1 files changed, 1015 insertions, 0 deletions

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
new file mode 100644
index 000000000000..782172f073c5
--- /dev/null
+++ b/kernel/livepatch/core.c
@@ -0,0 +1,1015 @@
+/*
+ * core.c - Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
+ * Copyright (C) 2014 SUSE
+ *
+ * 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/>.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+#include <linux/ftrace.h>
+#include <linux/list.h>
+#include <linux/kallsyms.h>
+#include <linux/livepatch.h>
+
+/**
+ * struct klp_ops - structure for tracking registered ftrace ops structs
+ *
+ * A single ftrace_ops is shared between all enabled replacement functions
+ * (klp_func structs) which have the same old_addr.  This allows the switch
+ * between function versions to happen instantaneously by updating the klp_ops
+ * struct's func_stack list.  The winner is the klp_func at the top of the
+ * func_stack (front of the list).
+ *
+ * @node:       node for the global klp_ops list
+ * @func_stack: list head for the stack of klp_func's (active func is on top)
+ * @fops:       registered ftrace ops struct
+ */
+struct klp_ops {
+        struct list_head node;
+        struct list_head func_stack;
+        struct ftrace_ops fops;
+};
+
+/*
+ * The klp_mutex protects the global lists and state transitions of any
+ * structure reachable from them.  References to any structure must be obtained
+ * under mutex protection (except in klp_ftrace_handler(), which uses RCU to
+ * ensure it gets consistent data).
+ */
+static DEFINE_MUTEX(klp_mutex);
+
+static LIST_HEAD(klp_patches);
+static LIST_HEAD(klp_ops);
+
+static struct kobject *klp_root_kobj;
+
+static struct klp_ops *klp_find_ops(unsigned long old_addr)
+{
+        struct klp_ops *ops;
+        struct klp_func *func;
+
+        list_for_each_entry(ops, &klp_ops, node) {
+                func = list_first_entry(&ops->func_stack, struct klp_func,
+                                        stack_node);
+                if (func->old_addr == old_addr)
+                        return ops;
+        }
+
+        return NULL;
+}
+
+static bool klp_is_module(struct klp_object *obj)
+{
+        return obj->name;
+}
+
+static bool klp_is_object_loaded(struct klp_object *obj)
+{
+        return !obj->name || obj->mod;
+}
+
+/* sets obj->mod if object is not vmlinux and module is found */
+static void klp_find_object_module(struct klp_object *obj)
+{
+        if (!klp_is_module(obj))
+                return;
+
+        mutex_lock(&module_mutex);
+        /*
+         * We don't need to take a reference on the module here because we have
+         * the klp_mutex, which is also taken by the module notifier.  This
+         * prevents any module from unloading until we release the klp_mutex.
+         */
+        obj->mod = find_module(obj->name);
+        mutex_unlock(&module_mutex);
+}
+
+/* klp_mutex must be held by caller */
+static bool klp_is_patch_registered(struct klp_patch *patch)
+{
+        struct klp_patch *mypatch;
+
+        list_for_each_entry(mypatch, &klp_patches, list)
+                if (mypatch == patch)
+                        return true;
+
+        return false;
+}
+
+static bool klp_initialized(void)
+{
+        return klp_root_kobj;
+}
+
+struct klp_find_arg {
+        const char *objname;
+        const char *name;
+        unsigned long addr;
+        /*
+         * If count == 0, the symbol was not found. If count == 1, a unique
+         * match was found and addr is set.  If count > 1, there is
+         * unresolvable ambiguity among "count" number of symbols with the same
+         * name in the same object.
+         */
+        unsigned long count;
+};
+
+static int klp_find_callback(void *data, const char *name,
+                             struct module *mod, unsigned long addr)
+{
+        struct klp_find_arg *args = data;
+
+        if ((mod && !args->objname) || (!mod && args->objname))
+                return 0;
+
+        if (strcmp(args->name, name))
+                return 0;
+
+        if (args->objname && strcmp(args->objname, mod->name))
+                return 0;
+
+        /*
+         * args->addr might be overwritten if another match is found
+         * but klp_find_object_symbol() handles this and only returns the
+         * addr if count == 1.
