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 X-Spam-Level: X-Spam-Status: No, score=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 50DB0C47255 for ; Mon, 11 May 2020 04:54:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2879720820 for ; Mon, 11 May 2020 04:54:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589172849; bh=284oPI9GIPHpEC5gNFA9Sv4pwU6P4+U98zOmf/LPL2M=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=KHhbG+Qgc2ts221bwSLHeN2xAMgh2bdFb7F7QH7pAehkfln1udw8fufKgdrCzYi/+ T1p4sewQ94Bw2IGMs/lwdyV1TC8mpiMC8mUc66lWb6p4mwxZ1jgZyR2oI1mEyU0A4r HGTHjKX1/K102K+jDpgeQ22yuF/i6gvGq89Cc/9A= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729243AbgEKEyI (ORCPT ); Mon, 11 May 2020 00:54:08 -0400 Received: from mail.kernel.org ([198.145.29.99]:37984 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728750AbgEKExq (ORCPT ); Mon, 11 May 2020 00:53:46 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D13402063A; Mon, 11 May 2020 04:53:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589172825; bh=284oPI9GIPHpEC5gNFA9Sv4pwU6P4+U98zOmf/LPL2M=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=D6rCWsGUNmFE2wgipUWge3Igud3unskkHO3DxOvxdRCL3qseYR1z836Y3PZA7Zf99 tCmZ63mzy8MBghSopVk0zkd/6rQ3RUpVQIT+K2EcdoBg/H4KobzTqz3t0v55QUP45E a4pAEmgoWVOz1h9Pc49E/ILOT5OfRslxgyd7hJds= From: Sasha Levin To: linux-kernel@vger.kernel.org, tglx@linutronix.de, bp@alien8.de, luto@kernel.org Cc: hpa@zytor.com, dave.hansen@intel.com, tony.luck@intel.com, ak@linux.intel.com, ravi.v.shankar@intel.com, chang.seok.bae@intel.com, Sasha Levin Subject: [PATCH v12 14/18] x86/speculation/swapgs: Check FSGSBASE in enabling SWAPGS mitigation Date: Mon, 11 May 2020 00:53:07 -0400 Message-Id: <20200511045311.4785-15-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200511045311.4785-1-sashal@kernel.org> References: <20200511045311.4785-1-sashal@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Tony Luck Before enabling FSGSBASE the kernel could safely assume that the content of GS base was a user address. Thus any speculative access as the result of a mispredicted branch controlling the execution of SWAPGS would be to a user address. So systems with speculation-proof SMAP did not need to add additional LFENCE instructions to mitigate. With FSGSBASE enabled a hostile user can set GS base to a kernel address. So they can make the kernel speculatively access data they wish to leak via a side channel. This means that SMAP provides no protection. Add FSGSBASE as an additional condition to enable the fence-based SWAPGS mitigation. Signed-off-by: Tony Luck Signed-off-by: Chang S. Bae Signed-off-by: Sasha Levin Cc: Thomas Gleixner Cc: Borislav Petkov Cc: Andy Lutomirski Cc: H. Peter Anvin Cc: Dave Hansen Cc: Tony Luck Cc: Andi Kleen --- arch/x86/kernel/cpu/bugs.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index ed54b3b21c396..487603ea51cd1 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -450,14 +450,12 @@ static void __init spectre_v1_select_mitigation(void) * If FSGSBASE is enabled, the user can put a kernel address in * GS, in which case SMAP provides no protection. * - * [ NOTE: Don't check for X86_FEATURE_FSGSBASE until the - * FSGSBASE enablement patches have been merged. ] - * * If FSGSBASE is disabled, the user can only put a user space * address in GS. That makes an attack harder, but still * possible if there's no SMAP protection. */ - if (!smap_works_speculatively()) { + if (boot_cpu_has(X86_FEATURE_FSGSBASE) || + !smap_works_speculatively()) { /* * Mitigation can be provided from SWAPGS itself or * PTI as the CR3 write in the Meltdown mitigation -- 2.20.1