2 * core.c - Kernel Live Patching Core
4 * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
5 * Copyright (C) 2014 SUSE
7 * This program is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public License
9 * as published by the Free Software Foundation; either version 2
10 * of the License, or (at your option) any later version.
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
17 * You should have received a copy of the GNU General Public License
18 * along with this program; if not, see <http://www.gnu.org/licenses/>.
21 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
23 #include <linux/module.h>
24 #include <linux/kernel.h>
25 #include <linux/mutex.h>
26 #include <linux/slab.h>
27 #include <linux/list.h>
28 #include <linux/kallsyms.h>
29 #include <linux/livepatch.h>
30 #include <linux/elf.h>
31 #include <linux/moduleloader.h>
32 #include <linux/completion.h>
33 #include <linux/memory.h>
34 #include <asm/cacheflush.h>
37 #include "transition.h"
40 * klp_mutex is a coarse lock which serializes access to klp data. All
41 * accesses to klp-related variables and structures must have mutex protection,
42 * except within the following functions which carefully avoid the need for it:
44 * - klp_ftrace_handler()
45 * - klp_update_patch_state()
47 DEFINE_MUTEX(klp_mutex);
49 static LIST_HEAD(klp_patches);
51 static struct kobject *klp_root_kobj;
53 static bool klp_is_module(struct klp_object *obj)
58 static bool klp_is_object_loaded(struct klp_object *obj)
60 return !obj->name || obj->mod;
63 /* sets obj->mod if object is not vmlinux and module is found */
64 static void klp_find_object_module(struct klp_object *obj)
68 if (!klp_is_module(obj))
71 mutex_lock(&module_mutex);
73 * We do not want to block removal of patched modules and therefore
74 * we do not take a reference here. The patches are removed by
75 * klp_module_going() instead.
77 mod = find_module(obj->name);
79 * Do not mess work of klp_module_coming() and klp_module_going().
80 * Note that the patch might still be needed before klp_module_going()
81 * is called. Module functions can be called even in the GOING state
82 * until mod->exit() finishes. This is especially important for
83 * patches that modify semantic of the functions.
85 if (mod && mod->klp_alive)
88 mutex_unlock(&module_mutex);
91 static bool klp_is_patch_registered(struct klp_patch *patch)
93 struct klp_patch *mypatch;
95 list_for_each_entry(mypatch, &klp_patches, list)
102 static bool klp_initialized(void)
104 return !!klp_root_kobj;
107 struct klp_find_arg {
115 static int klp_find_callback(void *data, const char *name,
116 struct module *mod, unsigned long addr)
118 struct klp_find_arg *args = data;
120 if ((mod && !args->objname) || (!mod && args->objname))
123 if (strcmp(args->name, name))
126 if (args->objname && strcmp(args->objname, mod->name))
133 * Finish the search when the symbol is found for the desired position
134 * or the position is not defined for a non-unique symbol.
136 if ((args->pos && (args->count == args->pos)) ||
137 (!args->pos && (args->count > 1)))
143 static int klp_find_object_symbol(const char *objname, const char *name,
144 unsigned long sympos, unsigned long *addr)
146 struct klp_find_arg args = {
154 mutex_lock(&module_mutex);
156 module_kallsyms_on_each_symbol(klp_find_callback, &args);
158 kallsyms_on_each_symbol(klp_find_callback, &args);
159 mutex_unlock(&module_mutex);
162 * Ensure an address was found. If sympos is 0, ensure symbol is unique;
163 * otherwise ensure the symbol position count matches sympos.
166 pr_err("symbol '%s' not found in symbol table\n", name);
167 else if (args.count > 1 && sympos == 0) {
168 pr_err("unresolvable ambiguity for symbol '%s' in object '%s'\n",
170 } else if (sympos != args.count && sympos > 0) {
171 pr_err("symbol position %lu for symbol '%s' in object '%s' not found\n",
172 sympos, name, objname ? objname : "vmlinux");
182 static int klp_resolve_symbols(Elf_Shdr *relasec, struct module *pmod)
184 int i, cnt, vmlinux, ret;
185 char objname[MODULE_NAME_LEN];
186 char symname[KSYM_NAME_LEN];
187 char *strtab = pmod->core_kallsyms.strtab;
190 unsigned long sympos, addr;
193 * Since the field widths for objname and symname in the sscanf()
194 * call are hard-coded and correspond to MODULE_NAME_LEN and
195 * KSYM_NAME_LEN respectively, we must make sure that MODULE_NAME_LEN
196 * and KSYM_NAME_LEN have the values we expect them to have.