+         */
+        args->addr = addr;
+        args->count++;
+
+        return 0;
+}
+
+static int klp_find_object_symbol(const char *objname, const char *name,
+                                  unsigned long *addr)
+{
+        struct klp_find_arg args = {
+                .objname = objname,
+                .name = name,
+                .addr = 0,
+                .count = 0
+        };
+
+        kallsyms_on_each_symbol(klp_find_callback, &args);
+
+        if (args.count == 0)
+                pr_err("symbol '%s' not found in symbol table\n", name);
+        else if (args.count > 1)
+                pr_err("unresolvable ambiguity (%lu matches) on symbol '%s' in object '%s'\n",
+                       args.count, name, objname);
+        else {
+                *addr = args.addr;
+                return 0;
+        }
+
+        *addr = 0;
+        return -EINVAL;
+}
+
+struct klp_verify_args {
+        const char *name;
+        const unsigned long addr;
+};
+
+static int klp_verify_callback(void *data, const char *name,
+                               struct module *mod, unsigned long addr)
+{
+        struct klp_verify_args *args = data;
+
+        if (!mod &&
+            !strcmp(args->name, name) &&
+            args->addr == addr)
+                return 1;
+
+        return 0;
+}
+
+static int klp_verify_vmlinux_symbol(const char *name, unsigned long addr)
+{
+        struct klp_verify_args args = {
+                .name = name,
+                .addr = addr,
+        };
+
+        if (kallsyms_on_each_symbol(klp_verify_callback, &args))
+                return 0;
+
+        pr_err("symbol '%s' not found at specified address 0x%016lx, kernel mismatch?\n",
+                name, addr);
+        return -EINVAL;
+}
+
+static int klp_find_verify_func_addr(struct klp_object *obj,
+                                     struct klp_func *func)
+{
+        int ret;
+
+#if defined(CONFIG_RANDOMIZE_BASE)
+        /* KASLR is enabled, disregard old_addr from user */
+        func->old_addr = 0;
+#endif
+
+        if (!func->old_addr || klp_is_module(obj))
+                ret = klp_find_object_symbol(obj->name, func->old_name,
+                                             &func->old_addr);
+        else
+                ret = klp_verify_vmlinux_symbol(func->old_name,
+                                                func->old_addr);
+
+        return ret;
+}
+
+/*
+ * external symbols are located outside the parent object (where the parent
+ * object is either vmlinux or the kmod being patched).
+ */
+static int klp_find_external_symbol(struct module *pmod, const char *name,
+                                    unsigned long *addr)
+{
+        const struct kernel_symbol *sym;
+
+        /* first, check if it's an exported symbol */
+        preempt_disable();
+        sym = find_symbol(name, NULL, NULL, true, true);
+        preempt_enable();
+        if (sym) {
+                *addr = sym->value;
+                return 0;
+        }
+
+        /* otherwise check if it's in another .o within the patch module */
+        return klp_find_object_symbol(pmod->name, name, addr);
+}
+
+static int klp_write_object_relocations(struct module *pmod,
+                                        struct klp_object *obj)
+{
+        int ret;
+        struct klp_reloc *reloc;
+
+        if (WARN_ON(!klp_is_object_loaded(obj)))
+                return -EINVAL;
+
+        if (WARN_ON(!obj->relocs))
+                return -EINVAL;
+
+        for (reloc = obj->relocs; reloc->name; reloc++) {
+                if (!klp_is_module(obj)) {
+                        ret = klp_verify_vmlinux_symbol(reloc->name,
+                                                        reloc->val);
+                        if (ret)
+                                return ret;
+                } else {
+                        /* module, reloc->val needs to be discovered */
+                        if (reloc->external)
+                                ret = klp_find_external_symbol(pmod,
+                                                               reloc->name,
+                                                               &reloc->val);
