/* * 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> #include <linux/elf.h> #include <linux/moduleloader.h> #include <asm/cacheflush.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) { 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); } /* 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; 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); 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", 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", 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", 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 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(); } /* * Convert a function address into the appropriate ftrace location. * * Usually this is just the address of the function, but on some architectures * it's more complicated so allow them to provide a custom behaviour. */ #ifndef klp_get_ftrace_location static unsigned long klp_get_ftrace_location(unsigned long faddr) { return faddr; } #endif static void klp_disable_func(struct klp_func *func) { struct klp_ops *ops; if (WARN_ON(func->state != KLP_ENABLED)) return; if (WARN_ON(!func->old_addr)) return; ops = klp_find_ops(func->old_addr); if (WARN_ON(!ops)) return; if (list_is_singular(&ops->func_stack)) { unsigned long ftrace_loc; ftrace_loc = klp_get_ftrace_location(func->old_addr); if (WARN_ON(!ftrace_loc)) return; WARN_ON(unregister_ftrace_function(&ops->fops)); WARN_ON(ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0)); list_del_rcu(&func->stack_node); list_del(&ops->node); kfree(ops); } else { list_del_rcu(&func->stack_node); } func->state = KLP_DISABLED; } 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) { unsigned long ftrace_loc; ftrace_loc = klp_get_ftrace_location(func->old_addr); if (!ftrace_loc) { pr_err("failed to find location for function '%s'\n", func->old_name); return -EINVAL; } 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, ftrace_loc, 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, ftrace_loc, 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 void klp_disable_object(struct klp_object *obj) { struct klp_func *func; klp_for_each_func(obj, func) if (func->state == KLP_ENABLED) klp_disable_func(func); obj->state = KLP_DISABLED; } 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; klp_for_each_func(obj, func) { ret = klp_enable_func(func); if (ret) { klp_disable_object(obj); return ret; } } obj->state = KLP_ENABLED; return 0; } static int __klp_disable_patch(struct klp_patch *patch) { struct klp_object *obj; /* 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); klp_for_each_object(patch, obj) { if (obj->state == KLP_ENABLED) klp_disable_object(obj); } 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("enabling patch '%s'\n", patch->mod->name); klp_for_each_object(patch, 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>/<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; 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_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); kobject_put(&patch->kobj); } 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->state = KLP_DISABLED; /* 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; } 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; 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->state = KLP_DISABLED; ret = kobject_init_and_add(&patch->kobj, &klp_ktype_patch, klp_root_kobj, "%s", patch->mod->name); if (ret) goto unlock; 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); 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 (!patch || !patch->mod) return -EINVAL; if (!is_livepatch_module(patch->mod)) { pr_err("module %s is not marked as a livepatch module", patch->mod->name); return -EINVAL; } if (!klp_initialized()) return -ENODEV; /* * 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); 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; } if (patch->state == KLP_DISABLED) break; pr_notice("applying patch '%s' to loading module '%s'\n", patch->mod->name, obj->mod->name); ret = klp_enable_object(obj); if (ret) { pr_warn("failed to apply patch '%s' to module '%s' (%d)\n", patch->mod->name, obj->mod->name, ret); goto err; } 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_free_object_loaded(obj); mutex_unlock(&klp_mutex); return ret; } void klp_module_going(struct module *mod) { struct klp_patch *patch; struct klp_object *obj; 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; 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; if (patch->state != KLP_DISABLED) { pr_notice("reverting patch '%s' on unloading module '%s'\n", patch->mod->name, obj->mod->name); klp_disable_object(obj); } klp_free_object_loaded(obj); break; } } 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);