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 2B0A6C433FE for ; Thu, 10 Mar 2022 14:21:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243333AbiCJOV7 (ORCPT ); Thu, 10 Mar 2022 09:21:59 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40398 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243651AbiCJOSO (ORCPT ); Thu, 10 Mar 2022 09:18:14 -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 A8F6A1617DD; Thu, 10 Mar 2022 06:14:27 -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 33371B825F3; Thu, 10 Mar 2022 14:14:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8196CC340E8; Thu, 10 Mar 2022 14:14:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1646921664; bh=VTroE0o8H/coKQKT5Ucdb5Tee+fIceA46G9VPM0drL0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=xc3HgE18RkWcQOi/dO6rbBqIzjOXZhBobnnAZB+0INOGBhzxzGd5cZt61wOJHo6lq uu5wFBdEhvF5LDCUqTVWQ1jfs3v8LH/LMVHNV+4xyFFYa3C/Z1aCs8dzIcIwfj8L6R RNTb3K7Q+yPcQO6SJzta8DSwVcmOfzKm2IQM5GTw= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Josh Poimboeuf , Borislav Petkov , Ben Hutchings Subject: [PATCH 4.9 15/38] x86/speculation: Warn about Spectre v2 LFENCE mitigation Date: Thu, 10 Mar 2022 15:13:28 +0100 Message-Id: <20220310140808.582689668@linuxfoundation.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220310140808.136149678@linuxfoundation.org> References: <20220310140808.136149678@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: 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: Ben Hutchings 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 @@ -607,6 +607,7 @@ 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 @@ -928,6 +929,7 @@ 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; @@ -1694,6 +1696,9 @@ 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");