[PATCH v2] selftests: livepatch: test livepatching a kprobed function

[PATCH v2] selftests: livepatch: test livepatching a kprobed function

[Michael Vetter]

The test proves that a function that is being kprobed and uses a
post_handler cannot be livepatched.

Only one ftrace_ops with FTRACE_OPS_FL_IPMODIFY set may be registered
to any given function at a time.

Signed-off-by: Michael Vetter <mvetter@suse.com>
---
V2:
Save and restore kprobe state.

 tools/testing/selftests/livepatch/Makefile    |  3 +-
 .../selftests/livepatch/test-kprobe.sh        | 65 +++++++++++++++++++
 .../selftests/livepatch/test_modules/Makefile |  3 +-
 .../livepatch/test_modules/test_klp_kprobe.c  | 38 +++++++++++
 4 files changed, 107 insertions(+), 2 deletions(-)
 create mode 100755 tools/testing/selftests/livepatch/test-kprobe.sh
 create mode 100644 tools/testing/selftests/livepatch/test_modules/test_klp_kprobe.c

diff --git a/tools/testing/selftests/livepatch/Makefile b/tools/testing/selftests/livepatch/Makefile
index 35418a4790be..a080eb54a215 100644
--- a/tools/testing/selftests/livepatch/Makefile
+++ b/tools/testing/selftests/livepatch/Makefile
@@ -10,7 +10,8 @@ TEST_PROGS := \
 	test-state.sh \
 	test-ftrace.sh \
 	test-sysfs.sh \
-	test-syscall.sh
+	test-syscall.sh \
+	test-kprobe.sh
 
 TEST_FILES := settings
 
diff --git a/tools/testing/selftests/livepatch/test-kprobe.sh b/tools/testing/selftests/livepatch/test-kprobe.sh
new file mode 100755
index 000000000000..fb7e9914f4a0
--- /dev/null
+++ b/tools/testing/selftests/livepatch/test-kprobe.sh
@@ -0,0 +1,65 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2024 SUSE
+# Author: Michael Vetter <mvetter@suse.com>
+
+. $(dirname $0)/functions.sh
+
+MOD_LIVEPATCH=test_klp_livepatch
+MOD_KPROBE=test_klp_kprobe
+
+setup_config
+
+# Kprobe a function and verify that we can't livepatch that same function
+# when it uses a post_handler since only one IPMODIFY maybe be registered
+# to any given function at a time.
+
+start_test "livepatch interaction with kprobed function with post_handler"
+
+STATE=$(cat /sys/kernel/debug/kprobes/enabled)
+echo 1 > /sys/kernel/debug/kprobes/enabled
+
+load_mod $MOD_KPROBE has_post_handler=true
+load_failing_mod $MOD_LIVEPATCH
+unload_mod $MOD_KPROBE
+
+check_result "% insmod test_modules/test_klp_kprobe.ko has_post_handler=true
+% insmod test_modules/$MOD_LIVEPATCH.ko
+livepatch: enabling patch '$MOD_LIVEPATCH'
+livepatch: '$MOD_LIVEPATCH': initializing patching transition
+livepatch: failed to register ftrace handler for function 'cmdline_proc_show' (-16)
+livepatch: failed to patch object 'vmlinux'
+livepatch: failed to enable patch '$MOD_LIVEPATCH'
+livepatch: '$MOD_LIVEPATCH': canceling patching transition, going to unpatch
+livepatch: '$MOD_LIVEPATCH': completing unpatching transition
+livepatch: '$MOD_LIVEPATCH': unpatching complete
+insmod: ERROR: could not insert module test_modules/$MOD_LIVEPATCH.ko: Device or resource busy
+% rmmod test_klp_kprobe"
+
+start_test "livepatch interaction with kprobed function without post_handler"
+
+load_mod $MOD_KPROBE has_post_handler=false
+load_lp $MOD_LIVEPATCH
+
+unload_mod $MOD_KPROBE
+disable_lp $MOD_LIVEPATCH
+unload_lp $MOD_LIVEPATCH
+
+check_result "% insmod test_modules/test_klp_kprobe.ko has_post_handler=false
+% insmod test_modules/$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: '$MOD_LIVEPATCH': patching complete
+% rmmod test_klp_kprobe
+% echo 0 > /sys/kernel/livepatch/$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"
+
+echo $STATE > /sys/kernel/debug/kprobes/enabled
+
+exit 0
diff --git a/tools/testing/selftests/livepatch/test_modules/Makefile b/tools/testing/selftests/livepatch/test_modules/Makefile
index e6e638c4bcba..4981d270f128 100644
--- a/tools/testing/selftests/livepatch/test_modules/Makefile
+++ b/tools/testing/selftests/livepatch/test_modules/Makefile
@@ -11,7 +11,8 @@ obj-m += test_klp_atomic_replace.o \
 	test_klp_state2.o \
 	test_klp_state3.o \
 	test_klp_shadow_vars.o \
-	test_klp_syscall.o
+	test_klp_syscall.o \
+	test_klp_kprobe.o
 
