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Diffstat (limited to 'samples/livepatch/livepatch-shadow-mod.c')
| -rw-r--r-- | samples/livepatch/livepatch-shadow-mod.c | 217 |
1 files changed, 217 insertions, 0 deletions
diff --git a/samples/livepatch/livepatch-shadow-mod.c b/samples/livepatch/livepatch-shadow-mod.c new file mode 100644 index 0000000000..7e753b0d2f --- /dev/null +++ b/samples/livepatch/livepatch-shadow-mod.c @@ -0,0 +1,217 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com> + */ + +/* + * livepatch-shadow-mod.c - Shadow variables, buggy module demo + * + * Purpose + * ------- + * + * As a demonstration of livepatch shadow variable API, this module + * introduces memory leak behavior that livepatch modules + * livepatch-shadow-fix1.ko and livepatch-shadow-fix2.ko correct and + * enhance. + * + * WARNING - even though the livepatch-shadow-fix modules patch the + * memory leak, please load these modules at your own risk -- some + * amount of memory may leaked before the bug is patched. + * + * + * Usage + * ----- + * + * Step 1 - Load the buggy demonstration module: + * + * insmod samples/livepatch/livepatch-shadow-mod.ko + * + * Watch dmesg output for a few moments to see new dummy being allocated + * and a periodic cleanup check. (Note: a small amount of memory is + * being leaked.) + * + * + * Step 2 - Load livepatch fix1: + * + * insmod samples/livepatch/livepatch-shadow-fix1.ko + * + * Continue watching dmesg and note that now livepatch_fix1_dummy_free() + * and livepatch_fix1_dummy_alloc() are logging messages about leaked + * memory and eventually leaks prevented. + * + * + * Step 3 - Load livepatch fix2 (on top of fix1): + * + * insmod samples/livepatch/livepatch-shadow-fix2.ko + * + * This module extends functionality through shadow variables, as a new + * "check" counter is added to the dummy structure. Periodic dmesg + * messages will log these as dummies are cleaned up. + * + * + * Step 4 - Cleanup + * + * Unwind the demonstration by disabling the livepatch fix modules, then + * removing them and the demo module: + * + * echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix2/enabled + * echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix1/enabled + * rmmod livepatch-shadow-fix2 + * rmmod livepatch-shadow-fix1 + * rmmod livepatch-shadow-mod + */ + + +#include <linux/kernel.h> +#include <linux/module.h> +#include <linux/sched.h> +#include <linux/slab.h> +#include <linux/stat.h> +#include <linux/workqueue.h> + +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("Joe Lawrence <joe.lawrence@redhat.com>"); +MODULE_DESCRIPTION("Buggy module for shadow variable demo"); + +/* Allocate new dummies every second */ +#define ALLOC_PERIOD 1 +/* Check for expired dummies after a few new ones have been allocated */ +#define CLEANUP_PERIOD (3 * ALLOC_PERIOD) +/* Dummies expire after a few cleanup instances */ +#define EXPIRE_PERIOD (4 * CLEANUP_PERIOD) + +/* + * Keep a list of all the dummies so we can clean up any residual ones + * on module exit + */ +static LIST_HEAD(dummy_list); +static DEFINE_MUTEX(dummy_list_mutex); + +struct dummy { + struct list_head list; + unsigned long jiffies_expire; +}; + +static __used noinline struct dummy *dummy_alloc(void) +{ + struct dummy *d; + int *leak; + + d = kzalloc(sizeof(*d), GFP_KERNEL); + if (!d) + return NULL; + + d->jiffies_expire = jiffies + + msecs_to_jiffies(1000 * EXPIRE_PERIOD); + + /* Oops, forgot to save leak! */ + leak = kzalloc(sizeof(*leak), GFP_KERNEL); + if (!leak) { + kfree(d); + return NULL; + } + + pr_info("%s: dummy @ %p, expires @ %lx\n", + __func__, d, d->jiffies_expire); + + return d; +} + +static __used noinline void dummy_free(struct dummy *d) +{ + pr_info("%s: dummy @ %p, expired = %lx\n", + __func__, d, d->jiffies_expire); + + kfree(d); +} + +static __used noinline bool dummy_check(struct dummy *d, + unsigned long jiffies) +{ + return time_after(jiffies, d->jiffies_expire); +} + +/* + * alloc_work_func: allocates new dummy structures, allocates additional + * memory, aptly named "leak", but doesn't keep + * permanent record of it. + */ + +static void alloc_work_func(struct work_struct *work); +static DECLARE_DELAYED_WORK(alloc_dwork, alloc_work_func); + +static void alloc_work_func(struct work_struct *work) +{ + struct dummy *d; + + d = dummy_alloc(); + if (!d) + return; + + mutex_lock(&dummy_list_mutex); + list_add(&d->list, &dummy_list); + mutex_unlock(&dummy_list_mutex); + + schedule_delayed_work(&alloc_dwork, + msecs_to_jiffies(1000 * ALLOC_PERIOD)); +} + +/* + * cleanup_work_func: frees dummy structures. Without knownledge of + * "leak", it leaks the additional memory that + * alloc_work_func created. + */ + +static void cleanup_work_func(struct work_struct *work); +static DECLARE_DELAYED_WORK(cleanup_dwork, cleanup_work_func); + +static void cleanup_work_func(struct work_struct *work) +{ + struct dummy *d, *tmp; + unsigned long j; + + j = jiffies; + pr_info("%s: jiffies = %lx\n", __func__, j); + + mutex_lock(&dummy_list_mutex); + list_for_each_entry_safe(d, tmp, &dummy_list, list) { + + /* Kick out and free any expired dummies */ + if (dummy_check(d, j)) { + list_del(&d->list); + dummy_free(d); + } + } + mutex_unlock(&dummy_list_mutex); + + schedule_delayed_work(&cleanup_dwork, + msecs_to_jiffies(1000 * CLEANUP_PERIOD)); +} + +static int livepatch_shadow_mod_init(void) +{ + schedule_delayed_work(&alloc_dwork, + msecs_to_jiffies(1000 * ALLOC_PERIOD)); + schedule_delayed_work(&cleanup_dwork, + msecs_to_jiffies(1000 * CLEANUP_PERIOD)); + + return 0; +} + +static void livepatch_shadow_mod_exit(void) +{ + struct dummy *d, *tmp; + + /* Wait for any dummies at work */ + cancel_delayed_work_sync(&alloc_dwork); + cancel_delayed_work_sync(&cleanup_dwork); + + /* Cleanup residual dummies */ + list_for_each_entry_safe(d, tmp, &dummy_list, list) { + list_del(&d->list); + dummy_free(d); + } +} + +module_init(livepatch_shadow_mod_init); +module_exit(livepatch_shadow_mod_exit); |