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

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

[Harry Hsu]

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@kernel.org>
Signed-off-by: Harry Hsu <x90613@gmail.com>
---
This is the selftest I promised in the v2 thread [1].

It applies on top of patch 1/3 of the series [2] and does not touch the
rest of it.  Petr, since you are going to post v4 of the whole patchset
anyway, please feel free to fold this in as the last patch.  Otherwise I
am happy to resend it as a separate follow-up once the series lands --
whichever is less work for you.

Tested on arm64 with CONFIG_LIVEPATCH=y:

  # ./test-alias.sh
  TEST: livepatch of two aliased symbols in one object ... ok
  TEST: aliased symbols in a module coming after the livepatch ... ok

[1] https://lore.kernel.org/all/CAPhsuW70RpkZ1ciioSjt6qkQePWyeic_L+98d0h-Ao3ze-TmkA@mail.gmail.com/
[2] https://lore.kernel.org/all/20260830173343.52759-1-x90613@gmail.com/

 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@gmail.com>
+
+. $(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@gmail.com>
+
+#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@gmail.com>");
+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@gmail.com>
+
+#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@gmail.com>");
+MODULE_DESCRIPTION("Livepatch test: target module with two aliased symbols");
-- 
2.43.0

Re: [PATCH] selftests/livepatch: Test rejection of aliased symbols in one object

[Petr Mladek]

On Sat 2026-09-05 23:55:07, Harry Hsu wrote:
> 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@kernel.org>
> Signed-off-by: Harry Hsu <x90613@gmail.com>

Looks good to me and seems to work:

Reviewed-by: Petr Mladek <pmladek@suse.com>
Tested-by: Petr Mladek <pmladek@suse.com>

> This is the selftest I promised in the v2 thread [1].
> 
> It applies on top of patch 1/3 of the series [2] and does not touch the
> rest of it.  Petr, since you are going to post v4 of the whole patchset
> anyway, please feel free to fold this in as the last patch.  Otherwise I
> am happy to resend it as a separate follow-up once the series lands --
> whichever is less work for you.

Yup, I am working on v4 and included this patch.

Best Regards,
Petr

Re: [PATCH] selftests/livepatch: Test rejection of aliased symbols in one object

[Song Liu]

On Sat, Sep 5, 2026 at 8:55 AM Harry Hsu <x90613@gmail.com> wrote:
>
> 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@kernel.org>
> Signed-off-by: Harry Hsu <x90613@gmail.com>

LGTM. Thanks for adding the test!

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