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 != 128);
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[^.].%127[^,],%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>/<function,sympos>
329  */
330 static int __klp_disable_patch(struct klp_patch *patch);
331 
enabled_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)332 static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
333 			     const char *buf, size_t count)
334 {
335 	struct klp_patch *patch;
336 	int ret;
337 	bool enabled;
338 
339 	ret = kstrtobool(buf, &enabled);
340 	if (ret)
341 		return ret;
342 
343 	patch = container_of(kobj, struct klp_patch, kobj);
344 
345 	mutex_lock(&klp_mutex);
346 
347 	if (patch->enabled == enabled) {
348 		/* already in requested state */
349 		ret = -EINVAL;
350 		goto out;
351 	}
352 
353 	/*
354 	 * Allow to reverse a pending transition in both ways. It might be
355 	 * necessary to complete the transition without forcing and breaking
356 	 * the system integrity.
357 	 *
358 	 * Do not allow to re-enable a disabled patch.
359 	 */
360 	if (patch == klp_transition_patch)
361 		klp_reverse_transition();
362 	else if (!enabled)
363 		ret = __klp_disable_patch(patch);
364 	else
365 		ret = -EINVAL;
366 
367 out:
368 	mutex_unlock(&klp_mutex);
369 
370 	if (ret)
371 		return ret;
372 	return count;
373 }
374 
enabled_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)375 static ssize_t enabled_show(struct kobject *kobj,
376 			    struct kobj_attribute *attr, char *buf)
377 {
378 	struct klp_patch *patch;
379 
380 	patch = container_of(kobj, struct klp_patch, kobj);
381 	return snprintf(buf, PAGE_SIZE-1, "%d\n", patch->enabled);
382 }
383 
transition_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)384 static ssize_t transition_show(struct kobject *kobj,
385 			       struct kobj_attribute *attr, char *buf)
386 {
387 	struct klp_patch *patch;
388 
389 	patch = container_of(kobj, struct klp_patch, kobj);
390 	return snprintf(buf, PAGE_SIZE-1, "%d\n",
391 			patch == klp_transition_patch);
392 }
393 
force_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)394 static ssize_t force_store(struct kobject *kobj, struct kobj_attribute *attr,
395 			   const char *buf, size_t count)
396 {
397 	struct klp_patch *patch;
398 	int ret;
399 	bool val;
400 
401 	ret = kstrtobool(buf, &val);
402 	if (ret)
403 		return ret;
404 
405 	if (!val)
406 		return count;
407 
408 	mutex_lock(&klp_mutex);
409 
410 	patch = container_of(kobj, struct klp_patch, kobj);
411 	if (patch != klp_transition_patch) {
412 		mutex_unlock(&klp_mutex);
413 		return -EINVAL;
414 	}
415 
416 	klp_force_transition();
417 
418 	mutex_unlock(&klp_mutex);
419 
420 	return count;
421 }
422 
423 static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled);
424 static struct kobj_attribute transition_kobj_attr = __ATTR_RO(transition);
425 static struct kobj_attribute force_kobj_attr = __ATTR_WO(force);
426 static struct attribute *klp_patch_attrs[] = {
427 	&enabled_kobj_attr.attr,
428 	&transition_kobj_attr.attr,
429 	&force_kobj_attr.attr,
430 	NULL
431 };
432 ATTRIBUTE_GROUPS(klp_patch);
433 
klp_free_object_dynamic(struct klp_object * obj)434 static void klp_free_object_dynamic(struct klp_object *obj)
435 {
436 	kfree(obj->name);
437 	kfree(obj);
438 }
439 
440 static void klp_init_func_early(struct klp_object *obj,
441 				struct klp_func *func);
442 static void klp_init_object_early(struct klp_patch *patch,
443 				  struct klp_object *obj);
