[PATCH 2/2] lib/tests: Add KUnit test for struct stack_trace __counted_by_ptr attribute

[Bill Wendling <morbo@google.com>]

Add a custom KUnit test suite 'stacktrace_counted_by' to verify that the
__counted_by_ptr annotation on the 'entries' field of 'struct stack_trace'
behaves correctly.

The test verifies that 'max_entries' correctly limits and validates access
to 'entries' when CONFIG_ARCH_STACKWALK is not defined. If it is defined,
the test is cleanly skipped at runtime to prevent compile-time or runtime
failures due to 'struct stack_trace' being undefined on modern
architectures.

Assisted-by: Gemini Next
Signed-off-by: Bill Wendling <morbo@google.com>
---
Cc: Kees Cook <kees@kernel.org>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Gow <david@davidgow.net>
Cc: Rae Moar <raemoar63@gmail.com>
Cc: Ryota Sakamoto <sakamo.ryota@gmail.com>
Cc: Kuan-Wei Chiu <visitorckw@gmail.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Dmitry Antipov <dmantipov@yandex.ru>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Kir Chou <note351@hotmail.com>
Cc: codemender-patching+linux@google.com
Cc: linux-kernel@vger.kernel.org
Cc: linux-hardening@vger.kernel.org
Cc: linux-kselftest@vger.kernel.org
Cc: kunit-dev@googlegroups.com
Cc: linux-hardening@vger.kernel.org
---
 lib/Kconfig.debug            | 10 +++++++
 lib/kunit/.kunitconfig       |  1 +
 lib/tests/Makefile           |  1 +
 lib/tests/stacktrace_kunit.c | 51 ++++++++++++++++++++++++++++++++++++
 4 files changed, 63 insertions(+)
 create mode 100644 lib/tests/stacktrace_kunit.c

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index e97bdf3a42a8..51a6ac1a2461 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2716,6 +2716,16 @@ config BITOPS_KUNIT
 
 	  If unsure, say N.
 
+config STACKTRACE_KUNIT_TEST
+	tristate "KUnit test for stacktrace counted_by attribute" if !KUNIT_ALL_TESTS
+	depends on KUNIT
+	default KUNIT_ALL_TESTS
+	help
+	  This option enables the KUnit test for verifying the __counted_by_ptr
+	  attribute on struct stack_trace.
+
+	  If unsure, say N.
+
 config BITFIELD_KUNIT
 	tristate "KUnit test bitfield functions at runtime" if !KUNIT_ALL_TESTS
 	depends on KUNIT
diff --git a/lib/kunit/.kunitconfig b/lib/kunit/.kunitconfig
index 9235b7d42d38..b3761b41459e 100644
--- a/lib/kunit/.kunitconfig
+++ b/lib/kunit/.kunitconfig
@@ -1,3 +1,4 @@
 CONFIG_KUNIT=y
 CONFIG_KUNIT_TEST=y
 CONFIG_KUNIT_EXAMPLE_TEST=y
+CONFIG_STACKTRACE_KUNIT_TEST=y
diff --git a/lib/tests/Makefile b/lib/tests/Makefile
index 4ead57602eac..40875e729fc8 100644
--- a/lib/tests/Makefile
+++ b/lib/tests/Makefile
@@ -6,6 +6,7 @@
 CFLAGS_bitfield_kunit.o := $(DISABLE_STRUCTLEAK_PLUGIN)
 obj-$(CONFIG_BASE64_KUNIT) += base64_kunit.o
 obj-$(CONFIG_BITOPS_KUNIT) += bitops_kunit.o
+obj-$(CONFIG_STACKTRACE_KUNIT_TEST) += stacktrace_kunit.o
 obj-$(CONFIG_BITFIELD_KUNIT) += bitfield_kunit.o
 obj-$(CONFIG_BITS_TEST) += test_bits.o
 obj-$(CONFIG_SHDI3_KUNIT_TEST) += shdi3_kunit.o
diff --git a/lib/tests/stacktrace_kunit.c b/lib/tests/stacktrace_kunit.c
new file mode 100644
index 000000000000..7ec48edf84fe
--- /dev/null
+++ b/lib/tests/stacktrace_kunit.c
@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit test for struct stack_trace counted_by attribute.
+ */
+
+#include <kunit/test.h>
+#include <linux/stacktrace.h>
+
+#ifndef CONFIG_ARCH_STACKWALK
+static void test_stack_trace_counted_by(struct kunit *test)
+{
+	unsigned long entries_buf[4];
+	struct stack_trace trace = {
+		.entries = entries_buf,
+		.max_entries = 4,
+	};
+
+	KUNIT_EXPECT_EQ(test, trace.max_entries, 4U);
+	KUNIT_EXPECT_PTR_EQ(test, trace.entries, (unsigned long *)entries_buf);
+
+	/* Write to the allocated elements to verify access */
+	trace.entries[0] = 0xdeadbeef;
+	trace.entries[1] = 0xbeefcafe;
+	trace.entries[2] = 0xcafebabe;
+	trace.entries[3] = 0x12345678;
+
+	KUNIT_EXPECT_EQ(test, trace.entries[0], 0xdeadbeefUL);
+	KUNIT_EXPECT_EQ(test, trace.entries[1], 0xbeefcafeUL);
+	KUNIT_EXPECT_EQ(test, trace.entries[2], 0xcafebabeUL);
+	KUNIT_EXPECT_EQ(test, trace.entries[3], 0x12345678UL);
+}
+#else
+static void test_stack_trace_counted_by(struct kunit *test)
+{
+	kunit_skip(test, "CONFIG_ARCH_STACKWALK is enabled, struct stack_trace is not defined");
+}
+#endif
+
+static struct kunit_case stacktrace_test_cases[] = {
+	KUNIT_CASE(test_stack_trace_counted_by),
+	{}
+};
+
+static struct kunit_suite stacktrace_test_suite = {
+	.name = "stacktrace_counted_by",
+	.test_cases = stacktrace_test_cases,
+};
+
+kunit_test_suite(stacktrace_test_suite);
+
+MODULE_LICENSE("GPL");
-- 
2.55.0.860.g4b6b3295ed-goog