[PATCH v4 2/5] selftests/livepatch: Test rejection of aliased symbols in one object

[Petr Mladek]

From: Harry Hsu <x90613@xxxxxxxxx>

klp_init_object_loaded() now rejects an object whose klp_funcs resolve to
the same address, because aliased symbols would push two klp_funcs of one
livepatch onto a single ops->func_stack and leave the redirection
ambiguous.

Add a target module providing test_klp_alias_show() together with its
__alias() sibling, and a livepatch naming both of them.  Two test cases
cover both callers of klp_init_object_loaded(): the klp_enable_patch()
path, where the target module is loaded before the livepatch, and the
klp_module_coming() path, where the livepatch is loaded first and the
module loader has to refuse the target module.

Suggested-by: Song Liu <song@xxxxxxxxxx>
Signed-off-by: Harry Hsu <x90613@xxxxxxxxx>
---
 tools/testing/selftests/livepatch/Makefile    |  3 +-
 .../testing/selftests/livepatch/test-alias.sh | 81 +++++++++++++++++++
 .../selftests/livepatch/test_modules/Makefile |  4 +-
 .../test_modules/test_klp_alias_patch.c       | 62 ++++++++++++++
 .../test_modules/test_klp_alias_target.c      | 48 +++++++++++
 5 files changed, 196 insertions(+), 2 deletions(-)
 create mode 100755 tools/testing/selftests/livepatch/test-alias.sh
 create mode 100644 tools/testing/selftests/livepatch/test_modules/test_klp_alias_patch.c
 create mode 100644 tools/testing/selftests/livepatch/test_modules/test_klp_alias_target.c

diff --git a/tools/testing/selftests/livepatch/Makefile b/tools/testing/selftests/livepatch/Makefile
index a080eb54a215..ddbeff4cb53d 100644
--- a/tools/testing/selftests/livepatch/Makefile
+++ b/tools/testing/selftests/livepatch/Makefile
@@ -11,7 +11,8 @@ TEST_PROGS := \
 	test-ftrace.sh \
 	test-sysfs.sh \
 	test-syscall.sh \
-	test-kprobe.sh
+	test-kprobe.sh \
+	test-alias.sh
 
 TEST_FILES := settings
 
diff --git a/tools/testing/selftests/livepatch/test-alias.sh b/tools/testing/selftests/livepatch/test-alias.sh
new file mode 100755
index 000000000000..4ae701de0dbf
--- /dev/null
+++ b/tools/testing/selftests/livepatch/test-alias.sh
@@ -0,0 +1,81 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2026 Harry Hsu <x90613@xxxxxxxxx>
+
+. $(dirname $0)/functions.sh
+
+MOD_TARGET=test_klp_alias_target
+MOD_LIVEPATCH=test_klp_alias_patch
+
+setup_config
+
+
+# $MOD_TARGET provides two symbols that share a single address.  A
+# livepatch naming both of them would push two klp_funcs of the same
+# patch onto one ops->func_stack, leaving the redirection ambiguous, so
+# klp_init_object_loaded() has to reject the object.
+#
+# - load the target module and verify it produces the original output
+# - verify that a livepatch naming both aliases fails to load
+# - verify that the target module has been left unpatched
+
+start_test "livepatch of two aliased symbols in one object"
+
+load_mod $MOD_TARGET
+
+if [[ "$(cat /proc/$MOD_TARGET)" != "$MOD_TARGET: original output" ]] ; then
+	echo -e "FAIL\n\n"
+	die "livepatch kselftest(s) failed"
+fi
+
+load_failing_mod $MOD_LIVEPATCH
+
+if [[ "$(cat /proc/$MOD_TARGET)" != "$MOD_TARGET: original output" ]] ; then
+	echo -e "FAIL\n\n"
+	die "livepatch kselftest(s) failed"
+fi
+
+unload_mod $MOD_TARGET
+
+check_result "% insmod test_modules/$MOD_TARGET.ko
+$MOD_TARGET: ${MOD_TARGET}_init
+% insmod test_modules/$MOD_LIVEPATCH.ko
+livepatch: 'test_klp_alias_show' and 'test_klp_alias_show_alias' resolve to the same address, aliased symbols are not supported
+insmod: ERROR: could not insert module test_modules/$MOD_LIVEPATCH.ko: Invalid parameters
+% rmmod $MOD_TARGET
+$MOD_TARGET: ${MOD_TARGET}_exit"
+
+
+# The same object is initialized from klp_module_coming() when the
+# livepatch is loaded while the target module is still absent.  There
+# the error has to be propagated to the module loader instead.
+#
+# - load the livepatch, it is accepted because the object is not loaded
+# - verify that loading the target module is refused afterwards
+
+start_test "aliased symbols in a module coming after the livepatch"
+
+load_lp $MOD_LIVEPATCH
+load_failing_mod $MOD_TARGET
+disable_lp $MOD_LIVEPATCH
+unload_lp $MOD_LIVEPATCH
+
+check_result "% insmod test_modules/$MOD_LIVEPATCH.ko
+livepatch: enabling patch '$MOD_LIVEPATCH'
+livepatch: '$MOD_LIVEPATCH': initializing patching transition
+livepatch: '$MOD_LIVEPATCH': starting patching transition
+livepatch: '$MOD_LIVEPATCH': completing patching transition
+livepatch: '$MOD_LIVEPATCH': patching complete
+% insmod test_modules/$MOD_TARGET.ko
+livepatch: 'test_klp_alias_show' and 'test_klp_alias_show_alias' resolve to the same address, aliased symbols are not supported
+livepatch: failed to initialize patch '$MOD_LIVEPATCH' for module '$MOD_TARGET' (-22)
+livepatch: patch '$MOD_LIVEPATCH' failed for module '$MOD_TARGET', refusing to load module '$MOD_TARGET'
+insmod: ERROR: could not insert module test_modules/$MOD_TARGET.ko: Invalid parameters
+% echo 0 > $SYSFS_KLP_DIR/$MOD_LIVEPATCH/enabled
+livepatch: '$MOD_LIVEPATCH': initializing unpatching transition
+livepatch: '$MOD_LIVEPATCH': starting unpatching transition
+livepatch: '$MOD_LIVEPATCH': completing unpatching transition
+livepatch: '$MOD_LIVEPATCH': unpatching complete
+% rmmod $MOD_LIVEPATCH"
+
+exit 0
diff --git a/tools/testing/selftests/livepatch/test_modules/Makefile b/tools/testing/selftests/livepatch/test_modules/Makefile
index a13d398585dc..532403e2b5ff 100644
--- a/tools/testing/selftests/livepatch/test_modules/Makefile
+++ b/tools/testing/selftests/livepatch/test_modules/Makefile
@@ -1,7 +1,9 @@
 TESTMODS_DIR := $(realpath $(dir $(abspath $(lastword $(MAKEFILE_LIST)))))
 KDIR ?= /lib/modules/$(shell uname -r)/build
 
