xref: /openbmc/linux/kernel/livepatch/core.c (revision fe998f4c)
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  * - __klp_sched_try_switch()
37  */
38 DEFINE_MUTEX(klp_mutex);
39 
40 /*
41  * Actively used patches: enabled or in transition. Note that replaced
42  * or disabled patches are not listed even though the related kernel
43  * module still can be loaded.
44  */
45 LIST_HEAD(klp_patches);
46 
47 static struct kobject *klp_root_kobj;
48 
klp_is_module(struct klp_object * obj)49 static bool klp_is_module(struct klp_object *obj)
50 {
51 	return obj->name;
52 }
53 
54 /* sets obj->mod if object is not vmlinux and module is found */
klp_find_object_module(struct klp_object * obj)55 static void klp_find_object_module(struct klp_object *obj)
56 {
57 	struct module *mod;
58 
59 	if (!klp_is_module(obj))
60 		return;
61 
62 	rcu_read_lock_sched();
63 	/*
64 	 * We do not want to block removal of patched modules and therefore
65 	 * we do not take a reference here. The patches are removed by
66 	 * klp_module_going() instead.
67 	 */
68 	mod = find_module(obj->name);
69 	/*
70 	 * Do not mess work of klp_module_coming() and klp_module_going().
71 	 * Note that the patch might still be needed before klp_module_going()
72 	 * is called. Module functions can be called even in the GOING state
73 	 * until mod->exit() finishes. This is especially important for
74 	 * patches that modify semantic of the functions.
75 	 */
76 	if (mod && mod->klp_alive)
77 		obj->mod = mod;
78 
79 	rcu_read_unlock_sched();
80 }
81 
klp_initialized(void)82 static bool klp_initialized(void)
83 {
84 	return !!klp_root_kobj;
85 }
86 
klp_find_func(struct klp_object * obj,struct klp_func * old_func)87 static struct klp_func *klp_find_func(struct klp_object *obj,
88 				      struct klp_func *old_func)
89 {
90 	struct klp_func *func;
91 
92 	klp_for_each_func(obj, func) {
93 		if ((strcmp(old_func->old_name, func->old_name) == 0) &&
94 		    (old_func->old_sympos == func->old_sympos)) {
95 			return func;
96 		}
97 	}
98 
99 	return NULL;
100 }
101 
klp_find_object(struct klp_patch * patch,struct klp_object * old_obj)102 static struct klp_object *klp_find_object(struct klp_patch *patch,
103 					  struct klp_object *old_obj)
104 {
105 	struct klp_object *obj;
106 
107 	klp_for_each_object(patch, obj) {
108 		if (klp_is_module(old_obj)) {
109 			if (klp_is_module(obj) &&
110 			    strcmp(old_obj->name, obj->name) == 0) {
111 				return obj;
112 			}
113 		} else if (!klp_is_module(obj)) {
114 			return obj;
115 		}
116 	}
117 
118 	return NULL;
119 }
120 
121 struct klp_find_arg {
122 	const char *name;
123 	unsigned long addr;
124 	unsigned long count;
125 	unsigned long pos;
126 };
127 
klp_match_callback(void * data,unsigned long addr)128 static int klp_match_callback(void *data, unsigned long addr)
129 {
130 	struct klp_find_arg *args = data;
131 
132 	args->addr = addr;
133 	args->count++;
134 
135 	/*
136 	 * Finish the search when the symbol is found for the desired position
137 	 * or the position is not defined for a non-unique symbol.
138 	 */
139 	if ((args->pos && (args->count == args->pos)) ||
140 	    (!args->pos && (args->count > 1)))
141 		return 1;
142 
143 	return 0;
144 }
145 
klp_find_callback(void * data,const char * name,unsigned long addr)146 static int klp_find_callback(void *data, const char *name, unsigned long addr)
147 {
148 	struct klp_find_arg *args = data;
149 
150 	if (strcmp(args->name, name))
151 		return 0;
152 
153 	return klp_match_callback(data, addr);
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 		.name = name,
161 		.addr = 0,
162 		.count = 0,
163 		.pos = sympos,
164 	};
165 
166 	if (objname)
167 		module_kallsyms_on_each_symbol(objname, klp_find_callback, &args);
168 	else
169 		kallsyms_on_each_match_symbol(klp_match_callback, name, &args);
170 
171 	/*
172 	 * Ensure an address was found. If sympos is 0, ensure symbol is unique;
173 	 * otherwise ensure the symbol position count matches sympos.
