From mboxrd@z Thu Jan 1 00:00:00 1970 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 D42FFC433EF for ; Mon, 23 May 2022 13:58:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236786AbiEWN60 (ORCPT ); Mon, 23 May 2022 09:58:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56054 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236746AbiEWN6Z (ORCPT ); Mon, 23 May 2022 09:58:25 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 51C5256FBF for ; Mon, 23 May 2022 06:58:24 -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 89F446114C; Mon, 23 May 2022 13:58:23 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 54A97C385AA; Mon, 23 May 2022 13:58:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1653314303; bh=bMQ76dp2HmQ3uXRMykYlpLogfkiug4VqJggIc37zUrM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Rhu8OE2IygT78Kmgi0veHK3UCRU45Wa1lKf0qRn0eRRSfxWy/znDUceR1oMSY55by b/Qjp4WqXMjPxggvmrJcC0RWd7ISbVc4buSL335hPdmnd2FbWEy07P0apQgYY7H11+ NFlr8OEtHhW7GJ19ciDaIYgTWsKV1vSBJJWX4qSZ5rMgEPypBdhRc5bD8iHWcFmgwf if4LTn3sIyl73Q+1hgTvOuYTzaXOBuU1ZdpC5irzwKSc81r7BU7d44Qfg04P23t3Wj xjPCV1EQ8qgX5fLkrsY98A1lDRWt1NrDy4qNgFPCtMrf6R9Y+4BKiSHtAS13/wW86d X2gY2kmU5w6bQ== Message-ID: <8e440c28-d4b9-2fc6-0294-f77544264d5c@kernel.org> Date: Mon, 23 May 2022 08:58:16 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.1 Subject: Re: [PATCH v4 06/11] nios2: use fallback for random_get_entropy() instead of zero Content-Language: en-US To: "Jason A. Donenfeld" , linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, tglx@linutronix.de, arnd@arndb.de Cc: 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 , 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 References: <20220413115411.21489-1-Jason@zx2c4.com> <20220413115411.21489-7-Jason@zx2c4.com> From: Dinh Nguyen In-Reply-To: <20220413115411.21489-7-Jason@zx2c4.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-m68k@vger.kernel.org On 4/13/22 06:54, Jason A. Donenfeld wrote: > 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 random_get_entropy_fallback() would be > preferable, because that always needs to return _something_, even > falling back to jiffies eventually. It's not as though > random_get_entropy_fallback() 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: Dinh Nguyen > Signed-off-by: Jason A. Donenfeld > --- > arch/nios2/include/asm/timex.h | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/arch/nios2/include/asm/timex.h b/arch/nios2/include/asm/timex.h > index a769f871b28d..d9a3f426cdda 100644 > --- a/arch/nios2/include/asm/timex.h > +++ b/arch/nios2/include/asm/timex.h > @@ -9,4 +9,6 @@ typedef unsigned long cycles_t; > > extern cycles_t get_cycles(void); > > +#define random_get_entropy() (((unsigned long)get_cycles()) ?: random_get_entropy_fallback()) > + > #endif Acked-by: Dinh Nguyen