linux-kernel - [PATCH v1 2/4] powerpc/ftrace: Add recursion protection in prepare_ftrace

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Date:   Tue, 15 Feb 2022 19:31:23 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        "Naveen N . Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Subject: [PATCH v1 2/4] powerpc/ftrace: Add recursion protection in prepare_ftrace_return()

The function_graph_enter() does not provide any recursion protection.

Add a protection in prepare_ftrace_return() in case
function_graph_enter() calls something that gets
function graph traced.

Reported-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
Fixes: 830213786c49 ("powerpc/ftrace: directly call of function graph tracer by ftrace caller")
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/kernel/trace/ftrace.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
index 74a176e394ef..f21b8fbd418e 100644
--- a/arch/powerpc/kernel/trace/ftrace.c
+++ b/arch/powerpc/kernel/trace/ftrace.c
@@ -944,6 +944,7 @@ unsigned long prepare_ftrace_return(unsigned long parent, unsigned long ip,
 						unsigned long sp)
 {
 	unsigned long return_hooker;
+	int bit;
 
 	if (unlikely(ftrace_graph_is_dead()))
 		goto out;
@@ -951,10 +952,16 @@ unsigned long prepare_ftrace_return(unsigned long parent, unsigned long ip,
 	if (unlikely(atomic_read(&current->tracing_graph_pause)))
 		goto out;
 
+	bit = ftrace_test_recursion_trylock(ip, parent);
+	if (bit < 0)
+		goto out;
+
 	return_hooker = ppc_function_entry(return_to_handler);
 
 	if (!function_graph_enter(parent, ip, 0, (unsigned long *)sp))
 		parent = return_hooker;
+
+	ftrace_test_recursion_unlock(bit);
 out:
 	return parent;
 }
-- 
2.34.1