Commit 13f3ea9a authored Nov 05, 2020 by Steven Rostedt (VMware)

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/20201028115613.291169246@goodmis.org
Link: https://lkml.kernel.org/r/20201106023547.122802424@goodmis.org



Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Joe Lawrence <joe.lawrence@redhat.com>
Cc: live-patching@vger.kernel.org
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

parent c536aa1c

kernel/livepatch/patch.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -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);
		}

		/*

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