198 * Because the value of MODULE_NAME_LEN can differ among architectures,
199 * we use the smallest/strictest upper bound possible (56, based on
200 * the current definition of MODULE_NAME_LEN) to prevent overflows.
202 BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 128);
204 relas = (Elf_Rela *) relasec->sh_addr;
205 /* For each rela in this klp relocation section */
206 for (i = 0; i < relasec->sh_size / sizeof(Elf_Rela); i++) {
207 sym = pmod->core_kallsyms.symtab + ELF_R_SYM(relas[i].r_info);
208 if (sym->st_shndx != SHN_LIVEPATCH) {
209 pr_err("symbol %s is not marked as a livepatch symbol\n",
210 strtab + sym->st_name);
214 /* Format: .klp.sym.objname.symname,sympos */
215 cnt = sscanf(strtab + sym->st_name,
216 ".klp.sym.%55[^.].%127[^,],%lu",
217 objname, symname, &sympos);
219 pr_err("symbol %s has an incorrectly formatted name\n",
220 strtab + sym->st_name);
224 /* klp_find_object_symbol() treats a NULL objname as vmlinux */
225 vmlinux = !strcmp(objname, "vmlinux");
226 ret = klp_find_object_symbol(vmlinux ? NULL : objname,
227 symname, sympos, &addr);
231 sym->st_value = addr;
237 static int klp_write_object_relocations(struct module *pmod,
238 struct klp_object *obj)
241 const char *objname, *secname;
242 char sec_objname[MODULE_NAME_LEN];
245 if (WARN_ON(!klp_is_object_loaded(obj)))
248 objname = klp_is_module(obj) ? obj->name : "vmlinux";
250 /* For each klp relocation section */
251 for (i = 1; i < pmod->klp_info->hdr.e_shnum; i++) {
252 sec = pmod->klp_info->sechdrs + i;
253 secname = pmod->klp_info->secstrings + sec->sh_name;
254 if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
258 * Format: .klp.rela.sec_objname.section_name
259 * See comment in klp_resolve_symbols() for an explanation
260 * of the selected field width value.
262 cnt = sscanf(secname, ".klp.rela.%55[^.]", sec_objname);
264 pr_err("section %s has an incorrectly formatted name\n",
270 if (strcmp(objname, sec_objname))
273 ret = klp_resolve_symbols(sec, pmod);
277 ret = apply_relocate_add(pmod->klp_info->sechdrs,
278 pmod->core_kallsyms.strtab,
279 pmod->klp_info->symndx, i, pmod);
287 static int __klp_disable_patch(struct klp_patch *patch)
289 if (klp_transition_patch)
292 /* enforce stacking: only the last enabled patch can be disabled */
293 if (!list_is_last(&patch->list, &klp_patches) &&
294 list_next_entry(patch, list)->enabled)
297 klp_init_transition(patch, KLP_UNPATCHED);
300 * Enforce the order of the func->transition writes in
301 * klp_init_transition() and the TIF_PATCH_PENDING writes in
302 * klp_start_transition(). In the rare case where klp_ftrace_handler()
303 * is called shortly after klp_update_patch_state() switches the task,
304 * this ensures the handler sees that func->transition is set.
308 klp_start_transition();
309 klp_try_complete_transition();
310 patch->enabled = false;
316 * klp_disable_patch() - disables a registered patch
317 * @patch: The registered, enabled patch to be disabled
319 * Unregisters the patched functions from ftrace.
321 * Return: 0 on success, otherwise error
323 int klp_disable_patch(struct klp_patch *patch)
327 mutex_lock(&klp_mutex);
329 if (!klp_is_patch_registered(patch)) {
334 if (!patch->enabled) {
339 ret = __klp_disable_patch(patch);
342 mutex_unlock(&klp_mutex);
345 EXPORT_SYMBOL_GPL(klp_disable_patch);
347 static int __klp_enable_patch(struct klp_patch *patch)
349 struct klp_object *obj;
352 if (klp_transition_patch)
355 if (WARN_ON(patch->enabled))
358 /* enforce stacking: only the first disabled patch can be enabled */
359 if (patch->list.prev != &klp_patches &&
360 !list_prev_entry(patch, list)->enabled)
364 * A reference is taken on the patch module to prevent it from being
367 * Note: For immediate (no consistency model) patches we don't allow
368 * patch modules to unload since there is no safe/sane method to
369 * determine if a thread is still running in the patched code contained
370 * in the patch module once the ftrace registration is successful.
