[PATCH 6/9] livepatch/ftrace: Add recursion protection to the ftrace callback

Steven Rostedt
2020-10-29T00:58:04Z

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

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 assume recursion protection unless
otherwise specified.

Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Joe Lawrence <joe.lawrence@redhat.com>
Cc: live-patching@vger.kernel.org
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/livepatch/patch.c | 5 +++++
1 file changed, 5 insertions(+)

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);
}

/*
--
2.28.0