1 files changed, 224 insertions, 0 deletions

diff --git a/samples/livepatch/livepatch-shadow-mod.c b/samples/livepatch/livepatch-shadow-mod.c
new file mode 100644
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+++ b/samples/livepatch/livepatch-shadow-mod.c
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+/*
+ * Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * 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
+ */
+LIST_HEAD(dummy_list);
+DEFINE_MUTEX(dummy_list_mutex);
+
+struct dummy {
+        struct list_head list;
+        unsigned long jiffies_expire;
+};
+
+noinline struct dummy *dummy_alloc(void)
+{
+        struct dummy *d;
+        void *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(int), GFP_KERNEL);
+
+        pr_info("%s: dummy @ %p, expires @ %lx\n",
+                __func__, d, d->jiffies_expire);
+
+        return d;
+}
+
+noinline void dummy_free(struct dummy *d)
+{
+        pr_info("%s: dummy @ %p, expired = %lx\n",
+                __func__, d, d->jiffies_expire);
+
+        kfree(d);
+}
+
+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);