split dev_queue

[cor.git] / kernel / livepatch / core.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * core.c - Kernel Live Patching Core
 *
 * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
 * Copyright (C) 2014 SUSE
 */

#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 <linux/memory.h>
#include <asm/cacheflush.h>
#include "core.h"
#include "patch.h"
#include "state.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);

/*
 * Actively used patches: enabled or in transition. Note that replaced
 * or disabled patches are not listed even though the related kernel
 * module still can be loaded.
 */
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_initialized(void)
{
        return !!klp_root_kobj;
}

static struct klp_func *klp_find_func(struct klp_object *obj,
                                      struct klp_func *old_func)
{
        struct klp_func *func;

        klp_for_each_func(obj, func) {
                if ((strcmp(old_func->old_name, func->old_name) == 0) &&
                    (old_func->old_sympos == func->old_sympos)) {
                        return func;
                }
        }

        return NULL;
}

static struct klp_object *klp_find_object(struct klp_patch *patch,
                                          struct klp_object *old_obj)
{
        struct klp_object *obj;

        klp_for_each_object(patch, obj) {
                if (klp_is_module(old_obj)) {
                        if (klp_is_module(obj) &&
                            strcmp(old_obj->name, obj->name) == 0) {
                                return obj;
                        }
                } else if (!klp_is_module(obj)) {
                        return obj;
                }
        }

        return NULL;
}

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;
}

/*
 * Sysfs Interface
 *
 * /sys/kernel/livepatch
 * /sys/kernel/livepatch/<patch>
 * /sys/kernel/livepatch/<patch>/enabled
 * /sys/kernel/livepatch/<patch>/transition
 * /sys/kernel/livepatch/<patch>/force
 * /sys/kernel/livepatch/<patch>/<object>
 * /sys/kernel/livepatch/<patch>/<object>/<function,sympos>
 */
static int __klp_disable_patch(struct klp_patch *patch);

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

        /*
         * Allow to reverse a pending transition in both ways. It might be
         * necessary to complete the transition without forcing and breaking
         * the system integrity.
         *
         * Do not allow to re-enable a disabled patch.
         */
        if (patch == klp_transition_patch)
                klp_reverse_transition();
        else if (!enabled)
                ret = __klp_disable_patch(patch);
        else
                ret = -EINVAL;

out:
        mutex_unlock(&klp_mutex);

        if (ret)
                return ret;
        return count;
}

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

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

        if (!val)
                return count;

        mutex_lock(&klp_mutex);

        patch = container_of(kobj, struct klp_patch, kobj);
        if (patch != klp_transition_patch) {
                mutex_unlock(&klp_mutex);
                return -EINVAL;
        }

        klp_force_transition();

        mutex_unlock(&klp_mutex);

        return count;
}

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

static void klp_free_object_dynamic(struct klp_object *obj)
{
        kfree(obj->name);
        kfree(obj);
}

static void klp_init_func_early(struct klp_object *obj,
                                struct klp_func *func);
static void klp_init_object_early(struct klp_patch *patch,
                                  struct klp_object *obj);

static struct klp_object *klp_alloc_object_dynamic(const char *name,
                                                   struct klp_patch *patch)
{
        struct klp_object *obj;

        obj = kzalloc(sizeof(*obj), GFP_KERNEL);
        if (!obj)
                return NULL;

        if (name) {
                obj->name = kstrdup(name, GFP_KERNEL);
                if (!obj->name) {
                        kfree(obj);
                        return NULL;
                }
        }

        klp_init_object_early(patch, obj);
        obj->dynamic = true;

        return obj;
}

static void klp_free_func_nop(struct klp_func *func)
{
        kfree(func->old_name);
        kfree(func);
}

static struct klp_func *klp_alloc_func_nop(struct klp_func *old_func,
                                           struct klp_object *obj)
{
        struct klp_func *func;

        func = kzalloc(sizeof(*func), GFP_KERNEL);
        if (!func)
                return NULL;

