Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751753AbbGWHNz (ORCPT ); Thu, 23 Jul 2015 03:13:55 -0400 Received: from prv-mh.provo.novell.com ([137.65.248.74]:35992 "EHLO prv-mh.provo.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751000AbbGWHNs convert rfc822-to-8bit (ORCPT ); Thu, 23 Jul 2015 03:13:48 -0400 Message-Id: <55B0B04A02000078000945AF@prv-mh.provo.novell.com> X-Mailer: Novell GroupWise Internet Agent 14.0.1 Date: Thu, 23 Jul 2015 01:13:46 -0600 From: "Jan Beulich" To: "Andy Lutomirski" Cc: "Borislav Petkov" , "Andrew Cooper" , "Steven Rostedt" , "Peter Zijlstra" , "security@kernel.org" , "X86 ML" , "xen-devel" , "Boris Ostrovsky" , "Konrad Rzeszutek Wilk" , "Sasha Levin" , Subject: Re: [PATCH v3 2/3] x86/ldt: Make modify_ldt optional References: <7bfde005b84a90a83bf668a320c7d4ad1b940065.1437592883.git.luto@kernel.org> In-Reply-To: <7bfde005b84a90a83bf668a320c7d4ad1b940065.1437592883.git.luto@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1738 Lines: 44 >>> On 22.07.15 at 21:23, wrote: > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -1015,6 +1015,7 @@ config VM86 > config X86_16BIT > bool "Enable support for 16-bit segments" if EXPERT > default y > + depends on MODIFY_LDT_SYSCALL > ---help--- > This option is required by programs like Wine to run 16-bit > protected mode legacy code on x86 processors. Disabling > @@ -2053,6 +2054,22 @@ config CMDLINE_OVERRIDE > This is used to work around broken boot loaders. This should > be set to 'N' under normal conditions. > > +config MODIFY_LDT_SYSCALL > + bool "Enable the LDT (local descriptor table)" if EXPERT > + default y > + ---help--- > + Linux can allow user programs to install a per-process x86 > + Local Descriptor Table (LDT) using the modify_ldt(2) system > + call. This is required to run 16-bit or segmented code such as > + DOSEMU or some Wine programs. It is also used by some very old > + threading libraries. > + > + Enabling this feature adds a small amount of overhead to > + context switches and increases the low-level kernel attack > + surface. Disabling it removes the modify_ldt(2) system call. > + > + Saying 'N' here may make sense for embedded or server kernels. > + I think it would be better to place this ahead of the one being made dependent on it, to avoid the user being prompted for X86_16BIT despite it possibly becoming unavailable (when this one gets set to n). Jan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/