1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * core.c - Kernel Live Patching Core
4 *
5 * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
6 * Copyright (C) 2014 SUSE
7 */
8
9 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
10
11 #include <linux/module.h>
12 #include <linux/kernel.h>
13 #include <linux/mutex.h>
14 #include <linux/slab.h>
15 #include <linux/list.h>
16 #include <linux/kallsyms.h>
17 #include <linux/livepatch.h>
18 #include <linux/elf.h>
19 #include <linux/moduleloader.h>
20 #include <linux/completion.h>
21 #include <linux/memory.h>
22 #include <linux/rcupdate.h>
23 #include <asm/cacheflush.h>
24 #include "core.h"
25 #include "patch.h"
26 #include "state.h"
27 #include "transition.h"
28
29 /*
30 * klp_mutex is a coarse lock which serializes access to klp data. All
31 * accesses to klp-related variables and structures must have mutex protection,
32 * except within the following functions which carefully avoid the need for it:
33 *
34 * - klp_ftrace_handler()
35 * - klp_update_patch_state()
36 */
37 DEFINE_MUTEX(klp_mutex);
38
39 /*
40 * Actively used patches: enabled or in transition. Note that replaced
41 * or disabled patches are not listed even though the related kernel
42 * module still can be loaded.
43 */
44 LIST_HEAD(klp_patches);
45
46 static struct kobject *klp_root_kobj;
47
klp_is_module(struct klp_object * obj)48 static bool klp_is_module(struct klp_object *obj)
49 {
50 return obj->name;
51 }
52
53 /* sets obj->mod if object is not vmlinux and module is found */
klp_find_object_module(struct klp_object * obj)54 static void klp_find_object_module(struct klp_object *obj)
55 {
56 struct module *mod;
57
58 if (!klp_is_module(obj))
59 return;
60
61 rcu_read_lock_sched();
62 /*
63 * We do not want to block removal of patched modules and therefore
64 * we do not take a reference here. The patches are removed by
65 * klp_module_going() instead.
66 */
67 mod = find_module(obj->name);
68 /*
69 * Do not mess work of klp_module_coming() and klp_module_going().
70 * Note that the patch might still be needed before klp_module_going()
71 * is called. Module functions can be called even in the GOING state
72 * until mod->exit() finishes. This is especially important for
73 * patches that modify semantic of the functions.
74 */
75 if (mod && mod->klp_alive)
76 obj->mod = mod;
77
78 rcu_read_unlock_sched();
79 }
80
klp_initialized(void)81 static bool klp_initialized(void)
82 {
83 return !!klp_root_kobj;
84 }
85
klp_find_func(struct klp_object * obj,struct klp_func * old_func)86 static struct klp_func *klp_find_func(struct klp_object *obj,
87 struct klp_func *old_func)
88 {
89 struct klp_func *func;
90
91 klp_for_each_func(obj, func) {
92 if ((strcmp(old_func->old_name, func->old_name) == 0) &&
93 (old_func->old_sympos == func->old_sympos)) {
94 return func;
95 }
96 }
97
98 return NULL;
99 }
100
klp_find_object(struct klp_patch * patch,struct klp_object * old_obj)101 static struct klp_object *klp_find_object(struct klp_patch *patch,
102 struct klp_object *old_obj)
103 {
104 struct klp_object *obj;
105
106 klp_for_each_object(patch, obj) {
107 if (klp_is_module(old_obj)) {
108 if (klp_is_module(obj) &&
109 strcmp(old_obj->name, obj->name) == 0) {
110 return obj;
111 }
112 } else if (!klp_is_module(obj)) {
113 return obj;
114 }
115 }
116
117 return NULL;
118 }
119
120 struct klp_find_arg {
121 const char *objname;
122 const char *name;
123 unsigned long addr;
124 unsigned long count;
125 unsigned long pos;
126 };
127
klp_find_callback(void * data,const char * name,struct module * mod,unsigned long addr)128 static int klp_find_callback(void *data, const char *name,
129 struct module *mod, unsigned long addr)
130 {
131 struct klp_find_arg *args = data;
132
133 if ((mod && !args->objname) || (!mod && args->objname))
134 return 0;
135
136 if (strcmp(args->name, name))
137 return 0;
138
139 if (args->objname && strcmp(args->objname, mod->name))
140 return 0;
141
142 args->addr = addr;
143 args->count++;
144
145 /*
146 * Finish the search when the symbol is found for the desired position
147 * or the position is not defined for a non-unique symbol.
148 */
149 if ((args->pos && (args->count == args->pos)) ||
150 (!args->pos && (args->count > 1)))
151 return 1;
152
153 return 0;
154 }
155
klp_find_object_symbol(const char * objname,const char * name,unsigned long sympos,unsigned long * addr)156 static int klp_find_object_symbol(const char *objname, const char *name,
157 unsigned long sympos, unsigned long *addr)
158 {
159 struct klp_find_arg args = {
160 .objname = objname,
161 .name = name,
162 .addr = 0,
163 .count = 0,
164 .pos = sympos,
165 };
166
167 if (objname)
168 module_kallsyms_on_each_symbol(klp_find_callback, &args);
169 else
170 kallsyms_on_each_symbol(klp_find_callback, &args);
171
172 /*
173 * Ensure an address was found. If sympos is 0, ensure symbol is unique;
174 * otherwise ensure the symbol position count matches sympos.