+                        else
+                                ret = klp_find_object_symbol(obj->mod->name,
+                                                             reloc->name,
+                                                             &reloc->val);
+                        if (ret)
+                                return ret;
+                }
+                ret = klp_write_module_reloc(pmod, reloc->type, reloc->loc,
+                                             reloc->val + reloc->addend);
+                if (ret) {
+                        pr_err("relocation failed for symbol '%s' at 0x%016lx (%d)\n",
+                               reloc->name, reloc->val, ret);
+                        return ret;
+                }
+        }
+
+        return 0;
+}
+
+static void notrace klp_ftrace_handler(unsigned long ip,
+                                       unsigned long parent_ip,
+                                       struct ftrace_ops *fops,
+                                       struct pt_regs *regs)
+{
+        struct klp_ops *ops;
+        struct klp_func *func;
+
+        ops = container_of(fops, struct klp_ops, fops);
+
+        rcu_read_lock();
+        func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
+                                      stack_node);
+        if (WARN_ON_ONCE(!func))
+                goto unlock;
+
+        klp_arch_set_pc(regs, (unsigned long)func->new_func);
+unlock:
+        rcu_read_unlock();
+}
+
+static int klp_disable_func(struct klp_func *func)
+{
+        struct klp_ops *ops;
+        int ret;
+
+        if (WARN_ON(func->state != KLP_ENABLED))
+                return -EINVAL;
+
+        if (WARN_ON(!func->old_addr))
+                return -EINVAL;
+
+        ops = klp_find_ops(func->old_addr);
+        if (WARN_ON(!ops))
+                return -EINVAL;
+
+        if (list_is_singular(&ops->func_stack)) {
+                ret = unregister_ftrace_function(&ops->fops);
+                if (ret) {
+                        pr_err("failed to unregister ftrace handler for function '%s' (%d)\n",
+                               func->old_name, ret);
+                        return ret;
+                }
+
+                ret = ftrace_set_filter_ip(&ops->fops, func->old_addr, 1, 0);
+                if (ret)
+                        pr_warn("function unregister succeeded but failed to clear the filter\n");
+
+                list_del_rcu(&func->stack_node);
+                list_del(&ops->node);
+                kfree(ops);
+        } else {
+                list_del_rcu(&func->stack_node);
+        }
+
+        func->state = KLP_DISABLED;
+
+        return 0;
+}
+
+static int klp_enable_func(struct klp_func *func)
+{
+        struct klp_ops *ops;
+        int ret;
+
+        if (WARN_ON(!func->old_addr))
+                return -EINVAL;
+
+        if (WARN_ON(func->state != KLP_DISABLED))
+                return -EINVAL;
+
+        ops = klp_find_ops(func->old_addr);
+        if (!ops) {
+                ops = kzalloc(sizeof(*ops), GFP_KERNEL);
+                if (!ops)
+                        return -ENOMEM;
+
+                ops->fops.func = klp_ftrace_handler;
+                ops->fops.flags = FTRACE_OPS_FL_SAVE_REGS |
+                                  FTRACE_OPS_FL_DYNAMIC |
+                                  FTRACE_OPS_FL_IPMODIFY;
+
+                list_add(&ops->node, &klp_ops);
+
+                INIT_LIST_HEAD(&ops->func_stack);
+                list_add_rcu(&func->stack_node, &ops->func_stack);
+
+                ret = ftrace_set_filter_ip(&ops->fops, func->old_addr, 0, 0);
+                if (ret) {
+                        pr_err("failed to set ftrace filter for function '%s' (%d)\n",
+                               func->old_name, ret);
+                        goto err;
+                }
+
+                ret = register_ftrace_function(&ops->fops);
+                if (ret) {
+                        pr_err("failed to register ftrace handler for function '%s' (%d)\n",
+                               func->old_name, ret);
+                        ftrace_set_filter_ip(&ops->fops, func->old_addr, 1, 0);