444 
klp_alloc_object_dynamic(const char * name,struct klp_patch * patch)445 static struct klp_object *klp_alloc_object_dynamic(const char *name,
446 						   struct klp_patch *patch)
447 {
448 	struct klp_object *obj;
449 
450 	obj = kzalloc(sizeof(*obj), GFP_KERNEL);
451 	if (!obj)
452 		return NULL;
453 
454 	if (name) {
455 		obj->name = kstrdup(name, GFP_KERNEL);
456 		if (!obj->name) {
457 			kfree(obj);
458 			return NULL;
459 		}
460 	}
461 
462 	klp_init_object_early(patch, obj);
463 	obj->dynamic = true;
464 
465 	return obj;
466 }
467 
klp_free_func_nop(struct klp_func * func)468 static void klp_free_func_nop(struct klp_func *func)
469 {
470 	kfree(func->old_name);
471 	kfree(func);
472 }
473 
klp_alloc_func_nop(struct klp_func * old_func,struct klp_object * obj)474 static struct klp_func *klp_alloc_func_nop(struct klp_func *old_func,
475 					   struct klp_object *obj)
476 {
477 	struct klp_func *func;
478 
479 	func = kzalloc(sizeof(*func), GFP_KERNEL);
480 	if (!func)
481 		return NULL;
482 
483 	if (old_func->old_name) {
484 		func->old_name = kstrdup(old_func->old_name, GFP_KERNEL);
485 		if (!func->old_name) {
486 			kfree(func);
487 			return NULL;
488 		}
489 	}
490 
491 	klp_init_func_early(obj, func);
492 	/*
493 	 * func->new_func is same as func->old_func. These addresses are
494 	 * set when the object is loaded, see klp_init_object_loaded().
495 	 */
496 	func->old_sympos = old_func->old_sympos;
497 	func->nop = true;
498 
499 	return func;
500 }
501 
klp_add_object_nops(struct klp_patch * patch,struct klp_object * old_obj)502 static int klp_add_object_nops(struct klp_patch *patch,
503 			       struct klp_object *old_obj)
504 {
505 	struct klp_object *obj;
506 	struct klp_func *func, *old_func;
507 
508 	obj = klp_find_object(patch, old_obj);
509 
510 	if (!obj) {
511 		obj = klp_alloc_object_dynamic(old_obj->name, patch);
512 		if (!obj)
513 			return -ENOMEM;
514 	}
515 
516 	klp_for_each_func(old_obj, old_func) {
517 		func = klp_find_func(obj, old_func);
518 		if (func)
519 			continue;
520 
521 		func = klp_alloc_func_nop(old_func, obj);
522 		if (!func)
523 			return -ENOMEM;
524 	}
525 
526 	return 0;
527 }
528 
529 /*
530  * Add 'nop' functions which simply return to the caller to run
531  * the original function. The 'nop' functions are added to a
532  * patch to facilitate a 'replace' mode.
533  */
klp_add_nops(struct klp_patch * patch)534 static int klp_add_nops(struct klp_patch *patch)
535 {
536 	struct klp_patch *old_patch;
537 	struct klp_object *old_obj;
538 
539 	klp_for_each_patch(old_patch) {
540 		klp_for_each_object(old_patch, old_obj) {
541 			int err;
542 
543 			err = klp_add_object_nops(patch, old_obj);
544 			if (err)
545 				return err;
546 		}
547 	}
548 
549 	return 0;
550 }
551 
klp_kobj_release_patch(struct kobject * kobj)552 static void klp_kobj_release_patch(struct kobject *kobj)
553 {
554 	struct klp_patch *patch;
555 
556 	patch = container_of(kobj, struct klp_patch, kobj);
557 	complete(&patch->finish);
558 }
559 
560 static struct kobj_type klp_ktype_patch = {
561 	.release = klp_kobj_release_patch,
562 	.sysfs_ops = &kobj_sysfs_ops,
563 	.default_groups = klp_patch_groups,
564 };
565 
klp_kobj_release_object(struct kobject * kobj)566 static void klp_kobj_release_object(struct kobject *kobj)
567 {
568 	struct klp_object *obj;
569 
570 	obj = container_of(kobj, struct klp_object, kobj);
571 
572 	if (obj->dynamic)
573 		klp_free_object_dynamic(obj);
574 }
575 