174 	 */
175 	if (args.addr == 0)
176 		pr_err("symbol '%s' not found in symbol table\n", name);
177 	else if (args.count > 1 && sympos == 0) {
178 		pr_err("unresolvable ambiguity for symbol '%s' in object '%s'\n",
179 		       name, objname);
180 	} else if (sympos != args.count && sympos > 0) {
181 		pr_err("symbol position %lu for symbol '%s' in object '%s' not found\n",
182 		       sympos, name, objname ? objname : "vmlinux");
183 	} else {
184 		*addr = args.addr;
185 		return 0;
186 	}
187 
188 	*addr = 0;
189 	return -EINVAL;
190 }
191 
klp_resolve_symbols(Elf_Shdr * sechdrs,const char * strtab,unsigned int symndx,Elf_Shdr * relasec,const char * sec_objname)192 static int klp_resolve_symbols(Elf_Shdr *sechdrs, const char *strtab,
193 			       unsigned int symndx, Elf_Shdr *relasec,
194 			       const char *sec_objname)
195 {
196 	int i, cnt, ret;
197 	char sym_objname[MODULE_NAME_LEN];
198 	char sym_name[KSYM_NAME_LEN];
199 	Elf_Rela *relas;
200 	Elf_Sym *sym;
201 	unsigned long sympos, addr;
202 	bool sym_vmlinux;
203 	bool sec_vmlinux = !strcmp(sec_objname, "vmlinux");
204 
205 	/*
206 	 * Since the field widths for sym_objname and sym_name in the sscanf()
207 	 * call are hard-coded and correspond to MODULE_NAME_LEN and
208 	 * KSYM_NAME_LEN respectively, we must make sure that MODULE_NAME_LEN
209 	 * and KSYM_NAME_LEN have the values we expect them to have.
210 	 *
211 	 * Because the value of MODULE_NAME_LEN can differ among architectures,
212 	 * we use the smallest/strictest upper bound possible (56, based on
213 	 * the current definition of MODULE_NAME_LEN) to prevent overflows.
214 	 */
215 	BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 512);
216 
217 	relas = (Elf_Rela *) relasec->sh_addr;
218 	/* For each rela in this klp relocation section */
219 	for (i = 0; i < relasec->sh_size / sizeof(Elf_Rela); i++) {
220 		sym = (Elf_Sym *)sechdrs[symndx].sh_addr + ELF_R_SYM(relas[i].r_info);
221 		if (sym->st_shndx != SHN_LIVEPATCH) {
222 			pr_err("symbol %s is not marked as a livepatch symbol\n",
223 			       strtab + sym->st_name);
224 			return -EINVAL;
225 		}
226 
227 		/* Format: .klp.sym.sym_objname.sym_name,sympos */
228 		cnt = sscanf(strtab + sym->st_name,
229 			     ".klp.sym.%55[^.].%511[^,],%lu",
230 			     sym_objname, sym_name, &sympos);
231 		if (cnt != 3) {
232 			pr_err("symbol %s has an incorrectly formatted name\n",
233 			       strtab + sym->st_name);
234 			return -EINVAL;
235 		}
236 
237 		sym_vmlinux = !strcmp(sym_objname, "vmlinux");
238 
239 		/*
240 		 * Prevent module-specific KLP rela sections from referencing
241 		 * vmlinux symbols.  This helps prevent ordering issues with
242 		 * module special section initializations.  Presumably such
243 		 * symbols are exported and normal relas can be used instead.
