From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932969AbcFORFz (ORCPT ); Wed, 15 Jun 2016 13:05:55 -0400 Received: from mail-lf0-f52.google.com ([209.85.215.52]:34489 "EHLO mail-lf0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932473AbcFORFw (ORCPT ); Wed, 15 Jun 2016 13:05:52 -0400 MIME-Version: 1.0 In-Reply-To: References: From: Kees Cook Date: Wed, 15 Jun 2016 10:05:49 -0700 X-Google-Sender-Auth: 2-1DnW9xvAZwz3Xol3viEk4Yb44 Message-ID: Subject: Re: Playing with virtually mapped stacks (with guard pages!) To: Andy Lutomirski Cc: "kernel-hardening@lists.openwall.com" , "linux-kernel@vger.kernel.org" , X86 ML , Borislav Petkov , "linux-mm@kvack.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 14, 2016 at 11:01 PM, Andy Lutomirski wrote: > Hi all- > > If you want to play with virtually mapped stacks, I have it more or > less working on x86 in a branch here: > > https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/log/?h=x86/vmap_stack > > The core bit (virtually map the stack and fix the accounting) is just > a config option, but it needs the arch to opt-in. I suspect that > every arch will have its own set of silly issues to address to make it > work well. For x86, the silly issues are getting the OOPS to work > right and handling some vmalloc_fault oddities to avoid panicing at > random. Awesome! Some notes/questions: - there are a number of typos in commit messages and comments, just FYI - where is the guard page added? I don't see anything leaving a hole at the end? - where is thread_info? I understand there to be two benefits from vmalloc stack: 1) thread_info can live elsewhere, 2) guard page can exist easily - this seems like it should Oops not warn: WARN_ON_ONCE(vm->nr_pages != THREAD_SIZE / PAGE_SIZE); that being wrong seems like a very bad state to continue from - bikeshed: I think the CONFIG should live in arch/Kconfig (with a description of what an arch needs to support for it) and be called HAVE_ARCH_VMAP_STACK so that archs can select it instead of having multiple definitions of CONFIG_VMAP_STACK in each arch. Thanks for digging into this! -Kees -- Kees Cook Chrome OS & Brillo Security