Message-ID: <f9d82fa6-08d7-4ab6-badc-691987b37a82@linuxfoundation.org>
Date:   Thu, 30 Nov 2023 16:24:26 -0700
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Marcos Paulo de Souza <mpdesouza@...e.com>,
        Shuah Khan <shuah@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>
Cc:     linux-kselftest@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        live-patching@...r.kernel.org,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v3 3/3] selftests: livepatch: Test livepatching a heavily
 called syscall

On 10/31/23 15:10, Marcos Paulo de Souza wrote:
> The test proves that a syscall can be livepatched. It is interesting
> because syscalls are called a tricky way. Also the process gets
> livepatched either when sleeping in the userspace or when entering
> or leaving the kernel space.
> 
> The livepatch is a bit tricky:
>    1. The syscall function name is architecture specific. Also
>       ARCH_HAS_SYSCALL_WRAPPER must be taken in account.
> 
>    2. The syscall must stay working the same way for other processes
>       on the system. It is solved by decrementing a counter only
>       for PIDs of the test processes. It means that the test processes
>       has to call the livepatched syscall at least once.
> 
> The test creates one userspace process per online cpu. The processes
> are calling getpid in a busy loop. The intention is to create random
> locations when the livepatch gets enabled. Nothing is guarantted.
> The magic is in the randomness.
> 
> Signed-off-by: Marcos Paulo de Souza <mpdesouza@...e.com>
> ---
>   tools/testing/selftests/livepatch/Makefile         |   4 +-
>   tools/testing/selftests/livepatch/test-syscall.sh  |  53 ++++++++++
>   .../selftests/livepatch/test_klp-call_getpid.c     |  44 ++++++++
>   .../selftests/livepatch/test_modules/Makefile      |   3 +-
>   .../livepatch/test_modules/test_klp_syscall.c      | 116 +++++++++++++++++++++
>   5 files changed, 218 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/livepatch/Makefile b/tools/testing/selftests/livepatch/Makefile
> index 119e2bbebe5d..35418a4790be 100644
> --- a/tools/testing/selftests/livepatch/Makefile
> +++ b/tools/testing/selftests/livepatch/Makefile
> @@ -1,5 +1,6 @@
>   # SPDX-License-Identifier: GPL-2.0
>   
> +TEST_GEN_FILES := test_klp-call_getpid
>   TEST_GEN_MODS_DIR := test_modules
>   TEST_PROGS_EXTENDED := functions.sh
>   TEST_PROGS := \
> @@ -8,7 +9,8 @@ TEST_PROGS := \
>   	test-shadow-vars.sh \
>   	test-state.sh \
>   	test-ftrace.sh \
> -	test-sysfs.sh
> +	test-sysfs.sh \
> +	test-syscall.sh
>   
>   TEST_FILES := settings
>   
> diff --git a/tools/testing/selftests/livepatch/test-syscall.sh b/tools/testing/selftests/livepatch/test-syscall.sh
> new file mode 100755
> index 000000000000..b76a881d4013
> --- /dev/null
> +++ b/tools/testing/selftests/livepatch/test-syscall.sh
> @@ -0,0 +1,53 @@
> +#!/bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (C) 2023 SUSE
> +# Author: Marcos Paulo de Souza <mpdesouza@...e.com>
> +
> +. $(dirname $0)/functions.sh
> +
> +MOD_SYSCALL=test_klp_syscall
> +
> +setup_config
> +
> +# - Start _NRPROC processes calling getpid and load a livepatch to patch the
> +#   getpid syscall. Check if all the processes transitioned to the livepatched
> +#   state.
> +
> +start_test "patch getpid syscall while being heavily hammered"
> +
> +for i in $(seq 1 $(getconf _NPROCESSORS_ONLN)); do
> +	./test_klp-call_getpid &
> +	pids[$i]="$!"