372 if (!try_module_get(patch->mod))
375 pr_notice("enabling patch '%s'\n", patch->mod->name);
377 klp_init_transition(patch, KLP_PATCHED);
380 * Enforce the order of the func->transition writes in
381 * klp_init_transition() and the ops->func_stack writes in
382 * klp_patch_object(), so that klp_ftrace_handler() will see the
383 * func->transition updates before the handler is registered and the
384 * new funcs become visible to the handler.
388 klp_for_each_object(patch, obj) {
389 if (!klp_is_object_loaded(obj))
392 ret = klp_patch_object(obj);
394 pr_warn("failed to enable patch '%s'\n",
397 klp_cancel_transition();
402 klp_start_transition();
403 klp_try_complete_transition();
404 patch->enabled = true;
410 * klp_enable_patch() - enables a registered patch
411 * @patch: The registered, disabled patch to be enabled
413 * Performs the needed symbol lookups and code relocations,
414 * then registers the patched functions with ftrace.
416 * Return: 0 on success, otherwise error
418 int klp_enable_patch(struct klp_patch *patch)
422 mutex_lock(&klp_mutex);
424 if (!klp_is_patch_registered(patch)) {
429 ret = __klp_enable_patch(patch);
432 mutex_unlock(&klp_mutex);
435 EXPORT_SYMBOL_GPL(klp_enable_patch);
440 * /sys/kernel/livepatch
441 * /sys/kernel/livepatch/<patch>
442 * /sys/kernel/livepatch/<patch>/enabled
443 * /sys/kernel/livepatch/<patch>/transition
444 * /sys/kernel/livepatch/<patch>/<object>
445 * /sys/kernel/livepatch/<patch>/<object>/<function,sympos>
448 static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
449 const char *buf, size_t count)
451 struct klp_patch *patch;
455 ret = kstrtobool(buf, &enabled);
459 patch = container_of(kobj, struct klp_patch, kobj);
461 mutex_lock(&klp_mutex);
463 if (!klp_is_patch_registered(patch)) {
465 * Module with the patch could either disappear meanwhile or is
466 * not properly initialized yet.
472 if (patch->enabled == enabled) {
473 /* already in requested state */
478 if (patch == klp_transition_patch) {
479 klp_reverse_transition();
480 } else if (enabled) {
481 ret = __klp_enable_patch(patch);
485 ret = __klp_disable_patch(patch);
490 mutex_unlock(&klp_mutex);
495 mutex_unlock(&klp_mutex);
499 static ssize_t enabled_show(struct kobject *kobj,
500 struct kobj_attribute *attr, char *buf)
502 struct klp_patch *patch;
504 patch = container_of(kobj, struct klp_patch, kobj);
505 return snprintf(buf, PAGE_SIZE-1, "%d\n", patch->enabled);
508 static ssize_t transition_show(struct kobject *kobj,
509 struct kobj_attribute *attr, char *buf)
511 struct klp_patch *patch;
513 patch = container_of(kobj, struct klp_patch, kobj);
514 return snprintf(buf, PAGE_SIZE-1, "%d\n",
515 patch == klp_transition_patch);
518 static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled);
519 static struct kobj_attribute transition_kobj_attr = __ATTR_RO(transition);
520 static struct attribute *klp_patch_attrs[] = {
521 &enabled_kobj_attr.attr,
522 &transition_kobj_attr.attr,
526 static void klp_kobj_release_patch(struct kobject *kobj)
528 struct klp_patch *patch;
530 patch = container_of(kobj, struct klp_patch, kobj);
531 complete(&patch->finish);
534 static struct kobj_type klp_ktype_patch = {
535 .release = klp_kobj_release_patch,
536 .sysfs_ops = &kobj_sysfs_ops,
537 .default_attrs = klp_patch_attrs,
540 static void klp_kobj_release_object(struct kobject *kobj)
544 static struct kobj_type klp_ktype_object = {
545 .release = klp_kobj_release_object,
546 .sysfs_ops = &kobj_sysfs_ops,
549 static void klp_kobj_release_func(struct kobject *kobj)
553 static struct kobj_type klp_ktype_func = {
554 .release = klp_kobj_release_func,
555 .sysfs_ops = &kobj_sysfs_ops,
559 * Free all functions' kobjects in the array up to some limit. When limit is
560 * NULL, all kobjects are freed.