175 */
176 if (args.addr == 0)
177 pr_err("symbol '%s' not found in symbol table\n", name);
178 else if (args.count > 1 && sympos == 0) {
179 pr_err("unresolvable ambiguity for symbol '%s' in object '%s'\n",
180 name, objname);
181 } else if (sympos != args.count && sympos > 0) {
182 pr_err("symbol position %lu for symbol '%s' in object '%s' not found\n",
183 sympos, name, objname ? objname : "vmlinux");
184 } else {
185 *addr = args.addr;
186 return 0;
187 }
188
189 *addr = 0;
190 return -EINVAL;
191 }
192
klp_resolve_symbols(Elf_Shdr * sechdrs,const char * strtab,unsigned int symndx,Elf_Shdr * relasec,const char * sec_objname)193 static int klp_resolve_symbols(Elf_Shdr *sechdrs, const char *strtab,
194 unsigned int symndx, Elf_Shdr *relasec,
195 const char *sec_objname)
196 {
197 int i, cnt, ret;
198 char sym_objname[MODULE_NAME_LEN];
199 char sym_name[KSYM_NAME_LEN];
200 Elf_Rela *relas;
201 Elf_Sym *sym;
202 unsigned long sympos, addr;
203 bool sym_vmlinux;
204 bool sec_vmlinux = !strcmp(sec_objname, "vmlinux");
205
206 /*
207 * Since the field widths for sym_objname and sym_name in the sscanf()
208 * call are hard-coded and correspond to MODULE_NAME_LEN and
209 * KSYM_NAME_LEN respectively, we must make sure that MODULE_NAME_LEN
210 * and KSYM_NAME_LEN have the values we expect them to have.
211 *
212 * Because the value of MODULE_NAME_LEN can differ among architectures,
213 * we use the smallest/strictest upper bound possible (56, based on
214 * the current definition of MODULE_NAME_LEN) to prevent overflows.
215 */
216 BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 512);
217
218 relas = (Elf_Rela *) relasec->sh_addr;
219 /* For each rela in this klp relocation section */
220 for (i = 0; i < relasec->sh_size / sizeof(Elf_Rela); i++) {
221 sym = (Elf_Sym *)sechdrs[symndx].sh_addr + ELF_R_SYM(relas[i].r_info);
222 if (sym->st_shndx != SHN_LIVEPATCH) {
223 pr_err("symbol %s is not marked as a livepatch symbol\n",
224 strtab + sym->st_name);
225 return -EINVAL;
226 }
227
228 /* Format: .klp.sym.sym_objname.sym_name,sympos */
229 cnt = sscanf(strtab + sym->st_name,
230 ".klp.sym.%55[^.].%511[^,],%lu",
231 sym_objname, sym_name, &sympos);
232 if (cnt != 3) {
233 pr_err("symbol %s has an incorrectly formatted name\n",
234 strtab + sym->st_name);
235 return -EINVAL;
236 }
237
238 sym_vmlinux = !strcmp(sym_objname, "vmlinux");
239
240 /*
241 * Prevent module-specific KLP rela sections from referencing
242 * vmlinux symbols. This helps prevent ordering issues with
243 * module special section initializations. Presumably such
244 * symbols are exported and normal relas can be used instead.
245 */
246 if (!sec_vmlinux && sym_vmlinux) {
247 pr_err("invalid access to vmlinux symbol '%s' from module-specific livepatch relocation section",
248 sym_name);
249 return -EINVAL;
250 }
251
252 /* klp_find_object_symbol() treats a NULL objname as vmlinux */
253 ret = klp_find_object_symbol(sym_vmlinux ? NULL : sym_objname,
254 sym_name, sympos, &addr);
255 if (ret)
256 return ret;
257
258 sym->st_value = addr;
259 }
260
261 return 0;
262 }
263
264 /*
265 * At a high-level, there are two types of klp relocation sections: those which
266 * reference symbols which live in vmlinux; and those which reference symbols
267 * which live in other modules. This function is called for both types:
268 *
269 * 1) When a klp module itself loads, the module code calls this function to
270 * write vmlinux-specific klp relocations (.klp.rela.vmlinux.* sections).
271 * These relocations are written to the klp module text to allow the patched
272 * code/data to reference unexported vmlinux symbols. They're written as
273 * early as possible to ensure that other module init code (.e.g.,
274 * jump_label_apply_nops) can access any unexported vmlinux symbols which
275 * might be referenced by the klp module's special sections.
276 *
277 * 2) When a to-be-patched module loads -- or is already loaded when a
278 * corresponding klp module loads -- klp code calls this function to write
279 * module-specific klp relocations (.klp.rela.{module}.* sections). These
280 * are written to the klp module text to allow the patched code/data to
281 * reference symbols which live in the to-be-patched module or one of its
282 * module dependencies. Exported symbols are supported, in addition to
283 * unexported symbols, in order to enable late module patching, which allows
284 * the to-be-patched module to be loaded and patched sometime *after* the
285 * klp module is loaded.
286 */
klp_apply_section_relocs(struct module * pmod,Elf_Shdr * sechdrs,const char * shstrtab,const char * strtab,unsigned int symndx,unsigned int secndx,const char * objname)287 int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
288 const char *shstrtab, const char *strtab,
289 unsigned int symndx, unsigned int secndx,
290 const char *objname)
291 {
292 int cnt, ret;
293 char sec_objname[MODULE_NAME_LEN];
294 Elf_Shdr *sec = sechdrs + secndx;
295
296 /*
297 * Format: .klp.rela.sec_objname.section_name
298 * See comment in klp_resolve_symbols() for an explanation
299 * of the selected field width value.
