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Date: Sat, 2 Jul 2016 13:34:51 -0500
From: Josh Poimboeuf <jpoimboe@...hat.com>
To: Borislav Petkov <bp@...en8.de>
Cc: Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
Nadav Amit <nadav.amit@...il.com>, Kees Cook <keescook@...omium.org>,
Brian Gerst <brgerst@...il.com>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Jann Horn <jann@...jh.net>, Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH v4 10/29] x86/die: Don't try to recover from an OOPS on a
non-default stack
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 <luto@...nel.org>
> > ---
> > 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
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