562 static void klp_free_funcs_limited(struct klp_object *obj,
563 struct klp_func *limit)
565 struct klp_func *func;
567 for (func = obj->funcs; func->old_name && func != limit; func++)
568 kobject_put(&func->kobj);
571 /* Clean up when a patched object is unloaded */
572 static void klp_free_object_loaded(struct klp_object *obj)
574 struct klp_func *func;
578 klp_for_each_func(obj, func)
583 * Free all objects' kobjects in the array up to some limit. When limit is
584 * NULL, all kobjects are freed.
586 static void klp_free_objects_limited(struct klp_patch *patch,
587 struct klp_object *limit)
589 struct klp_object *obj;
591 for (obj = patch->objs; obj->funcs && obj != limit; obj++) {
592 klp_free_funcs_limited(obj, NULL);
593 kobject_put(&obj->kobj);
597 static void klp_free_patch(struct klp_patch *patch)
599 klp_free_objects_limited(patch, NULL);
600 if (!list_empty(&patch->list))
601 list_del(&patch->list);
604 static int klp_init_func(struct klp_object *obj, struct klp_func *func)
606 if (!func->old_name || !func->new_func)
609 if (strlen(func->old_name) >= KSYM_NAME_LEN)
612 INIT_LIST_HEAD(&func->stack_node);
613 func->patched = false;
614 func->transition = false;
616 /* The format for the sysfs directory is <function,sympos> where sympos
617 * is the nth occurrence of this symbol in kallsyms for the patched
618 * object. If the user selects 0 for old_sympos, then 1 will be used
619 * since a unique symbol will be the first occurrence.
621 return kobject_init_and_add(&func->kobj, &klp_ktype_func,
622 &obj->kobj, "%s,%lu", func->old_name,
623 func->old_sympos ? func->old_sympos : 1);
626 /* Arches may override this to finish any remaining arch-specific tasks */
627 void __weak arch_klp_init_object_loaded(struct klp_patch *patch,
628 struct klp_object *obj)
632 /* parts of the initialization that is done only when the object is loaded */
633 static int klp_init_object_loaded(struct klp_patch *patch,
634 struct klp_object *obj)
636 struct klp_func *func;
639 mutex_lock(&text_mutex);
641 module_disable_ro(patch->mod);
642 ret = klp_write_object_relocations(patch->mod, obj);
644 module_enable_ro(patch->mod, true);
645 mutex_unlock(&text_mutex);
649 arch_klp_init_object_loaded(patch, obj);
650 module_enable_ro(patch->mod, true);
652 mutex_unlock(&text_mutex);
654 klp_for_each_func(obj, func) {
655 ret = klp_find_object_symbol(obj->name, func->old_name,
661 ret = kallsyms_lookup_size_offset(func->old_addr,
662 &func->old_size, NULL);
664 pr_err("kallsyms size lookup failed for '%s'\n",
669 ret = kallsyms_lookup_size_offset((unsigned long)func->new_func,
670 &func->new_size, NULL);
672 pr_err("kallsyms size lookup failed for '%s' replacement\n",
681 static int klp_init_object(struct klp_patch *patch, struct klp_object *obj)
683 struct klp_func *func;
690 if (klp_is_module(obj) && strlen(obj->name) >= MODULE_NAME_LEN)
693 obj->patched = false;
696 klp_find_object_module(obj);
698 name = klp_is_module(obj) ? obj->name : "vmlinux";
699 ret = kobject_init_and_add(&obj->kobj, &klp_ktype_object,
700 &patch->kobj, "%s", name);
704 klp_for_each_func(obj, func) {
705 ret = klp_init_func(obj, func);
710 if (klp_is_object_loaded(obj)) {
711 ret = klp_init_object_loaded(patch, obj);
719 klp_free_funcs_limited(obj, func);
720 kobject_put(&obj->kobj);
724 static int klp_init_patch(struct klp_patch *patch)
726 struct klp_object *obj;
732 mutex_lock(&klp_mutex);
734 patch->enabled = false;
735 init_completion(&patch->finish);
737 ret = kobject_init_and_add(&patch->kobj, &klp_ktype_patch,
738 klp_root_kobj, "%s", patch->mod->name);
740 mutex_unlock(&klp_mutex);
744 klp_for_each_object(patch, obj) {
745 ret = klp_init_object(patch, obj);
750 list_add_tail(&patch->list, &klp_patches);
752 mutex_unlock(&klp_mutex);
757 klp_free_objects_limited(patch, obj);
759 mutex_unlock(&klp_mutex);
761 kobject_put(&patch->kobj);
762 wait_for_completion(&patch->finish);
768 * klp_unregister_patch() - unregisters a patch
769 * @patch: Disabled patch to be unregistered
771 * Frees the data structures and removes the sysfs interface.
