Linux 4.15.6

[linux/fpc-iii.git] / kernel / livepatch / core.c

/*
 * 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/list.h>
#include <linux/kallsyms.h>
#include <linux/livepatch.h>
#include <linux/elf.h>
#include <linux/moduleloader.h>
#include <linux/completion.h>
#include <asm/cacheflush.h>
#include "core.h"
#include "patch.h"
#include "transition.h"

/*
 * klp_mutex is a coarse lock which serializes access to klp data.  All
 * accesses to klp-related variables and structures must have mutex protection,
 * except within the following functions which carefully avoid the need for it:
 *
 * - klp_ftrace_handler()
 * - klp_update_patch_state()
 */
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;
}

/* sets obj->mod if object is not vmlinux and module is found */
static void klp_find_object_module(struct klp_object *obj)
{
        struct module *mod;

        if (!klp_is_module(obj))
                return;

        mutex_lock(&module_mutex);
        /*
         * We do not want to block removal of patched modules and therefore
         * we do not take a reference here. The patches are removed by
         * klp_module_going() instead.
         */
        mod = find_module(obj->name);
        /*
         * Do not mess work of klp_module_coming() and klp_module_going().
         * Note that the patch might still be needed before klp_module_going()
         * is called. Module functions can be called even in the GOING state
         * until mod->exit() finishes. This is especially important for
         * patches that modify semantic of the functions.
         */
        if (mod && mod->klp_alive)
                obj->mod = mod;

        mutex_unlock(&module_mutex);
}

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;
        unsigned long count;
        unsigned long pos;
};

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 = addr;
        args->count++;

        /*
         * Finish the search when the symbol is found for the desired position
         * or the position is not defined for a non-unique symbol.
         */
        if ((args->pos && (args->count == args->pos)) ||
            (!args->pos && (args->count > 1)))
                return 1;

        return 0;
}

static int klp_find_object_symbol(const char *objname, const char *name,
                                  unsigned long sympos, unsigned long *addr)
{
        struct klp_find_arg args = {
                .objname = objname,
                .name = name,
                .addr = 0,
                .count = 0,
                .pos = sympos,
        };

        mutex_lock(&module_mutex);
        if (objname)
                module_kallsyms_on_each_symbol(klp_find_callback, &args);
        else
                kallsyms_on_each_symbol(klp_find_callback, &args);
        mutex_unlock(&module_mutex);

        /*
         * Ensure an address was found. If sympos is 0, ensure symbol is unique;
         * otherwise ensure the symbol position count matches sympos.
         */
        if (args.addr == 0)
                pr_err("symbol '%s' not found in symbol table\n", name);
        else if (args.count > 1 && sympos == 0) {
                pr_err("unresolvable ambiguity for symbol '%s' in object '%s'\n",
                       name, objname);
        } else if (sympos != args.count && sympos > 0) {
                pr_err("symbol position %lu for symbol '%s' in object '%s' not found\n",
                       sympos, name, objname ? objname : "vmlinux");
        } else {
                *addr = args.addr;
                return 0;
        }

        *addr = 0;
        return -EINVAL;
}

static int klp_resolve_symbols(Elf_Shdr *relasec, struct module *pmod)
{
        int i, cnt, vmlinux, ret;
        char objname[MODULE_NAME_LEN];
        char symname[KSYM_NAME_LEN];
        char *strtab = pmod->core_kallsyms.strtab;
        Elf_Rela *relas;
        Elf_Sym *sym;
        unsigned long sympos, addr;