576 static struct kobj_type klp_ktype_object = {
577 	.release = klp_kobj_release_object,
578 	.sysfs_ops = &kobj_sysfs_ops,
579 };
580 
klp_kobj_release_func(struct kobject * kobj)581 static void klp_kobj_release_func(struct kobject *kobj)
582 {
583 	struct klp_func *func;
584 
585 	func = container_of(kobj, struct klp_func, kobj);
586 
587 	if (func->nop)
588 		klp_free_func_nop(func);
589 }
590 
591 static struct kobj_type klp_ktype_func = {
592 	.release = klp_kobj_release_func,
593 	.sysfs_ops = &kobj_sysfs_ops,
594 };
595 
__klp_free_funcs(struct klp_object * obj,bool nops_only)596 static void __klp_free_funcs(struct klp_object *obj, bool nops_only)
597 {
598 	struct klp_func *func, *tmp_func;
599 
600 	klp_for_each_func_safe(obj, func, tmp_func) {
601 		if (nops_only && !func->nop)
602 			continue;
603 
604 		list_del(&func->node);
605 		kobject_put(&func->kobj);
606 	}
607 }
608 
609 /* Clean up when a patched object is unloaded */
klp_free_object_loaded(struct klp_object * obj)610 static void klp_free_object_loaded(struct klp_object *obj)
611 {
612 	struct klp_func *func;
613 
614 	obj->mod = NULL;
615 
616 	klp_for_each_func(obj, func) {
617 		func->old_func = NULL;
618 
619 		if (func->nop)
620 			func->new_func = NULL;
621 	}
622 }
623 
__klp_free_objects(struct klp_patch * patch,bool nops_only)624 static void __klp_free_objects(struct klp_patch *patch, bool nops_only)
625 {
626 	struct klp_object *obj, *tmp_obj;
627 
628 	klp_for_each_object_safe(patch, obj, tmp_obj) {
629 		__klp_free_funcs(obj, nops_only);
630 
631 		if (nops_only && !obj->dynamic)
632 			continue;
633 
634 		list_del(&obj->node);
635 		kobject_put(&obj->kobj);
636 	}
637 }
638 
klp_free_objects(struct klp_patch * patch)639 static void klp_free_objects(struct klp_patch *patch)
640 {
641 	__klp_free_objects(patch, false);
642 }
643 
klp_free_objects_dynamic(struct klp_patch * patch)644 static void klp_free_objects_dynamic(struct klp_patch *patch)
645 {
646 	__klp_free_objects(patch, true);
647 }
648 
649 /*
650  * This function implements the free operations that can be called safely
651  * under klp_mutex.
652  *
653  * The operation must be completed by calling klp_free_patch_finish()
654  * outside klp_mutex.
655  */
klp_free_patch_start(struct klp_patch * patch)656 static void klp_free_patch_start(struct klp_patch *patch)
657 {
658 	if (!list_empty(&patch->list))
659 		list_del(&patch->list);
660 
661 	klp_free_objects(patch);
662 }
663 
664 /*
665  * This function implements the free part that must be called outside
666  * klp_mutex.
667  *
668  * It must be called after klp_free_patch_start(). And it has to be
669  * the last function accessing the livepatch structures when the patch
670  * gets disabled.
671  */
klp_free_patch_finish(struct klp_patch * patch)672 static void klp_free_patch_finish(struct klp_patch *patch)
673 {
674 	/*
675 	 * Avoid deadlock with enabled_store() sysfs callback by
676 	 * calling this outside klp_mutex. It is safe because
677 	 * this is called when the patch gets disabled and it
678 	 * cannot get enabled again.
679 	 */
680 	kobject_put(&patch->kobj);
681 	wait_for_completion(&patch->finish);
682 
683 	/* Put the module after the last access to struct klp_patch. */
684 	if (!patch->forced)
685 		module_put(patch->mod);
686 }
687 
688 /*
689  * The livepatch might be freed from sysfs interface created by the patch.
690  * This work allows to wait until the interface is destroyed in a separate
691  * context.
