Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754925AbbGYGYm (ORCPT ); Sat, 25 Jul 2015 02:24:42 -0400 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:10838 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754729AbbGYGYl (ORCPT ); Sat, 25 Jul 2015 02:24:41 -0400 Date: Sat, 25 Jul 2015 08:23:43 +0200 From: Willy Tarreau To: Andy Lutomirski Cc: Peter Zijlstra , Steven Rostedt , "security@kernel.org" , X86 ML , Borislav Petkov , Sasha Levin , linux-kernel@vger.kernel.org, Konrad Rzeszutek Wilk , Boris Ostrovsky , Andrew Cooper , Jan Beulich , xen-devel Subject: Re: [PATCH v4 2/3] x86/ldt: Make modify_ldt optional Message-ID: <20150725062343.GA3902@1wt.eu> References: <7286d77aa81abc38dc40362e2439861427064f6f.1437802102.git.luto@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7286d77aa81abc38dc40362e2439861427064f6f.1437802102.git.luto@kernel.org> User-Agent: Mutt/1.4.2.3i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1168 Lines: 27 On Fri, Jul 24, 2015 at 10:36:45PM -0700, Andy Lutomirski wrote: > The modify_ldt syscall exposes a large attack surface and is > unnecessary for modern userspace. Make it optional. Andy, you didn't respond whether you think it wouldn't be better to make it runtime-configurable instead. The goal here is to ensure distros ship with modify_ldt disabled by default. But if it means breaking compatibility with (rare) existing applications, I'm seeing a risk that they'll ship with it enabled instead, which would make the config option useless. The CONFIG_DEFAULT_MMAP_ADDR was a good example of successful deployment of a hardening measure that has been widely adopted despite its (low) risk of breakage in field because it was adjustable in field. That's why here I think we should do the same, and possibly even emit a warning once to report the first user of modify_ldt if that can help. What do you think ? Willy -- 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/