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From:   Oscar Carter <oscar.carter@gmx.com>
To:     Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Kees Cook <keescook@chromium.org>
Cc:     Oscar Carter <oscar.carter@gmx.com>, linux-kernel@vger.kernel.org,
        kernel-hardening@lists.openwall.com, Jann Horn <jannh@google.com>
Subject: [PATCH v2 2/2] kernel/trace: Remove function callback casts
Date:   Sun, 19 Jul 2020 17:50:33 +0200
Message-Id: <20200719155033.24201-3-oscar.carter@gmx.com>
In-Reply-To: <20200719155033.24201-1-oscar.carter@gmx.com>
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In an effort to enable -Wcast-function-type in the top-level Makefile to
support Control Flow Integrity builds, there are the need to remove all
the function callback casts.

ftrace_ops_list_func() can no longer be defined as ftrace_ops_no_ops().
The reason for ftrace_ops_no_ops() is to use that when an architecture
calls ftrace_ops_list_func() with only two parameters (called from
assembly). And to make sure there's no C side-effects, those archs call
ftrace_ops_no_ops() which only has two parameters, as the function
ftrace_ops_list_func() has four parameters.

This patch removes the no longer needed function ftrace_ops_no_ops() and
all the function callback casts using the previous defined ftrace_func
union and the two function helpers called ftrace_set_ufunc() and
ftrace_same_address_ufunc().

Signed-off-by: Oscar Carter <oscar.carter@gmx.com>
=2D--
 kernel/trace/ftrace.c | 48 ++++++++++++++++++++++++++-----------------
 1 file changed, 29 insertions(+), 19 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index fd8fbb422860..124ccf914657 100644
=2D-- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -143,9 +143,7 @@ static inline bool ftrace_same_address_ufunc(union ftr=
ace_func *ufunc,
 	return (ufunc->ops =3D=3D func);
 }
 #else
-/* See comment below, where ftrace_ops_list_func is defined */
-static void ftrace_ops_no_ops(unsigned long ip, unsigned long parent_ip);
-#define ftrace_ops_list_func ((ftrace_func_t)ftrace_ops_no_ops)
+static void ftrace_ops_list_func(unsigned long ip, unsigned long parent_i=
p);

 static inline void ftrace_set_ufunc(union ftrace_func *ufunc,
 				    ftrace_func_no_ops_t func)
@@ -198,22 +196,29 @@ static void ftrace_sync_ipi(void *data)
 	smp_rmb();
 }

-static ftrace_func_t ftrace_ops_get_list_func(struct ftrace_ops *ops)
+static union ftrace_func ftrace_ops_get_list_func(struct ftrace_ops *ops)
 {
+	union ftrace_func list_func;
+
 	/*
 	 * If this is a dynamic, RCU, or per CPU ops, or we force list func,
 	 * then it needs to call the list anyway.
 	 */
 	if (ops->flags & (FTRACE_OPS_FL_DYNAMIC | FTRACE_OPS_FL_RCU) ||
 	    FTRACE_FORCE_LIST_FUNC)
-		return ftrace_ops_list_func;
+		ftrace_set_ufunc(&list_func, ftrace_ops_list_func);
+	else
+		list_func.ops =3D ftrace_ops_get_func(ops);

-	return ftrace_ops_get_func(ops);
+	return list_func;
 }

 static void update_ftrace_function(void)
 {
-	ftrace_func_t func;
+	union ftrace_func func;
+#ifndef CONFIG_DYNAMIC_FTRACE
+	union ftrace_func tmp;
+#endif

 	/*
 	 * Prepare the ftrace_ops that the arch callback will use.
@@ -225,7 +230,7 @@ static void update_ftrace_function(void)

 	/* If there's no ftrace_ops registered, just call the stub function */
 	if (set_function_trace_op =3D=3D &ftrace_list_end) {
-		func =3D ftrace_stub;
+		func.ops =3D ftrace_stub;