692  */
klp_free_patch_work_fn(struct work_struct * work)693 static void klp_free_patch_work_fn(struct work_struct *work)
694 {
695 	struct klp_patch *patch =
696 		container_of(work, struct klp_patch, free_work);
697 
698 	klp_free_patch_finish(patch);
699 }
700 
klp_free_patch_async(struct klp_patch * patch)701 void klp_free_patch_async(struct klp_patch *patch)
702 {
703 	klp_free_patch_start(patch);
704 	schedule_work(&patch->free_work);
705 }
706 
klp_free_replaced_patches_async(struct klp_patch * new_patch)707 void klp_free_replaced_patches_async(struct klp_patch *new_patch)
708 {
709 	struct klp_patch *old_patch, *tmp_patch;
710 
711 	klp_for_each_patch_safe(old_patch, tmp_patch) {
712 		if (old_patch == new_patch)
713 			return;
714 		klp_free_patch_async(old_patch);
715 	}
716 }
717 
klp_init_func(struct klp_object * obj,struct klp_func * func)718 static int klp_init_func(struct klp_object *obj, struct klp_func *func)
719 {
720 	if (!func->old_name)
721 		return -EINVAL;
722 
723 	/*
724 	 * NOPs get the address later. The patched module must be loaded,
725 	 * see klp_init_object_loaded().
726 	 */
727 	if (!func->new_func && !func->nop)
728 		return -EINVAL;
729 
730 	if (strlen(func->old_name) >= KSYM_NAME_LEN)
731 		return -EINVAL;
732 
733 	INIT_LIST_HEAD(&func->stack_node);
734 	func->patched = false;
735 	func->transition = false;
736 
737 	/* The format for the sysfs directory is <function,sympos> where sympos
738 	 * is the nth occurrence of this symbol in kallsyms for the patched
739 	 * object. If the user selects 0 for old_sympos, then 1 will be used
740 	 * since a unique symbol will be the first occurrence.
741 	 */
742 	return kobject_add(&func->kobj, &obj->kobj, "%s,%lu",
743 			   func->old_name,
744 			   func->old_sympos ? func->old_sympos : 1);
745 }
746 
klp_apply_object_relocs(struct klp_patch * patch,struct klp_object * obj)747 static int klp_apply_object_relocs(struct klp_patch *patch,
748 				   struct klp_object *obj)
749 {
750 	int i, ret;
751 	struct klp_modinfo *info = patch->mod->klp_info;
752 
753 	for (i = 1; i < info->hdr.e_shnum; i++) {
754 		Elf_Shdr *sec = info->sechdrs + i;
755 
756 		if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
757 			continue;
758 
759 		ret = klp_apply_section_relocs(patch->mod, info->sechdrs,
760 					       info->secstrings,
761 					       patch->mod->core_kallsyms.strtab,
762 					       info->symndx, i, obj->name);
763 		if (ret)
764 			return ret;
765 	}
766 
767 	return 0;
768 }
769 
770 /* 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)771 static int klp_init_object_loaded(struct klp_patch *patch,
772 				  struct klp_object *obj)
773 {
774 	struct klp_func *func;
775 	int ret;
776 
777 	if (klp_is_module(obj)) {
778 		/*
779 		 * Only write module-specific relocations here
780 		 * (.klp.rela.{module}.*).  vmlinux-specific relocations were
781 		 * written earlier during the initialization of the klp module
782 		 * itself.