 # Ensure that KDIR exists, otherwise skip the compilation
 modules:
diff --git a/tools/testing/selftests/livepatch/test_modules/test_klp_kprobe.c b/tools/testing/selftests/livepatch/test_modules/test_klp_kprobe.c
new file mode 100644
index 000000000000..49b579ea1054
--- /dev/null
+++ b/tools/testing/selftests/livepatch/test_modules/test_klp_kprobe.c
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2024 Marcos Paulo de Souza <mpdesouza@suse.com>
+// Copyright (C) 2024 Michael Vetter <mvetter@suse.com>
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/kprobes.h>
+
+static bool has_post_handler = true;
+module_param(has_post_handler, bool, 0444);
+
+static void __kprobes post_handler(struct kprobe *p, struct pt_regs *regs,
+				unsigned long flags)
+{
+}
+
+static struct kprobe kp = {
+	.symbol_name = "cmdline_proc_show",
+};
+
+static int __init kprobe_init(void)
+{
+	if (has_post_handler)
+		kp.post_handler = post_handler;
+
+	return register_kprobe(&kp);
+}
+
+static void __exit kprobe_exit(void)
+{
+	unregister_kprobe(&kp);
+}
+
+module_init(kprobe_init)
+module_exit(kprobe_exit)
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Michael Vetter <mvetter@suse.com>");
+MODULE_DESCRIPTION("Livepatch test: livepatch kprobed function");
-- 
2.46.0

Re: [PATCH v2] selftests: livepatch: test livepatching a kprobed function

[Petr Mladek]

On Tue 2024-09-17 15:50:53, Michael Vetter wrote:
> The test proves that a function that is being kprobed and uses a
> post_handler cannot be livepatched.
> 
> Only one ftrace_ops with FTRACE_OPS_FL_IPMODIFY set may be registered
> to any given function at a time.
> 
> --- /dev/null
> +++ b/tools/testing/selftests/livepatch/test-kprobe.sh
> @@ -0,0 +1,65 @@
> +#!/bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (C) 2024 SUSE
> +# Author: Michael Vetter <mvetter@suse.com>
> +
> +. $(dirname $0)/functions.sh
> +
> +MOD_LIVEPATCH=test_klp_livepatch
> +MOD_KPROBE=test_klp_kprobe
> +
> +setup_config
> +
> +# Kprobe a function and verify that we can't livepatch that same function
> +# when it uses a post_handler since only one IPMODIFY maybe be registered
> +# to any given function at a time.
> +
> +start_test "livepatch interaction with kprobed function with post_handler"
> +
> +STATE=$(cat /sys/kernel/debug/kprobes/enabled)
> +echo 1 > /sys/kernel/debug/kprobes/enabled
> +
> +load_mod $MOD_KPROBE has_post_handler=true
> +load_failing_mod $MOD_LIVEPATCH
> +unload_mod $MOD_KPROBE
[...]
> +echo $STATE > /sys/kernel/debug/kprobes/enabled

The original state won't get restored when the test fails.

A better solution would be to integrate this into setup_config()
and cleanup() in /tools/testing/selftests/livepatch/functions.sh

Also it would be great to avoid hard-coding /sys/kernel/debug.
See KLP_SYSFS_DIR="/sys/kernel/livepatch" in
/tools/testing/selftests/livepatch/functions.sh

I would replace it with:

KERNEL_SYSFS_DIR="/sys/kernel"
KLP_SYSFS_DIR="$KERNEL_SYSFS_DIR/livepatch"
DEBUG_SYSFS_DIR="$KERNEL_SYSFS_DIR/debug"
KPROBES_SYSFS_DIR="$DEBUG_SYSFS_DIR/kprobes"

It would actually look better with switched ordering:

SYSFS_KERNEL_DIR="/sys/kernel"
SYSFS_KLP_DIR="$SYSFS_KERNEL_DIR/livepatch"
SYSFS_DEBUG_DIR="$SYSFS_KERNEL_DIR/debug"
SYSFS_KPROBES_DIR="$SYSFS_DEBUG_DIR/kprobes"

But this would require renaming KLP_SYSFS_DIR everywhere in
a separate (prerequisite) patch. It would be nice but
I do not want to force you to do it ;-)

> --- a/tools/testing/selftests/livepatch/test_modules/Makefile
> +++ b/tools/testing/selftests/livepatch/test_modules/Makefile
> @@ -11,7 +11,8 @@ obj-m += test_klp_atomic_replace.o \
>  	test_klp_state2.o \
>  	test_klp_state3.o \
>  	test_klp_shadow_vars.o \
> -	test_klp_syscall.o
> +	test_klp_syscall.o \
> +	test_klp_kprobe.o

Nit: Please, put it in alphabetical order. It is not a big deal.
     The ordering helps searching. The list already is almost sorted.
     And the patch needs to be updated anyway.

>  # Ensure that KDIR exists, otherwise skip the compilation
>  modules:
> diff --git a/tools/testing/selftests/livepatch/test_modules/test_klp_kprobe.c b/tools/testing/selftests/livepatch/test_modules/test_klp_kprobe.c
> new file mode 100644
> index 000000000000..49b579ea1054
> --- /dev/null
> +++ b/tools/testing/selftests/livepatch/test_modules/test_klp_kprobe.c
> @@ -0,0 +1,38 @@
[...]
> +module_init(kprobe_init)
> +module_exit(kprobe_exit)
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Michael Vetter <mvetter@suse.com>");
> +MODULE_DESCRIPTION("Livepatch test: livepatch kprobed function");

Nit: The module adds a kprobe. I would invert the logic:

MODULE_DESCRIPTION("Livepatch test: kprobe livepatched function");

Best Regards,
Petr