From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753911AbbCISgi (ORCPT <rfc822;w@1wt.eu>);
	Mon, 9 Mar 2015 14:36:38 -0400
Received: from mail-la0-f48.google.com ([209.85.215.48]:45220 "EHLO
	mail-la0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751599AbbCISgg (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Mon, 9 Mar 2015 14:36:36 -0400
MIME-Version: 1.0
In-Reply-To: <CA+55aFyVh=bLtC+vVvZ4id09gn0tvGPSXwEyNdzGwLNTsDKJQA@mail.gmail.com>
References: <1425909943-14687-1-git-send-email-dvlasenk@redhat.com>
 <CA+55aFzck8nuV06AZhhFXgUQEsujZCtufw0jY4iswJUggh6ruA@mail.gmail.com>
 <54FDDB90.9010706@zytor.com> <CALCETrV8BhaL9MUv9ZroyWwrBKdDXL+ZwY3dELO80N3bcsxi5A@mail.gmail.com>
 <CA+55aFz2HOnPg9i4WSeL4rQgSJDUXbiWjbqnODib=vyWrPuJEg@mail.gmail.com>
 <CALCETrVt5AnrdHrj=HcWrLRHT7TN1ZoFb3cqj0VoktCn4c0W6A@mail.gmail.com> <CA+55aFyVh=bLtC+vVvZ4id09gn0tvGPSXwEyNdzGwLNTsDKJQA@mail.gmail.com>
From: Andy Lutomirski <luto@amacapital.net>
Date: Mon, 9 Mar 2015 11:36:14 -0700
Message-ID: <CALCETrVLSgayUzP4nrjXVjGwcFQ=Ue6OvQkKHRio_y8Y0oWLVA@mail.gmail.com>
Subject: Re: [PATCH] x86: entry_32.S: change ESPFIX test to not touch PT_OLDSS(%esp)
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Denys Vlasenko <dvlasenk@redhat.com>,
        Steven Rostedt <rostedt@goodmis.org>, Ingo Molnar <mingo@kernel.org>,
        Borislav Petkov <bp@alien8.de>, Oleg Nesterov <oleg@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Alexei Starovoitov <ast@plumgrid.com>, Will Drewry <wad@chromium.org>,
        Kees Cook <keescook@chromium.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset=UTF-8
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Mon, Mar 9, 2015 at 11:16 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Mon, Mar 9, 2015 at 11:04 AM, Andy Lutomirski <luto@amacapital.net> wrote:
>>
>> One option would be to change the NMI entry code to move itself down 8
>> bytes if this happens (came from kernel mode or sp == sp0 - 12,
>> perhaps).
>
> Hmm. That whole code currently depends on the stack setup being just a
> single instruction (the move to esp). And that simplifies things, I'd
> like to keep it that way.
>
> I'd *much* rather just keep the 8-byte padding. What was so
> problematic with that? It worked. It's been around forever. Removing
> it is the bug.

Let's at least fix it, then.  processor.h has:

#define INIT_TSS  {                              \
    .x86_tss = {                              \
        .sp0        = sizeof(init_stack) + (long)&init_stack, \

(moved in -tip)

That's bogus, and this bogosity is why I broke 32-bit -next in the
first place: I assumed it was correct.

I'll get it if no one beats me to it.

--Andy

>
>                         Linus



-- 
Andy Lutomirski
AMA Capital Management, LLC