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: 12807065 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 1C5EFC433F5 for ; Fri, 8 Apr 2022 18:25:27 +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=mjLxM1FrqZFsofTS8tnR56ltz22IYVWf0nGymRl2OnA=; b=TbTQcAZFXHA2zh hhYeDpPeJsmQ9Qcp1wyeOm57Yu8aAeLmtXeqSoktCxO3vPOoKN2O26Mqq9hotW05GnRYzGRc5CbBI bpOHsHCuwUCR/Vj7ER4jMntX+WDMv+iKPS0PmdGC+e0ZbW6DNsIW0QLe1M8LkEQVnXI86cAiW8Rhq hvDW7lhJ8ZyCEA/0dfIvDdaNHzXiCzooZppm2pI6vqHQyznC1Q3c60E2oCufqJYSpfHCMiWXE/cM6 7UnNLnCcaChapNsc92r0YzPdXQcFhbZMDfSgo4ZhCJWhYF8YS+lC50/YS6nlAjdH4u/qaeBcp6C0p xVej6kg8S7RUSpbE0O2Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nctHH-000smH-SW; Fri, 08 Apr 2022 18:24:12 +0000 Received: from ams.source.kernel.org ([2604:1380:4601:e00::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nctG6-000rqT-0t; Fri, 08 Apr 2022 18:22:59 +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 99B97B82CDC; Fri, 8 Apr 2022 18:22:56 +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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220408_112258_368993_9CA85B9F X-CRM114-Status: GOOD ( 14.62 ) 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 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