linux-kernel - [PATCH 04/11 v2] pstore/ftrace: Add recursion protection to the ftrace callback

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Message-ID: <20201030214013.668563396@goodmis.org>
Date:   Fri, 30 Oct 2020 17:31:46 -0400
From:   Steven Rostedt <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>, Thomas Meyer <thomas@...3r.de>,
        Kees Cook <keescook@...omium.org>
Subject: [PATCH 04/11 v2] pstore/ftrace: Add recursion protection to the ftrace callback

From: "Steven Rostedt (VMware)" <rostedt@...dmis.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 change. It will expect that handlers
provide their own recursion protection, unless its ftrace_ops states
otherwise.

Link: https://lkml.kernel.org/r/20201028115612.990886844@goodmis.org

Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Thomas Meyer <thomas@...3r.de>
Reviewed-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 fs/pstore/ftrace.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/pstore/ftrace.c b/fs/pstore/ftrace.c
index 5c0450701293..816210fc5d3a 100644
--- a/fs/pstore/ftrace.c
+++ b/fs/pstore/ftrace.c
@@ -28,6 +28,7 @@ static void notrace pstore_ftrace_call(unsigned long ip,
 				       struct ftrace_ops *op,
 				       struct pt_regs *regs)
 {
+	int bit;
 	unsigned long flags;
 	struct pstore_ftrace_record rec = {};
 	struct pstore_record record = {
@@ -40,6 +41,10 @@ static void notrace pstore_ftrace_call(unsigned long ip,
 	if (unlikely(oops_in_progress))
 		return;
 
+	bit = ftrace_test_recursion_trylock();
+	if (bit < 0)
+		return;
+
 	local_irq_save(flags);
 
 	rec.ip = ip;
@@ -49,6 +54,7 @@ static void notrace pstore_ftrace_call(unsigned long ip,
 	psinfo->write(&record);
 
 	local_irq_restore(flags);
+	ftrace_test_recursion_unlock(bit);
 }
 
 static struct ftrace_ops pstore_ftrace_ops __read_mostly = {
-- 
2.28.0