Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932923AbbGHStH (ORCPT ); Wed, 8 Jul 2015 14:49:07 -0400 Received: from mail-ig0-f173.google.com ([209.85.213.173]:37866 "EHLO mail-ig0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758240AbbGHSs5 (ORCPT ); Wed, 8 Jul 2015 14:48:57 -0400 MIME-Version: 1.0 In-Reply-To: References: <23d4709cee2fe92c32d41b99c7a3c1823725925a.1436312944.git.luto@kernel.org> <559C8BFE.6050604@linux.intel.com> Date: Wed, 8 Jul 2015 11:48:56 -0700 X-Google-Sender-Auth: zblexGNoUTDaq6WwusuzQnVz4yo Message-ID: Subject: Re: [PATCH] x86/kconfig/32: Mark CONFIG_VM86 as BROKEN From: Kees Cook To: Linus Torvalds Cc: Andy Lutomirski , Arjan van de Ven , Andy Lutomirski , "the arch/x86 maintainers" , Linux Kernel Mailing List , Oleg Nesterov , 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: 1612 Lines: 38 On Wed, Jul 8, 2015 at 10:55 AM, Linus Torvalds wrote: > On Wed, Jul 8, 2015 at 10:49 AM, Andy Lutomirski wrote: >> >> I don't know how to tell whether something is trying to use real mode, >> but I can play this just fine in DOSEMU on my 64-bit laptop: > > So a 64-bit distro obviously will never have used vm86 mode - it > doesn't work there. Never has. There's no sane way to get to vm86 mode > from long mode, that's just how the 64-bit extensions worked. > > (64-bit hardware obviously does support vm86 mode, but you have to > play games with mixing long mode and CPL0 32-bit protected mode to get > there, and we never did that). > > It's the 32-bit distros I would worry about. The ones that may have > well disabled emulation, because they have vm86 mode enabled. Speaking as the dosemu maintainer in Debian and Ubuntu, I can confirm what Andy mentioned: dosemu will kick over to emulation if SYS_vm86 and SYS_vm86old fail. The other area I remember that used vm86 mode was non-KMS Xorg drivers and anything using svgalib that tried to do video card BIOS initialization. Also, Andy, I think you weren't looking at i386 builds of Ubuntu. Current Ubuntu, and 12.04 ("Precise") LTS (supported until 2017), and 14.04 LTS (until 2019) releases all have CONFIG_VM86. -Kees -- Kees Cook Chrome OS Security -- 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/