1-Jason@zx2c4.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.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 ktime_read_raw_clock() would be preferable, because that always needs to return _something_, even falling back to jiffies eventually. It's not as though ktime_read_raw_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 56502b338287..4050f68c34cb 100644 --- a/include/linux/timex.h +++ b/include/linux/timex.h @@ -76,8 +76,14 @@ extern u64 ktime_read_raw_clock(void); * * 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)ktime_read_raw_clock()) +#endif #endif /*