        /*
         * Since the field widths for objname and symname in the sscanf()
         * call are hard-coded and correspond to MODULE_NAME_LEN and
         * KSYM_NAME_LEN respectively, we must make sure that MODULE_NAME_LEN
         * and KSYM_NAME_LEN have the values we expect them to have.
         *
         * Because the value of MODULE_NAME_LEN can differ among architectures,
         * we use the smallest/strictest upper bound possible (56, based on
         * the current definition of MODULE_NAME_LEN) to prevent overflows.
         */
        BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 128);

        relas = (Elf_Rela *) relasec->sh_addr;
        /* For each rela in this klp relocation section */
        for (i = 0; i < relasec->sh_size / sizeof(Elf_Rela); i++) {
                sym = pmod->core_kallsyms.symtab + ELF_R_SYM(relas[i].r_info);
                if (sym->st_shndx != SHN_LIVEPATCH) {
                        pr_err("symbol %s is not marked as a livepatch symbol\n",
                               strtab + sym->st_name);
                        return -EINVAL;
                }

                /* Format: .klp.sym.objname.symname,sympos */
                cnt = sscanf(strtab + sym->st_name,
                             ".klp.sym.%55[^.].%127[^,],%lu",
                             objname, symname, &sympos);
                if (cnt != 3) {
                        pr_err("symbol %s has an incorrectly formatted name\n",
                               strtab + sym->st_name);
                        return -EINVAL;
                }

                /* klp_find_object_symbol() treats a NULL objname as vmlinux */
                vmlinux = !strcmp(objname, "vmlinux");
                ret = klp_find_object_symbol(vmlinux ? NULL : objname,
                                             symname, sympos, &addr);
                if (ret)
                        return ret;

                sym->st_value = addr;
        }

        return 0;
}

static int klp_write_object_relocations(struct module *pmod,
                                        struct klp_object *obj)
{
        int i, cnt, ret = 0;
        const char *objname, *secname;
        char sec_objname[MODULE_NAME_LEN];
        Elf_Shdr *sec;

        if (WARN_ON(!klp_is_object_loaded(obj)))
                return -EINVAL;

        objname = klp_is_module(obj) ? obj->name : "vmlinux";

        /* For each klp relocation section */
        for (i = 1; i < pmod->klp_info->hdr.e_shnum; i++) {
                sec = pmod->klp_info->sechdrs + i;
                secname = pmod->klp_info->secstrings + sec->sh_name;
                if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
                        continue;

                /*
                 * Format: .klp.rela.sec_objname.section_name
                 * See comment in klp_resolve_symbols() for an explanation
                 * of the selected field width value.
                 */
                cnt = sscanf(secname, ".klp.rela.%55[^.]", sec_objname);
                if (cnt != 1) {
                        pr_err("section %s has an incorrectly formatted name\n",
                               secname);
                        ret = -EINVAL;
                        break;
                }

                if (strcmp(objname, sec_objname))
                        continue;

                ret = klp_resolve_symbols(sec, pmod);
                if (ret)
                        break;

                ret = apply_relocate_add(pmod->klp_info->sechdrs,
                                         pmod->core_kallsyms.strtab,
                                         pmod->klp_info->symndx, i, pmod);
                if (ret)
                        break;
        }

        return ret;
}

static int __klp_disable_patch(struct klp_patch *patch)
{
        struct klp_object *obj;

        if (WARN_ON(!patch->enabled))
                return -EINVAL;

        if (klp_transition_patch)
                return -EBUSY;

        /* enforce stacking: only the last enabled patch can be disabled */
        if (!list_is_last(&patch->list, &klp_patches) &&
            list_next_entry(patch, list)->enabled)
                return -EBUSY;

        klp_init_transition(patch, KLP_UNPATCHED);

        klp_for_each_object(patch, obj)
                if (obj->patched)
                        klp_pre_unpatch_callback(obj);

        /*
         * Enforce the order of the func->transition writes in
         * klp_init_transition() and the TIF_PATCH_PENDING writes in
         * klp_start_transition().  In the rare case where klp_ftrace_handler()
         * is called shortly after klp_update_patch_state() switches the task,
         * this ensures the handler sees that func->transition is set.
         */
        smp_wmb();

        klp_start_transition();
        klp_try_complete_transition();
        patch->enabled = false;