+                        goto err;
+                }
+
+
+        } else {
+                list_add_rcu(&func->stack_node, &ops->func_stack);
+        }
+
+        func->state = KLP_ENABLED;
+
+        return 0;
+
+err:
+        list_del_rcu(&func->stack_node);
+        list_del(&ops->node);
+        kfree(ops);
+        return ret;
+}
+
+static int klp_disable_object(struct klp_object *obj)
+{
+        struct klp_func *func;
+        int ret;
+
+        for (func = obj->funcs; func->old_name; func++) {
+                if (func->state != KLP_ENABLED)
+                        continue;
+
+                ret = klp_disable_func(func);
+                if (ret)
+                        return ret;
+        }
+
+        obj->state = KLP_DISABLED;
+
+        return 0;
+}
+
+static int klp_enable_object(struct klp_object *obj)
+{
+        struct klp_func *func;
+        int ret;
+
+        if (WARN_ON(obj->state != KLP_DISABLED))
+                return -EINVAL;
+
+        if (WARN_ON(!klp_is_object_loaded(obj)))
+                return -EINVAL;
+
+        for (func = obj->funcs; func->old_name; func++) {
+                ret = klp_enable_func(func);
+                if (ret)
+                        goto unregister;
+        }
+        obj->state = KLP_ENABLED;
+
+        return 0;
+
+unregister:
+        WARN_ON(klp_disable_object(obj));
+        return ret;
+}
+
+static int __klp_disable_patch(struct klp_patch *patch)
+{
+        struct klp_object *obj;
+        int ret;
+
+        /* enforce stacking: only the last enabled patch can be disabled */
+        if (!list_is_last(&patch->list, &klp_patches) &&
+            list_next_entry(patch, list)->state == KLP_ENABLED)
+                return -EBUSY;
+
+        pr_notice("disabling patch '%s'\n", patch->mod->name);
+
+        for (obj = patch->objs; obj->funcs; obj++) {
+                if (obj->state != KLP_ENABLED)
+                        continue;
+
+                ret = klp_disable_object(obj);
+                if (ret)
+                        return ret;
+        }
+
+        patch->state = KLP_DISABLED;
+
+        return 0;
+}
+
+/**
+ * klp_disable_patch() - disables a registered patch
+ * @patch:      The registered, enabled patch to be disabled
+ *
+ * Unregisters the patched functions from ftrace.
+ *
+ * Return: 0 on success, otherwise error
+ */
+int klp_disable_patch(struct klp_patch *patch)
+{
+        int ret;
+
+        mutex_lock(&klp_mutex);
+
+        if (!klp_is_patch_registered(patch)) {
+                ret = -EINVAL;
+                goto err;
+        }
+
+        if (patch->state == KLP_DISABLED) {
+                ret = -EINVAL;
+                goto err;
+        }
+
+        ret = __klp_disable_patch(patch);
+
+err:
+        mutex_unlock(&klp_mutex);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(klp_disable_patch);
+
+static int __klp_enable_patch(struct klp_patch *patch)
+{
+        struct klp_object *obj;
+        int ret;
+
+        if (WARN_ON(patch->state != KLP_DISABLED))
+                return -EINVAL;
+
+        /* enforce stacking: only the first disabled patch can be enabled */
+        if (patch->list.prev != &klp_patches &&
+            list_prev_entry(patch, list)->state == KLP_DISABLED)
+                return -EBUSY;
+
+        pr_notice_once("tainting kernel with TAINT_LIVEPATCH\n");
+        add_taint(TAINT_LIVEPATCH, LOCKDEP_STILL_OK);
+
+        pr_notice("enabling patch '%s'\n", patch->mod->name);
+
+        for (obj = patch->objs; obj->funcs; obj++) {
+                klp_find_object_module(obj);
+
+                if (!klp_is_object_loaded(obj))
+                        continue;
+
+                ret = klp_enable_object(obj);
+                if (ret)
+                        goto unregister;
+        }
+
+        patch->state = KLP_ENABLED;
+
+        return 0;
+
+unregister:
+        WARN_ON(__klp_disable_patch(patch));
+        return ret;
+}
+
+/**
+ * klp_enable_patch() - enables a registered patch
+ * @patch:      The registered, disabled patch to be enabled
+ *
+ * Performs the needed symbol lookups and code relocations,
+ * then registers the patched functions with ftrace.
