livepatch: introduce shadow variable API

[linux-2.6-microblaze.git] / samples / livepatch / livepatch-shadow-fix1.c

diff --git a/samples/livepatch/livepatch-shadow-fix1.c b/samples/livepatch/livepatch-shadow-fix1.c
new file mode 100644 (file)
index 0000000..fbe0a1f
--- /dev/null
+++ b/samples/livepatch/livepatch-shadow-fix1.c
@@ -0,0 +1,173 @@
+/*
+ * 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-fix1.c - Shadow variables, livepatch demo
+ *
+ * Purpose
+ * -------
+ *
+ * Fixes the memory leak introduced in livepatch-shadow-mod through the
+ * use of a shadow variable.  This fix demonstrates the "extending" of
+ * short-lived data structures by patching its allocation and release
+ * functions.
+ *
+ *
+ * Usage
+ * -----
+ *
+ * This module is not intended to be standalone.  See the "Usage"
+ * section of livepatch-shadow-mod.c.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/livepatch.h>
+#include <linux/slab.h>
+
+/* Shadow variable enums */
+#define SV_LEAK                1
+
+/* 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)
+
+struct dummy {
+       struct list_head list;
+       unsigned long jiffies_expire;
+};
+
+struct dummy *livepatch_fix1_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);
+
+       /*
+        * Patch: save the extra memory location into a SV_LEAK shadow
+        * variable.  A patched dummy_free routine can later fetch this
+        * pointer to handle resource release.
+        */
+       leak = kzalloc(sizeof(int), GFP_KERNEL);
+       klp_shadow_alloc(d, SV_LEAK, &leak, sizeof(leak), GFP_KERNEL);
+
+       pr_info("%s: dummy @ %p, expires @ %lx\n",
+               __func__, d, d->jiffies_expire);
+
+       return d;
+}
+
+void livepatch_fix1_dummy_free(struct dummy *d)
+{
+       void **shadow_leak, *leak;
+
+       /*
+        * Patch: fetch the saved SV_LEAK shadow variable, detach and
+        * free it.  Note: handle cases where this shadow variable does
+        * not exist (ie, dummy structures allocated before this livepatch
+        * was loaded.)
+        */
+       shadow_leak = klp_shadow_get(d, SV_LEAK);
+       if (shadow_leak) {
+               leak = *shadow_leak;
+               klp_shadow_free(d, SV_LEAK);
+               kfree(leak);
+               pr_info("%s: dummy @ %p, prevented leak @ %p\n",
+                        __func__, d, leak);
+       } else {
+               pr_info("%s: dummy @ %p leaked!\n", __func__, d);
+       }
+
+       kfree(d);
+}
+
+static struct klp_func funcs[] = {
+       {
+               .old_name = "dummy_alloc",
+               .new_func = livepatch_fix1_dummy_alloc,
+       },
+       {
+               .old_name = "dummy_free",
+               .new_func = livepatch_fix1_dummy_free,
+       }, { }
+};
+
+static struct klp_object objs[] = {
+       {
+               .name = "livepatch_shadow_mod",
+               .funcs = funcs,
+       }, { }
+};
+
+static struct klp_patch patch = {
+       .mod = THIS_MODULE,
+       .objs = objs,
+};
+
+static int livepatch_shadow_fix1_init(void)
+{
+       int ret;
+
+       if (!klp_have_reliable_stack() && !patch.immediate) {
+               /*
+                * WARNING: Be very careful when using 'patch.immediate' in
+                * your patches.  It's ok to use it for simple patches like
+                * this, but for more complex patches which change function
+                * semantics, locking semantics, or data structures, it may not
+                * be safe.  Use of this option will also prevent removal of
+                * the patch.
+                *
+                * See Documentation/livepatch/livepatch.txt for more details.
+                */
+               patch.immediate = true;
+               pr_notice("The consistency model isn't supported for your architecture.  Bypassing safety mechanisms and applying the patch immediately.\n");
+       }
+
+       ret = klp_register_patch(&patch);
+       if (ret)
+               return ret;
+       ret = klp_enable_patch(&patch);
+       if (ret) {
+               WARN_ON(klp_unregister_patch(&patch));
+               return ret;
+       }
+       return 0;
+}
+
+static void livepatch_shadow_fix1_exit(void)
+{
+       /* Cleanup any existing SV_LEAK shadow variables */
+       klp_shadow_free_all(SV_LEAK);
+
+       WARN_ON(klp_unregister_patch(&patch));
+}
+
+module_init(livepatch_shadow_fix1_init);
+module_exit(livepatch_shadow_fix1_exit);
+MODULE_LICENSE("GPL");
+MODULE_INFO(livepatch, "Y");