300 */
301 cnt = sscanf(shstrtab + sec->sh_name, ".klp.rela.%55[^.]",
302 sec_objname);
303 if (cnt != 1) {
304 pr_err("section %s has an incorrectly formatted name\n",
305 shstrtab + sec->sh_name);
306 return -EINVAL;
307 }
308
309 if (strcmp(objname ? objname : "vmlinux", sec_objname))
310 return 0;
311
312 ret = klp_resolve_symbols(sechdrs, strtab, symndx, sec, sec_objname);
313 if (ret)
314 return ret;
315
316 return apply_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
317 }
318
319 /*
320 * Sysfs Interface
321 *
322 * /sys/kernel/livepatch
323 * /sys/kernel/livepatch/<patch>
324 * /sys/kernel/livepatch/<patch>/enabled
325 * /sys/kernel/livepatch/<patch>/transition
326 * /sys/kernel/livepatch/<patch>/force
327 * /sys/kernel/livepatch/<patch>/<object>
328 * /sys/kernel/livepatch/<patch>/<object>/patched
329 * /sys/kernel/livepatch/<patch>/<object>/<function,sympos>
330 */
331 static int __klp_disable_patch(struct klp_patch *patch);
332
enabled_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)333 static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
334 const char *buf, size_t count)
335 {
336 struct klp_patch *patch;
337 int ret;
338 bool enabled;
339
340 ret = kstrtobool(buf, &enabled);
341 if (ret)
342 return ret;
343
344 patch = container_of(kobj, struct klp_patch, kobj);
345
346 mutex_lock(&klp_mutex);
347
348 if (patch->enabled == enabled) {
349 /* already in requested state */
350 ret = -EINVAL;
351 goto out;
352 }
353
354 /*
355 * Allow to reverse a pending transition in both ways. It might be
356 * necessary to complete the transition without forcing and breaking
357 * the system integrity.
358 *
359 * Do not allow to re-enable a disabled patch.
360 */
361 if (patch == klp_transition_patch)
362 klp_reverse_transition();
363 else if (!enabled)
364 ret = __klp_disable_patch(patch);
365 else
366 ret = -EINVAL;
367
368 out:
369 mutex_unlock(&klp_mutex);
370
371 if (ret)
372 return ret;
373 return count;
374 }
375
enabled_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)376 static ssize_t enabled_show(struct kobject *kobj,
377 struct kobj_attribute *attr, char *buf)
378 {
379 struct klp_patch *patch;
380
381 patch = container_of(kobj, struct klp_patch, kobj);
382 return snprintf(buf, PAGE_SIZE-1, "%d\n", patch->enabled);
383 }
384
transition_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)385 static ssize_t transition_show(struct kobject *kobj,
386 struct kobj_attribute *attr, char *buf)
387 {
388 struct klp_patch *patch;
389
390 patch = container_of(kobj, struct klp_patch, kobj);
391 return snprintf(buf, PAGE_SIZE-1, "%d\n",
392 patch == klp_transition_patch);
393 }
394
force_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)395 static ssize_t force_store(struct kobject *kobj, struct kobj_attribute *attr,
396 const char *buf, size_t count)
397 {
398 struct klp_patch *patch;
399 int ret;
400 bool val;
401
402 ret = kstrtobool(buf, &val);
403 if (ret)
404 return ret;
405
406 if (!val)
407 return count;
408
409 mutex_lock(&klp_mutex);
410
411 patch = container_of(kobj, struct klp_patch, kobj);
412 if (patch != klp_transition_patch) {
413 mutex_unlock(&klp_mutex);
414 return -EINVAL;
415 }
416
417 klp_force_transition();
418
419 mutex_unlock(&klp_mutex);
420
421 return count;
422 }
423
424 static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled);
425 static struct kobj_attribute transition_kobj_attr = __ATTR_RO(transition);
426 static struct kobj_attribute force_kobj_attr = __ATTR_WO(force);
427 static struct attribute *klp_patch_attrs[] = {
428 &enabled_kobj_attr.attr,
429 &transition_kobj_attr.attr,
430 &force_kobj_attr.attr,
431 NULL
432 };
433 ATTRIBUTE_GROUPS(klp_patch);
434
patched_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)435 static ssize_t patched_show(struct kobject *kobj,
436 struct kobj_attribute *attr, char *buf)
437 {
438 struct klp_object *obj;
439
440 obj = container_of(kobj, struct klp_object, kobj);
441 return sysfs_emit(buf, "%d\n", obj->patched);
442 }
443
444 static struct kobj_attribute patched_kobj_attr = __ATTR_RO(patched);
445 static struct attribute *klp_object_attrs[] = {
446 &patched_kobj_attr.attr,
447 NULL,
448 };
449 ATTRIBUTE_GROUPS(klp_object);
450
klp_free_object_dynamic(struct klp_object * obj)451 static void klp_free_object_dynamic(struct klp_object *obj)
452 {
453 kfree(obj->name);
454 kfree(obj);
455 }
456
457 static void klp_init_func_early(struct klp_object *obj,
458 struct klp_func *func);
459 static void klp_init_object_early(struct klp_patch *patch,
460 struct klp_object *obj);
461
klp_alloc_object_dynamic(const char * name,struct klp_patch * patch)462 static struct klp_object *klp_alloc_object_dynamic(const char *name,
463 struct klp_patch *patch)
464 {
465 struct klp_object *obj;
466
467 obj = kzalloc(sizeof(*obj), GFP_KERNEL);
468 if (!obj)
469 return NULL;
470
471 if (name) {
472 obj->name = kstrdup(name, GFP_KERNEL);
473 if (!obj->name) {
474 kfree(obj);
475 return NULL;
476 }
477 }
478
479 klp_init_object_early(patch, obj);
480 obj->dynamic = true;
481
482 return obj;
483 }
484
klp_free_func_nop(struct klp_func * func)485 static void klp_free_func_nop(struct klp_func *func)
486 {
487 kfree(func->old_name);
488 kfree(func);
489 }
490
klp_alloc_func_nop(struct klp_func * old_func,struct klp_object * obj)491 static struct klp_func *klp_alloc_func_nop(struct klp_func *old_func,
492 struct klp_object *obj)
493 {
494 struct klp_func *func;
495
496 func = kzalloc(sizeof(*func), GFP_KERNEL);
497 if (!func)
498 return NULL;
499
500 if (old_func->old_name) {
501 func->old_name = kstrdup(old_func->old_name, GFP_KERNEL);
502 if (!func->old_name) {
503 kfree(func);
504 return NULL;
505 }
506 }
507
508 klp_init_func_early(obj, func);
509 /*
510 * func->new_func is same as func->old_func. These addresses are
511 * set when the object is loaded, see klp_init_object_loaded().
