From patchwork Fri Apr 8 18:21:42 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: 12807067 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 2B15FC433EF for ; Fri, 8 Apr 2022 18:26:30 +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=nBOD8KIdzj+ljhcBMQw1KhOTpMpZCE2Skz0QQWHRpVQ=; b=J0w/0kt64EXh3o 7w7WXuogF3fZDzzuPHp36pqHF1cMFuYZNXGeuM0TSJchFWuvLd/urII1A/IsJ2Eip9KSbywyjm0s+ 3mPTol9DfX/a1NSyY0kx25y0BOwDPKbxKYbqPT3K4Q1fKIp8FkjfXvXYnD6u6hKCU7OAtE58DvxxE nZysfNuPjzNEAPxOfSWTCIZsATFDN0vs7sJK4DrmdTlcLLPrf1DdjfOvqmw78NH4nufDsY8J5+SNk zLl47VbcOyqyAt/yEV4+9l8+rq0F0H1q7kNtpKdMUijGzZdogsQgY6aMSVZCmQtjhkQd/0H2JITGI qWls6QKRGW5mR2dt/CEQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nctIG-000tWw-Ag; Fri, 08 Apr 2022 18:25:13 +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 1nctGL-000s1v-T8; Fri, 08 Apr 2022 18:23:15 +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 8413EB82CDE; Fri, 8 Apr 2022 18:23:12 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 96180C385A3; Fri, 8 Apr 2022 18:23:07 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="bHvsH7he" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1649442186; 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=78dSRR6cg4Cb6xE6wzqZl0y3T/C5RqbL9OTQfhaSus0=; b=bHvsH7heTJ22wd9kOVkjQRjB8qxqDYb0Neo0BG7ETnElqZmWD+KvzZiWfTFZwr1zQmUbC5 XXdPLoX/hfqwadSYoHEgXfmb2MBW+rOO7AO7VyqUuq9QbfjjauYGlTUsreemS7BXRmsC9S aoLAL9JjFgYgrOUBP32exCl+fVMfezY= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 2a1ba7e8 (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Fri, 8 Apr 2022 18:23:06 +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 07/10] arm64: use sched_clock() for random_get_entropy() instead of zero Date: Fri, 8 Apr 2022 20:21:42 +0200 Message-Id: <20220408182145.142506-8-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_112314_271522_5493F781 X-CRM114-Status: GOOD ( 15.27 ) 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. If CONFIG_ARM_ARCH_TIMER=n, then get_cycles() will return 0, so we only need the fallback code for that case. Cc: Arnd Bergmann Cc: Catalin Marinas Cc: Will Deacon Signed-off-by: Jason A. Donenfeld --- arch/arm64/include/asm/timex.h | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/arm64/include/asm/timex.h b/arch/arm64/include/asm/timex.h index cf59ce91b22d..bfebd2e1ce45 100644 --- a/arch/arm64/include/asm/timex.h +++ b/arch/arm64/include/asm/timex.h @@ -13,6 +13,15 @@ */ #define get_cycles() arch_timer_read_counter() +#ifndef CONFIG_ARM_ARCH_TIMER +/* + * The default implementation of random_get_entropy() calls get_cycles(), + * which will return 0 if CONFIG_ARM_ARCH_TIMER=n, so we fall back to + * sched_clock() here. Not a great situation, but better than nothing. + */ +#define random_get_entropy() ((unsigned long)sched_clock()) +#endif + #include #endif