        if (old_func->old_name) {
                func->old_name = kstrdup(old_func->old_name, GFP_KERNEL);
                if (!func->old_name) {
                        kfree(func);
                        return NULL;
                }
        }

        klp_init_func_early(obj, func);
        /*
         * func->new_func is same as func->old_func. These addresses are
         * set when the object is loaded, see klp_init_object_loaded().
         */
        func->old_sympos = old_func->old_sympos;
        func->nop = true;

        return func;
}

static int klp_add_object_nops(struct klp_patch *patch,
                               struct klp_object *old_obj)
{
        struct klp_object *obj;
        struct klp_func *func, *old_func;

        obj = klp_find_object(patch, old_obj);

        if (!obj) {
                obj = klp_alloc_object_dynamic(old_obj->name, patch);
                if (!obj)
                        return -ENOMEM;
        }

        klp_for_each_func(old_obj, old_func) {
                func = klp_find_func(obj, old_func);
                if (func)
                        continue;

                func = klp_alloc_func_nop(old_func, obj);
                if (!func)
                        return -ENOMEM;
        }

        return 0;
}

/*
 * Add 'nop' functions which simply return to the caller to run
 * the original function. The 'nop' functions are added to a
 * patch to facilitate a 'replace' mode.
 */
static int klp_add_nops(struct klp_patch *patch)
{
        struct klp_patch *old_patch;
        struct klp_object *old_obj;

        klp_for_each_patch(old_patch) {
                klp_for_each_object(old_patch, old_obj) {
                        int err;

                        err = klp_add_object_nops(patch, old_obj);
                        if (err)
                                return err;
                }
        }

        return 0;
}

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_groups = klp_patch_groups,
};

static void klp_kobj_release_object(struct kobject *kobj)
{
        struct klp_object *obj;

        obj = container_of(kobj, struct klp_object, kobj);

        if (obj->dynamic)
                klp_free_object_dynamic(obj);
}

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)
{
        struct klp_func *func;

        func = container_of(kobj, struct klp_func, kobj);

        if (func->nop)
                klp_free_func_nop(func);
}

static struct kobj_type klp_ktype_func = {
        .release = klp_kobj_release_func,
        .sysfs_ops = &kobj_sysfs_ops,
};

static void __klp_free_funcs(struct klp_object *obj, bool nops_only)
{
        struct klp_func *func, *tmp_func;

        klp_for_each_func_safe(obj, func, tmp_func) {
                if (nops_only && !func->nop)
                        continue;

                list_del(&func->node);
                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_func = NULL;

                if (func->nop)
                        func->new_func = NULL;
        }
}

static void __klp_free_objects(struct klp_patch *patch, bool nops_only)
{
        struct klp_object *obj, *tmp_obj;

        klp_for_each_object_safe(patch, obj, tmp_obj) {
                __klp_free_funcs(obj, nops_only);

                if (nops_only && !obj->dynamic)
                        continue;

                list_del(&obj->node);
                kobject_put(&obj->kobj);
        }
}

static void klp_free_objects(struct klp_patch *patch)
{
        __klp_free_objects(patch, false);
}

static void klp_free_objects_dynamic(struct klp_patch *patch)
{
        __klp_free_objects(patch, true);
}

/*
 * This function implements the free operations that can be called safely
 * under klp_mutex.
 *
 * The operation must be completed by calling klp_free_patch_finish()
 * outside klp_mutex.
 */
static void klp_free_patch_start(struct klp_patch *patch)
{
        if (!list_empty(&patch->list))
                list_del(&patch->list);

        klp_free_objects(patch);
}

/*
 * This function implements the free part that must be called outside
 * klp_mutex.
 *
 * It must be called after klp_free_patch_start(). And it has to be
 * the last function accessing the livepatch structures when the patch
 * gets disabled.
 */
static void klp_free_patch_finish(struct klp_patch *patch)
{
        /*
         * Avoid deadlock with enabled_store() sysfs callback by
         * calling this outside klp_mutex. It is safe because
         * this is called when the patch gets disabled and it
         * cannot get enabled again.
         */
        kobject_put(&patch->kobj);
        wait_for_completion(&patch->finish);

