From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756937AbbAHWaU (ORCPT ); Thu, 8 Jan 2015 17:30:20 -0500 Received: from mga03.intel.com ([134.134.136.65]:9925 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754692AbbAHWaP (ORCPT ); Thu, 8 Jan 2015 17:30:15 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.97,862,1389772800"; d="scan'208";a="438213197" Subject: [PATCH 1/3] x86, mpx: explicitly disable 32-bit MPX support on 64-bit kernels To: linux-kernel@vger.kernel.org Cc: tglx@linutronix.de, x86@kernel.org, luto@amacapital.net, Dave Hansen , dave.hansen@linux.intel.com From: Dave Hansen Date: Thu, 08 Jan 2015 14:30:20 -0800 References: <20150108223018.A57DEE63@viggo.jf.intel.com> In-Reply-To: <20150108223018.A57DEE63@viggo.jf.intel.com> Message-Id: <20150108223020.9E9AA511@viggo.jf.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dave Hansen We had originally planned on submitting MPX support in one patch set. We eventually broke it up in to two pieces for easier review. One of the features that didn't make the first round was supporting 32-bit binaries on 64-bit kernels. Once we split the set up, we never added code to restrict 32-bit binaries from _using_ MPX on 64-bit kernels. The 32-bit bounds tables are a different format than the 64-bit ones. Without this patch, the kernel will try to read a 32-bit binary's tables as if they were the 64-bit version. They will likely be noticed as being invalid rather quickly and the app will get killed, but that's kinda mean. This patch adds an explicit check, and will make a 64-bit kernel essentially behave as if it has no MPX support when called from a 32-bit binary. I intend to remove this check once the mixed binary support is added. Those patches are posted if anyone is interested: https://lkml.org/lkml/2014/12/12/632 Signed-off-by: Dave Hansen Cc: Andy Lutomirski --- b/arch/x86/mm/mpx.c | 6 ++++++ 1 file changed, 6 insertions(+) diff -puN arch/x86/mm/mpx.c~x86-mpx-explicitly-disable-32-bit-on-64-bit-for-3_19 arch/x86/mm/mpx.c --- a/arch/x86/mm/mpx.c~x86-mpx-explicitly-disable-32-bit-on-64-bit-for-3_19 2015-01-08 12:48:09.123864625 -0800 +++ b/arch/x86/mm/mpx.c 2015-01-08 12:48:09.126864760 -0800 @@ -349,6 +349,12 @@ static __user void *task_get_bounds_dir( return MPX_INVALID_BOUNDS_DIR; /* + * 32-bit binaries on 64-bit kernels are currently + * unsupported. + */ + if (IS_ENABLED(CONFIG_X86_64) && test_thread_flag(TIF_IA32)) + return MPX_INVALID_BOUNDS_DIR; + /* * The bounds directory pointer is stored in a register * only accessible if we first do an xsave. */ _