From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Lutomirski Subject: Re: [PATCH v4 10/29] x86/die: Don't try to recover from an OOPS on a non-default stack Date: Sun, 3 Jul 2016 07:25:05 -0700 Message-ID: References: <37ac7589ff0ea147e8a21cda5eb84d3af1f6cd60.1466974736.git.luto@kernel.org> <20160702172441.GA22748@pd.tnic> <20160702183451.e2nlfkfxlsuicbqd@treble> Reply-To: kernel-hardening@lists.openwall.com Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: List-Post: List-Help: List-Unsubscribe: List-Subscribe: In-Reply-To: <20160702183451.e2nlfkfxlsuicbqd@treble> To: Josh Poimboeuf Cc: Borislav Petkov , Andy Lutomirski , X86 ML , "linux-kernel@vger.kernel.org" , linux-arch , Nadav Amit , Kees Cook , Brian Gerst , "kernel-hardening@lists.openwall.com" , Linus Torvalds , Jann Horn , Heiko Carstens List-Id: linux-arch.vger.kernel.org On Sat, Jul 2, 2016 at 11:34 AM, Josh Poimboeuf wrote: > 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()'. > Given that the very next patch deletes this code, I vote for leaving it alone. Or I could fold the patches together. --Andy From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-vk0-f41.google.com ([209.85.213.41]:33815 "EHLO mail-vk0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752669AbcGCOZZ (ORCPT ); Sun, 3 Jul 2016 10:25:25 -0400 Received: by mail-vk0-f41.google.com with SMTP id c2so205747010vkg.1 for ; Sun, 03 Jul 2016 07:25:25 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20160702183451.e2nlfkfxlsuicbqd@treble> References: <37ac7589ff0ea147e8a21cda5eb84d3af1f6cd60.1466974736.git.luto@kernel.org> <20160702172441.GA22748@pd.tnic> <20160702183451.e2nlfkfxlsuicbqd@treble> From: Andy Lutomirski Date: Sun, 3 Jul 2016 07:25:05 -0700 Message-ID: Subject: Re: [PATCH v4 10/29] x86/die: Don't try to recover from an OOPS on a non-default stack Content-Type: text/plain; charset=UTF-8 Sender: linux-arch-owner@vger.kernel.org List-ID: To: Josh Poimboeuf Cc: Borislav Petkov , Andy Lutomirski , X86 ML , "linux-kernel@vger.kernel.org" , linux-arch , Nadav Amit , Kees Cook , Brian Gerst , "kernel-hardening@lists.openwall.com" , Linus Torvalds , Jann Horn , Heiko Carstens Message-ID: <20160703142505.-TZ3lvFA5i6_ZNqSy2BTNjL8RICm-LZWlsYJ2wY4KGs@z> On Sat, Jul 2, 2016 at 11:34 AM, Josh Poimboeuf wrote: > 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()'. > Given that the very next patch deletes this code, I vote for leaving it alone. Or I could fold the patches together. --Andy