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 B02B9C433F5 for ; Wed, 9 Mar 2022 16:13:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233541AbiCIQOn (ORCPT ); Wed, 9 Mar 2022 11:14:43 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41404 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234888AbiCIQIM (ORCPT ); Wed, 9 Mar 2022 11:08:12 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 288EF123434; Wed, 9 Mar 2022 08:04:39 -0800 (PST) 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 ACDB8B82226; Wed, 9 Mar 2022 16:04:38 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 19A9CC340E8; Wed, 9 Mar 2022 16:04:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1646841877; bh=6ZUZk/4wbx82Pve13fPW/pPb9Ysl0rgYv9e7dSH/l5M=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GkYOBd6zWDZ6Ym62NjRrmy6PeLwMSC1LZEOyaZ83lwJOMtEjr0kP2VVPTWzSLRqdB myeJ0BccvOTbAcwt5Zlypgn+5RbKr/xhe2fqZkAZAfEPlJhk+4gbxxy9EM5bv9bwIT Rnh+deIw6lnwKcpXDu5cvMsqBz9RkDRl95RFREV8= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Josh Poimboeuf , Borislav Petkov Subject: [PATCH 5.4 09/18] x86/speculation: Warn about Spectre v2 LFENCE mitigation Date: Wed, 9 Mar 2022 16:59:58 +0100 Message-Id: <20220309155856.829049784@linuxfoundation.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220309155856.552503355@linuxfoundation.org> References: <20220309155856.552503355@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: Josh Poimboeuf commit eafd987d4a82c7bb5aa12f0e3b4f8f3dea93e678 upstream. With: f8a66d608a3e ("x86,bugs: Unconditionally allow spectre_v2=retpoline,amd") it became possible to enable the LFENCE "retpoline" on Intel. However, Intel doesn't recommend it, as it has some weaknesses compared to retpoline. Now AMD doesn't recommend it either. It can still be left available as a cmdline option. It's faster than retpoline but is weaker in certain scenarios -- particularly SMT, but even non-SMT may be vulnerable in some cases. So just unconditionally warn if the user requests it on the cmdline. [ bp: Massage commit message. ] Signed-off-by: Josh Poimboeuf Signed-off-by: Borislav Petkov Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/cpu/bugs.c | 5 +++++ 1 file changed, 5 insertions(+) --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -608,6 +608,7 @@ static inline const char *spectre_v2_mod static inline const char *spectre_v2_module_string(void) { return ""; } #endif +#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" #ifdef CONFIG_BPF_SYSCALL @@ -929,6 +930,7 @@ static void __init spectre_v2_select_mit break; case SPECTRE_V2_CMD_RETPOLINE_LFENCE: + pr_err(SPECTRE_V2_LFENCE_MSG); mode = SPECTRE_V2_LFENCE; break; @@ -1705,6 +1707,9 @@ static char *ibpb_state(void) static ssize_t spectre_v2_show_state(char *buf) { + if (spectre_v2_enabled == SPECTRE_V2_LFENCE) + return sprintf(buf, "Vulnerable: LFENCE\n"); + if (spectre_v2_enabled == SPECTRE_V2_EIBRS && unprivileged_ebpf_enabled()) return sprintf(buf, "Vulnerable: Unprivileged eBPF enabled\n");