From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755099AbbICMJx (ORCPT ); Thu, 3 Sep 2015 08:09:53 -0400 Received: from smtp45.i.mail.ru ([94.100.177.105]:39409 "EHLO smtp45.i.mail.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754032AbbICMJw (ORCPT ); Thu, 3 Sep 2015 08:09:52 -0400 Subject: Re: stop breaking dosemu (Re: x86/kconfig/32: Rename CONFIG_VM86 and default it to 'n') To: Austin S Hemmelgarn , Andy Lutomirski References: <55E6C36F.6080309@list.ru> <55E736E9.2000201@list.ru> <55E7607B.4070800@list.ru> <55E7663B.30402@list.ru> <55E83697.7090707@gmail.com> Cc: Josh Boyer , "linux-kernel@vger.kernel.org" , "Andrew Bird (Sphere Systems)" , Linus Torvalds , Ingo Molnar , Kees Cook , Brian Gerst From: Stas Sergeev X-Enigmail-Draft-Status: N1110 Message-ID: <55E8387F.9070001@list.ru> Date: Thu, 3 Sep 2015 15:09:35 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 MIME-Version: 1.0 In-Reply-To: <55E83697.7090707@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Mras: Ok Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 03.09.2015 15:01, Austin S Hemmelgarn пишет: > On 2015-09-02 17:12, Stas Sergeev wrote: >> 02.09.2015 23:55, Andy Lutomirski пишет: >>> On Wed, Sep 2, 2015 at 1:47 PM, Stas Sergeev wrote: >>>> 02.09.2015 23:22, Josh Boyer пишет: >>>>> On Wed, Sep 2, 2015 at 1:50 PM, Stas Sergeev wrote: >>>>>> 02.09.2015 20:46, Josh Boyer пишет: >>>>>>> On Wed, Sep 2, 2015 at 10:08 AM, Andy Lutomirski >>>>>>> >>>>>>> wrote: >>>>>>>> I'd be amenable to switching the default back to y and perhaps >>>>>>>> adding >>>>>>>> a sysctl to make the distros more comfortable. Ingo, Kees, Brian, >>>>>>>> what do you think? >>>>>>> Can you please leave the default as N, and have a sysctl option to >>>>>>> enable it instead? While dosemu might still be in use, it isn't >>>>>>> going >>>>>>> to be the common case at all. So from a distro perspective, I think >>>>>>> we'd probably rather have the default match the common case. >>>>>> The fact that fedora doesn't package dosemu, doesn't automatically >>>>>> mean all other distros do not too. Since when kernel defaults should >>>>>> match the ones of fedora? >>>>> I didn't say that. >>>> What you said was: >>>> --- >>>> >>>> While dosemu might still be in use, it isn't going >>>> to be the common case at all. So from a distro perspective >>>> >>>> --- >>>> ... which is likely true only in fedora circe. >>>> >>>>> The default right now is N. >>>> In a not yet released kernel, unless I am mistaken. >>>> If fedora already provides that kernel, other distros likely not. >>>> >>>>> I asked it be left >>>>> that way. That's all. >>>> Lets assume its not yet N, unless there was a kernel release already. >>>> Its easy to get back if its not too late. >>> How about CONFIG_SYSCTL_VM86_DEFAULT which defaults to Y? Fedora >>> could set it to N. >> Sorry, I don't understand this sysctl proposal. >> Could you please educate me what is it all about? >> This sysctl will disable or enable the vm86() syscall at run-time, >> right? What does it give us? If you disable something in the >> config, this gives you, say, smaller kernel image. If OTOH you >> add the run-time switch, it gives you a bigger image, regardless >> of its default value. >> I might be missing something, but I don't understand what >> problem will this solve? Have I missed some earlier message >> in this thread? > The problem this solves is not kernel size, that is not the only reason for wanting to disable a system call. In this case, it's a system call that is unused by all but a very few programs, which are > in turn used by a small percentage of users, and said system call does quite a few things that are potentially very dangerous. Disabling it reduces the attack surface of the system. Well, thanks for explaining the marketing part of the problem (initially I wasn't aware, but now Andy already spelled it too), but the reality is different.