783 		 */
784 		ret = klp_apply_object_relocs(patch, obj);
785 		if (ret)
786 			return ret;
787 	}
788 
789 	klp_for_each_func(obj, func) {
790 		ret = klp_find_object_symbol(obj->name, func->old_name,
791 					     func->old_sympos,
792 					     (unsigned long *)&func->old_func);
793 		if (ret)
794 			return ret;
795 
796 		ret = kallsyms_lookup_size_offset((unsigned long)func->old_func,
797 						  &func->old_size, NULL);
798 		if (!ret) {
799 			pr_err("kallsyms size lookup failed for '%s'\n",
800 			       func->old_name);
801 			return -ENOENT;
802 		}
803 
804 		if (func->nop)
805 			func->new_func = func->old_func;
806 
807 		ret = kallsyms_lookup_size_offset((unsigned long)func->new_func,
808 						  &func->new_size, NULL);
809 		if (!ret) {
810 			pr_err("kallsyms size lookup failed for '%s' replacement\n",
811 			       func->old_name);
812 			return -ENOENT;
813 		}
814 	}
815 
816 	return 0;
817 }
818 
klp_init_object(struct klp_patch * patch,struct klp_object * obj)819 static int klp_init_object(struct klp_patch *patch, struct klp_object *obj)
820 {
821 	struct klp_func *func;
822 	int ret;
823 	const char *name;
824 
825 	if (klp_is_module(obj) && strlen(obj->name) >= MODULE_NAME_LEN)
826 		return -EINVAL;
827 
828 	obj->patched = false;
829 	obj->mod = NULL;
830 
831 	klp_find_object_module(obj);
832 
833 	name = klp_is_module(obj) ? obj->name : "vmlinux";
834 	ret = kobject_add(&obj->kobj, &patch->kobj, "%s", name);
835 	if (ret)
836 		return ret;
837 
838 	klp_for_each_func(obj, func) {
839 		ret = klp_init_func(obj, func);
840 		if (ret)
841 			return ret;
842 	}
843 
844 	if (klp_is_object_loaded(obj))
845 		ret = klp_init_object_loaded(patch, obj);
846 
847 	return ret;
848 }
849 
klp_init_func_early(struct klp_object * obj,struct klp_func * func)850 static void klp_init_func_early(struct klp_object *obj,
851 				struct klp_func *func)
852 {
853 	kobject_init(&func->kobj, &klp_ktype_func);
854 	list_add_tail(&func->node, &obj->func_list);
855 }
856 
klp_init_object_early(struct klp_patch * patch,struct klp_object * obj)857 static void klp_init_object_early(struct klp_patch *patch,
858 				  struct klp_object *obj)
859 {
860 	INIT_LIST_HEAD(&obj->func_list);
861 	kobject_init(&obj->kobj, &klp_ktype_object);
862 	list_add_tail(&obj->node, &patch->obj_list);
863 }
864 
klp_init_patch_early(struct klp_patch * patch)865 static void klp_init_patch_early(struct klp_patch *patch)
866 {
867 	struct klp_object *obj;
868 	struct klp_func *func;
869 
870 	INIT_LIST_HEAD(&patch->list);
871 	INIT_LIST_HEAD(&patch->obj_list);
872 	kobject_init(&patch->kobj, &klp_ktype_patch);
873 	patch->enabled = false;
874 	patch->forced = false;
875 	INIT_WORK(&patch->free_work, klp_free_patch_work_fn);
876 	init_completion(&patch->finish);
877 
878 	klp_for_each_object_static(patch, obj) {
879 		klp_init_object_early(patch, obj);
880 
881 		klp_for_each_func_static(obj, func) {
882 			klp_init_func_early(obj, func);
883 		}
884 	}
885 }
886 
klp_init_patch(struct klp_patch * patch)887 static int klp_init_patch(struct klp_patch *patch)
888 {
889 	struct klp_object *obj;
890 	int ret;
891 
892 	ret = kobject_add(&patch->kobj, klp_root_kobj, "%s", patch->mod->name);
893 	if (ret)
894 		return ret;
895 
896 	if (patch->replace) {
897 		ret = klp_add_nops(patch);
898 		if (ret)
899 			return ret;
900 	}
901 
902 	klp_for_each_object(patch, obj) {
903 		ret = klp_init_object(patch, obj);
904 		if (ret)
905 			return ret;
906 	}
907 
908 	list_add_tail(&patch->list, &klp_patches);
909 
910 	return 0;
911 }
912 
__klp_disable_patch(struct klp_patch * patch)913 static int __klp_disable_patch(struct klp_patch *patch)
914 {
915 	struct klp_object *obj;
916 
917 	if (WARN_ON(!patch->enabled))
918 		return -EINVAL;
919 
920 	if (klp_transition_patch)
921 		return -EBUSY;
922 
923 	klp_init_transition(patch, KLP_UNPATCHED);
924 
925 	klp_for_each_object(patch, obj)
926 		if (obj->patched)
927 			klp_pre_unpatch_callback(obj);
928 
929 	/*
930 	 * Enforce the order of the func->transition writes in
931 	 * klp_init_transition() and the TIF_PATCH_PENDING writes in
932 	 * klp_start_transition().  In the rare case where klp_ftrace_handler()
933 	 * is called shortly after klp_update_patch_state() switches the task,
934 	 * this ensures the handler sees that func->transition is set.
