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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