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 DBBF7C433EF for ; Thu, 23 Jun 2022 17:04:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232820AbiFWRE5 (ORCPT ); Thu, 23 Jun 2022 13:04:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55856 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233795AbiFWRDN (ORCPT ); Thu, 23 Jun 2022 13:03:13 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A82D250E3C; Thu, 23 Jun 2022 09:54:59 -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 59CABB82493; Thu, 23 Jun 2022 16:54:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AA0FCC341C5; Thu, 23 Jun 2022 16:54:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1656003279; bh=Lsq0eKPBVfKBPWTnlRqD63GU+emiQfb0lgDGZ+bos/4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=dusmGuodjLMNSeV5//DYnPhpK4RQJ/IDmlFrcosLTVg/DimebmnZWxlppkPy73CbN M8Wmrs8VgRkuiyRAaQmXFnP+JBewLbPgpZM4N0oTPPf5RbzDXLMrDqSeJHklh9NtWo LQ/62+NoWRgT+4xzzwU5Y3vcN9WvCraNksjl5bhk= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Jason A. Donenfeld" , Thomas Gleixner , Arnd Bergmann , Borislav Petkov , x86@kernel.org Subject: [PATCH 4.9 188/264] x86/tsc: Use fallback for random_get_entropy() instead of zero Date: Thu, 23 Jun 2022 18:43:01 +0200 Message-Id: <20220623164349.387531048@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220623164344.053938039@linuxfoundation.org> References: <20220623164344.053938039@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Jason A. Donenfeld" commit 3bd4abc07a267e6a8b33d7f8717136e18f921c53 upstream. In the event that random_get_entropy() can't access a cycle counter or similar, falling back to returning 0 is suboptimal. Instead, fallback to calling random_get_entropy_fallback(), which isn't extremely high precision or guaranteed to be entropic, but is certainly better than returning zero all the time. If CONFIG_X86_TSC=n, then it's possible for the kernel to run on systems without RDTSC, such as 486 and certain 586, so the fallback code is only required for that case. As well, fix up both the new function and the get_cycles() function from which it was derived to use cpu_feature_enabled() rather than boot_cpu_has(), and use !IS_ENABLED() instead of #ifndef. Signed-off-by: Jason A. Donenfeld Reviewed-by: Thomas Gleixner Cc: Thomas Gleixner Cc: Arnd Bergmann Cc: Borislav Petkov Cc: x86@kernel.org Signed-off-by: Jason A. Donenfeld Signed-off-by: Greg Kroah-Hartman --- arch/x86/include/asm/timex.h | 9 +++++++++ arch/x86/include/asm/tsc.h | 7 +++---- 2 files changed, 12 insertions(+), 4 deletions(-) --- a/arch/x86/include/asm/timex.h +++ b/arch/x86/include/asm/timex.h @@ -4,6 +4,15 @@ #include #include +static inline unsigned long random_get_entropy(void) +{ + if (!IS_ENABLED(CONFIG_X86_TSC) && + !cpu_feature_enabled(X86_FEATURE_TSC)) + return random_get_entropy_fallback(); + return rdtsc(); +} +#define random_get_entropy random_get_entropy + /* Assume we use the PIT time source for the clock tick */ #define CLOCK_TICK_RATE PIT_TICK_RATE --- a/arch/x86/include/asm/tsc.h +++ b/arch/x86/include/asm/tsc.h @@ -21,13 +21,12 @@ extern void disable_TSC(void); static inline cycles_t get_cycles(void) { -#ifndef CONFIG_X86_TSC - if (!boot_cpu_has(X86_FEATURE_TSC)) + if (!IS_ENABLED(CONFIG_X86_TSC) && + !cpu_feature_enabled(X86_FEATURE_TSC)) return 0; -#endif - return rdtsc(); } +#define get_cycles get_cycles extern struct system_counterval_t convert_art_to_tsc(cycle_t art);