Re: [PATCH v3 3/3] selftests: livepatch: Test livepatching a heavily called syscall

Marcos Paulo de Souza
2023-12-01T13:13:16Z

On Thu, Nov 30, 2023 at 04:24:26PM -0700, Shuah Khan wrote:
> 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@suse.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@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
> > 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@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;
> > +}
> > 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@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;
> > +
> > +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");
>
> Missing module name? Is there a reason to not name this module?

Can you please elaborate? This new module use the same MODULE_ macros used by
the current livepatch selftests. What do you mean by module name?

Thanks in advance,
Marcos

>
> thanks,
> -- Shuah