        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->enabled) {
                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 (klp_transition_patch)
                return -EBUSY;

        if (WARN_ON(patch->enabled))
                return -EINVAL;

        /* enforce stacking: only the first disabled patch can be enabled */
        if (patch->list.prev != &klp_patches &&
            !list_prev_entry(patch, list)->enabled)
                return -EBUSY;

        /*
         * A reference is taken on the patch module to prevent it from being
         * unloaded.
         *
         * Note: For immediate (no consistency model) patches we don't allow
         * patch modules to unload since there is no safe/sane 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;

        pr_notice("enabling patch '%s'\n", patch->mod->name);

        klp_init_transition(patch, KLP_PATCHED);

        /*
         * Enforce the order of the func->transition writes in
         * klp_init_transition() and the ops->func_stack writes in
         * klp_patch_object(), so that klp_ftrace_handler() will see the
         * func->transition updates before the handler is registered and the
         * new funcs become visible to the handler.
         */
        smp_wmb();

        klp_for_each_object(patch, obj) {
                if (!klp_is_object_loaded(obj))
                        continue;

                ret = klp_pre_patch_callback(obj);
                if (ret) {
                        pr_warn("pre-patch callback failed for object '%s'\n",
                                klp_is_module(obj) ? obj->name : "vmlinux");
                        goto err;
                }

                ret = klp_patch_object(obj);
                if (ret) {
                        pr_warn("failed to patch object '%s'\n",
                                klp_is_module(obj) ? obj->name : "vmlinux");
                        goto err;
                }
        }

        klp_start_transition();
        klp_try_complete_transition();
        patch->enabled = true;

        return 0;
err:
        pr_warn("failed to enable patch '%s'\n", patch->mod->name);

        klp_cancel_transition();
        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>/transition
 * /sys/kernel/livepatch/<patch>/<object>
 * /sys/kernel/livepatch/<patch>/<object>/<function,sympos>
 */

static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
                             const char *buf, size_t count)
{
        struct klp_patch *patch;
        int ret;
        bool enabled;

        ret = kstrtobool(buf, &enabled);
        if (ret)
                return ret;

        patch = container_of(kobj, struct klp_patch, kobj);

        mutex_lock(&klp_mutex);

        if (!klp_is_patch_registered(patch)) {
                /*
                 * Module with the patch could either disappear meanwhile or is
                 * not properly initialized yet.
                 */
                ret = -EINVAL;
                goto err;
        }

        if (patch->enabled == enabled) {
                /* already in requested state */
                ret = -EINVAL;
                goto err;
        }

        if (patch == klp_transition_patch) {
                klp_reverse_transition();
        } else if (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->enabled);
}

static ssize_t transition_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 == klp_transition_patch);
}

static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled);
static struct kobj_attribute transition_kobj_attr = __ATTR_RO(transition);
static struct attribute *klp_patch_attrs[] = {
        &enabled_kobj_attr.attr,
        &transition_kobj_attr.attr,
        NULL
};

static void klp_kobj_release_patch(struct kobject *kobj)
{
        struct klp_patch *patch;

        patch = container_of(kobj, struct klp_patch, kobj);
        complete(&patch->finish);
}

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_object(struct kobject *kobj)
{
}

static struct kobj_type klp_ktype_object = {
        .release = klp_kobj_release_object,
        .sysfs_ops = &kobj_sysfs_ops,
};

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;

        klp_for_each_func(obj, 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);
}

static int klp_init_func(struct klp_object *obj, struct klp_func *func)
{
        if (!func->old_name || !func->new_func)
                return -EINVAL;

        INIT_LIST_HEAD(&func->stack_node);
        func->patched = false;
        func->transition = false;