        /* Put the module after the last access to struct klp_patch. */
        if (!patch->forced)
                module_put(patch->mod);
}

/*
 * The livepatch might be freed from sysfs interface created by the patch.
 * This work allows to wait until the interface is destroyed in a separate
 * context.
 */
static void klp_free_patch_work_fn(struct work_struct *work)
{
        struct klp_patch *patch =
                container_of(work, struct klp_patch, free_work);

        klp_free_patch_finish(patch);
}

void klp_free_patch_async(struct klp_patch *patch)
{
        klp_free_patch_start(patch);
        schedule_work(&patch->free_work);
}

void klp_free_replaced_patches_async(struct klp_patch *new_patch)
{
        struct klp_patch *old_patch, *tmp_patch;

        klp_for_each_patch_safe(old_patch, tmp_patch) {
                if (old_patch == new_patch)
                        return;
                klp_free_patch_async(old_patch);
        }
}

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

        /*
         * NOPs get the address later. The patched module must be loaded,
         * see klp_init_object_loaded().
         */
        if (!func->new_func && !func->nop)
                return -EINVAL;

        if (strlen(func->old_name) >= KSYM_NAME_LEN)
                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_add(&func->kobj, &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;

        mutex_lock(&text_mutex);

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

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

        mutex_unlock(&text_mutex);

        klp_for_each_func(obj, func) {
                ret = klp_find_object_symbol(obj->name, func->old_name,
                                             func->old_sympos,
                                             (unsigned long *)&func->old_func);
                if (ret)
                        return ret;

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

                if (func->nop)
                        func->new_func = func->old_func;

                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 (klp_is_module(obj) && strlen(obj->name) >= MODULE_NAME_LEN)
                return -EINVAL;

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

        klp_find_object_module(obj);

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

        klp_for_each_func(obj, func) {
                ret = klp_init_func(obj, func);
                if (ret)
                        return ret;
        }

        if (klp_is_object_loaded(obj))
                ret = klp_init_object_loaded(patch, obj);

        return ret;
}

static void klp_init_func_early(struct klp_object *obj,
                                struct klp_func *func)
{
        kobject_init(&func->kobj, &klp_ktype_func);
        list_add_tail(&func->node, &obj->func_list);
}

static void klp_init_object_early(struct klp_patch *patch,
                                  struct klp_object *obj)
{
        INIT_LIST_HEAD(&obj->func_list);
        kobject_init(&obj->kobj, &klp_ktype_object);
        list_add_tail(&obj->node, &patch->obj_list);
}

static int klp_init_patch_early(struct klp_patch *patch)
{
        struct klp_object *obj;
        struct klp_func *func;

        if (!patch->objs)
                return -EINVAL;

        INIT_LIST_HEAD(&patch->list);
        INIT_LIST_HEAD(&patch->obj_list);
        kobject_init(&patch->kobj, &klp_ktype_patch);
        patch->enabled = false;
        patch->forced = false;
        INIT_WORK(&patch->free_work, klp_free_patch_work_fn);
        init_completion(&patch->finish);

        klp_for_each_object_static(patch, obj) {
                if (!obj->funcs)
                        return -EINVAL;

                klp_init_object_early(patch, obj);

                klp_for_each_func_static(obj, func) {
                        klp_init_func_early(obj, func);
                }
        }

        if (!try_module_get(patch->mod))
                return -ENODEV;

        return 0;
}

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

        ret = kobject_add(&patch->kobj, klp_root_kobj, "%s", patch->mod->name);
        if (ret)
                return ret;

        if (patch->replace) {
                ret = klp_add_nops(patch);
                if (ret)
                        return ret;
        }

        klp_for_each_object(patch, obj) {
                ret = klp_init_object(patch, obj);
                if (ret)
                        return ret;
        }

        list_add_tail(&patch->list, &klp_patches);

        return 0;
}

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;