512 */
513 func->old_sympos = old_func->old_sympos;
514 func->nop = true;
515
516 return func;
517 }
518
klp_add_object_nops(struct klp_patch * patch,struct klp_object * old_obj)519 static int klp_add_object_nops(struct klp_patch *patch,
520 struct klp_object *old_obj)
521 {
522 struct klp_object *obj;
523 struct klp_func *func, *old_func;
524
525 obj = klp_find_object(patch, old_obj);
526
527 if (!obj) {
528 obj = klp_alloc_object_dynamic(old_obj->name, patch);
529 if (!obj)
530 return -ENOMEM;
531 }
532
533 klp_for_each_func(old_obj, old_func) {
534 func = klp_find_func(obj, old_func);
535 if (func)
536 continue;
537
538 func = klp_alloc_func_nop(old_func, obj);
539 if (!func)
540 return -ENOMEM;
541 }
542
543 return 0;
544 }
545
546 /*
547 * Add 'nop' functions which simply return to the caller to run
548 * the original function. The 'nop' functions are added to a
549 * patch to facilitate a 'replace' mode.
550 */
klp_add_nops(struct klp_patch * patch)551 static int klp_add_nops(struct klp_patch *patch)
552 {
553 struct klp_patch *old_patch;
554 struct klp_object *old_obj;
555
556 klp_for_each_patch(old_patch) {
557 klp_for_each_object(old_patch, old_obj) {
558 int err;
559
560 err = klp_add_object_nops(patch, old_obj);
561 if (err)
562 return err;
563 }
564 }
565
566 return 0;
567 }
568
klp_kobj_release_patch(struct kobject * kobj)569 static void klp_kobj_release_patch(struct kobject *kobj)
570 {
571 struct klp_patch *patch;
572
573 patch = container_of(kobj, struct klp_patch, kobj);
574 complete(&patch->finish);
575 }
576
577 static struct kobj_type klp_ktype_patch = {
578 .release = klp_kobj_release_patch,
579 .sysfs_ops = &kobj_sysfs_ops,
580 .default_groups = klp_patch_groups,
581 };
582
klp_kobj_release_object(struct kobject * kobj)583 static void klp_kobj_release_object(struct kobject *kobj)
584 {
585 struct klp_object *obj;
586
587 obj = container_of(kobj, struct klp_object, kobj);
588
589 if (obj->dynamic)
590 klp_free_object_dynamic(obj);
591 }
592
593 static struct kobj_type klp_ktype_object = {
594 .release = klp_kobj_release_object,
595 .sysfs_ops = &kobj_sysfs_ops,
596 .default_groups = klp_object_groups,
597 };
598
klp_kobj_release_func(struct kobject * kobj)599 static void klp_kobj_release_func(struct kobject *kobj)
600 {
601 struct klp_func *func;
602
603 func = container_of(kobj, struct klp_func, kobj);
604
605 if (func->nop)
606 klp_free_func_nop(func);
607 }
608
609 static struct kobj_type klp_ktype_func = {
610 .release = klp_kobj_release_func,
611 .sysfs_ops = &kobj_sysfs_ops,
612 };
613
__klp_free_funcs(struct klp_object * obj,bool nops_only)614 static void __klp_free_funcs(struct klp_object *obj, bool nops_only)
615 {
616 struct klp_func *func, *tmp_func;
617
618 klp_for_each_func_safe(obj, func, tmp_func) {
619 if (nops_only && !func->nop)
620 continue;
621
622 list_del(&func->node);
623 kobject_put(&func->kobj);
624 }
625 }
626
627 /* Clean up when a patched object is unloaded */
klp_free_object_loaded(struct klp_object * obj)628 static void klp_free_object_loaded(struct klp_object *obj)
629 {
630 struct klp_func *func;
631
632 obj->mod = NULL;
633
634 klp_for_each_func(obj, func) {
635 func->old_func = NULL;
636
637 if (func->nop)
638 func->new_func = NULL;
639 }
640 }
641
__klp_free_objects(struct klp_patch * patch,bool nops_only)642 static void __klp_free_objects(struct klp_patch *patch, bool nops_only)
643 {
644 struct klp_object *obj, *tmp_obj;
645
646 klp_for_each_object_safe(patch, obj, tmp_obj) {
647 __klp_free_funcs(obj, nops_only);
648
649 if (nops_only && !obj->dynamic)
650 continue;
651
652 list_del(&obj->node);
653 kobject_put(&obj->kobj);
654 }
655 }
656
klp_free_objects(struct klp_patch * patch)657 static void klp_free_objects(struct klp_patch *patch)
658 {
659 __klp_free_objects(patch, false);
660 }
661
klp_free_objects_dynamic(struct klp_patch * patch)662 static void klp_free_objects_dynamic(struct klp_patch *patch)
663 {
664 __klp_free_objects(patch, true);
665 }
666
667 /*
668 * This function implements the free operations that can be called safely
669 * under klp_mutex.
