Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753784AbbHNTG0 (ORCPT ); Fri, 14 Aug 2015 15:06:26 -0400 Received: from mail-io0-f181.google.com ([209.85.223.181]:34838 "EHLO mail-io0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752356AbbHNTGZ (ORCPT ); Fri, 14 Aug 2015 15:06:25 -0400 MIME-Version: 1.0 In-Reply-To: References: <20150814071500.GA2678@gmail.com> Date: Fri, 14 Aug 2015 12:06:24 -0700 X-Google-Sender-Auth: ZMBSkqmPfl8d4RRuiK5UQMR9n2A Message-ID: Subject: Re: [GIT PULL] x86 fixes From: Linus Torvalds To: Andy Lutomirski Cc: Ingo Molnar , Juergen Gross , Andy Lutomirski , Linux Kernel Mailing List , Thomas Gleixner , "H. Peter Anvin" , Peter Zijlstra , Brian Gerst , Denys Vlasenko , Andrew Morton 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: 1566 Lines: 34 On Fri, Aug 14, 2015 at 11:57 AM, Linus Torvalds wrote: > > That code seems fine to me (and explicitly errors out when it's not in > the LDT). FPU_CS is actually the CS selector value. > > So testing that for being in the LDT by checking bit #2, and then > using FPU_get_ldt_descriptor() on it actually seems *correct*. > > It's the actual instruction data segment handling that looks entirely > broken, and was explicitly made *more* broken by that commit. Note that in practice, it's *probably* true that if CS ends up being in the LDT (so we're running something odd like Wine), then *probably* the data segments are going to be in the LDT too. So the old code that unconditionally looked things up in the LDT probably worked in practice, even if it was wrong. The new code cannot *possibly* work at all, because even if the data segment register is in the LDT, it uses the wrong thing to look up the LDT entry, so it will get the wrong base. But as mentioned, it will only *matter* on something like a 486SX, and only when the whole "CS/DS didn't match the default flat segments" case triggers, so not only do you have to run on a 486SX, you will have to run something like Wine on it. So it sounds very very unlikely that this bug matters in practice. Linus -- 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/