+ *
+ * Return: 0 on success, otherwise error
+ */
+int klp_enable_patch(struct klp_patch *patch)
+{
+        int ret;
+
+        mutex_lock(&klp_mutex);
+
+        if (!klp_is_patch_registered(patch)) {
+                ret = -EINVAL;
+                goto err;
+        }
+
+        ret = __klp_enable_patch(patch);
+
+err:
+        mutex_unlock(&klp_mutex);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(klp_enable_patch);
+
+/*
+ * Sysfs Interface
+ *
+ * /sys/kernel/livepatch
+ * /sys/kernel/livepatch/<patch>
+ * /sys/kernel/livepatch/<patch>/enabled
+ * /sys/kernel/livepatch/<patch>/<object>
+ * /sys/kernel/livepatch/<patch>/<object>/<func>
+ */
+
+static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
+                             const char *buf, size_t count)
+{
+        struct klp_patch *patch;
+        int ret;
+        unsigned long val;
+
+        ret = kstrtoul(buf, 10, &val);
+        if (ret)
+                return -EINVAL;
+
+        if (val != KLP_DISABLED && val != KLP_ENABLED)
+                return -EINVAL;
+
+        patch = container_of(kobj, struct klp_patch, kobj);
+
+        mutex_lock(&klp_mutex);
+
+        if (val == patch->state) {
+                /* already in requested state */
+                ret = -EINVAL;
+                goto err;
+        }
+
+        if (val == KLP_ENABLED) {
+                ret = __klp_enable_patch(patch);
+                if (ret)
+                        goto err;
+        } else {
+                ret = __klp_disable_patch(patch);
+                if (ret)
+                        goto err;
+        }
+
+        mutex_unlock(&klp_mutex);
+
+        return count;
+
+err:
+        mutex_unlock(&klp_mutex);
+        return ret;
+}
+
+static ssize_t enabled_show(struct kobject *kobj,
+                            struct kobj_attribute *attr, char *buf)
+{
+        struct klp_patch *patch;
+
+        patch = container_of(kobj, struct klp_patch, kobj);
+        return snprintf(buf, PAGE_SIZE-1, "%d\n", patch->state);
+}
+
+static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled);
+static struct attribute *klp_patch_attrs[] = {
+        &enabled_kobj_attr.attr,
+        NULL
+};
+
+static void klp_kobj_release_patch(struct kobject *kobj)
+{
+        /*
+         * Once we have a consistency model we'll need to module_put() the
+         * patch module here.  See klp_register_patch() for more details.
+         */
+}
+
+static struct kobj_type klp_ktype_patch = {
+        .release = klp_kobj_release_patch,
+        .sysfs_ops = &kobj_sysfs_ops,
+        .default_attrs = klp_patch_attrs,
+};
+
+static void klp_kobj_release_func(struct kobject *kobj)
+{
+}
+
+static struct kobj_type klp_ktype_func = {
+        .release = klp_kobj_release_func,
+        .sysfs_ops = &kobj_sysfs_ops,
+};
+
+/*
+ * Free all functions' kobjects in the array up to some limit. When limit is
+ * NULL, all kobjects are freed.
+ */
+static void klp_free_funcs_limited(struct klp_object *obj,
+                                   struct klp_func *limit)
+{
+        struct klp_func *func;
+
+        for (func = obj->funcs; func->old_name && func != limit; func++)
+                kobject_put(&func->kobj);
+}
+
+/* Clean up when a patched object is unloaded */
+static void klp_free_object_loaded(struct klp_object *obj)
+{
+        struct klp_func *func;
+
+        obj->mod = NULL;
+
+        for (func = obj->funcs; func->old_name; func++)
+                func->old_addr = 0;
+}
+
+/*
+ * Free all objects' kobjects in the array up to some limit. When limit is
+ * NULL, all kobjects are freed.
