Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932689AbbGJOhn (ORCPT ); Fri, 10 Jul 2015 10:37:43 -0400 Received: from mail-lb0-f170.google.com ([209.85.217.170]:35470 "EHLO mail-lb0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932218AbbGJOhg (ORCPT ); Fri, 10 Jul 2015 10:37:36 -0400 MIME-Version: 1.0 In-Reply-To: <87twtc14po.fsf@x220.int.ebiederm.org> References: <23d4709cee2fe92c32d41b99c7a3c1823725925a.1436312944.git.luto@kernel.org> <559C8BFE.6050604@linux.intel.com> <87twtc14po.fsf@x220.int.ebiederm.org> From: Andy Lutomirski Date: Fri, 10 Jul 2015 07:37:15 -0700 Message-ID: Subject: Re: [PATCH] x86/kconfig/32: Mark CONFIG_VM86 as BROKEN To: "Eric W. Biederman" Cc: Linus Torvalds , Arjan van de Ven , Andy Lutomirski , "the arch/x86 maintainers" , Linux Kernel Mailing List , Oleg Nesterov , Kees Cook , Peter Zijlstra , Borislav Petkov Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1823 Lines: 42 On Fri, Jul 10, 2015 at 7:12 AM, Eric W. Biederman wrote: > Andy Lutomirski writes: > >> On the other hand, sys_vm86 fails if the syscall slow path is in use. >> That means that quite a few Fedora versions (auditing), anything with >> ptrace, seccomp (before 3.16 IIRC), and anything with context tracking >> is probably actually *improved* by turning off the vm86 syscalls even >> for dosemu users. > > Is there any chance that vm86 is sufficiently badly broken before this > that we can conclude vm86 is not in use? It would really simplify this > discussion if we could point to code rot and say that it is clear that > no one has been testing this code path for ages, and that the code can't > possibly work the way it is now. That would just let us remove vm86. > Having just written a pile of tests for it, I don't think so, as long as none of the syscall slow path stuff is in use :( >> It only says "[OK]" because my test case isn't careful enough. That's >> a failure. I suspect it was a much worse failure a couple versions >> ago before my ENOSYS-reworking patch went in. >> >> I'll try to confirm later this week that dosemu can really handle real >> mode without sys_vm86. > > I have not looked in ages but certainly on 64bit dosemu can. > > As someone else pointed out dosemu maps the zero page so that may also > be a point where vm86 support gets broken. Right. And someone pointed out that vbetool sometimes needs access to virtual (or emulated virtual) addresses above 3GB, and vm86 can't do that. --Andy -- 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/