From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754045AbcFPSQp (ORCPT ); Thu, 16 Jun 2016 14:16:45 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44267 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751563AbcFPSQo (ORCPT ); Thu, 16 Jun 2016 14:16:44 -0400 Date: Thu, 16 Jun 2016 13:16:42 -0500 From: Josh Poimboeuf To: Andy Lutomirski Cc: "linux-kernel@vger.kernel.org" , x86@kernel.org, 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: <20160616181642.r2bpceuvvffttp7r@treble> References: 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 18:16:43 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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...) > + > while (valid_stack_ptr(tinfo, stack, sizeof(*stack), end)) { > unsigned long addr; -- Josh