935 	 */
936 	smp_wmb();
937 
938 	klp_start_transition();
939 	patch->enabled = false;
940 	klp_try_complete_transition();
941 
942 	return 0;
943 }
944 
__klp_enable_patch(struct klp_patch * patch)945 static int __klp_enable_patch(struct klp_patch *patch)
946 {
947 	struct klp_object *obj;
948 	int ret;
949 
950 	if (klp_transition_patch)
951 		return -EBUSY;
952 
953 	if (WARN_ON(patch->enabled))
954 		return -EINVAL;
955 
956 	pr_notice("enabling patch '%s'\n", patch->mod->name);
957 
958 	klp_init_transition(patch, KLP_PATCHED);
959 
960 	/*
961 	 * Enforce the order of the func->transition writes in
962 	 * klp_init_transition() and the ops->func_stack writes in
963 	 * klp_patch_object(), so that klp_ftrace_handler() will see the
964 	 * func->transition updates before the handler is registered and the
965 	 * new funcs become visible to the handler.
966 	 */
967 	smp_wmb();
968 
969 	klp_for_each_object(patch, obj) {
970 		if (!klp_is_object_loaded(obj))
971 			continue;
972 
973 		ret = klp_pre_patch_callback(obj);
974 		if (ret) {
975 			pr_warn("pre-patch callback failed for object '%s'\n",
976 				klp_is_module(obj) ? obj->name : "vmlinux");
977 			goto err;
978 		}
979 
980 		ret = klp_patch_object(obj);
981 		if (ret) {
982 			pr_warn("failed to patch object '%s'\n",
983 				klp_is_module(obj) ? obj->name : "vmlinux");
984 			goto err;
985 		}
986 	}
987 
988 	klp_start_transition();
989 	patch->enabled = true;
990 	klp_try_complete_transition();
991 
992 	return 0;
993 err:
994 	pr_warn("failed to enable patch '%s'\n", patch->mod->name);
995 
996 	klp_cancel_transition();
997 	return ret;
998 }
999 
1000 /**
1001  * klp_enable_patch() - enable the livepatch
1002  * @patch:	patch to be enabled
1003  *
1004  * Initializes the data structure associated with the patch, creates the sysfs
1005  * interface, performs the needed symbol lookups and code relocations,
1006  * registers the patched functions with ftrace.
1007  *
1008  * This function is supposed to be called from the livepatch module_init()
1009  * callback.
1010  *
1011  * Return: 0 on success, otherwise error
1012  */
klp_enable_patch(struct klp_patch * patch)1013 int klp_enable_patch(struct klp_patch *patch)
1014 {
1015 	int ret;
1016 	struct klp_object *obj;
1017 
1018 	if (!patch || !patch->mod || !patch->objs)
1019 		return -EINVAL;
1020 
1021 	klp_for_each_object_static(patch, obj) {
1022 		if (!obj->funcs)
1023 			return -EINVAL;
1024 	}
1025 
1026 
1027 	if (!is_livepatch_module(patch->mod)) {
1028 		pr_err("module %s is not marked as a livepatch module\n",
1029 		       patch->mod->name);
1030 		return -EINVAL;
1031 	}
1032 
1033 	if (!klp_initialized())
1034 		return -ENODEV;
1035 
1036 	if (!klp_have_reliable_stack()) {
1037 		pr_warn("This architecture doesn't have support for the livepatch consistency model.\n");
1038 		pr_warn("The livepatch transition may never complete.\n");
1039 	}
1040 
1041 	mutex_lock(&klp_mutex);
1042 
1043 	if (!klp_is_patch_compatible(patch)) {
1044 		pr_err("Livepatch patch (%s) is not compatible with the already installed livepatches.\n",
1045 			patch->mod->name);
1046 		mutex_unlock(&klp_mutex);
1047 		return -EINVAL;
1048 	}
1049 
1050 	if (!try_module_get(patch->mod)) {
1051 		mutex_unlock(&klp_mutex);
1052 		return -ENODEV;
1053 	}
1054 
1055 	klp_init_patch_early(patch);
1056 
1057 	ret = klp_init_patch(patch);
1058 	if (ret)
1059 		goto err;
1060 
1061 	ret = __klp_enable_patch(patch);
1062 	if (ret)
1063 		goto err;
1064 
1065 	mutex_unlock(&klp_mutex);
1066 
1067 	return 0;
1068 
1069 err:
1070 	klp_free_patch_start(patch);
1071 
1072 	mutex_unlock(&klp_mutex);
1073 
1074 	klp_free_patch_finish(patch);
1075 
1076 	return ret;
1077 }
1078 EXPORT_SYMBOL_GPL(klp_enable_patch);
1079 
1080 /*
1081  * This function unpatches objects from the replaced livepatches.
