Date: Sun, 3 Jul 2016 07:25:05 -0700 From: Andy Lutomirski <luto@...capital.net> To: Josh Poimboeuf <jpoimboe@...hat.com> Cc: Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, linux-arch <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 2, 2016 at 11:34 AM, Josh Poimboeuf <jpoimboe@...hat.com> 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 <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()'. > Given that the very next patch deletes this code, I vote for leaving it alone. Or I could fold the patches together. --Andy
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