From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754820AbbICMBt (ORCPT ); Thu, 3 Sep 2015 08:01:49 -0400 Received: from mail-io0-f172.google.com ([209.85.223.172]:33383 "EHLO mail-io0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754235AbbICMBq (ORCPT ); Thu, 3 Sep 2015 08:01:46 -0400 Subject: Re: stop breaking dosemu (Re: x86/kconfig/32: Rename CONFIG_VM86 and default it to 'n') To: Stas Sergeev , Andy Lutomirski References: <55E6C36F.6080309@list.ru> <55E736E9.2000201@list.ru> <55E7607B.4070800@list.ru> <55E7663B.30402@list.ru> Cc: Josh Boyer , "linux-kernel@vger.kernel.org" , "Andrew Bird (Sphere Systems)" , Linus Torvalds , Ingo Molnar , Kees Cook , Brian Gerst From: Austin S Hemmelgarn Message-ID: <55E83697.7090707@gmail.com> Date: Thu, 3 Sep 2015 08:01:27 -0400 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <55E7663B.30402@list.ru> Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-512; boundary="------------ms080607040802060905060008" X-Antivirus: avast! (VPS 150903-0, 2015-09-03), Outbound message X-Antivirus-Status: Clean Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is a cryptographically signed message in MIME format. --------------ms080607040802060905060008 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 2015-09-02 17:12, Stas Sergeev wrote: > 02.09.2015 23:55, Andy Lutomirski =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >> On Wed, Sep 2, 2015 at 1:47 PM, Stas Sergeev wrote: >>> 02.09.2015 23:22, Josh Boyer =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >>>> On Wed, Sep 2, 2015 at 1:50 PM, Stas Sergeev wrote: >>>>> 02.09.2015 20:46, Josh Boyer =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >>>>>> 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 thi= nk >>>>>> 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 shoul= d >>>>> 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=20 for wanting to disable a system call. In this case, it's a system call=20 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=20 things that are potentially very dangerous. 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