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 S1751073AbcGLSDZ (ORCPT <rfc822;w@1wt.eu>);
	Tue, 12 Jul 2016 14:03:25 -0400
Received: from mail-vk0-f48.google.com ([209.85.213.48]:36655 "EHLO
	mail-vk0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1750739AbcGLSDW (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 12 Jul 2016 14:03:22 -0400
MIME-Version: 1.0
In-Reply-To: <57852E3D.6010107@intel.com>
References: <cover.1468270393.git.luto@kernel.org> <3213d3f31959a6467b1feb80a384c1e11341b2be.1468270393.git.luto@kernel.org>
 <57852E3D.6010107@intel.com>
From: Andy Lutomirski <luto@amacapital.net>
Date: Tue, 12 Jul 2016 11:03:02 -0700
Message-ID: <CALCETrXc58v2PbJyTOYmX0AV6Ud39sQitbFBcMrSccwR=K9Dbg@mail.gmail.com>
Subject: Re: [kernel-hardening] [PATCH v5 13/32] x86/mm/64: In
 vmalloc_fault(), use CR3 instead of current->active_mm
To: Dave Hansen <dave.hansen@intel.com>
Cc: "kernel-hardening@lists.openwall.com" 
	<kernel-hardening@lists.openwall.com>,
        X86 ML <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Borislav Petkov <bp@alien8.de>, Nadav Amit <nadav.amit@gmail.com>,
        Kees Cook <keescook@chromium.org>, Brian Gerst <brgerst@gmail.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>, Jann Horn <jann@thejh.net>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Andy Lutomirski <luto@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 Tue, Jul 12, 2016 at 10:51 AM, Dave Hansen <dave.hansen@intel.com> wrote:
> On 07/11/2016 01:53 PM, Andy Lutomirski wrote:
>> If we get a vmalloc fault while current->active_mm->pgd doesn't
>> match CR3, we'll crash without this change.  I've seen this failure
>> mode on heavily instrumented kernels with virtually mapped stacks.
>
> When does this happen, btw?  Crossing page boundaries on the stack
> between the time we swap mm's and the time we switch stacks?

This can happen for any vmalloc fault between the mm swap and writing
to current or current->active_mm.  I hit it when playing with KASAN
during the first clone.  (KASAN has other issues, but this was one of
them AFAICT.)

--Andy