1082  *
1083  * We could be pretty aggressive here. It is called in the situation where
1084  * these structures are no longer accessed from the ftrace handler.
1085  * All functions are redirected by the klp_transition_patch. They
1086  * use either a new code or they are in the original code because
1087  * of the special nop function patches.
1088  *
1089  * The only exception is when the transition was forced. In this case,
1090  * klp_ftrace_handler() might still see the replaced patch on the stack.
1091  * Fortunately, it is carefully designed to work with removed functions
1092  * thanks to RCU. We only have to keep the patches on the system. Also
1093  * this is handled transparently by patch->module_put.
1094  */
klp_unpatch_replaced_patches(struct klp_patch * new_patch)1095 void klp_unpatch_replaced_patches(struct klp_patch *new_patch)
1096 {
1097 	struct klp_patch *old_patch;
1098 
1099 	klp_for_each_patch(old_patch) {
1100 		if (old_patch == new_patch)
1101 			return;
1102 
1103 		old_patch->enabled = false;
1104 		klp_unpatch_objects(old_patch);
1105 	}
1106 }
1107 
1108 /*
1109  * This function removes the dynamically allocated 'nop' functions.
1110  *
1111  * We could be pretty aggressive. NOPs do not change the existing
1112  * behavior except for adding unnecessary delay by the ftrace handler.
1113  *
1114  * It is safe even when the transition was forced. The ftrace handler
1115  * will see a valid ops->func_stack entry thanks to RCU.
1116  *
1117  * We could even free the NOPs structures. They must be the last entry
1118  * in ops->func_stack. Therefore unregister_ftrace_function() is called.
1119  * It does the same as klp_synchronize_transition() to make sure that
1120  * nobody is inside the ftrace handler once the operation finishes.
1121  *
1122  * IMPORTANT: It must be called right after removing the replaced patches!
1123  */
klp_discard_nops(struct klp_patch * new_patch)1124 void klp_discard_nops(struct klp_patch *new_patch)
1125 {
1126 	klp_unpatch_objects_dynamic(klp_transition_patch);
1127 	klp_free_objects_dynamic(klp_transition_patch);
1128 }
1129 
1130 /*
1131  * Remove parts of patches that touch a given kernel module. The list of
1132  * patches processed might be limited. When limit is NULL, all patches
1133  * will be handled.