> +done
> +
> +pid_list=$(echo ${pids[@]} | tr ' ' ',')
> +load_lp $MOD_SYSCALL klp_pids=$pid_list
> +
> +# wait for all tasks to transition to patched state
> +loop_until 'grep -q '^0$' /sys/kernel/test_klp_syscall/npids'
> +
> +pending_pids=$(cat /sys/kernel/test_klp_syscall/npids)
> +log "$MOD_SYSCALL: Remaining not livepatched processes: $pending_pids"
> +
> +for pid in ${pids[@]}; do
> +	kill $pid || true
> +done
> +
> +disable_lp $MOD_SYSCALL
> +unload_lp $MOD_SYSCALL
> +
> +check_result "% insmod test_modules/$MOD_SYSCALL.ko klp_pids=$pid_list
> +livepatch: enabling patch '$MOD_SYSCALL'
> +livepatch: '$MOD_SYSCALL': initializing patching transition
> +livepatch: '$MOD_SYSCALL': starting patching transition
> +livepatch: '$MOD_SYSCALL': completing patching transition
> +livepatch: '$MOD_SYSCALL': patching complete
> +$MOD_SYSCALL: Remaining not livepatched processes: 0
> +% echo 0 > /sys/kernel/livepatch/$MOD_SYSCALL/enabled
> +livepatch: '$MOD_SYSCALL': initializing unpatching transition
> +livepatch: '$MOD_SYSCALL': starting unpatching transition
> +livepatch: '$MOD_SYSCALL': completing unpatching transition
> +livepatch: '$MOD_SYSCALL': unpatching complete
> +% rmmod $MOD_SYSCALL"
> +
> +exit 0
> diff --git a/tools/testing/selftests/livepatch/test_klp-call_getpid.c b/tools/testing/selftests/livepatch/test_klp-call_getpid.c
> new file mode 100644
> index 000000000000..ce321a2d7308
> --- /dev/null
> +++ b/tools/testing/selftests/livepatch/test_klp-call_getpid.c
> @@ -0,0 +1,44 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2023 SUSE
> + * Authors: Libor Pechacek <lpechacek@...e.cz>
> + *          Marcos Paulo de Souza <mpdesouza@...e.com>
> + */
> +
> +#include <stdio.h>
> +#include <unistd.h>
> +#include <sys/syscall.h>
> +#include <sys/types.h>
> +#include <signal.h>
> +
> +static int stop;
> +static int sig_int;
> +
> +void hup_handler(int signum)
> +{
> +	stop = 1;
> +}
> +
> +void int_handler(int signum)
> +{
> +	stop = 1;
> +	sig_int = 1;
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +	long count = 0;
> +
> +	signal(SIGHUP, &hup_handler);
> +	signal(SIGINT, &int_handler);
> +
> +	while (!stop) {
> +		(void)syscall(SYS_getpid);
> +		count++;
> +	}
> +
> +	if (sig_int)
> +		printf("%ld iterations done\n", count);
> +
> +	return 0;
> +}
> diff --git a/tools/testing/selftests/livepatch/test_modules/Makefile b/tools/testing/selftests/livepatch/test_modules/Makefile
> index 6f7c2103d27d..f5e880269bff 100644
> --- a/tools/testing/selftests/livepatch/test_modules/Makefile
> +++ b/tools/testing/selftests/livepatch/test_modules/Makefile
> @@ -10,7 +10,8 @@ obj-m += test_klp_atomic_replace.o \
>   	test_klp_state.o \
>   	test_klp_state2.o \
>   	test_klp_state3.o \
> -	test_klp_shadow_vars.o
> +	test_klp_shadow_vars.o \
> +	test_klp_syscall.o
>   
>   modules:
>   	$(Q)$(MAKE) -C $(KDIR) modules KBUILD_EXTMOD=$(TESTMODS_DIR)
> diff --git a/tools/testing/selftests/livepatch/test_modules/test_klp_syscall.c b/tools/testing/selftests/livepatch/test_modules/test_klp_syscall.c
> new file mode 100644
> index 000000000000..619496cc3481
> --- /dev/null
