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 2CE69C4167D for ; Wed, 9 Mar 2022 16:12:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235528AbiCIQNc (ORCPT ); Wed, 9 Mar 2022 11:13:32 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44782 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235561AbiCIQI5 (ORCPT ); Wed, 9 Mar 2022 11:08:57 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E70F013FAD7; Wed, 9 Mar 2022 08:06:10 -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 dfw.source.kernel.org (Postfix) with ESMTPS id E5CA561666; Wed, 9 Mar 2022 16:05:31 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E8232C340E8; Wed, 9 Mar 2022 16:05:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1646841931; bh=jr+6+1MnJQNcfljlgg0AAAnKF+/2D+Wgaosbrook0EU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=XoNBeee9Gx8wZLxqTLRA9AcwaAVOvYc1oMbGZtcPYpVBuwX9MyCchfxbK7oeT8Uy1 viGGwexQN/XOuQnnjJJzhyWyPPAop5bhKEIyrX2js4P3E7Wkjm1XRLbT7cKgZ2YRT9 PbJwtY2L4PIvNZg4ZZ0VUyQoaOPGNFsat4GSRwuo= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Josh Poimboeuf , Borislav Petkov Subject: [PATCH 5.10 08/43] x86/speculation: Warn about Spectre v2 LFENCE mitigation Date: Wed, 9 Mar 2022 16:59:41 +0100 Message-Id: <20220309155859.484314370@linuxfoundation.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220309155859.239810747@linuxfoundation.org> References: <20220309155859.239810747@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 @@ -614,6 +614,7 @@ 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 @@ -935,6 +936,7 @@ 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; @@ -1717,6 +1719,9 @@ 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");