livepatch: kernel: add support for live patching

This commit introduces code for the live patching core.  It implements
an ftrace-based mechanism and kernel interface for doing live patching
of kernel and kernel module functions.

It represents the greatest common functionality set between kpatch and
kgraft and can accept patches built using either method.

This first version does not implement any consistency mechanism that
ensures that old and new code do not run together.  In practice, ~90% of
CVEs are safe to apply in this way, since they simply add a conditional
check.  However, any function change that can not execute safely with
the old version of the function can _not_ be safely applied in this
version.

[ jkosina@suse.cz: due to the number of contributions that got folded into
  this original patch from Seth Jennings, add SUSE's copyright as well, as
  discussed via e-mail ]

Signed-off-by: Seth Jennings <sjenning@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Petr Mladek <pmladek@suse.cz>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Petr Mladek <pmladek@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

3 files changed, 951 insertions, 0 deletions

diff --git a/kernel/livepatch/Kconfig b/kernel/livepatch/Kconfig
new file mode 100644
index 000000000000..96da00fbc120
--- /dev/null
+++ b/kernel/livepatch/Kconfig
@@ -0,0 +1,18 @@
+config ARCH_HAVE_LIVE_PATCHING
+	boolean
+	help
+	  Arch supports kernel live patching
+
+config LIVE_PATCHING
+	boolean "Kernel Live Patching"
+	depends on DYNAMIC_FTRACE_WITH_REGS
+	depends on MODULES
+	depends on SYSFS
+	depends on KALLSYMS_ALL
+	depends on ARCH_HAVE_LIVE_PATCHING
+	help
+	  Say Y here if you want to support kernel live patching.
+	  This option has no runtime impact until a kernel "patch"
+	  module uses the interface provided by this option to register
+	  a patch, causing calls to patched functions to be redirected
+	  to new function code contained in the patch module.
diff --git a/kernel/livepatch/Makefile b/kernel/livepatch/Makefile
new file mode 100644
index 000000000000..7c1f00861428
--- /dev/null
+++ b/kernel/livepatch/Makefile
@@ -0,0 +1,3 @@
+obj-$(CONFIG_LIVE_PATCHING) += livepatch.o
+
+livepatch-objs := core.o
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
new file mode 100644
index 000000000000..f99fe189d596
--- /dev/null
+++ b/kernel/livepatch/core.c
@@ -0,0 +1,930 @@
+/*
+ * 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>
+
+/*
+ * The klp_mutex protects the klp_patches list and state transitions of any
+ * structure reachable from the patches list.  References to any structure must
+ * be obtained under mutex protection.
+ */
+
+static DEFINE_MUTEX(klp_mutex);
+static LIST_HEAD(klp_patches);
+
+static struct kobject *klp_root_kobj;
+
+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?",
+		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 *ops,
+				       struct pt_regs *regs)
+{
+	struct klp_func *func = ops->private;
+
+	regs->ip = (unsigned long)func->new_func;
+}
+
+static int klp_disable_func(struct klp_func *func)
+{
+	int ret;
+
+	if (WARN_ON(func->state != KLP_ENABLED))
+		return -EINVAL;
+
+	if (WARN_ON(!func->old_addr))
+		return -EINVAL;
+
+	ret = unregister_ftrace_function(func->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(func->fops, func->old_addr, 1, 0);
+	if (ret)
+		pr_warn("function unregister succeeded but failed to clear the filter\n");
+
+	func->state = KLP_DISABLED;
+
+	return 0;
+}
+
+static int klp_enable_func(struct klp_func *func)
+{
+	int ret;
+
+	if (WARN_ON(!func->old_addr))
+		return -EINVAL;
+
+	if (WARN_ON(func->state != KLP_DISABLED))
+		return -EINVAL;
+
+	ret = ftrace_set_filter_ip(func->fops, func->old_addr, 0, 0);
+	if (ret) {
+		pr_err("failed to set ftrace filter for function '%s' (%d)\n",
+		       func->old_name, ret);
+		return ret;
+	}
+
+	ret = register_ftrace_function(func->fops);
+	if (ret) {
+		pr_err("failed to register ftrace handler for function '%s' (%d)\n",
+		       func->old_name, ret);
+		ftrace_set_filter_ip(func->fops, func->old_addr, 1, 0);
+	} else {
+		func->state = KLP_ENABLED;
+	}
+
+	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;
+
+	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;
+
+	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)
+{
+	struct klp_func *func;
+
+	func = container_of(kobj, struct klp_func, kobj);
+	kfree(func->fops);
+}
+
+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)
+{
+	struct ftrace_ops *ops;
+	int ret;
+
+	ops = kzalloc(sizeof(*ops), GFP_KERNEL);
+	if (!ops)
+		return -ENOMEM;
+
+	ops->private = func;
+	ops->func = klp_ftrace_handler;
+	ops->flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_DYNAMIC;
+	func->fops = ops;
+	func->state = KLP_DISABLED;
+
+	ret = kobject_init_and_add(&func->kobj, &klp_ktype_func,
+				   obj->kobj, func->old_name);
+	if (ret) {
+		kfree(func->fops);
+		return ret;
+	}
+
+	return 0;
+}
+
+/* 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, 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(&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 = 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);