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:

quoted

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@kernel.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