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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 CEC9BC04AAC for ; Mon, 20 May 2019 12:48:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A534520645 for ; Mon, 20 May 2019 12:48:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1558356510; bh=+GH+DCDK/EE36J4OWkKzbGvcyDu4QdcaLRrUrfIowyM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=kxk/GQfO5DpGAK3+28aK+qQFQFGAPaviE8/xMZyY05z2CurK6GMdzqL43WDwRTHNT d6elqm58vdb4tuNgkpx/mVc3A9l1bCzfTZGxHN03XpMvSD9iGIYex0BTxK16xW20MA QYyJTlUm59HEAjLFbzz1/j8RdtfVnp2mDw+BQcKQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388129AbfETMsZ (ORCPT ); Mon, 20 May 2019 08:48:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:37162 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388262AbfETMW6 (ORCPT ); Mon, 20 May 2019 08:22:58 -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 845E521783; Mon, 20 May 2019 12:22:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1558354978; bh=+GH+DCDK/EE36J4OWkKzbGvcyDu4QdcaLRrUrfIowyM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ynf6dIs9mPD3VHriFfqXPgkRLdqHOddecOCKkbfCeJ/uJUoXZyw3eJ3tiHLt8EupF BiwRULXFLU6oBGxsF93vyssC6Q494V6jLLpSG86GODFkRx6Zs/iUVe65fdEkiUjghj N09B+zFZWoyHONs2NfLzWOVeRUFkHk7tkaIxlhTA= 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 4.19 002/105] x86/speculation/mds: Revert CPU buffer clear on double fault exit Date: Mon, 20 May 2019 14:13:08 +0200 Message-Id: <20190520115247.226620319@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190520115247.060821231@linuxfoundation.org> References: <20190520115247.060821231@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@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 @@ -58,7 +58,6 @@ #include #include #include -#include #include #include #include @@ -388,13 +387,6 @@ dotraplinkage void do_double_fault(struc regs->ip = (unsigned long)general_protection; regs->sp = (unsigned long)&gpregs->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