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

        return 0;
}

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;

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

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

        klp_cancel_transition();
        return ret;
}

/**
 * klp_enable_patch() - enable the livepatch
 * @patch:      patch to be enabled
 *
 * Initializes the data structure associated with the patch, creates the sysfs
 * interface, performs the needed symbol lookups and code relocations,
 * registers the patched functions with ftrace.
 *
 * This function is supposed to be called from the livepatch module_init()
 * callback.
 *
 * Return: 0 on success, otherwise error
 */
int klp_enable_patch(struct klp_patch *patch)
{
        int ret;

        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;

        if (!klp_have_reliable_stack()) {
                pr_warn("This architecture doesn't have support for the livepatch consistency model.\n");
                pr_warn("The livepatch transition may never complete.\n");
        }

        mutex_lock(&klp_mutex);

        if (!klp_is_patch_compatible(patch)) {
                pr_err("Livepatch patch (%s) is not compatible with the already installed livepatches.\n",
                        patch->mod->name);
                mutex_unlock(&klp_mutex);
                return -EINVAL;
        }

        ret = klp_init_patch_early(patch);
        if (ret) {
                mutex_unlock(&klp_mutex);
                return ret;
        }

        ret = klp_init_patch(patch);
        if (ret)
                goto err;

        ret = __klp_enable_patch(patch);
        if (ret)
                goto err;

        mutex_unlock(&klp_mutex);

        return 0;

err:
        klp_free_patch_start(patch);

        mutex_unlock(&klp_mutex);

        klp_free_patch_finish(patch);

        return ret;
}
EXPORT_SYMBOL_GPL(klp_enable_patch);

/*
 * This function unpatches objects from the replaced livepatches.
 *
 * We could be pretty aggressive here. It is called in the situation where
 * these structures are no longer accessed from the ftrace handler.
 * All functions are redirected by the klp_transition_patch. They
 * use either a new code or they are in the original code because
 * of the special nop function patches.
 *
 * The only exception is when the transition was forced. In this case,
 * klp_ftrace_handler() might still see the replaced patch on the stack.
 * Fortunately, it is carefully designed to work with removed functions
 * thanks to RCU. We only have to keep the patches on the system. Also
 * this is handled transparently by patch->module_put.
 */
void klp_unpatch_replaced_patches(struct klp_patch *new_patch)
{
        struct klp_patch *old_patch;

        klp_for_each_patch(old_patch) {
                if (old_patch == new_patch)
                        return;

                old_patch->enabled = false;
                klp_unpatch_objects(old_patch);
        }
}

/*
 * This function removes the dynamically allocated 'nop' functions.
 *
 * We could be pretty aggressive. NOPs do not change the existing
 * behavior except for adding unnecessary delay by the ftrace handler.
 *
 * It is safe even when the transition was forced. The ftrace handler
 * will see a valid ops->func_stack entry thanks to RCU.
 *
 * We could even free the NOPs structures. They must be the last entry
 * in ops->func_stack. Therefore unregister_ftrace_function() is called.
 * It does the same as klp_synchronize_transition() to make sure that
 * nobody is inside the ftrace handler once the operation finishes.
 *
 * IMPORTANT: It must be called right after removing the replaced patches!
 */
void klp_discard_nops(struct klp_patch *new_patch)
{
        klp_unpatch_objects_dynamic(klp_transition_patch);
        klp_free_objects_dynamic(klp_transition_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;

        klp_for_each_patch(patch) {
                if (patch == limit)
                        break;

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

                        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;

        klp_for_each_patch(patch) {
                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;
                        }

                        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;
        obj->mod = NULL;
        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)
{
        klp_root_kobj = kobject_create_and_add("livepatch", kernel_kobj);
        if (!klp_root_kobj)
                return -ENOMEM;

        return 0;
}

module_init(klp_init);