-obj-m += test_klp_atomic_replace.o \
+obj-m += test_klp_alias_patch.o \
+	test_klp_alias_target.o \
+	test_klp_atomic_replace.o \
 	test_klp_callbacks_busy.o \
 	test_klp_callbacks_demo.o \
 	test_klp_callbacks_demo2.o \
diff --git a/tools/testing/selftests/livepatch/test_modules/test_klp_alias_patch.c b/tools/testing/selftests/livepatch/test_modules/test_klp_alias_patch.c
new file mode 100644
index 000000000000..1b50088bc92d
--- /dev/null
+++ b/tools/testing/selftests/livepatch/test_modules/test_klp_alias_patch.c
@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2026 Harry Hsu <x90613@xxxxxxxxx>
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/livepatch.h>
+#include <linux/seq_file.h>
+
+static int livepatch_alias_show(struct seq_file *m, void *v)
+{
+	seq_printf(m, "%s: %s\n", THIS_MODULE->name,
+		   "this has been live patched");
+	return 0;
+}
+
+/*
+ * Both names resolve to one address, so they end up on a single
+ * ops->func_stack and the redirection would be ambiguous.  Loading this
+ * livepatch is expected to fail.
+ */
+static struct klp_func funcs[] = {
+	{
+		.old_name = "test_klp_alias_show",
+		.new_func = livepatch_alias_show,
+	},
+	{
+		.old_name = "test_klp_alias_show_alias",
+		.new_func = livepatch_alias_show,
+	},
+	{},
+};
+
+static struct klp_object objs[] = {
+	{
+		.name = "test_klp_alias_target",
+		.funcs = funcs,
+	},
+	{},
+};
+
+static struct klp_patch patch = {
+	.mod = THIS_MODULE,
+	.objs = objs,
+};
+
+static int test_klp_alias_patch_init(void)
+{
+	return klp_enable_patch(&patch);
+}
+
+static void test_klp_alias_patch_exit(void)
+{
+}
+
+module_init(test_klp_alias_patch_init);
+module_exit(test_klp_alias_patch_exit);
+MODULE_LICENSE("GPL");
+MODULE_INFO(livepatch, "Y");
+MODULE_AUTHOR("Harry Hsu <x90613@xxxxxxxxx>");
+MODULE_DESCRIPTION("Livepatch test: patch two aliased symbols of one object");
diff --git a/tools/testing/selftests/livepatch/test_modules/test_klp_alias_target.c b/tools/testing/selftests/livepatch/test_modules/test_klp_alias_target.c
new file mode 100644
index 000000000000..b0f5fc35adf8
--- /dev/null
+++ b/tools/testing/selftests/livepatch/test_modules/test_klp_alias_target.c
@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2026 Harry Hsu <x90613@xxxxxxxxx>
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+
+static struct proc_dir_entry *pde;
+
+static noinline int test_klp_alias_show(struct seq_file *m, void *v)
+{
+	seq_printf(m, "%s: %s\n", THIS_MODULE->name, "original output");
+	return 0;
+}
+
+/*
+ * Alias the function above so that both names resolve to one address, the
+ * way __do_sys_fork(), __ia32_sys_fork() and __x64_sys_fork() do in vmlinux.
+ * Nothing calls the alias, it only has to show up in the module's symbol
+ * table for the livepatch to name it.
+ */
+static int test_klp_alias_show_alias(struct seq_file *m, void *v)
+	__used __alias(test_klp_alias_show);
+
+static int test_klp_alias_target_init(void)
+{
+	pr_info("%s\n", __func__);
+	pde = proc_create_single("test_klp_alias_target", 0, NULL,
+				 test_klp_alias_show);
+	if (!pde)
+		return -ENOMEM;
+	return 0;
+}
+
+static void test_klp_alias_target_exit(void)
+{
+	pr_info("%s\n", __func__);
+	proc_remove(pde);
+}
+
+module_init(test_klp_alias_target_init);
+module_exit(test_klp_alias_target_exit);
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Harry Hsu <x90613@xxxxxxxxx>");
+MODULE_DESCRIPTION("Livepatch test: target module with two aliased symbols");
-- 
2.55.0