        /* The format for the sysfs directory is <function,sympos> where sympos
         * is the nth occurrence of this symbol in kallsyms for the patched
         * object. If the user selects 0 for old_sympos, then 1 will be used
         * since a unique symbol will be the first occurrence.
         */
        return kobject_init_and_add(&func->kobj, &klp_ktype_func,
                                    &obj->kobj, "%s,%lu", func->old_name,
                                    func->old_sympos ? func->old_sympos : 1);
}

/* Arches may override this to finish any remaining arch-specific tasks */
void __weak arch_klp_init_object_loaded(struct klp_patch *patch,
                                        struct klp_object *obj)
{
}

/* 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;

        module_disable_ro(patch->mod);
        ret = klp_write_object_relocations(patch->mod, obj);
        if (ret) {
                module_enable_ro(patch->mod, true);
                return ret;
        }

        arch_klp_init_object_loaded(patch, obj);
        module_enable_ro(patch->mod, true);

        klp_for_each_func(obj, func) {
                ret = klp_find_object_symbol(obj->name, func->old_name,
                                             func->old_sympos,
                                             &func->old_addr);
                if (ret)
                        return ret;

                ret = kallsyms_lookup_size_offset(func->old_addr,
                                                  &func->old_size, NULL);
                if (!ret) {
                        pr_err("kallsyms size lookup failed for '%s'\n",
                               func->old_name);
                        return -ENOENT;
                }

                ret = kallsyms_lookup_size_offset((unsigned long)func->new_func,
                                                  &func->new_size, NULL);
                if (!ret) {
                        pr_err("kallsyms size lookup failed for '%s' replacement\n",
                               func->old_name);
                        return -ENOENT;
                }
        }

        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->patched = false;
        obj->mod = NULL;

        klp_find_object_module(obj);

        name = klp_is_module(obj) ? obj->name : "vmlinux";
        ret = kobject_init_and_add(&obj->kobj, &klp_ktype_object,
                                   &patch->kobj, "%s", name);
        if (ret)
                return ret;

        klp_for_each_func(obj, 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->enabled = false;
        init_completion(&patch->finish);

        ret = kobject_init_and_add(&patch->kobj, &klp_ktype_patch,
                                   klp_root_kobj, "%s", patch->mod->name);
        if (ret) {
                mutex_unlock(&klp_mutex);
                return ret;
        }

        klp_for_each_object(patch, 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);

        mutex_unlock(&klp_mutex);

        kobject_put(&patch->kobj);
        wait_for_completion(&patch->finish);

        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;

        mutex_lock(&klp_mutex);

        if (!klp_is_patch_registered(patch)) {
                ret = -EINVAL;
                goto err;
        }

        if (patch->enabled) {
                ret = -EBUSY;
                goto err;
        }

        klp_free_patch(patch);

        mutex_unlock(&klp_mutex);

        kobject_put(&patch->kobj);
        wait_for_completion(&patch->finish);

        return 0;
err:
        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.
 *
 * There is no need to take the reference on the patch module here. It is done
 * later when the patch is enabled.
 *
 * Return: 0 on success, otherwise error
 */
int klp_register_patch(struct klp_patch *patch)
{
        if (!patch || !patch->mod)
                return -EINVAL;

        if (!is_livepatch_module(patch->mod)) {
                pr_err("module %s is not marked as a livepatch module\n",
                       patch->mod->name);
                return -EINVAL;
        }

        if (!klp_initialized())
                return -ENODEV;

        /*
         * Architectures without reliable stack traces have to set
         * patch->immediate because there's currently no way to patch kthreads
         * with the consistency model.
         */
        if (!klp_have_reliable_stack() && !patch->immediate) {
                pr_err("This architecture doesn't have support for the livepatch consistency model.\n");
                return -ENOSYS;
        }

        return klp_init_patch(patch);
}
EXPORT_SYMBOL_GPL(klp_register_patch);