 	/*
 	 * If we are at the end of the list and this ops is
@@ -239,21 +244,21 @@ static void update_ftrace_function(void)
 	} else {
 		/* Just use the default ftrace_ops */
 		set_function_trace_op =3D &ftrace_list_end;
-		func =3D ftrace_ops_list_func;
+		ftrace_set_ufunc(&func, ftrace_ops_list_func);
 	}

 	update_function_graph_func();

 	/* If there's no change, then do nothing more here */
-	if (ftrace_trace_function =3D=3D func)
+	if (ftrace_trace_function =3D=3D func.ops)
 		return;

 	/*
 	 * If we are using the list function, it doesn't care
 	 * about the function_trace_ops.
 	 */
-	if (func =3D=3D ftrace_ops_list_func) {
-		ftrace_trace_function =3D func;
+	if (ftrace_same_address_ufunc(&func, ftrace_ops_list_func)) {
+		ftrace_trace_function =3D func.ops;
 		/*
 		 * Don't even bother setting function_trace_ops,
 		 * it would be racy to do so anyway.
@@ -272,7 +277,9 @@ static void update_ftrace_function(void)
 	 * function we want, albeit indirectly, but it handles the
 	 * ftrace_ops and doesn't depend on function_trace_op.
 	 */
-	ftrace_trace_function =3D ftrace_ops_list_func;
+	ftrace_set_ufunc(&tmp, ftrace_ops_list_func);
+	ftrace_trace_function =3D tmp.ops;
+
 	/*
 	 * Make sure all CPUs see this. Yes this is slow, but static
 	 * tracing is slow and nasty to have enabled.
@@ -287,7 +294,7 @@ static void update_ftrace_function(void)
 	/* OK, we are all set to update the ftrace_trace_function now! */
 #endif /* !CONFIG_DYNAMIC_FTRACE */

-	ftrace_trace_function =3D func;
+	ftrace_trace_function =3D func.ops;
 }

 static void add_ftrace_ops(struct ftrace_ops __rcu **list,
@@ -2680,6 +2687,7 @@ void ftrace_modify_all_code(int command)
 	int update =3D command & FTRACE_UPDATE_TRACE_FUNC;
 	int mod_flags =3D 0;
 	int err =3D 0;
+	union ftrace_func func;

 	if (command & FTRACE_MAY_SLEEP)
 		mod_flags =3D FTRACE_MODIFY_MAY_SLEEP_FL;
@@ -2695,7 +2703,8 @@ void ftrace_modify_all_code(int command)
 	 * traced.
 	 */
 	if (update) {
-		err =3D ftrace_update_ftrace_func(ftrace_ops_list_func);
+		ftrace_set_ufunc(&func, ftrace_ops_list_func);
+		err =3D ftrace_update_ftrace_func(func.ops);
 		if (FTRACE_WARN_ON(err))
 			return;
 	}
@@ -2705,7 +2714,9 @@ void ftrace_modify_all_code(int command)
 	else if (command & FTRACE_DISABLE_CALLS)
 		ftrace_replace_code(mod_flags);

-	if (update && ftrace_trace_function !=3D ftrace_ops_list_func) {
+	ftrace_set_ufunc(&func, ftrace_ops_list_func);
+
+	if (update && ftrace_trace_function !=3D func.ops) {
 		function_trace_op =3D set_function_trace_op;
 		smp_wmb();
 		/* If irqs are disabled, we are in stop machine */
@@ -6890,14 +6901,13 @@ static void ftrace_ops_list_func(unsigned long ip,=
 unsigned long parent_ip,
 {
 	__ftrace_ops_list_func(ip, parent_ip, NULL, regs);
 }
-NOKPROBE_SYMBOL(ftrace_ops_list_func);
 #else
-static void ftrace_ops_no_ops(unsigned long ip, unsigned long parent_ip)
+static void ftrace_ops_list_func(unsigned long ip, unsigned long parent_i=
p)
 {
 	__ftrace_ops_list_func(ip, parent_ip, NULL, NULL);
 }
-NOKPROBE_SYMBOL(ftrace_ops_no_ops);
 #endif
+NOKPROBE_SYMBOL(ftrace_ops_list_func);

 /*
  * If there's only one function registered but it does not support
=2D-
2.20.1