livepatch/ftrace: Add recursion protection to the ftrace callback

If a ftrace callback does not supply its own recursion protection and
does not set the RECURSION_SAFE flag in its ftrace_ops, then ftrace will
make a helper trampoline to do so before calling the callback instead of
just calling the callback directly.

The default for ftrace_ops is going to change. It will expect that handlers
provide their own recursion protection, unless its ftrace_ops states
otherwise.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]

Cc: Peter Zijlstra <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Jiri Kosina <[email protected]>
Cc: Joe Lawrence <[email protected]>
Cc: [email protected]
Reviewed-by: Petr Mladek <[email protected]>
Acked-by: Miroslav Benes <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>

1 files changed, 5 insertions, 0 deletions

diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
index b552cf2d85f8..6c0164d24bbd 100644
--- a/kernel/livepatch/patch.c
+++ b/kernel/livepatch/patch.c
@@ -45,9 +45,13 @@ static void notrace klp_ftrace_handler(unsigned long ip,
 	struct klp_ops *ops;
 	struct klp_func *func;
 	int patch_state;
+	int bit;
 
 	ops = container_of(fops, struct klp_ops, fops);
 
+	bit = ftrace_test_recursion_trylock();
+	if (bit < 0)
+		return;
 	/*
 	 * A variant of synchronize_rcu() is used to allow patching functions
 	 * where RCU is not watching, see klp_synchronize_transition().
@@ -117,6 +121,7 @@ static void notrace klp_ftrace_handler(unsigned long ip,
 
 unlock:
 	preempt_enable_notrace();
+	ftrace_test_recursion_unlock(bit);
 }
 
 /*