670 *
671 * The operation must be completed by calling klp_free_patch_finish()
672 * outside klp_mutex.
673 */
klp_free_patch_start(struct klp_patch * patch)674 static void klp_free_patch_start(struct klp_patch *patch)
675 {
676 if (!list_empty(&patch->list))
677 list_del(&patch->list);
678
679 klp_free_objects(patch);
680 }
681
682 /*
683 * This function implements the free part that must be called outside
684 * klp_mutex.
685 *
686 * It must be called after klp_free_patch_start(). And it has to be
687 * the last function accessing the livepatch structures when the patch
688 * gets disabled.
689 */
klp_free_patch_finish(struct klp_patch * patch)690 static void klp_free_patch_finish(struct klp_patch *patch)
691 {
692 /*
693 * Avoid deadlock with enabled_store() sysfs callback by
694 * calling this outside klp_mutex. It is safe because
695 * this is called when the patch gets disabled and it
696 * cannot get enabled again.
697 */
698 kobject_put(&patch->kobj);
699 wait_for_completion(&patch->finish);
700
701 /* Put the module after the last access to struct klp_patch. */
702 if (!patch->forced)
703 module_put(patch->mod);
704 }
705
706 /*
707 * The livepatch might be freed from sysfs interface created by the patch.
708 * This work allows to wait until the interface is destroyed in a separate
709 * context.
710 */
klp_free_patch_work_fn(struct work_struct * work)711 static void klp_free_patch_work_fn(struct work_struct *work)
712 {
713 struct klp_patch *patch =
714 container_of(work, struct klp_patch, free_work);
715
716 klp_free_patch_finish(patch);
717 }
718
klp_free_patch_async(struct klp_patch * patch)719 void klp_free_patch_async(struct klp_patch *patch)
720 {
721 klp_free_patch_start(patch);
722 schedule_work(&patch->free_work);
723 }
724
klp_free_replaced_patches_async(struct klp_patch * new_patch)725 void klp_free_replaced_patches_async(struct klp_patch *new_patch)
726 {
727 struct klp_patch *old_patch, *tmp_patch;
728
729 klp_for_each_patch_safe(old_patch, tmp_patch) {
730 if (old_patch == new_patch)
731 return;
732 klp_free_patch_async(old_patch);
733 }
734 }
735
klp_init_func(struct klp_object * obj,struct klp_func * func)736 static int klp_init_func(struct klp_object *obj, struct klp_func *func)
737 {
738 if (!func->old_name)
739 return -EINVAL;
740
741 /*
742 * NOPs get the address later. The patched module must be loaded,
743 * see klp_init_object_loaded().
744 */
745 if (!func->new_func && !func->nop)
746 return -EINVAL;
747
748 if (strlen(func->old_name) >= KSYM_NAME_LEN)
749 return -EINVAL;
750
751 INIT_LIST_HEAD(&func->stack_node);
752 func->patched = false;
753 func->transition = false;
754
755 /* The format for the sysfs directory is <function,sympos> where sympos
756 * is the nth occurrence of this symbol in kallsyms for the patched
757 * object. If the user selects 0 for old_sympos, then 1 will be used
758 * since a unique symbol will be the first occurrence.
759 */
760 return kobject_add(&func->kobj, &obj->kobj, "%s,%lu",
761 func->old_name,
762 func->old_sympos ? func->old_sympos : 1);
763 }
764
klp_apply_object_relocs(struct klp_patch * patch,struct klp_object * obj)765 static int klp_apply_object_relocs(struct klp_patch *patch,
766 struct klp_object *obj)
767 {
768 int i, ret;
769 struct klp_modinfo *info = patch->mod->klp_info;
770
771 for (i = 1; i < info->hdr.e_shnum; i++) {
772 Elf_Shdr *sec = info->sechdrs + i;
773
774 if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
775 continue;
776
777 ret = klp_apply_section_relocs(patch->mod, info->sechdrs,
778 info->secstrings,
779 patch->mod->core_kallsyms.strtab,
780 info->symndx, i, obj->name);
781 if (ret)
782 return ret;
783 }
784
785 return 0;
786 }
787
788 /* parts of the initialization that is done only when the object is loaded */
klp_init_object_loaded(struct klp_patch * patch,struct klp_object * obj)789 static int klp_init_object_loaded(struct klp_patch *patch,
790 struct klp_object *obj)
791 {
792 struct klp_func *func;
793 int ret;
794
795 if (klp_is_module(obj)) {
796 /*
797 * Only write module-specific relocations here
798 * (.klp.rela.{module}.*). vmlinux-specific relocations were
799 * written earlier during the initialization of the klp module
800 * itself.
