selftests: livepatch: Test livepatching a heavily called syscall

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.

Reviewed-by: Joe Lawrence <joe.lawrence@redhat.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

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
 

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@suse.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

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@suse.cz>
+ *          Marcos Paulo de Souza <mpdesouza@suse.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;
+}

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)

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@suse.cz>
+ *          Nicolai Stange <nstange@suse.de>
+ *          Marcos Paulo de Souza <mpdesouza@suse.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;
+
+static 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@suse.cz>");
+MODULE_AUTHOR("Nicolai Stange <nstange@suse.de>");
+MODULE_AUTHOR("Marcos Paulo de Souza <mpdesouza@suse.com>");
+MODULE_DESCRIPTION("Livepatch test: syscall transition");