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 BA9ECC19F2B for ; Wed, 27 Jul 2022 17:18:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241760AbiG0RSc (ORCPT ); Wed, 27 Jul 2022 13:18:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33508 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241757AbiG0RR5 (ORCPT ); Wed, 27 Jul 2022 13:17:57 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F1B274D15D; Wed, 27 Jul 2022 09:43:36 -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 AB468B8200C; Wed, 27 Jul 2022 16:43:35 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 081BDC433D6; Wed, 27 Jul 2022 16:43:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1658940214; bh=xzLNXcz4miuOscNHT52+ulkgeYXs8Noj2UPKsvKI/sE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=pxdYjgHKZ8s8YgmKdXT8Z/SsL4lDHSGwv+EWvf8wMNFN+FdH8ZD83u/FlTHRY3UpH sFtJaLR44fepa2T/VF+VKLbEvWIl8FU8zaededKFyTYjIfjnpE0Y7nu2FwYbPiUI4o zhTp9Jwuu0cEMjOrXxmtdzaRFKAoxOv29inWdkVE= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Pawan Gupta , "Peter Zijlstra (Intel)" , Thadeu Lima de Souza Cascardo Subject: [PATCH 5.15 138/201] x86/bugs: Warn when "ibrs" mitigation is selected on Enhanced IBRS parts Date: Wed, 27 Jul 2022 18:10:42 +0200 Message-Id: <20220727161033.522685816@linuxfoundation.org> X-Mailer: git-send-email 2.37.1 In-Reply-To: <20220727161026.977588183@linuxfoundation.org> References: <20220727161026.977588183@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: stable@vger.kernel.org From: Pawan Gupta commit eb23b5ef9131e6d65011de349a4d25ef1b3d4314 upstream. IBRS mitigation for spectre_v2 forces write to MSR_IA32_SPEC_CTRL at every kernel entry/exit. On Enhanced IBRS parts setting MSR_IA32_SPEC_CTRL[IBRS] only once at boot is sufficient. MSR writes at every kernel entry/exit incur unnecessary performance loss. When Enhanced IBRS feature is present, print a warning about this unnecessary performance loss. Signed-off-by: Pawan Gupta Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Thadeu Lima de Souza Cascardo Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/2a5eaf54583c2bfe0edc4fea64006656256cca17.1657814857.git.pawan.kumar.gupta@linux.intel.com Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/cpu/bugs.c | 3 +++ 1 file changed, 3 insertions(+) --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -968,6 +968,7 @@ static inline const char *spectre_v2_mod #define SPECTRE_V2_LFENCE_MSG "WARNING: LFENCE mitigation is not recommended for this CPU, data leaks possible!\n" #define SPECTRE_V2_EIBRS_EBPF_MSG "WARNING: Unprivileged eBPF is enabled with eIBRS on, data leaks possible via Spectre v2 BHB attacks!\n" #define SPECTRE_V2_EIBRS_LFENCE_EBPF_SMT_MSG "WARNING: Unprivileged eBPF is enabled with eIBRS+LFENCE mitigation and SMT, data leaks possible via Spectre v2 BHB attacks!\n" +#define SPECTRE_V2_IBRS_PERF_MSG "WARNING: IBRS mitigation selected on Enhanced IBRS CPU, this may cause unnecessary performance loss\n" #ifdef CONFIG_BPF_SYSCALL void unpriv_ebpf_notify(int new_state) @@ -1408,6 +1409,8 @@ static void __init spectre_v2_select_mit case SPECTRE_V2_IBRS: setup_force_cpu_cap(X86_FEATURE_KERNEL_IBRS); + if (boot_cpu_has(X86_FEATURE_IBRS_ENHANCED)) + pr_warn(SPECTRE_V2_IBRS_PERF_MSG); break; case SPECTRE_V2_LFENCE: