[PATCH v3 8/8] livepatch: Add tests for klp-build toolchain

[Song Liu <song@kernel.org>]

Add selftests for the klp-build toolchain. This includes kernel side test
code and .patch files. The tests cover both livepatch to vmlinux and kernel
modules.

Check tools/testing/selftests/livepatch/test_patches/README for
instructions to run these tests.

Signed-off-by: Song Liu <song@kernel.org>

---

AI was used to wrote the test code and .patch files in this.
---
 kernel/livepatch/Kconfig                      |  20 +++
 kernel/livepatch/Makefile                     |   2 +
 kernel/livepatch/tests/Makefile               |   6 +
 kernel/livepatch/tests/klp_test_module.c      | 111 ++++++++++++++
 kernel/livepatch/tests/klp_test_module.h      |   8 +
 kernel/livepatch/tests/klp_test_vmlinux.c     | 138 ++++++++++++++++++
 kernel/livepatch/tests/klp_test_vmlinux.h     |  16 ++
 kernel/livepatch/tests/klp_test_vmlinux_aux.c |  59 ++++++++
 .../selftests/livepatch/test_patches/README   |  15 ++
 .../test_patches/klp_test_hash_change.patch   |  30 ++++
 .../test_patches/klp_test_module.patch        |  18 +++
 .../klp_test_nonstatic_to_static.patch        |  40 +++++
 .../klp_test_static_to_nonstatic.patch        |  39 +++++
 .../test_patches/klp_test_vmlinux.patch       |  18 +++
 14 files changed, 520 insertions(+)
 create mode 100644 kernel/livepatch/tests/Makefile
 create mode 100644 kernel/livepatch/tests/klp_test_module.c
 create mode 100644 kernel/livepatch/tests/klp_test_module.h
 create mode 100644 kernel/livepatch/tests/klp_test_vmlinux.c
 create mode 100644 kernel/livepatch/tests/klp_test_vmlinux.h
 create mode 100644 kernel/livepatch/tests/klp_test_vmlinux_aux.c
 create mode 100644 tools/testing/selftests/livepatch/test_patches/README
 create mode 100644 tools/testing/selftests/livepatch/test_patches/klp_test_hash_change.patch
 create mode 100644 tools/testing/selftests/livepatch/test_patches/klp_test_module.patch
 create mode 100644 tools/testing/selftests/livepatch/test_patches/klp_test_nonstatic_to_static.patch
 create mode 100644 tools/testing/selftests/livepatch/test_patches/klp_test_static_to_nonstatic.patch
 create mode 100644 tools/testing/selftests/livepatch/test_patches/klp_test_vmlinux.patch

diff --git a/kernel/livepatch/Kconfig b/kernel/livepatch/Kconfig
index 4c0a9c18d0b2..852049601389 100644
--- a/kernel/livepatch/Kconfig
+++ b/kernel/livepatch/Kconfig
@@ -30,3 +30,23 @@ config KLP_BUILD
 	select OBJTOOL
 	help
 	  Enable klp-build support
+
+config KLP_TEST
+	bool "Livepatch test code"
+	depends on LIVEPATCH
+	help
+	  Dummy kernel code for testing the klp-build livepatch toolchain.
+	  Provides built-in vmlinux functions with sysfs interfaces for
+	  verifying livepatches.
+
+	  If unsure, say N.
+
+config KLP_TEST_MODULE
+	tristate "Livepatch test module (klp_test_module)"
+	depends on KLP_TEST && m
+	help
+	  Test module for livepatch testing. Dummy kernel module for
+	  testing the klp-build toolchain. Provides sysfs interfaces for
+	  verifying livepatches.
+
+	  If unsure, say N.
diff --git a/kernel/livepatch/Makefile b/kernel/livepatch/Makefile
index cf03d4bdfc66..751080a62cec 100644
--- a/kernel/livepatch/Makefile
+++ b/kernel/livepatch/Makefile
@@ -2,3 +2,5 @@
 obj-$(CONFIG_LIVEPATCH) += livepatch.o
 
 livepatch-objs := core.o patch.o shadow.o state.o transition.o
+
+obj-$(CONFIG_KLP_TEST) += tests/
diff --git a/kernel/livepatch/tests/Makefile b/kernel/livepatch/tests/Makefile
new file mode 100644
index 000000000000..82ae48f54abe
--- /dev/null
+++ b/kernel/livepatch/tests/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
+obj-y                           += klp_test_vmlinux_all.o
+obj-$(CONFIG_KLP_TEST_MODULE)   += klp_test_module.o
+
+klp_test_vmlinux_all-y := klp_test_vmlinux.o \
+			   klp_test_vmlinux_aux.o
diff --git a/kernel/livepatch/tests/klp_test_module.c b/kernel/livepatch/tests/klp_test_module.c
new file mode 100644
index 000000000000..25cefbe36a2b
--- /dev/null
+++ b/kernel/livepatch/tests/klp_test_module.c
@@ -0,0 +1,111 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * klp_test_module.c - Single-file test module for livepatch/klp-build testing
+ *
+ * Copyright (C) 2026 Meta Platforms, Inc. and affiliates.
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/kobject.h>
+#include <linux/sysfs.h>
+#include <linux/string.h>
+#include "klp_test_module.h"
+#include "klp_test_vmlinux.h"
+
+static int klp_test_module_var1;
+static int klp_test_module_var2;
+
+static noinline ssize_t __klp_test_module_func1(char *buf, int len)
+{
+	ssize_t ret = 0;
+	int i;
+
+	for (i = 0; i < len; i++)
+		klp_test_module_var1 += i;
+
+	if (klp_test_module_var1 > 1000)
+		klp_test_module_var1 = 0;
+
+	ret = sysfs_emit(buf, "klp_test_module_func1 unpatched %d\n",
+			 klp_test_module_var1);
+	return ret;
+}
+
+ssize_t klp_test_module_func1(char *buf, int len)
+{
+	return __klp_test_module_func1(buf, len);
+}
+EXPORT_SYMBOL_GPL(klp_test_module_func1);
+
+static noinline ssize_t __klp_test_module_func2(char *buf, int len)
+{
+	ssize_t ret = 0;
+	int i;
+
+	for (i = 0; i < len; i++)
+		klp_test_module_var2 += i * 2;
+
+	if (klp_test_module_var2 > 1000)
+		klp_test_module_var2 = 0;
+
+	ret = sysfs_emit(buf, "klp_test_module_func2 unpatched %d\n",
+			 klp_test_module_var2);
+	return ret;
+}
+
+ssize_t klp_test_module_func2(char *buf, int len)
+{
+	return __klp_test_module_func2(buf, len);
+}
+EXPORT_SYMBOL_GPL(klp_test_module_func2);
+
+static ssize_t func1_show(struct kobject *kobj,
+			   struct kobj_attribute *attr, char *buf)
+{
+	return klp_test_module_func1(buf, 5);
+}
+
+static ssize_t func2_show(struct kobject *kobj,
+			   struct kobj_attribute *attr, char *buf)
+{
+	return klp_test_module_func2(buf, 5);
+}
+
+static struct kobj_attribute func1_attr = __ATTR_RO(func1);
+static struct kobj_attribute func2_attr = __ATTR_RO(func2);
+
+static struct attribute *klp_test_module_attrs[] = {
+	&func1_attr.attr,
+	&func2_attr.attr,
+	NULL,
+};
+
+static const struct attribute_group klp_test_module_attr_group = {
+	.attrs = klp_test_module_attrs,
+};
+
+static struct kobject *klp_test_module_kobj;
+
+static int __init klp_test_module_init(void)
+{
+	klp_test_module_kobj = kobject_create_and_add("module",
+						      klp_test_kobj);
+	if (!klp_test_module_kobj)
+		return -ENOMEM;
+
+	return sysfs_create_group(klp_test_module_kobj,
+				  &klp_test_module_attr_group);
+}
+
+static void __exit klp_test_module_exit(void)
+{
+	sysfs_remove_group(klp_test_module_kobj, &klp_test_module_attr_group);
+	kobject_put(klp_test_module_kobj);
+}
+
+module_init(klp_test_module_init);
+module_exit(klp_test_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Livepatch single-file test module");
diff --git a/kernel/livepatch/tests/klp_test_module.h b/kernel/livepatch/tests/klp_test_module.h
new file mode 100644
index 000000000000..56a766f4744b
--- /dev/null
+++ b/kernel/livepatch/tests/klp_test_module.h
@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _KLP_TEST_MODULE_H
+#define _KLP_TEST_MODULE_H
+
+ssize_t klp_test_module_func1(char *buf, int len);
+ssize_t klp_test_module_func2(char *buf, int len);
+
+#endif /* _KLP_TEST_MODULE_H */
diff --git a/kernel/livepatch/tests/klp_test_vmlinux.c b/kernel/livepatch/tests/klp_test_vmlinux.c
new file mode 100644
index 000000000000..bd4157ea97c0
--- /dev/null
+++ b/kernel/livepatch/tests/klp_test_vmlinux.c
@@ -0,0 +1,138 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * klp_test_vmlinux.c - Dummy built-in code for livepatch/klp-build testing
+ *
+ * Copyright (C) 2026 Meta Platforms, Inc. and affiliates.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/kobject.h>
+#include <linux/sysfs.h>
+#include <linux/init.h>
+#include <linux/string.h>
+#include "klp_test_vmlinux.h"
+
+static int klp_test_vmlinux_var1;
+static int klp_test_vmlinux_var2;
+
+static noinline int __helper(int x, int len)
+{
+	int i, sum = x;
+
+	for (i = 0; i < len; i++)
+		sum += i + 5;
+	if (sum > 1000)
+		sum = 0;
+	return sum;
+}
+
+static noinline ssize_t __klp_test_vmlinux_func1(char *buf, int len)
+{
+	ssize_t ret = 0;
+
+	klp_test_vmlinux_var1 = __helper(klp_test_vmlinux_var1, len);
+
+	ret = sysfs_emit(buf, "klp_test_vmlinux_func1 unpatched %d\n",
+			 klp_test_vmlinux_var1);
+	return ret;
+}
+
+ssize_t klp_test_vmlinux_func1(char *buf, int len)
+{
+	return __klp_test_vmlinux_func1(buf, len);
+}
+EXPORT_SYMBOL_GPL(klp_test_vmlinux_func1);
+
+static noinline ssize_t __klp_test_vmlinux_func2(char *buf, int len)
+{
+	ssize_t ret = 0;
+	int i;
+
+	for (i = 0; i < len; i++)
+		klp_test_vmlinux_var2 += i * 2;
+
+	if (klp_test_vmlinux_var2 > 1000)
+		klp_test_vmlinux_var2 = 0;
+
+	ret = sysfs_emit(buf, "klp_test_vmlinux_func2 unpatched %d\n",
+			 klp_test_vmlinux_var2);
+	return ret;
+}
+
+ssize_t klp_test_vmlinux_func2(char *buf, int len)
+{
+	return __klp_test_vmlinux_func2(buf, len);
+}
+EXPORT_SYMBOL_GPL(klp_test_vmlinux_func2);
+
+static ssize_t vmlinux_func1_show(struct kobject *kobj,
+				   struct kobj_attribute *attr, char *buf)
+{
+	return klp_test_vmlinux_func1(buf, 5);
+}
+
+static ssize_t vmlinux_func2_show(struct kobject *kobj,
+				   struct kobj_attribute *attr, char *buf)
+{
+	return klp_test_vmlinux_func2(buf, 5);
+}
+
+static struct kobj_attribute vmlinux_func1_attr = __ATTR_RO(vmlinux_func1);
+static struct kobj_attribute vmlinux_func2_attr = __ATTR_RO(vmlinux_func2);
+
+static struct attribute *klp_test_attrs[] = {
+	&vmlinux_func1_attr.attr,
+	&vmlinux_func2_attr.attr,
+	NULL,
+};
+
+static const struct attribute_group klp_test_attr_group = {
+	.attrs = klp_test_attrs,
+};
+
+static struct kobject *klp_test_vmlinux_kobj;
+struct kobject *klp_test_kobj;
+EXPORT_SYMBOL_GPL(klp_test_kobj);
+
+static int __init klp_test_vmlinux_init(void)
+{
+	int ret;
+
+	klp_test_kobj = kobject_create_and_add("klp_test", kernel_kobj);
+	if (!klp_test_kobj)
+		return -ENOMEM;
+
+	klp_test_vmlinux_kobj = kobject_create_and_add("vmlinux", klp_test_kobj);
+	if (!klp_test_vmlinux_kobj) {
+		kobject_put(klp_test_kobj);
+		return -ENOMEM;
+	}
+
+	ret = sysfs_create_group(klp_test_vmlinux_kobj, &klp_test_attr_group);
+	if (ret)
+		goto err_group;
+
+	ret = klp_test_vmlinux_aux_init(klp_test_vmlinux_kobj);
+	if (ret)
+		goto err_aux;
+
+	return 0;
+
+err_aux:
+	sysfs_remove_group(klp_test_vmlinux_kobj, &klp_test_attr_group);
+err_group:
+	kobject_put(klp_test_vmlinux_kobj);
+	kobject_put(klp_test_kobj);
+	return ret;
+}
+
+static void __exit klp_test_vmlinux_exit(void)
+{
+	klp_test_vmlinux_aux_exit(klp_test_vmlinux_kobj);
+	sysfs_remove_group(klp_test_vmlinux_kobj, &klp_test_attr_group);
+	kobject_put(klp_test_vmlinux_kobj);
+	kobject_put(klp_test_kobj);
+}
+
+late_initcall(klp_test_vmlinux_init);
diff --git a/kernel/livepatch/tests/klp_test_vmlinux.h b/kernel/livepatch/tests/klp_test_vmlinux.h
new file mode 100644
index 000000000000..56d9f7b6d350
--- /dev/null
+++ b/kernel/livepatch/tests/klp_test_vmlinux.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _KLP_TEST_VMLINUX_H
+#define _KLP_TEST_VMLINUX_H
+
+#include <linux/kobject.h>
+
+extern struct kobject *klp_test_kobj;
+
+ssize_t klp_test_vmlinux_func1(char *buf, int len);
+ssize_t klp_test_vmlinux_func2(char *buf, int len);
+ssize_t klp_test_vmlinux_func3(char *buf, int len);
+
+int klp_test_vmlinux_aux_init(struct kobject *parent);
+void klp_test_vmlinux_aux_exit(struct kobject *parent);
+
+#endif /* _KLP_TEST_VMLINUX_H */
diff --git a/kernel/livepatch/tests/klp_test_vmlinux_aux.c b/kernel/livepatch/tests/klp_test_vmlinux_aux.c
new file mode 100644
index 000000000000..1d76b0308a11
--- /dev/null
+++ b/kernel/livepatch/tests/klp_test_vmlinux_aux.c
@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * klp_test_vmlinux_aux.c - Auxiliary built-in code for livepatch/klp-build
+ *                          testing. This file has its own static __helper()
+ *                          to test ThinLTO .llvm.<hash> suffix handling.
+ *
+ * Copyright (C) 2026 Meta Platforms, Inc. and affiliates.
+ */
+
+#include <linux/kernel.h>
+#include <linux/kobject.h>
+#include <linux/sysfs.h>
+#include <linux/string.h>
+#include "klp_test_vmlinux.h"
+
+static int klp_test_vmlinux_var3;
+
+static noinline int __helper(int x, int len)
+{
+	int i, sum = x;
+
+	for (i = 0; i < len; i++)
+		sum += i + 10;
+	if (sum > 1000)
+		sum = 0;
+	return sum;
+}
+
+static noinline ssize_t __klp_test_vmlinux_func3(char *buf, int len)
+{
+	klp_test_vmlinux_var3 = __helper(klp_test_vmlinux_var3, len);
+
+	return sysfs_emit(buf, "klp_test_vmlinux_func3 unpatched %d\n",
+			 klp_test_vmlinux_var3);
+}
+
+ssize_t klp_test_vmlinux_func3(char *buf, int len)
+{
+	return __klp_test_vmlinux_func3(buf, len);
+}
+EXPORT_SYMBOL_GPL(klp_test_vmlinux_func3);
+
+static ssize_t vmlinux_func3_show(struct kobject *kobj,
+				   struct kobj_attribute *attr, char *buf)
+{
+	return klp_test_vmlinux_func3(buf, 5);
+}
+
+static struct kobj_attribute vmlinux_func3_attr = __ATTR_RO(vmlinux_func3);
+
+int klp_test_vmlinux_aux_init(struct kobject *parent)
+{
+	return sysfs_create_file(parent, &vmlinux_func3_attr.attr);
+}
+
+void klp_test_vmlinux_aux_exit(struct kobject *parent)
+{
+	sysfs_remove_file(parent, &vmlinux_func3_attr.attr);
+}
diff --git a/tools/testing/selftests/livepatch/test_patches/README b/tools/testing/selftests/livepatch/test_patches/README
new file mode 100644
index 000000000000..8266348aab57
--- /dev/null
+++ b/tools/testing/selftests/livepatch/test_patches/README
@@ -0,0 +1,15 @@
+This is folder contains patches to test the klp-build toolchain.
+
+To run the test:
+
+1. Enable CONFIG_KLP_TEST and CONFIG_KLP_TEST_MODULE, and build the kernel.
+
+2. Build these patches with:
+
+  ./scripts/livepatch/klp-build tools/testing/selftests/livepatch/test_patches/*.patch
+
+3. Verify the correctness with:
+
+  modprobe klp_test_module
+  kpatch load livepatch-patch.ko
+  grep -q unpatched /sys/kernel/klp_test/*/* && echo FAIL || echo PASS
diff --git a/tools/testing/selftests/livepatch/test_patches/klp_test_hash_change.patch b/tools/testing/selftests/livepatch/test_patches/klp_test_hash_change.patch
new file mode 100644
index 000000000000..609d54d6d6f6
--- /dev/null
+++ b/tools/testing/selftests/livepatch/test_patches/klp_test_hash_change.patch
@@ -0,0 +1,30 @@
+Test ThinLTO .llvm.<hash> suffix handling.
+
+Modify a static __helper() function whose body change causes its
+.llvm.<hash> suffix to change under ThinLTO. Both klp_test_vmlinux.c
+and klp_test_vmlinux_aux.c define static __helper() with different
+bodies, so ThinLTO promotes both to globals with different hashes.
+This patch changes the __helper() in the aux file, which changes its
+hash, and klp-build must correctly match the old and new symbols.
+
+diff --git i/kernel/livepatch/tests/klp_test_vmlinux_aux.c w/kernel/livepatch/tests/klp_test_vmlinux_aux.c
+--- i/kernel/livepatch/tests/klp_test_vmlinux_aux.c
++++ w/kernel/livepatch/tests/klp_test_vmlinux_aux.c
+@@ -20,7 +20,7 @@
+ 	int i, sum = x;
+ 
+ 	for (i = 0; i < len; i++)
+-		sum += i + 10;
++		sum += i * 2 + 10;
+ 	if (sum > 1000)
+ 		sum = 0;
+ 	return sum;
+@@ -30,7 +30,7 @@
+ {
+ 	klp_test_vmlinux_var3 = __helper(klp_test_vmlinux_var3, len);
+ 
+-	return sysfs_emit(buf, "klp_test_vmlinux_func3 unpatched %d\n",
++	return sysfs_emit(buf, "klp_test_vmlinux_func3 hash_patched %d\n",
+ 			 klp_test_vmlinux_var3);
+ }
+ 
diff --git a/tools/testing/selftests/livepatch/test_patches/klp_test_module.patch b/tools/testing/selftests/livepatch/test_patches/klp_test_module.patch
new file mode 100644
index 000000000000..d86e75618136
--- /dev/null
+++ b/tools/testing/selftests/livepatch/test_patches/klp_test_module.patch
@@ -0,0 +1,18 @@
+Test basic module patching.
+
+Patch a loadable module function to verify that klp-build can generate
+a livepatch for module code. Changes __klp_test_module_func1() output
+from "unpatched" to "patched".
+
+diff --git i/kernel/livepatch/tests/klp_test_module.c w/kernel/livepatch/tests/klp_test_module.c
+--- i/kernel/livepatch/tests/klp_test_module.c
++++ w/kernel/livepatch/tests/klp_test_module.c
+@@ -27,7 +27,7 @@
+ 	if (klp_test_module_var1 > 1000)
+ 		klp_test_module_var1 = 0;
+ 
+-	ret = sysfs_emit(buf, "klp_test_module_func1 unpatched %d\n",
++	ret = sysfs_emit(buf, "klp_test_module_func1 patched %d\n",
+ 			 klp_test_module_var1);
+ 	return ret;
+ }
diff --git a/tools/testing/selftests/livepatch/test_patches/klp_test_nonstatic_to_static.patch b/tools/testing/selftests/livepatch/test_patches/klp_test_nonstatic_to_static.patch
new file mode 100644
index 000000000000..f26711c6bfac
--- /dev/null
+++ b/tools/testing/selftests/livepatch/test_patches/klp_test_nonstatic_to_static.patch
@@ -0,0 +1,40 @@
+Test nonstatic-to-static symbol change.
+
+Change klp_test_module_func2() from nonstatic (global) to static and
+remove its EXPORT_SYMBOL_GPL. Also remove its declaration from the
+header file. This tests klp-build's ability to handle symbol visibility
+changes where a function that was originally global becomes static in
+the patched kernel.
+
+diff --git i/kernel/livepatch/tests/klp_test_module.c w/kernel/livepatch/tests/klp_test_module.c
+--- i/kernel/livepatch/tests/klp_test_module.c
++++ w/kernel/livepatch/tests/klp_test_module.c
+@@ -49,16 +49,15 @@
+ 	if (klp_test_module_var2 > 1000)
+ 		klp_test_module_var2 = 0;
+
+-	ret = sysfs_emit(buf, "klp_test_module_func2 unpatched %d\n",
++	ret = sysfs_emit(buf, "klp_test_module_func2 patched_nts %d\n",
+ 			 klp_test_module_var2);
+ 	return ret;
+ }
+
+-ssize_t klp_test_module_func2(char *buf, int len)
++static noinline ssize_t klp_test_module_func2(char *buf, int len)
+ {
+ 	return __klp_test_module_func2(buf, len);
+ }
+-EXPORT_SYMBOL_GPL(klp_test_module_func2);
+
+ static ssize_t func1_show(struct kobject *kobj,
+ 			   struct kobj_attribute *attr, char *buf)
+diff --git i/kernel/livepatch/tests/klp_test_module.h w/kernel/livepatch/tests/klp_test_module.h
+--- i/kernel/livepatch/tests/klp_test_module.h
++++ w/kernel/livepatch/tests/klp_test_module.h
+@@ -3,6 +3,5 @@
+ #define _KLP_TEST_MODULE_H
+
+ ssize_t klp_test_module_func1(char *buf, int len);
+-ssize_t klp_test_module_func2(char *buf, int len);
+
+ #endif /* _KLP_TEST_MODULE_H */
diff --git a/tools/testing/selftests/livepatch/test_patches/klp_test_static_to_nonstatic.patch b/tools/testing/selftests/livepatch/test_patches/klp_test_static_to_nonstatic.patch
new file mode 100644
index 000000000000..673f6c42f698
--- /dev/null
+++ b/tools/testing/selftests/livepatch/test_patches/klp_test_static_to_nonstatic.patch
@@ -0,0 +1,39 @@
+Test static-to-nonstatic symbol change.
+
+Change __klp_test_vmlinux_func2() from static to nonstatic (global).
+This tests klp-build's ability to handle symbol visibility changes
+where a function that was originally static becomes globally visible
+in the patched kernel.
+
+diff --git i/kernel/livepatch/tests/klp_test_vmlinux.c w/kernel/livepatch/tests/klp_test_vmlinux.c
+--- i/kernel/livepatch/tests/klp_test_vmlinux.c
++++ w/kernel/livepatch/tests/klp_test_vmlinux.c
+@@ -44,7 +44,7 @@
+ }
+ EXPORT_SYMBOL_GPL(klp_test_vmlinux_func1);
+
+-static noinline ssize_t __klp_test_vmlinux_func2(char *buf, int len)
++noinline ssize_t __klp_test_vmlinux_func2(char *buf, int len)
+ {
+ 	ssize_t ret = 0;
+ 	int i;
+@@ -55,7 +55,7 @@
+ 	if (klp_test_vmlinux_var2 > 1000)
+ 		klp_test_vmlinux_var2 = 0;
+
+-	ret = sysfs_emit(buf, "klp_test_vmlinux_func2 unpatched %d\n",
++	ret = sysfs_emit(buf, "klp_test_vmlinux_func2 patched_stn %d\n",
+ 			 klp_test_vmlinux_var2);
+ 	return ret;
+ }
+diff --git i/kernel/livepatch/tests/klp_test_vmlinux.h w/kernel/livepatch/tests/klp_test_vmlinux.h
+--- i/kernel/livepatch/tests/klp_test_vmlinux.h
++++ w/kernel/livepatch/tests/klp_test_vmlinux.h
+@@ -9,6 +9,7 @@
+ ssize_t klp_test_vmlinux_func1(char *buf, int len);
+ ssize_t klp_test_vmlinux_func2(char *buf, int len);
+ ssize_t klp_test_vmlinux_func3(char *buf, int len);
++ssize_t __klp_test_vmlinux_func2(char *buf, int len);
+
+ int klp_test_vmlinux_aux_init(struct kobject *parent);
+ void klp_test_vmlinux_aux_exit(struct kobject *parent);
diff --git a/tools/testing/selftests/livepatch/test_patches/klp_test_vmlinux.patch b/tools/testing/selftests/livepatch/test_patches/klp_test_vmlinux.patch
new file mode 100644
index 000000000000..8b1d91381728
--- /dev/null
+++ b/tools/testing/selftests/livepatch/test_patches/klp_test_vmlinux.patch
@@ -0,0 +1,18 @@
+Test basic vmlinux patching.
+
+Patch a built-in vmlinux function to verify that klp-build can generate
+a livepatch for vmlinux code. Changes __klp_test_vmlinux_func1() output
+from "unpatched" to "patched".
+
+diff --git i/kernel/livepatch/tests/klp_test_vmlinux.c w/kernel/livepatch/tests/klp_test_vmlinux.c
+--- i/kernel/livepatch/tests/klp_test_vmlinux.c
++++ w/kernel/livepatch/tests/klp_test_vmlinux.c
+@@ -33,7 +33,7 @@
+ 
+ 	klp_test_vmlinux_var1 = __helper(klp_test_vmlinux_var1, len);
+ 
+-	ret = sysfs_emit(buf, "klp_test_vmlinux_func1 unpatched %d\n",
++	ret = sysfs_emit(buf, "klp_test_vmlinux_func1 patched %d\n",
+ 			 klp_test_vmlinux_var1);
+ 	return ret;
+ }
-- 
2.47.3