801 */
802 ret = klp_apply_object_relocs(patch, obj);
803 if (ret)
804 return ret;
805 }
806
807 klp_for_each_func(obj, func) {
808 ret = klp_find_object_symbol(obj->name, func->old_name,
809 func->old_sympos,
810 (unsigned long *)&func->old_func);
811 if (ret)
812 return ret;
813
814 ret = kallsyms_lookup_size_offset((unsigned long)func->old_func,
815 &func->old_size, NULL);
816 if (!ret) {
817 pr_err("kallsyms size lookup failed for '%s'\n",
818 func->old_name);
819 return -ENOENT;
820 }
821
822 if (func->nop)
823 func->new_func = func->old_func;
824
825 ret = kallsyms_lookup_size_offset((unsigned long)func->new_func,
826 &func->new_size, NULL);
827 if (!ret) {
828 pr_err("kallsyms size lookup failed for '%s' replacement\n",
829 func->old_name);
830 return -ENOENT;
831 }
832 }
833
834 return 0;
835 }
836
klp_init_object(struct klp_patch * patch,struct klp_object * obj)837 static int klp_init_object(struct klp_patch *patch, struct klp_object *obj)
838 {
839 struct klp_func *func;
840 int ret;
841 const char *name;
842
843 if (klp_is_module(obj) && strlen(obj->name) >= MODULE_NAME_LEN)
844 return -EINVAL;
845
846 obj->patched = false;
847 obj->mod = NULL;
848
849 klp_find_object_module(obj);
850
851 name = klp_is_module(obj) ? obj->name : "vmlinux";
852 ret = kobject_add(&obj->kobj, &patch->kobj, "%s", name);
853 if (ret)
854 return ret;
855
856 klp_for_each_func(obj, func) {
857 ret = klp_init_func(obj, func);
858 if (ret)
859 return ret;
860 }
861
862 if (klp_is_object_loaded(obj))
863 ret = klp_init_object_loaded(patch, obj);
864
865 return ret;
866 }
867
klp_init_func_early(struct klp_object * obj,struct klp_func * func)868 static void klp_init_func_early(struct klp_object *obj,
869 struct klp_func *func)
870 {
871 kobject_init(&func->kobj, &klp_ktype_func);
872 list_add_tail(&func->node, &obj->func_list);
873 }
874
klp_init_object_early(struct klp_patch * patch,struct klp_object * obj)875 static void klp_init_object_early(struct klp_patch *patch,
876 struct klp_object *obj)
877 {
878 INIT_LIST_HEAD(&obj->func_list);
879 kobject_init(&obj->kobj, &klp_ktype_object);
880 list_add_tail(&obj->node, &patch->obj_list);
881 }
882
klp_init_patch_early(struct klp_patch * patch)883 static void klp_init_patch_early(struct klp_patch *patch)
884 {
885 struct klp_object *obj;
886 struct klp_func *func;
887
888 INIT_LIST_HEAD(&patch->list);
889 INIT_LIST_HEAD(&patch->obj_list);
890 kobject_init(&patch->kobj, &klp_ktype_patch);
891 patch->enabled = false;
892 patch->forced = false;
893 INIT_WORK(&patch->free_work, klp_free_patch_work_fn);
894 init_completion(&patch->finish);
895
896 klp_for_each_object_static(patch, obj) {
897 klp_init_object_early(patch, obj);
898
899 klp_for_each_func_static(obj, func) {
900 klp_init_func_early(obj, func);
901 }
902 }
903 }
904
klp_init_patch(struct klp_patch * patch)905 static int klp_init_patch(struct klp_patch *patch)
906 {
907 struct klp_object *obj;
908 int ret;
909
910 ret = kobject_add(&patch->kobj, klp_root_kobj, "%s", patch->mod->name);
911 if (ret)
912 return ret;
913
914 if (patch->replace) {
915 ret = klp_add_nops(patch);
916 if (ret)
917 return ret;
918 }
919
920 klp_for_each_object(patch, obj) {
921 ret = klp_init_object(patch, obj);
922 if (ret)
923 return ret;
924 }
925
926 list_add_tail(&patch->list, &klp_patches);
927
928 return 0;
929 }
930
__klp_disable_patch(struct klp_patch * patch)931 static int __klp_disable_patch(struct klp_patch *patch)
932 {
933 struct klp_object *obj;
934
935 if (WARN_ON(!patch->enabled))
936 return -EINVAL;
937
938 if (klp_transition_patch)
939 return -EBUSY;
940
941 klp_init_transition(patch, KLP_UNPATCHED);
942
943 klp_for_each_object(patch, obj)
944 if (obj->patched)
945 klp_pre_unpatch_callback(obj);
946
947 /*
948 * Enforce the order of the func->transition writes in
949 * klp_init_transition() and the TIF_PATCH_PENDING writes in
950 * klp_start_transition(). In the rare case where klp_ftrace_handler()
951 * is called shortly after klp_update_patch_state() switches the task,
952 * this ensures the handler sees that func->transition is set.