> +++ b/tools/testing/selftests/livepatch/test_modules/test_klp_syscall.c
> @@ -0,0 +1,116 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2017-2023 SUSE
> + * Authors: Libor Pechacek <lpechacek@...e.cz>
> + *          Nicolai Stange <nstange@...e.de>
> + *          Marcos Paulo de Souza <mpdesouza@...e.com>
> + */
> +
> +#include <linux/module.h>
> +#include <linux/kernel.h>
> +#include <linux/sched.h>
> +#include <linux/slab.h>
> +#include <linux/livepatch.h>
> +
> +#if defined(__x86_64__)
> +#define FN_PREFIX __x64_
> +#elif defined(__s390x__)
> +#define FN_PREFIX __s390x_
> +#elif defined(__aarch64__)
> +#define FN_PREFIX __arm64_
> +#else
> +/* powerpc does not select ARCH_HAS_SYSCALL_WRAPPER */
> +#define FN_PREFIX
> +#endif
> +
> +/* Protects klp_pids */
> +static DEFINE_MUTEX(kpid_mutex);
> +
> +static unsigned int npids, npids_pending;
> +static int klp_pids[NR_CPUS];
> +module_param_array(klp_pids, int, &npids_pending, 0);
> +MODULE_PARM_DESC(klp_pids, "Array of pids to be transitioned to livepatched state.");
> +
> +static ssize_t npids_show(struct kobject *kobj, struct kobj_attribute *attr,
> +			  char *buf)
> +{
> +	return sprintf(buf, "%u\n", npids_pending);
> +}
> +
> +static struct kobj_attribute klp_attr = __ATTR_RO(npids);
> +static struct kobject *klp_kobj;
> +
> +asmlinkage long lp_sys_getpid(void)
> +{
> +	int i;
> +
> +	mutex_lock(&kpid_mutex);
> +	if (npids_pending > 0) {
> +		for (i = 0; i < npids; i++) {
> +			if (current->pid == klp_pids[i]) {
> +				klp_pids[i] = 0;
> +				npids_pending--;
> +				break;
> +			}
> +		}
> +	}
> +	mutex_unlock(&kpid_mutex);
> +
> +	return task_tgid_vnr(current);
> +}
> +
> +static struct klp_func vmlinux_funcs[] = {
> +	{
> +		.old_name = __stringify(FN_PREFIX) "sys_getpid",
> +		.new_func = lp_sys_getpid,
> +	}, {}
> +};
> +
> +static struct klp_object objs[] = {
> +	{
> +		/* name being NULL means vmlinux */
> +		.funcs = vmlinux_funcs,
> +	}, {}
> +};
> +
> +static struct klp_patch patch = {
> +	.mod = THIS_MODULE,
> +	.objs = objs,
> +};
> +
> +static int livepatch_init(void)
> +{
> +	int ret;
> +
> +	klp_kobj = kobject_create_and_add("test_klp_syscall", kernel_kobj);
> +	if (!klp_kobj)
> +		return -ENOMEM;
> +
> +	ret = sysfs_create_file(klp_kobj, &klp_attr.attr);
> +	if (ret) {
> +		kobject_put(klp_kobj);
> +		return ret;
> +	}
> +
> +	/*
> +	 * Save the number pids to transition to livepatched state before the
> +	 * number of pending pids is decremented.
> +	 */
> +	npids = npids_pending;
> +
> +	return klp_enable_patch(&patch);
> +}
> +
> +static void livepatch_exit(void)
> +{
> +	kobject_put(klp_kobj);
> +}
> +
> +module_init(livepatch_init);
> +module_exit(livepatch_exit);
> +MODULE_LICENSE("GPL");
> +MODULE_INFO(livepatch, "Y");
> +MODULE_AUTHOR("Libor Pechacek <lpechacek@...e.cz>");
> +MODULE_AUTHOR("Nicolai Stange <nstange@...e.de>");
> +MODULE_AUTHOR("Marcos Paulo de Souza <mpdesouza@...e.com>");
> +MODULE_DESCRIPTION("Livepatch test: syscall transition");

Missing module name? Is there a reason to not name this module?

thanks,
-- Shuah

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