/*
 * Remove parts of patches that touch a given kernel module. The list of
 * patches processed might be limited. When limit is NULL, all patches
 * will be handled.
 */
static void klp_cleanup_module_patches_limited(struct module *mod,
                                               struct klp_patch *limit)
{
        struct klp_patch *patch;
        struct klp_object *obj;

        list_for_each_entry(patch, &klp_patches, list) {
                if (patch == limit)
                        break;

                klp_for_each_object(patch, obj) {
                        if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
                                continue;

                        /*
                         * Only unpatch the module if the patch is enabled or
                         * is in transition.
                         */
                        if (patch->enabled || patch == klp_transition_patch) {

                                if (patch != klp_transition_patch)
                                        klp_pre_unpatch_callback(obj);

                                pr_notice("reverting patch '%s' on unloading module '%s'\n",
                                          patch->mod->name, obj->mod->name);
                                klp_unpatch_object(obj);

                                klp_post_unpatch_callback(obj);
                        }

                        klp_free_object_loaded(obj);
                        break;
                }
        }
}

int klp_module_coming(struct module *mod)
{
        int ret;
        struct klp_patch *patch;
        struct klp_object *obj;

        if (WARN_ON(mod->state != MODULE_STATE_COMING))
                return -EINVAL;

        mutex_lock(&klp_mutex);
        /*
         * Each module has to know that klp_module_coming()
         * has been called. We never know what module will
         * get patched by a new patch.
         */
        mod->klp_alive = true;

        list_for_each_entry(patch, &klp_patches, list) {
                klp_for_each_object(patch, obj) {
                        if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
                                continue;

                        obj->mod = mod;

                        ret = klp_init_object_loaded(patch, obj);
                        if (ret) {
                                pr_warn("failed to initialize patch '%s' for module '%s' (%d)\n",
                                        patch->mod->name, obj->mod->name, ret);
                                goto err;
                        }

                        /*
                         * Only patch the module if the patch is enabled or is
                         * in transition.
                         */
                        if (!patch->enabled && patch != klp_transition_patch)
                                break;

                        pr_notice("applying patch '%s' to loading module '%s'\n",
                                  patch->mod->name, obj->mod->name);

                        ret = klp_pre_patch_callback(obj);
                        if (ret) {
                                pr_warn("pre-patch callback failed for object '%s'\n",
                                        obj->name);
                                goto err;
                        }

                        ret = klp_patch_object(obj);
                        if (ret) {
                                pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
                                        patch->mod->name, obj->mod->name, ret);

                                klp_post_unpatch_callback(obj);
                                goto err;
                        }

                        if (patch != klp_transition_patch)
                                klp_post_patch_callback(obj);

                        break;
                }
        }

        mutex_unlock(&klp_mutex);

        return 0;

err:
        /*
         * If a patch is unsuccessfully applied, return
         * error to the module loader.
         */
        pr_warn("patch '%s' failed for module '%s', refusing to load module '%s'\n",
                patch->mod->name, obj->mod->name, obj->mod->name);
        mod->klp_alive = false;
        klp_cleanup_module_patches_limited(mod, patch);
        mutex_unlock(&klp_mutex);

        return ret;
}

void klp_module_going(struct module *mod)
{
        if (WARN_ON(mod->state != MODULE_STATE_GOING &&
                    mod->state != MODULE_STATE_COMING))
                return;

        mutex_lock(&klp_mutex);
        /*
         * Each module has to know that klp_module_going()
         * has been called. We never know what module will
         * get patched by a new patch.
         */
        mod->klp_alive = false;

        klp_cleanup_module_patches_limited(mod, NULL);

        mutex_unlock(&klp_mutex);
}

static int __init klp_init(void)
{
        int ret;

        ret = klp_check_compiler_support();
        if (ret) {
                pr_info("Your compiler is too old; turning off.\n");
                return -EINVAL;
        }

        klp_root_kobj = kobject_create_and_add("livepatch", kernel_kobj);
        if (!klp_root_kobj)
                return -ENOMEM;

        return 0;
}

module_init(klp_init);