244 		 */
245 		if (!sec_vmlinux && sym_vmlinux) {
246 			pr_err("invalid access to vmlinux symbol '%s' from module-specific livepatch relocation section\n",
247 			       sym_name);
248 			return -EINVAL;
249 		}
250 
251 		/* klp_find_object_symbol() treats a NULL objname as vmlinux */
252 		ret = klp_find_object_symbol(sym_vmlinux ? NULL : sym_objname,
253 					     sym_name, sympos, &addr);
254 		if (ret)
255 			return ret;
256 
257 		sym->st_value = addr;
258 	}
259 
260 	return 0;
261 }
262 
clear_relocate_add(Elf_Shdr * sechdrs,const char * strtab,unsigned int symindex,unsigned int relsec,struct module * me)263 void __weak clear_relocate_add(Elf_Shdr *sechdrs,
264 		   const char *strtab,
265 		   unsigned int symindex,
266 		   unsigned int relsec,
267 		   struct module *me)
268 {
269 }
270 
271 /*
272  * At a high-level, there are two types of klp relocation sections: those which
273  * reference symbols which live in vmlinux; and those which reference symbols
274  * which live in other modules.  This function is called for both types:
275  *
276  * 1) When a klp module itself loads, the module code calls this function to
277  *    write vmlinux-specific klp relocations (.klp.rela.vmlinux.* sections).
278  *    These relocations are written to the klp module text to allow the patched
279  *    code/data to reference unexported vmlinux symbols.  They're written as
280  *    early as possible to ensure that other module init code (.e.g.,
281  *    jump_label_apply_nops) can access any unexported vmlinux symbols which
282  *    might be referenced by the klp module's special sections.
283  *
284  * 2) When a to-be-patched module loads -- or is already loaded when a
285  *    corresponding klp module loads -- klp code calls this function to write
286  *    module-specific klp relocations (.klp.rela.{module}.* sections).  These
287  *    are written to the klp module text to allow the patched code/data to
288  *    reference symbols which live in the to-be-patched module or one of its
289  *    module dependencies.  Exported symbols are supported, in addition to
290  *    unexported symbols, in order to enable late module patching, which allows
291  *    the to-be-patched module to be loaded and patched sometime *after* the
292  *    klp module is loaded.
293  */
klp_write_section_relocs(struct module * pmod,Elf_Shdr * sechdrs,const char * shstrtab,const char * strtab,unsigned int symndx,unsigned int secndx,const char * objname,bool apply)294 static int klp_write_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
295 				    const char *shstrtab, const char *strtab,
296 				    unsigned int symndx, unsigned int secndx,
297 				    const char *objname, bool apply)
298 {
299 	int cnt, ret;
300 	char sec_objname[MODULE_NAME_LEN];
301 	Elf_Shdr *sec = sechdrs + secndx;
302 
303 	/*
304 	 * Format: .klp.rela.sec_objname.section_name
305 	 * See comment in klp_resolve_symbols() for an explanation
306 	 * of the selected field width value.
