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

[Petr Mladek <pmladek@suse.com>]

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