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,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 CC95DC433DF for ; Fri, 3 Jul 2020 17:03:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A3D002088E for ; Fri, 3 Jul 2020 17:03:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593795790; bh=m3e/FHb743juz8MYek0OvVhLTMbLckgasucbPdaxygo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=W0I9vrn2FcKWu2LqFYpUQqM7tHPhUwm/I0wpyRzc1yom804KcNddApkUdw7X8ZO6f wQFSrIN3Ta4kR5c18HGC2zkMIIWOe8I4I5i2sZtZKVxo6vRyWoDymt8hmJLIlEoyQp L9ylIH32PmbXSBLBceyIUWr17FnM/uXlkIPHgsmA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726800AbgGCRDJ (ORCPT ); Fri, 3 Jul 2020 13:03:09 -0400 Received: from mail.kernel.org ([198.145.29.99]:32780 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726768AbgGCRDF (ORCPT ); Fri, 3 Jul 2020 13:03:05 -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 0774620870; Fri, 3 Jul 2020 17:03:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593795785; bh=m3e/FHb743juz8MYek0OvVhLTMbLckgasucbPdaxygo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=VWcP9iqyLBv+86u0kYw4lUSLm+N0UmdFgSu2iLSK/GNJbApYwyDnhINaz+bNEs1p7 hMN7C4m0zSYIchwEG8Qlg7Nybl2H9E5LR33crsBr5uZqjHRo4Lrdk7IdDIhVUPkoSE iyuR325fUMzGJ+5l9/AFowXNnZBgraNpJFaIUuF4= From: Andy Lutomirski To: x86@kernel.org Cc: Andrew Cooper , Juergen Gross , LKML , Andy Lutomirski Subject: [PATCH entry v2 5/6] x86/ldt: Disable 16-bit segments on Xen PV Date: Fri, 3 Jul 2020 10:02:57 -0700 Message-Id: <92b2975459dfe5929ecf34c3896ad920bd9e3f2d.1593795633.git.luto@kernel.org> X-Mailer: git-send-email 2.25.4 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 Xen PV doesn't implement ESPFIX64, so they don't work right. Disable them. Also print a warning the first time anyone tries to use a 16-bit segment on a Xen PV guest that would otherwise allow it to help people diagnose this change in behavior. This gets us closer to having all x86 selftests pass on Xen PV. Signed-off-by: Andy Lutomirski --- arch/x86/kernel/ldt.c | 35 ++++++++++++++++++++++++++++++++++- 1 file changed, 34 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c index 8748321c4486..34e918ad34d4 100644 --- a/arch/x86/kernel/ldt.c +++ b/arch/x86/kernel/ldt.c @@ -29,6 +29,8 @@ #include #include +#include + /* This is a multiple of PAGE_SIZE. */ #define LDT_SLOT_STRIDE (LDT_ENTRIES * LDT_ENTRY_SIZE) @@ -543,6 +545,37 @@ static int read_default_ldt(void __user *ptr, unsigned long bytecount) return bytecount; } +static bool allow_16bit_segments(void) +{ + if (!IS_ENABLED(CONFIG_X86_16BIT)) + return false; + +#ifdef CONFIG_XEN_PV + /* + * Xen PV does not implement ESPFIX64, which means that 16-bit + * segments will not work correctly. Until either Xen PV implements + * ESPFIX64 and can signal this fact to the guest or unless someone + * provides compelling evidence that allowing broken 16-bit segments + * is worthwhile, disallow 16-bit segments under Xen PV. + */ + if (xen_pv_domain()) { + static DEFINE_MUTEX(xen_warning); + static bool warned; + + mutex_lock(&xen_warning); + if (!warned) { + pr_info("Warning: 16-bit segments do not work correctly in a Xen PV guest\n"); + warned = true; + } + mutex_unlock(&xen_warning); + + return false; + } +#endif + + return true; +} + static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode) { struct mm_struct *mm = current->mm; @@ -574,7 +607,7 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode) /* The user wants to clear the entry. */ memset(&ldt, 0, sizeof(ldt)); } else { - if (!IS_ENABLED(CONFIG_X86_16BIT) && !ldt_info.seg_32bit) { + if (!ldt_info.seg_32bit && !allow_16bit_segments()) { error = -EINVAL; goto out; } -- 2.25.4