307 	 */
308 	cnt = sscanf(shstrtab + sec->sh_name, ".klp.rela.%55[^.]",
309 		     sec_objname);
310 	if (cnt != 1) {
311 		pr_err("section %s has an incorrectly formatted name\n",
312 		       shstrtab + sec->sh_name);
313 		return -EINVAL;
314 	}
315 
316 	if (strcmp(objname ? objname : "vmlinux", sec_objname))
317 		return 0;
318 
319 	if (apply) {
320 		ret = klp_resolve_symbols(sechdrs, strtab, symndx,
321 					  sec, sec_objname);
322 		if (ret)
323 			return ret;
324 
325 		return apply_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
326 	}
327 
328 	clear_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
329 	return 0;
330 }
331 
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)332 int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
333 			     const char *shstrtab, const char *strtab,
334 			     unsigned int symndx, unsigned int secndx,
335 			     const char *objname)
336 {
337 	return klp_write_section_relocs(pmod, sechdrs, shstrtab, strtab, symndx,
338 					secndx, objname, true);
339 }
340 
341 /*
342  * Sysfs Interface
343  *
344  * /sys/kernel/livepatch
345  * /sys/kernel/livepatch/<patch>
346  * /sys/kernel/livepatch/<patch>/enabled
347  * /sys/kernel/livepatch/<patch>/transition
348  * /sys/kernel/livepatch/<patch>/force
349  * /sys/kernel/livepatch/<patch>/<object>
350  * /sys/kernel/livepatch/<patch>/<object>/patched
351  * /sys/kernel/livepatch/<patch>/<object>/<function,sympos>
352  */
353 static int __klp_disable_patch(struct klp_patch *patch);
354 
enabled_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)355 static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
356 			     const char *buf, size_t count)
357 {
358 	struct klp_patch *patch;
359 	int ret;
360 	bool enabled;
361 
362 	ret = kstrtobool(buf, &enabled);
363 	if (ret)
364 		return ret;
365 
366 	patch = container_of(kobj, struct klp_patch, kobj);
367 
368 	mutex_lock(&klp_mutex);
369 
370 	if (patch->enabled == enabled) {
371 		/* already in requested state */
372 		ret = -EINVAL;
373 		goto out;
374 	}
375 
376 	/*
377 	 * Allow to reverse a pending transition in both ways. It might be
378 	 * necessary to complete the transition without forcing and breaking
379 	 * the system integrity.
380 	 *
381 	 * Do not allow to re-enable a disabled patch.
382 	 */
383 	if (patch == klp_transition_patch)
384 		klp_reverse_transition();
385 	else if (!enabled)
386 		ret = __klp_disable_patch(patch);
387 	else
388 		ret = -EINVAL;
389 
390 out:
391 	mutex_unlock(&klp_mutex);
392 
393 	if (ret)
394 		return ret;
395 	return count;
396 }
397 
enabled_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)398 static ssize_t enabled_show(struct kobject *kobj,
399 			    struct kobj_attribute *attr, char *buf)
400 {
401 	struct klp_patch *patch;
402 
403 	patch = container_of(kobj, struct klp_patch, kobj);
404 	return snprintf(buf, PAGE_SIZE-1, "%d\n", patch->enabled);
405 }
406 
transition_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)407 static ssize_t transition_show(struct kobject *kobj,
408 			       struct kobj_attribute *attr, char *buf)
409 {
410 	struct klp_patch *patch;
411 
412 	patch = container_of(kobj, struct klp_patch, kobj);
413 	return snprintf(buf, PAGE_SIZE-1, "%d\n",
414 			patch == klp_transition_patch);
415 }
416 
force_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)417 static ssize_t force_store(struct kobject *kobj, struct kobj_attribute *attr,
418 			   const char *buf, size_t count)
419 {
420 	struct klp_patch *patch;
421 	int ret;
422 	bool val;
423 
424 	ret = kstrtobool(buf, &val);
425 	if (ret)
426 		return ret;
427 
428 	if (!val)
429 		return count;
430 
431 	mutex_lock(&klp_mutex);
432 
433 	patch = container_of(kobj, struct klp_patch, kobj);
434 	if (patch != klp_transition_patch) {
435 		mutex_unlock(&klp_mutex);
