From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754186AbcFPSyu (ORCPT ); Thu, 16 Jun 2016 14:54:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54710 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753976AbcFPSyt (ORCPT ); Thu, 16 Jun 2016 14:54:49 -0400 Date: Thu, 16 Jun 2016 13:54:46 -0500 From: Josh Poimboeuf To: Andy Lutomirski Cc: Andy Lutomirski , "linux-kernel@vger.kernel.org" , X86 ML , Borislav Petkov , Nadav Amit , Kees Cook , Brian Gerst , "kernel-hardening@lists.openwall.com" , Linus Torvalds Subject: Re: [PATCH 10/13] x86/dumpstack: Try harder to get a call trace on stack overflow Message-ID: <20160616185446.rzlpbfeowsmzlqb4@treble> References: <20160616181642.r2bpceuvvffttp7r@treble> <20160616183303.puhiggbbxza2bxcv@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Thu, 16 Jun 2016 18:54:48 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 16, 2016 at 11:37:07AM -0700, Andy Lutomirski wrote: > On Thu, Jun 16, 2016 at 11:33 AM, Josh Poimboeuf wrote: > > On Thu, Jun 16, 2016 at 11:22:14AM -0700, Andy Lutomirski wrote: > >> On Thu, Jun 16, 2016 at 11:16 AM, Josh Poimboeuf wrote: > >> > On Wed, Jun 15, 2016 at 05:28:32PM -0700, Andy Lutomirski wrote: > >> >> If we overflow the stack, print_context_stack will abort. Detect > >> >> this case and rewind back into the valid part of the stack so that > >> >> we can trace it. > >> >> > >> >> Signed-off-by: Andy Lutomirski > >> >> --- > >> >> arch/x86/kernel/dumpstack.c | 7 +++++++ > >> >> 1 file changed, 7 insertions(+) > >> >> > >> >> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c > >> >> index d4d085e27d04..400a2e17c1d1 100644 > >> >> --- a/arch/x86/kernel/dumpstack.c > >> >> +++ b/arch/x86/kernel/dumpstack.c > >> >> @@ -100,6 +100,13 @@ print_context_stack(struct thread_info *tinfo, > >> >> { > >> >> struct stack_frame *frame = (struct stack_frame *)bp; > >> >> > >> >> + /* > >> >> + * If we overflowed the stack into a guard page, jump back to the > >> >> + * bottom of the usable stack. > >> >> + */ > >> >> + if ((unsigned long)tinfo - (unsigned long)stack < PAGE_SIZE) > >> >> + stack = (unsigned long *)tinfo + 1; > >> > > >> > That will start walking the stack in the middle of the thread_info > >> > struct. > >> > > >> > I think you meant: > >> > > >> > stack = (unsigned long *)(tinfo + 1) > >> > > >> > However, thread_info will have been overwritten anyway. So maybe it > >> > should just be: > >> > > >> > stack = tinfo; > >> > > >> > (Though that still wouldn't quite work because the valid_stack_ptr() > >> > check would fail...) > >> > >> I did mean what I wrote, because I wanted to start at the bottom of > >> the validly allocated area. IOW I wanted to do the minimum possible > >> backward jump to make the code display something. > > > > But why the "+ 1"? Is that a hack to make it pass the valid_stack_ptr() > > check? > > Yes. > > But hmm. Maybe the right fix is to drop the + 1 and to change the > last line of valid_stck_ptr from: > > return p > t && p < t + THREAD_SIZE - size; > > to: > > return p >= t && p < t + THREAD_SIZE - size; Yeah, I think that would be much better. Then it won't skip the first value on the page. -- Josh