+ */
+static void klp_free_objects_limited(struct klp_patch *patch,
+                                     struct klp_object *limit)
+{
+        struct klp_object *obj;
+
+        for (obj = patch->objs; obj->funcs && obj != limit; obj++) {
+                klp_free_funcs_limited(obj, NULL);
+                kobject_put(obj->kobj);
+        }
+}
+
+static void klp_free_patch(struct klp_patch *patch)
+{
+        klp_free_objects_limited(patch, NULL);
+        if (!list_empty(&patch->list))
+                list_del(&patch->list);
+        kobject_put(&patch->kobj);
+}
+
+static int klp_init_func(struct klp_object *obj, struct klp_func *func)
+{
+        INIT_LIST_HEAD(&func->stack_node);
+        func->state = KLP_DISABLED;
+
+        return kobject_init_and_add(&func->kobj, &klp_ktype_func,
+                                    obj->kobj, "%s", func->old_name);
+}
+
+/* parts of the initialization that is done only when the object is loaded */
+static int klp_init_object_loaded(struct klp_patch *patch,
+                                  struct klp_object *obj)
+{
+        struct klp_func *func;
+        int ret;
+
+        if (obj->relocs) {
+                ret = klp_write_object_relocations(patch->mod, obj);
+                if (ret)
+                        return ret;
+        }
+
+        for (func = obj->funcs; func->old_name; func++) {
+                ret = klp_find_verify_func_addr(obj, func);
+                if (ret)
+                        return ret;
+        }
+
+        return 0;
+}
+
+static int klp_init_object(struct klp_patch *patch, struct klp_object *obj)
+{
+        struct klp_func *func;
+        int ret;
+        const char *name;
+
+        if (!obj->funcs)
+                return -EINVAL;
+
+        obj->state = KLP_DISABLED;
+
+        klp_find_object_module(obj);
+
+        name = klp_is_module(obj) ? obj->name : "vmlinux";
+        obj->kobj = kobject_create_and_add(name, &patch->kobj);
+        if (!obj->kobj)
+                return -ENOMEM;
+
+        for (func = obj->funcs; func->old_name; func++) {
+                ret = klp_init_func(obj, func);
+                if (ret)
+                        goto free;
+        }
+
+        if (klp_is_object_loaded(obj)) {
+                ret = klp_init_object_loaded(patch, obj);
+                if (ret)
+                        goto free;
+        }
+
+        return 0;
+
+free:
+        klp_free_funcs_limited(obj, func);
+        kobject_put(obj->kobj);
+        return ret;
+}
+
+static int klp_init_patch(struct klp_patch *patch)
+{
+        struct klp_object *obj;
+        int ret;
+
+        if (!patch->objs)
+                return -EINVAL;
+
+        mutex_lock(&klp_mutex);
+
+        patch->state = KLP_DISABLED;
+
+        ret = kobject_init_and_add(&patch->kobj, &klp_ktype_patch,
+                                   klp_root_kobj, "%s", patch->mod->name);
+        if (ret)
+                goto unlock;
+
+        for (obj = patch->objs; obj->funcs; obj++) {
+                ret = klp_init_object(patch, obj);
+                if (ret)
+                        goto free;
+        }
+
+        list_add_tail(&patch->list, &klp_patches);
+
+        mutex_unlock(&klp_mutex);
+
+        return 0;
+
+free:
+        klp_free_objects_limited(patch, obj);
+        kobject_put(&patch->kobj);
+unlock:
+        mutex_unlock(&klp_mutex);
+        return ret;
+}
+
+/**
+ * klp_unregister_patch() - unregisters a patch
+ * @patch:      Disabled patch to be unregistered
+ *
+ * Frees the data structures and removes the sysfs interface.
+ *
+ * Return: 0 on success, otherwise error
+ */
+int klp_unregister_patch(struct klp_patch *patch)
+{
+        int ret = 0;
+
+        mutex_lock(&klp_mutex);
+
+        if (!klp_is_patch_registered(patch)) {
+                ret = -EINVAL;
+                goto out;
+        }
+
+        if (patch->state == KLP_ENABLED) {
+                ret = -EBUSY;
+                goto out;
+        }
+
+        klp_free_patch(patch);
+
+out:
+        mutex_unlock(&klp_mutex);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(klp_unregister_patch);
+
+/**
+ * klp_register_patch() - registers a patch
+ * @patch:      Patch to be registered
+ *
+ * Initializes the data structure associated with the patch and
+ * creates the sysfs interface.