436 		return -EINVAL;
437 	}
438 
439 	klp_force_transition();
440 
441 	mutex_unlock(&klp_mutex);
442 
443 	return count;
444 }
445 
446 static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled);
447 static struct kobj_attribute transition_kobj_attr = __ATTR_RO(transition);
448 static struct kobj_attribute force_kobj_attr = __ATTR_WO(force);
449 static struct attribute *klp_patch_attrs[] = {
450 	&enabled_kobj_attr.attr,
451 	&transition_kobj_attr.attr,
452 	&force_kobj_attr.attr,
453 	NULL
454 };
455 ATTRIBUTE_GROUPS(klp_patch);
456 
patched_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)457 static ssize_t patched_show(struct kobject *kobj,
458 			    struct kobj_attribute *attr, char *buf)
459 {
460 	struct klp_object *obj;
461 
462 	obj = container_of(kobj, struct klp_object, kobj);
463 	return sysfs_emit(buf, "%d\n", obj->patched);
464 }
465 
466 static struct kobj_attribute patched_kobj_attr = __ATTR_RO(patched);
467 static struct attribute *klp_object_attrs[] = {
468 	&patched_kobj_attr.attr,
469 	NULL,
470 };
471 ATTRIBUTE_GROUPS(klp_object);
472 
klp_free_object_dynamic(struct klp_object * obj)473 static void klp_free_object_dynamic(struct klp_object *obj)
474 {
475 	kfree(obj->name);
476 	kfree(obj);
477 }
478 
479 static void klp_init_func_early(struct klp_object *obj,
480 				struct klp_func *func);
481 static void klp_init_object_early(struct klp_patch *patch,
482 				  struct klp_object *obj);
483 
klp_alloc_object_dynamic(const char * name,struct klp_patch * patch)484 static struct klp_object *klp_alloc_object_dynamic(const char *name,
485 						   struct klp_patch *patch)
486 {
487 	struct klp_object *obj;
488 
489 	obj = kzalloc(sizeof(*obj), GFP_KERNEL);
490 	if (!obj)
491 		return NULL;
492 
493 	if (name) {
494 		obj->name = kstrdup(name, GFP_KERNEL);
495 		if (!obj->name) {
496 			kfree(obj);
497 			return NULL;
498 		}
499 	}
500 
501 	klp_init_object_early(patch, obj);
502 	obj->dynamic = true;
503 
504 	return obj;
505 }
506 
klp_free_func_nop(struct klp_func * func)507 static void klp_free_func_nop(struct klp_func *func)
508 {
509 	kfree(func->old_name);
510 	kfree(func);
511 }
512 
klp_alloc_func_nop(struct klp_func * old_func,struct klp_object * obj)513 static struct klp_func *klp_alloc_func_nop(struct klp_func *old_func,
514 					   struct klp_object *obj)
515 {
516 	struct klp_func *func;
517 
518 	func = kzalloc(sizeof(*func), GFP_KERNEL);
519 	if (!func)
520 		return NULL;
521 
522 	if (old_func->old_name) {
523 		func->old_name = kstrdup(old_func->old_name, GFP_KERNEL);
524 		if (!func->old_name) {
525 			kfree(func);
526 			return NULL;
527 		}
528 	}
529 
530 	klp_init_func_early(obj, func);
531 	/*
532 	 * func->new_func is same as func->old_func. These addresses are
533 	 * set when the object is loaded, see klp_init_object_loaded().
534 	 */
535 	func->old_sympos = old_func->old_sympos;
536 	func->nop = true;
537 
538 	return func;
539 }
540 
klp_add_object_nops(struct klp_patch * patch,struct klp_object * old_obj)541 static int klp_add_object_nops(struct klp_patch *patch,
542 			       struct klp_object *old_obj)
543 {
544 	struct klp_object *obj;
545 	struct klp_func *func, *old_func;
546 
547 	obj = klp_find_object(patch, old_obj);
548 
549 	if (!obj) {
550 		obj = klp_alloc_object_dynamic(old_obj->name, patch);
551 		if (!obj)
552 			return -ENOMEM;
553 	}
554 
555 	klp_for_each_func(old_obj, old_func) {
556 		func = klp_find_func(obj, old_func);
557 		if (func)
558 			continue;
559 
560 		func = klp_alloc_func_nop(old_func, obj);
561 		if (!func)
562 			return -ENOMEM;
563 	}
564 
565 	return 0;
566 }
567 
568 /*
569  * Add 'nop' functions which simply return to the caller to run
570  * the original function. The 'nop' functions are added to a
571  * patch to facilitate a 'replace' mode.
