linux-kernel - [PATCH 07/11 v3] livepatch: Trigger WARNING if livepatch function fails due to recursion

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Date:   Thu, 05 Nov 2020 21:32:42 -0500
From:   Steven Rostedt (VMware) <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        live-patching@...r.kernel.org
Subject: [PATCH 07/11 v3] livepatch: Trigger WARNING if livepatch function fails due to
 recursion

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

If for some reason a function is called that triggers the recursion
detection of live patching, trigger a warning. By not executing the live
patch code, it is possible that the old unpatched function will be called
placing the system into an unknown state.

Link: https://lore.kernel.org/r/20201029145709.GD16774@alley

Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Jiri Kosina <jikos@...nel.org>
Cc: Joe Lawrence <joe.lawrence@...hat.com>
Cc: live-patching@...r.kernel.org
Suggested-by: Miroslav Benes <mbenes@...e.cz>
Reviewed-by: Petr Mladek <pmladek@...e.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
Changes since v2:

 - Blame Miroslav instead of Petr ;-)

 kernel/livepatch/patch.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
index 6c0164d24bbd..15480bf3ce88 100644
--- a/kernel/livepatch/patch.c
+++ b/kernel/livepatch/patch.c
@@ -50,7 +50,7 @@ static void notrace klp_ftrace_handler(unsigned long ip,
 	ops = container_of(fops, struct klp_ops, fops);
 
 	bit = ftrace_test_recursion_trylock();
-	if (bit < 0)
+	if (WARN_ON_ONCE(bit < 0))
 		return;
 	/*
 	 * A variant of synchronize_rcu() is used to allow patching functions
-- 
2.28.0