From patchwork Sat Apr 23 21:26:16 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: 565407 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 766F5C433F5 for ; Sat, 23 Apr 2022 21:28:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237217AbiDWVbW (ORCPT ); Sat, 23 Apr 2022 17:31:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47632 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237227AbiDWVbC (ORCPT ); Sat, 23 Apr 2022 17:31:02 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 67F3C2ED58; Sat, 23 Apr 2022 14:27:33 -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 525816103B; Sat, 23 Apr 2022 21:27:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 169B5C385AC; Sat, 23 Apr 2022 21:27:31 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="W8LWzKxk" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1650749250; 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=cpbrBqankh2fsmUUGS4FsleJ1lhokYXdTSW/sLYtQ34=; b=W8LWzKxkm0b1alhY+kinODd9xzrT7cI+ej+3fcxkhcT+6jRUVPdNAhJTl/Wz8o1HaBdcaP /EtCUAwxsOyer7j6Q+7oI93AlDobKPeJNESIeBNrnS2iGLm8GbP1zsXkYHEJSEvm/DIyQr j2iVOxPjKbV9W8Sv6GDk/Hp7wcDi1Z4= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 1d021403 (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Sat, 23 Apr 2022 21:27:30 +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" , Russell King Subject: [PATCH v6 10/17] arm: use fallback for random_get_entropy() instead of zero Date: Sat, 23 Apr 2022 23:26:16 +0200 Message-Id: <20220423212623.1957011-11-Jason@zx2c4.com> In-Reply-To: <20220423212623.1957011-1-Jason@zx2c4.com> References: <20220423212623.1957011-1-Jason@zx2c4.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.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 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: Russell King Signed-off-by: Jason A. Donenfeld Reviewed-by: Russell King (Oracle) --- arch/arm/include/asm/timex.h | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/arm/include/asm/timex.h b/arch/arm/include/asm/timex.h index 7c3b3671d6c2..6d1337c169cd 100644 --- a/arch/arm/include/asm/timex.h +++ b/arch/arm/include/asm/timex.h @@ -11,5 +11,6 @@ typedef unsigned long cycles_t; #define get_cycles() ({ cycles_t c; read_current_timer(&c) ? 0 : c; }) +#define random_get_entropy() (((unsigned long)get_cycles()) ?: random_get_entropy_fallback()) #endif