1134  */
klp_cleanup_module_patches_limited(struct module * mod,struct klp_patch * limit)1135 static void klp_cleanup_module_patches_limited(struct module *mod,
1136 					       struct klp_patch *limit)
1137 {
1138 	struct klp_patch *patch;
1139 	struct klp_object *obj;
1140 
1141 	klp_for_each_patch(patch) {
1142 		if (patch == limit)
1143 			break;
1144 
1145 		klp_for_each_object(patch, obj) {
1146 			if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
1147 				continue;
1148 
1149 			if (patch != klp_transition_patch)
1150 				klp_pre_unpatch_callback(obj);
1151 
1152 			pr_notice("reverting patch '%s' on unloading module '%s'\n",
1153 				  patch->mod->name, obj->mod->name);
1154 			klp_unpatch_object(obj);
1155 
1156 			klp_post_unpatch_callback(obj);
1157 
1158 			klp_free_object_loaded(obj);
1159 			break;
1160 		}
1161 	}
1162 }
1163 
klp_module_coming(struct module * mod)1164 int klp_module_coming(struct module *mod)
1165 {
1166 	int ret;
1167 	struct klp_patch *patch;
1168 	struct klp_object *obj;
1169 
1170 	if (WARN_ON(mod->state != MODULE_STATE_COMING))
1171 		return -EINVAL;
1172 
1173 	if (!strcmp(mod->name, "vmlinux")) {
1174 		pr_err("vmlinux.ko: invalid module name");
1175 		return -EINVAL;
1176 	}
1177 
1178 	mutex_lock(&klp_mutex);
1179 	/*
1180 	 * Each module has to know that klp_module_coming()
1181 	 * has been called. We never know what module will
1182 	 * get patched by a new patch.
1183 	 */
1184 	mod->klp_alive = true;
1185 
1186 	klp_for_each_patch(patch) {
1187 		klp_for_each_object(patch, obj) {
1188 			if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
1189 				continue;
1190 
1191 			obj->mod = mod;
1192 
1193 			ret = klp_init_object_loaded(patch, obj);
1194 			if (ret) {
1195 				pr_warn("failed to initialize patch '%s' for module '%s' (%d)\n",
1196 					patch->mod->name, obj->mod->name, ret);
1197 				goto err;
1198 			}
1199 
1200 			pr_notice("applying patch '%s' to loading module '%s'\n",
1201 				  patch->mod->name, obj->mod->name);
1202 
1203 			ret = klp_pre_patch_callback(obj);
1204 			if (ret) {
1205 				pr_warn("pre-patch callback failed for object '%s'\n",
1206 					obj->name);
1207 				goto err;
1208 			}
1209 
1210 			ret = klp_patch_object(obj);
1211 			if (ret) {
1212 				pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
1213 					patch->mod->name, obj->mod->name, ret);
1214 
1215 				klp_post_unpatch_callback(obj);
1216 				goto err;
1217 			}
1218 
1219 			if (patch != klp_transition_patch)
1220 				klp_post_patch_callback(obj);
1221 
1222 			break;
1223 		}
1224 	}
1225 
1226 	mutex_unlock(&klp_mutex);
1227 
1228 	return 0;
1229 
1230 err:
1231 	/*
1232 	 * If a patch is unsuccessfully applied, return
1233 	 * error to the module loader.
1234 	 */
1235 	pr_warn("patch '%s' failed for module '%s', refusing to load module '%s'\n",
1236 		patch->mod->name, obj->mod->name, obj->mod->name);
1237 	mod->klp_alive = false;
1238 	obj->mod = NULL;
1239 	klp_cleanup_module_patches_limited(mod, patch);
1240 	mutex_unlock(&klp_mutex);
1241 
1242 	return ret;
1243 }
1244 
klp_module_going(struct module * mod)1245 void klp_module_going(struct module *mod)
1246 {
1247 	if (WARN_ON(mod->state != MODULE_STATE_GOING &&
1248 		    mod->state != MODULE_STATE_COMING))
1249 		return;
1250 
1251 	mutex_lock(&klp_mutex);
1252 	/*
1253 	 * Each module has to know that klp_module_going()
1254 	 * has been called. We never know what module will
1255 	 * get patched by a new patch.
1256 	 */
1257 	mod->klp_alive = false;
1258 
1259 	klp_cleanup_module_patches_limited(mod, NULL);
1260 
1261 	mutex_unlock(&klp_mutex);
1262 }
1263 
klp_init(void)1264 static int __init klp_init(void)
1265 {
1266 	klp_root_kobj = kobject_create_and_add("livepatch", kernel_kobj);
1267 	if (!klp_root_kobj)
1268 		return -ENOMEM;
1269 
1270 	return 0;
1271 }
1272 
1273 module_init(klp_init);
1274