kprobes: Warn if optprobe handler tries to change execution path

Warn if optprobe handler tries to change execution path.
As described in Documentation/kprobes.txt, with optprobe
user handler can not change instruction pointer. In that
case user must avoid optimizing the kprobes by setting
post_handler or break_handler.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Alexei Starovoitov <ast@fb.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E . McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/150581521955.32348.3615624715034787365.stgit@devbox
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 15fba7fe57c8..2d28377a0e32 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -387,7 +387,10 @@ void opt_pre_handler(struct kprobe *p, struct pt_regs *regs)
         list_for_each_entry_rcu(kp, &p->list, list) {
                 if (kp->pre_handler && likely(!kprobe_disabled(kp))) {
                         set_kprobe_instance(kp);
-                        kp->pre_handler(kp, regs);
+                        if (kp->pre_handler(kp, regs)) {
+                                if (WARN_ON_ONCE(1))
+                                        pr_err("Optprobe ignores instruction pointer changing.(%pF)\n", p->addr);
+                        }
                 }
                 reset_kprobe_instance();
         }