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=-9.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 65206C04AB4 for ; Tue, 14 May 2019 20:25:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3476020873 for ; Tue, 14 May 2019 20:25:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1557865511; bh=V8lGZOijGGroDQlnNtg2WHMwlbIFGtORUHrj5N/6N5M=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=vurm5AsvPLjsXtOf5C8MvjFJ5Qv/LndSdeVrNlhteFhRFkdmKfOgJvbWF4kTvhRC0 5l0uzrBC5qVrykQfxaUvVQfn+ea2PoOrjRQM3JEBnFbQWwN9+X4shkC9G4VFQGDAdG TOhlU0gQeZuPLhkea6EdJiocnB2NJwA07xQz13dY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726542AbfENUZJ (ORCPT ); Tue, 14 May 2019 16:25:09 -0400 Received: from mail.kernel.org ([198.145.29.99]:34698 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726448AbfENUZF (ORCPT ); Tue, 14 May 2019 16:25:05 -0400 Received: from localhost (c-67-180-165-146.hsd1.ca.comcast.net [67.180.165.146]) (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 4410321726; Tue, 14 May 2019 20:25:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1557865505; bh=V8lGZOijGGroDQlnNtg2WHMwlbIFGtORUHrj5N/6N5M=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=BKe0Vn5rSFeLvnBCMcdBjQAKWYOEpXQK9RMljVhjjKEiZA6Gmpj4B6Re7H5B1bEtK knwD7OfJ7ZtvkeCzHuOZu1FPMSbgWSCn0AhBBq7VGhCXqRWIN8zg23VPYMDyTlK3p4 6hRgRJfoTUiuqiTHJChgQeWeNQvTuwjge//9L4UM= From: Andy Lutomirski To: x86@kernel.org Cc: LKML , Andy Lutomirski , stable@vger.kernel.org, Greg Kroah-Hartman , Borislav Petkov , Frederic Weisbecker , Jon Masters Subject: [PATCH 1/2] x86/speculation/mds: Revert CPU buffer clear on double fault exit Date: Tue, 14 May 2019 13:24:39 -0700 Message-Id: X-Mailer: git-send-email 2.21.0 In-Reply-To: References: 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 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. Cc: stable@vger.kernel.org Cc: Greg Kroah-Hartman Cc: Borislav Petkov Cc: Frederic Weisbecker Cc: Jon Masters Fixes: 04dcbdb80578 ("x86/speculation/mds: Clear CPU buffers on exit to user") Signed-off-by: Andy Lutomirski --- Documentation/x86/mds.rst | 7 ------- arch/x86/kernel/traps.c | 8 -------- 2 files changed, 15 deletions(-) diff --git a/Documentation/x86/mds.rst b/Documentation/x86/mds.rst index 534e9baa4e1d..0dc812bb9249 100644 --- 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 diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 7de466eb960b..8b6d03e55d2f 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -58,7 +58,6 @@ #include #include #include -#include #include #include #include @@ -368,13 +367,6 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code) 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 -- 2.21.0