x86/entry: Fix idtentry unwind hint

x86/entry: Fix idtentry unwind hint

CVE-2017-5754

This fixes the following ORC warning in the 'int3' entry code:

  WARNING: can't dereference iret registers at ffff8801c5f17fe0 for ip ffffffff95f0d94b

The ORC metadata had the wrong stack offset for the iret registers.

Their location on the stack is dependent on whether the exception has an
error code.

Reported-and-tested-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 8c1f75587a18 ("x86/entry/64: Add unwind hint annotations")
Link: http://lkml.kernel.org/r/931d57f0551ed7979d5e7e05370d445c8e5137f8.1508516398.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 98990a33b77dda9babf91cb235654f6729e5702e)
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>