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=-6.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,T_DKIMWL_WL_HIGH,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 22116C28EBD for ; Sun, 9 Jun 2019 16:55:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EFC44206DF for ; Sun, 9 Jun 2019 16:55:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1560099349; bh=BT0+PLSHpy9Y6WnvFZU/IEPYQG63I+Jmn3K3hx214Do=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=TaikD76lcviuJJtNa5ABz78QaM3uHtDHayomeGoElDOjXM6T7k0Eo2FCN/HWABQ7g 7wl9FTeCGU1tBF8sFt2ffLF5Vc3ZSZygbp6ta+7ps90i9kCT7hTym5aibsnU3e7zev gtltDOyKgIMKSrJxFJbpRM2gJNZ3pnrjsq2dqxII= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732840AbfFIQzr (ORCPT ); Sun, 9 Jun 2019 12:55:47 -0400 Received: from mail.kernel.org ([198.145.29.99]:57928 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732824AbfFIQzo (ORCPT ); Sun, 9 Jun 2019 12:55:44 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 04813204EC; Sun, 9 Jun 2019 16:55:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1560099343; bh=BT0+PLSHpy9Y6WnvFZU/IEPYQG63I+Jmn3K3hx214Do=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=RyYdgiiiIl+uwzzBqFNwY7ZnMGg5kT1w6nf0XEewUO/s+iZpXN8b34lSDGsVawuCy 08b7oxpKummlSvqXyopDWaYZk5kRDAmttbJTh4ra2OE0SiKOcZXF9yjiUpkuqz3vKK MDksUxJU2ANDuzZBsi0UZorbbkrgt0g7CYbcWS/8= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Andy Lutomirski , Borislav Petkov , Frederic Weisbecker , Jon Masters , Linus Torvalds , Peter Zijlstra , Thomas Gleixner , Ingo Molnar Subject: [PATCH 4.4 001/241] x86/speculation/mds: Revert CPU buffer clear on double fault exit Date: Sun, 9 Jun 2019 18:39:03 +0200 Message-Id: <20190609164147.815178298@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190609164147.729157653@linuxfoundation.org> References: <20190609164147.729157653@linuxfoundation.org> User-Agent: quilt/0.66 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Andy Lutomirski commit 88640e1dcd089879530a49a8d212d1814678dfe7 upstream. The double fault ESPFIX path doesn't return to user mode at all -- it returns back to the kernel by simulating a #GP fault. prepare_exit_to_usermode() will run on the way out of general_protection before running user code. Signed-off-by: Andy Lutomirski Cc: Borislav Petkov Cc: Frederic Weisbecker Cc: Greg Kroah-Hartman Cc: Jon Masters Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: stable@vger.kernel.org Fixes: 04dcbdb80578 ("x86/speculation/mds: Clear CPU buffers on exit to user") Link: http://lkml.kernel.org/r/ac97612445c0a44ee10374f6ea79c222fe22a5c4.1557865329.git.luto@kernel.org Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- Documentation/x86/mds.rst | 7 ------- arch/x86/kernel/traps.c | 8 -------- 2 files changed, 15 deletions(-) --- a/Documentation/x86/mds.rst +++ b/Documentation/x86/mds.rst @@ -158,13 +158,6 @@ Mitigation points mitigated on the return from do_nmi() to provide almost complete coverage. - - Double fault (#DF): - - A double fault is usually fatal, but the ESPFIX workaround, which can - be triggered from user space through modify_ldt(2) is a recoverable - double fault. #DF uses the paranoid exit path, so explicit mitigation - in the double fault handler is required. - - Machine Check Exception (#MC): Another corner case is a #MC which hits between the CPU buffer clear --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -61,7 +61,6 @@ #include #include #include -#include #include #include @@ -338,13 +337,6 @@ dotraplinkage void do_double_fault(struc regs->ip = (unsigned long)general_protection; regs->sp = (unsigned long)&normal_regs->orig_ax; - /* - * This situation can be triggered by userspace via - * modify_ldt(2) and the return does not take the regular - * user space exit, so a CPU buffer clear is required when - * MDS mitigation is enabled. - */ - mds_user_clear_cpu_buffers(); return; } #endif