[PATCH 4.14.y 1/2] tracing/kprobes: Return EADDRNOTAVAIL when func matches several symbols

[PATCH 4.14.y 1/2] tracing/kprobes: Return EADDRNOTAVAIL when func matches several symbols

[Francis Laniel]

Commit b022f0c7e404887a7c5229788fc99eff9f9a80d5 upstream.

When a kprobe is attached to a function that's name is not unique (is
static and shares the name with other functions in the kernel), the
kprobe is attached to the first function it finds. This is a bug as the
function that it is attaching to is not necessarily the one that the
user wants to attach to.

Instead of blindly picking a function to attach to what is ambiguous,
error with EADDRNOTAVAIL to let the user know that this function is not
unique, and that the user must use another unique function with an
address offset to get to the function they want to attach to.

Link: https://lore.kernel.org/all/20231020104250.9537-2-flaniel@linux.microsoft.com/

Cc: stable@vger.kernel.org
Fixes: 413d37d1eb69 ("tracing: Add kprobe-based event tracer")
Suggested-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Francis Laniel <flaniel@linux.microsoft.com>
Link: https://lore.kernel.org/lkml/20230819101105.b0c104ae4494a7d1f2eea742@kernel.org/
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
(cherry picked from commit b022f0c7e404887a7c5229788fc99eff9f9a80d5)
---
 kernel/trace/trace_kprobe.c | 48 +++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index d66aed6e9c75..45779ec370fa 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -617,6 +617,36 @@ static inline void sanitize_event_name(char *name)
 			*name = '_';
 }
 
+struct count_symbols_struct {
+	const char *func_name;
+	unsigned int count;
+};
+
+static int count_symbols(void *data, const char *name, struct module *unused0,
+			 unsigned long unused1)
+{
+	struct count_symbols_struct *args = data;
+
+	if (strcmp(args->func_name, name))
+		return 0;
+
+	args->count++;
+
+	return 0;
+}
+
+static unsigned int number_of_same_symbols(char *func_name)
+{
+	struct count_symbols_struct args = {
+		.func_name = func_name,
+		.count = 0,
+	};
+
+	kallsyms_on_each_symbol(count_symbols, &args);
+
+	return args.count;
+}
+
 static int create_trace_kprobe(int argc, char **argv)
 {
 	/*
@@ -746,6 +776,24 @@ static int create_trace_kprobe(int argc, char **argv)
 	}
 	argc -= 2; argv += 2;
 
+	if (symbol && !strchr(symbol, ':')) {
+		unsigned int count;
+
+		count = number_of_same_symbols(symbol);
+		if (count > 1)
+			/*
+			 * Users should use ADDR to remove the ambiguity of
+			 * using KSYM only.
+			 */
+			return -EADDRNOTAVAIL;
+		else if (count == 0)
+			/*
+			 * We can return ENOENT earlier than when register the
+			 * kprobe.
+			 */
+			return -ENOENT;
+	}
+
 	/* setup a probe */
 	if (!event) {
 		/* Make a new event name */
-- 
2.34.1

[PATCH 4.14.y 2/2] selftests/ftrace: Add new test case which checks non unique symbol

[Francis Laniel]

Commit 03b80ff8023adae6780e491f66e932df8165e3a0 upstream.

If name_show() is non unique, this test will try to install a kprobe on this
function which should fail returning EADDRNOTAVAIL.
On kernel where name_show() is not unique, this test is skipped.

Link: https://lore.kernel.org/all/20231020104250.9537-3-flaniel@linux.microsoft.com/

Cc: stable@vger.kernel.org
Signed-off-by: Francis Laniel <flaniel@linux.microsoft.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 .../ftrace/test.d/kprobe/kprobe_non_uniq_symbol.tc  | 13 +++++++++++++
 1 file changed, 13 insertions(+)
 create mode 100644 tools/testing/selftests/ftrace/test.d/kprobe/kprobe_non_uniq_symbol.tc

diff --git a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_non_uniq_symbol.tc b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_non_uniq_symbol.tc
new file mode 100644
index 000000000000..bc9514428dba
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_non_uniq_symbol.tc
@@ -0,0 +1,13 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test failure of registering kprobe on non unique symbol
+# requires: kprobe_events
+
+SYMBOL='name_show'
+
+# We skip this test on kernel where SYMBOL is unique or does not exist.
+if [ "$(grep -c -E "[[:alnum:]]+ t ${SYMBOL}" /proc/kallsyms)" -le '1' ]; then
+	exit_unsupported
+fi
+
+! echo "p:test_non_unique ${SYMBOL}" > kprobe_events
-- 
2.34.1