953 */
954 smp_wmb();
955
956 klp_start_transition();
957 patch->enabled = false;
958 klp_try_complete_transition();
959
960 return 0;
961 }
962
__klp_enable_patch(struct klp_patch * patch)963 static int __klp_enable_patch(struct klp_patch *patch)
964 {
965 struct klp_object *obj;
966 int ret;
967
968 if (klp_transition_patch)
969 return -EBUSY;
970
971 if (WARN_ON(patch->enabled))
972 return -EINVAL;
973
974 pr_notice("enabling patch '%s'\n", patch->mod->name);
975
976 klp_init_transition(patch, KLP_PATCHED);
977
978 /*
979 * Enforce the order of the func->transition writes in
980 * klp_init_transition() and the ops->func_stack writes in
981 * klp_patch_object(), so that klp_ftrace_handler() will see the
982 * func->transition updates before the handler is registered and the
983 * new funcs become visible to the handler.
984 */
985 smp_wmb();
986
987 klp_for_each_object(patch, obj) {
988 if (!klp_is_object_loaded(obj))
989 continue;
990
991 ret = klp_pre_patch_callback(obj);
992 if (ret) {
993 pr_warn("pre-patch callback failed for object '%s'\n",
994 klp_is_module(obj) ? obj->name : "vmlinux");
995 goto err;
996 }
997
998 ret = klp_patch_object(obj);
999 if (ret) {
1000 pr_warn("failed to patch object '%s'\n",
1001 klp_is_module(obj) ? obj->name : "vmlinux");
1002 goto err;
1003 }
1004 }
1005
1006 klp_start_transition();
1007 patch->enabled = true;
1008 klp_try_complete_transition();
1009
1010 return 0;
1011 err:
1012 pr_warn("failed to enable patch '%s'\n", patch->mod->name);
1013
1014 klp_cancel_transition();
1015 return ret;
1016 }
1017
1018 /**
1019 * klp_enable_patch() - enable the livepatch
1020 * @patch: patch to be enabled
1021 *
1022 * Initializes the data structure associated with the patch, creates the sysfs
1023 * interface, performs the needed symbol lookups and code relocations,
1024 * registers the patched functions with ftrace.
1025 *
1026 * This function is supposed to be called from the livepatch module_init()
1027 * callback.
1028 *
1029 * Return: 0 on success, otherwise error
1030 */
klp_enable_patch(struct klp_patch * patch)1031 int klp_enable_patch(struct klp_patch *patch)
1032 {
1033 int ret;
1034 struct klp_object *obj;
1035
1036 if (!patch || !patch->mod || !patch->objs)
1037 return -EINVAL;
1038
1039 klp_for_each_object_static(patch, obj) {
1040 if (!obj->funcs)
1041 return -EINVAL;
1042 }
1043
1044
1045 if (!is_livepatch_module(patch->mod)) {
1046 pr_err("module %s is not marked as a livepatch module\n",
1047 patch->mod->name);
1048 return -EINVAL;
1049 }
1050
1051 if (!klp_initialized())
1052 return -ENODEV;
1053
1054 if (!klp_have_reliable_stack()) {
1055 pr_warn("This architecture doesn't have support for the livepatch consistency model.\n");
1056 pr_warn("The livepatch transition may never complete.\n");
1057 }
1058
1059 mutex_lock(&klp_mutex);
1060
1061 if (!klp_is_patch_compatible(patch)) {
1062 pr_err("Livepatch patch (%s) is not compatible with the already installed livepatches.\n",
1063 patch->mod->name);
1064 mutex_unlock(&klp_mutex);
1065 return -EINVAL;
1066 }
1067
1068 if (!try_module_get(patch->mod)) {
1069 mutex_unlock(&klp_mutex);
1070 return -ENODEV;
1071 }
1072
1073 klp_init_patch_early(patch);
1074
1075 ret = klp_init_patch(patch);
1076 if (ret)
1077 goto err;
1078
1079 ret = __klp_enable_patch(patch);
1080 if (ret)
1081 goto err;
1082
1083 mutex_unlock(&klp_mutex);
1084
1085 return 0;
1086
1087 err:
1088 klp_free_patch_start(patch);
1089
1090 mutex_unlock(&klp_mutex);
1091
1092 klp_free_patch_finish(patch);
1093
1094 return ret;
1095 }
1096 EXPORT_SYMBOL_GPL(klp_enable_patch);
1097
1098 /*
1099 * This function unpatches objects from the replaced livepatches.
1100 *
1101 * We could be pretty aggressive here. It is called in the situation where
1102 * these structures are no longer accessed from the ftrace handler.
1103 * All functions are redirected by the klp_transition_patch. They
1104 * use either a new code or they are in the original code because
1105 * of the special nop function patches.
1106 *
1107 * The only exception is when the transition was forced. In this case,
1108 * klp_ftrace_handler() might still see the replaced patch on the stack.
1109 * Fortunately, it is carefully designed to work with removed functions
1110 * thanks to RCU. We only have to keep the patches on the system. Also
1111 * this is handled transparently by patch->module_put.
1112 */
klp_unpatch_replaced_patches(struct klp_patch * new_patch)1113 void klp_unpatch_replaced_patches(struct klp_patch *new_patch)
1114 {
1115 struct klp_patch *old_patch;
1116
1117 klp_for_each_patch(old_patch) {
1118 if (old_patch == new_patch)
1119 return;
1120
1121 old_patch->enabled = false;
1122 klp_unpatch_objects(old_patch);
1123 }
1124 }
1125
1126 /*
1127 * This function removes the dynamically allocated 'nop' functions.
1128 *
1129 * We could be pretty aggressive. NOPs do not change the existing
1130 * behavior except for adding unnecessary delay by the ftrace handler.
