From mboxrd@z Thu Jan 1 00:00:00 1970 From: Josh Poimboeuf Subject: Re: [PATCH v4 10/29] x86/die: Don't try to recover from an OOPS on a non-default stack Date: Sat, 2 Jul 2016 13:34:51 -0500 Message-ID: <20160702183451.e2nlfkfxlsuicbqd@treble> References: <37ac7589ff0ea147e8a21cda5eb84d3af1f6cd60.1466974736.git.luto@kernel.org> <20160702172441.GA22748@pd.tnic> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Received: from mx1.redhat.com ([209.132.183.28]:42728 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752354AbcGBSez (ORCPT ); Sat, 2 Jul 2016 14:34:55 -0400 Content-Disposition: inline In-Reply-To: <20160702172441.GA22748@pd.tnic> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Borislav Petkov Cc: Andy Lutomirski , x86@kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Nadav Amit , Kees Cook , Brian Gerst , "kernel-hardening@lists.openwall.com" , Linus Torvalds , Jann Horn , Heiko Carstens On Sat, Jul 02, 2016 at 07:24:41PM +0200, Borislav Petkov wrote: > On Sun, Jun 26, 2016 at 02:55:32PM -0700, Andy Lutomirski wrote: > > It's not going to work, because the scheduler will explode if we try > > to schedule when running on an IST stack or similar. > > > > This will matter when we let kernel stack overflows (which are #DF) > > call die(). > > > > Signed-off-by: Andy Lutomirski > > --- > > arch/x86/kernel/dumpstack.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c > > index ef8017ca5ba9..352f022cfd5b 100644 > > --- a/arch/x86/kernel/dumpstack.c > > +++ b/arch/x86/kernel/dumpstack.c > > @@ -245,6 +245,9 @@ void oops_end(unsigned long flags, struct pt_regs *regs, int signr) > > return; > > if (in_interrupt()) > > panic("Fatal exception in interrupt"); > > + if (((current_stack_pointer() ^ (current_top_of_stack() - 1)) > > + & ~(THREAD_SIZE - 1)) != 0) > > Ugh, that's hard to parse. You could remove the "!= 0" at least to > shorten it a bit and have one less braces level. > > Or maybe even do something like that to make it a bit more readable: > > if ((current_stack_pointer() ^ (current_top_of_stack() - 1)) > & > ~(THREAD_SIZE - 1)) > panic("Fatal exception on non-default stack"); > > Meh. A helper function would be even better. The existing 'object_is_on_stack()' can probably be used: if (!object_is_on_stack(current_top_of_stack())) panic("..."); Though that function isn't quite accurately named. It should really have 'task_stack' in its name, like 'object_is_on_task_stack()'. Or even better, something more concise like 'on_task_stack()'. -- Josh