+ *
+ * Return: 0 on success, otherwise error
+ */
+int klp_register_patch(struct klp_patch *patch)
+{
+        int ret;
+
+        if (!klp_initialized())
+                return -ENODEV;
+
+        if (!patch || !patch->mod)
+                return -EINVAL;
+
+        /*
+         * A reference is taken on the patch module to prevent it from being
+         * unloaded.  Right now, we don't allow patch modules to unload since
+         * there is currently no method to determine if a thread is still
+         * running in the patched code contained in the patch module once
+         * the ftrace registration is successful.
+         */
+        if (!try_module_get(patch->mod))
+                return -ENODEV;
+
+        ret = klp_init_patch(patch);
+        if (ret)
+                module_put(patch->mod);
+
+        return ret;
+}
+EXPORT_SYMBOL_GPL(klp_register_patch);
+
+static void klp_module_notify_coming(struct klp_patch *patch,
+                                     struct klp_object *obj)
+{
+        struct module *pmod = patch->mod;
+        struct module *mod = obj->mod;
+        int ret;
+
+        ret = klp_init_object_loaded(patch, obj);
+        if (ret)
+                goto err;
+
+        if (patch->state == KLP_DISABLED)
+                return;
+
+        pr_notice("applying patch '%s' to loading module '%s'\n",
+                  pmod->name, mod->name);
+
+        ret = klp_enable_object(obj);
+        if (!ret)
+                return;
+
+err:
+        pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
+                pmod->name, mod->name, ret);
+}
+
+static void klp_module_notify_going(struct klp_patch *patch,
+                                    struct klp_object *obj)
+{
+        struct module *pmod = patch->mod;
+        struct module *mod = obj->mod;
+        int ret;
+
+        if (patch->state == KLP_DISABLED)
+                goto disabled;
+
+        pr_notice("reverting patch '%s' on unloading module '%s'\n",
+                  pmod->name, mod->name);
+
+        ret = klp_disable_object(obj);
+        if (ret)
+                pr_warn("failed to revert patch '%s' on module '%s' (%d)\n",
+                        pmod->name, mod->name, ret);
+
+disabled:
+        klp_free_object_loaded(obj);
+}
+
+static int klp_module_notify(struct notifier_block *nb, unsigned long action,
+                             void *data)
+{
+        struct module *mod = data;
+        struct klp_patch *patch;
+        struct klp_object *obj;
+
+        if (action != MODULE_STATE_COMING && action != MODULE_STATE_GOING)
+                return 0;
+
+        mutex_lock(&klp_mutex);
+
+        list_for_each_entry(patch, &klp_patches, list) {
+                for (obj = patch->objs; obj->funcs; obj++) {
+                        if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
+                                continue;
+
+                        if (action == MODULE_STATE_COMING) {
+                                obj->mod = mod;
+                                klp_module_notify_coming(patch, obj);
+                        } else /* MODULE_STATE_GOING */
+                                klp_module_notify_going(patch, obj);
+
+                        break;
+                }
+        }
+
+        mutex_unlock(&klp_mutex);
+
+        return 0;
+}
+
+static struct notifier_block klp_module_nb = {
+        .notifier_call = klp_module_notify,
+        .priority = INT_MIN+1, /* called late but before ftrace notifier */
+};
+
+static int klp_init(void)
+{
+        int ret;
+
+        ret = klp_check_compiler_support();
+        if (ret) {
+                pr_info("Your compiler is too old; turning off.\n");
+                return -EINVAL;
+        }
+
+        ret = register_module_notifier(&klp_module_nb);
+        if (ret)
+                return ret;
+
+        klp_root_kobj = kobject_create_and_add("livepatch", kernel_kobj);
+        if (!klp_root_kobj) {
+                ret = -ENOMEM;
+                goto unregister;
+        }
+
+        return 0;
+
+unregister:
+        unregister_module_notifier(&klp_module_nb);
+        return ret;
+}
+
+module_init(klp_init);