773 * Return: 0 on success, otherwise error
775 int klp_unregister_patch(struct klp_patch *patch)
779 mutex_lock(&klp_mutex);
781 if (!klp_is_patch_registered(patch)) {
786 if (patch->enabled) {
791 klp_free_patch(patch);
793 mutex_unlock(&klp_mutex);
795 kobject_put(&patch->kobj);
796 wait_for_completion(&patch->finish);
800 mutex_unlock(&klp_mutex);
803 EXPORT_SYMBOL_GPL(klp_unregister_patch);
806 * klp_register_patch() - registers a patch
807 * @patch: Patch to be registered
809 * Initializes the data structure associated with the patch and
810 * creates the sysfs interface.
812 * There is no need to take the reference on the patch module here. It is done
813 * later when the patch is enabled.
815 * Return: 0 on success, otherwise error
817 int klp_register_patch(struct klp_patch *patch)
819 if (!patch || !patch->mod)
822 if (!is_livepatch_module(patch->mod)) {
823 pr_err("module %s is not marked as a livepatch module\n",
828 if (!klp_initialized())
832 * Architectures without reliable stack traces have to set
833 * patch->immediate because there's currently no way to patch kthreads
834 * with the consistency model.
836 if (!klp_have_reliable_stack() && !patch->immediate) {
837 pr_err("This architecture doesn't have support for the livepatch consistency model.\n");
841 return klp_init_patch(patch);
843 EXPORT_SYMBOL_GPL(klp_register_patch);
846 * Remove parts of patches that touch a given kernel module. The list of
847 * patches processed might be limited. When limit is NULL, all patches
850 static void klp_cleanup_module_patches_limited(struct module *mod,
851 struct klp_patch *limit)
853 struct klp_patch *patch;
854 struct klp_object *obj;
856 list_for_each_entry(patch, &klp_patches, list) {
860 klp_for_each_object(patch, obj) {
861 if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
865 * Only unpatch the module if the patch is enabled or
868 if (patch->enabled || patch == klp_transition_patch) {
869 pr_notice("reverting patch '%s' on unloading module '%s'\n",
870 patch->mod->name, obj->mod->name);
871 klp_unpatch_object(obj);
874 klp_free_object_loaded(obj);
880 int klp_module_coming(struct module *mod)
883 struct klp_patch *patch;
884 struct klp_object *obj;
886 if (WARN_ON(mod->state != MODULE_STATE_COMING))
889 mutex_lock(&klp_mutex);
891 * Each module has to know that klp_module_coming()
892 * has been called. We never know what module will
893 * get patched by a new patch.
895 mod->klp_alive = true;
897 list_for_each_entry(patch, &klp_patches, list) {
898 klp_for_each_object(patch, obj) {
899 if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
904 ret = klp_init_object_loaded(patch, obj);
906 pr_warn("failed to initialize patch '%s' for module '%s' (%d)\n",
907 patch->mod->name, obj->mod->name, ret);
912 * Only patch the module if the patch is enabled or is
915 if (!patch->enabled && patch != klp_transition_patch)
918 pr_notice("applying patch '%s' to loading module '%s'\n",
919 patch->mod->name, obj->mod->name);
921 ret = klp_patch_object(obj);
923 pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
924 patch->mod->name, obj->mod->name, ret);
932 mutex_unlock(&klp_mutex);
938 * If a patch is unsuccessfully applied, return
939 * error to the module loader.
941 pr_warn("patch '%s' failed for module '%s', refusing to load module '%s'\n",
942 patch->mod->name, obj->mod->name, obj->mod->name);
943 mod->klp_alive = false;
945 klp_cleanup_module_patches_limited(mod, patch);
946 mutex_unlock(&klp_mutex);
951 void klp_module_going(struct module *mod)
953 if (WARN_ON(mod->state != MODULE_STATE_GOING &&
954 mod->state != MODULE_STATE_COMING))
957 mutex_lock(&klp_mutex);
959 * Each module has to know that klp_module_going()
960 * has been called. We never know what module will
961 * get patched by a new patch.
963 mod->klp_alive = false;
965 klp_cleanup_module_patches_limited(mod, NULL);
967 mutex_unlock(&klp_mutex);
970 static int __init klp_init(void)
974 ret = klp_check_compiler_support();
976 pr_info("Your compiler is too old; turning off.\n");
980 klp_root_kobj = kobject_create_and_add("livepatch", kernel_kobj);
987 module_init(klp_init);