1131 *
1132 * It is safe even when the transition was forced. The ftrace handler
1133 * will see a valid ops->func_stack entry thanks to RCU.
1134 *
1135 * We could even free the NOPs structures. They must be the last entry
1136 * in ops->func_stack. Therefore unregister_ftrace_function() is called.
1137 * It does the same as klp_synchronize_transition() to make sure that
1138 * nobody is inside the ftrace handler once the operation finishes.
1139 *
1140 * IMPORTANT: It must be called right after removing the replaced patches!
1141 */
klp_discard_nops(struct klp_patch * new_patch)1142 void klp_discard_nops(struct klp_patch *new_patch)
1143 {
1144 klp_unpatch_objects_dynamic(klp_transition_patch);
1145 klp_free_objects_dynamic(klp_transition_patch);
1146 }
1147
1148 /*
1149 * Remove parts of patches that touch a given kernel module. The list of
1150 * patches processed might be limited. When limit is NULL, all patches
1151 * will be handled.
1152 */
klp_cleanup_module_patches_limited(struct module * mod,struct klp_patch * limit)1153 static void klp_cleanup_module_patches_limited(struct module *mod,
1154 struct klp_patch *limit)
1155 {
1156 struct klp_patch *patch;
1157 struct klp_object *obj;
1158
1159 klp_for_each_patch(patch) {
1160 if (patch == limit)
1161 break;
1162
1163 klp_for_each_object(patch, obj) {
1164 if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
1165 continue;
1166
1167 if (patch != klp_transition_patch)
1168 klp_pre_unpatch_callback(obj);
1169
1170 pr_notice("reverting patch '%s' on unloading module '%s'\n",
1171 patch->mod->name, obj->mod->name);
1172 klp_unpatch_object(obj);
1173
1174 klp_post_unpatch_callback(obj);
1175
1176 klp_free_object_loaded(obj);
1177 break;
1178 }
1179 }
1180 }
1181
klp_module_coming(struct module * mod)1182 int klp_module_coming(struct module *mod)
1183 {
1184 int ret;
1185 struct klp_patch *patch;
1186 struct klp_object *obj;
1187
1188 if (WARN_ON(mod->state != MODULE_STATE_COMING))
1189 return -EINVAL;
1190
1191 if (!strcmp(mod->name, "vmlinux")) {
1192 pr_err("vmlinux.ko: invalid module name\n");
1193 return -EINVAL;
1194 }
1195
1196 mutex_lock(&klp_mutex);
1197 /*
1198 * Each module has to know that klp_module_coming()
1199 * has been called. We never know what module will
1200 * get patched by a new patch.
1201 */
1202 mod->klp_alive = true;
1203
1204 klp_for_each_patch(patch) {
1205 klp_for_each_object(patch, obj) {
1206 if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
1207 continue;
1208
1209 obj->mod = mod;
1210
1211 ret = klp_init_object_loaded(patch, obj);
1212 if (ret) {
1213 pr_warn("failed to initialize patch '%s' for module '%s' (%d)\n",
1214 patch->mod->name, obj->mod->name, ret);
1215 goto err;
1216 }
1217
1218 pr_notice("applying patch '%s' to loading module '%s'\n",
1219 patch->mod->name, obj->mod->name);
1220
1221 ret = klp_pre_patch_callback(obj);
1222 if (ret) {
1223 pr_warn("pre-patch callback failed for object '%s'\n",
1224 obj->name);
1225 goto err;
1226 }
1227
1228 ret = klp_patch_object(obj);
1229 if (ret) {
1230 pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
1231 patch->mod->name, obj->mod->name, ret);
1232
1233 klp_post_unpatch_callback(obj);
1234 goto err;
1235 }
1236
1237 if (patch != klp_transition_patch)
1238 klp_post_patch_callback(obj);
1239
1240 break;
1241 }
1242 }
1243
1244 mutex_unlock(&klp_mutex);
1245
1246 return 0;
1247
1248 err:
1249 /*
1250 * If a patch is unsuccessfully applied, return
1251 * error to the module loader.
1252 */
1253 pr_warn("patch '%s' failed for module '%s', refusing to load module '%s'\n",
1254 patch->mod->name, obj->mod->name, obj->mod->name);
1255 mod->klp_alive = false;
1256 obj->mod = NULL;
1257 klp_cleanup_module_patches_limited(mod, patch);
1258 mutex_unlock(&klp_mutex);
1259
1260 return ret;
1261 }
1262
klp_module_going(struct module * mod)1263 void klp_module_going(struct module *mod)
1264 {
1265 if (WARN_ON(mod->state != MODULE_STATE_GOING &&
1266 mod->state != MODULE_STATE_COMING))
1267 return;
1268
1269 mutex_lock(&klp_mutex);
1270 /*
1271 * Each module has to know that klp_module_going()
1272 * has been called. We never know what module will
1273 * get patched by a new patch.
1274 */
1275 mod->klp_alive = false;
1276
1277 klp_cleanup_module_patches_limited(mod, NULL);
1278
1279 mutex_unlock(&klp_mutex);
1280 }
1281
klp_init(void)1282 static int __init klp_init(void)
1283 {
1284 klp_root_kobj = kobject_create_and_add("livepatch", kernel_kobj);
1285 if (!klp_root_kobj)
1286 return -ENOMEM;
1287
1288 return 0;
1289 }
1290
1291 module_init(klp_init);
1292