572  */
klp_add_nops(struct klp_patch * patch)573 static int klp_add_nops(struct klp_patch *patch)
574 {
575 	struct klp_patch *old_patch;
576 	struct klp_object *old_obj;
577 
578 	klp_for_each_patch(old_patch) {
579 		klp_for_each_object(old_patch, old_obj) {
580 			int err;
581 
582 			err = klp_add_object_nops(patch, old_obj);
583 			if (err)
584 				return err;
585 		}
586 	}
587 
588 	return 0;
589 }
590 
klp_kobj_release_patch(struct kobject * kobj)591 static void klp_kobj_release_patch(struct kobject *kobj)
592 {
593 	struct klp_patch *patch;
594 
595 	patch = container_of(kobj, struct klp_patch, kobj);
596 	complete(&patch->finish);
597 }
598 
599 static const struct kobj_type klp_ktype_patch = {
600 	.release = klp_kobj_release_patch,
601 	.sysfs_ops = &kobj_sysfs_ops,
602 	.default_groups = klp_patch_groups,
603 };
604 
klp_kobj_release_object(struct kobject * kobj)605 static void klp_kobj_release_object(struct kobject *kobj)
606 {
607 	struct klp_object *obj;
608 
609 	obj = container_of(kobj, struct klp_object, kobj);
610 
611 	if (obj->dynamic)
612 		klp_free_object_dynamic(obj);
613 }
614 
615 static const struct kobj_type klp_ktype_object = {
616 	.release = klp_kobj_release_object,
617 	.sysfs_ops = &kobj_sysfs_ops,
618 	.default_groups = klp_object_groups,
619 };
620 
klp_kobj_release_func(struct kobject * kobj)621 static void klp_kobj_release_func(struct kobject *kobj)
622 {
623 	struct klp_func *func;
624 
625 	func = container_of(kobj, struct klp_func, kobj);
626 
627 	if (func->nop)
628 		klp_free_func_nop(func);
629 }
630 
631 static const struct kobj_type klp_ktype_func = {
632 	.release = klp_kobj_release_func,
633 	.sysfs_ops = &kobj_sysfs_ops,
634 };
635 
__klp_free_funcs(struct klp_object * obj,bool nops_only)636 static void __klp_free_funcs(struct klp_object *obj, bool nops_only)
637 {
638 	struct klp_func *func, *tmp_func;
639 
640 	klp_for_each_func_safe(obj, func, tmp_func) {
641 		if (nops_only && !func->nop)
642 			continue;
643 
644 		list_del(&func->node);
645 		kobject_put(&func->kobj);
646 	}
647 }
648 
649 /* Clean up when a patched object is unloaded */
klp_free_object_loaded(struct klp_object * obj)650 static void klp_free_object_loaded(struct klp_object *obj)
651 {
652 	struct klp_func *func;
653 
654 	obj->mod = NULL;
655 
656 	klp_for_each_func(obj, func) {
657 		func->old_func = NULL;
658 
659 		if (func->nop)
660 			func->new_func = NULL;
661 	}
662 }
663 
__klp_free_objects(struct klp_patch * patch,bool nops_only)664 static void __klp_free_objects(struct klp_patch *patch, bool nops_only)
665 {
666 	struct klp_object *obj, *tmp_obj;
667 
668 	klp_for_each_object_safe(patch, obj, tmp_obj) {
669 		__klp_free_funcs(obj, nops_only);
670 
671 		if (nops_only && !obj->dynamic)
672 			continue;
673 
674 		list_del(&obj->node);
675 		kobject_put(&obj->kobj);
676 	}
677 }
678 
klp_free_objects(struct klp_patch * patch)679 static void klp_free_objects(struct klp_patch *patch)
680 {
681 	__klp_free_objects(patch, false);
682 }
683 
klp_free_objects_dynamic(struct klp_patch * patch)684 static void klp_free_objects_dynamic(struct klp_patch *patch)
685 {
686 	__klp_free_objects(patch, true);
687 }
688 
689 /*
690  * This function implements the free operations that can be called safely
691  * under klp_mutex.
692  *
693  * The operation must be completed by calling klp_free_patch_finish()
694  * outside klp_mutex.
695  */
klp_free_patch_start(struct klp_patch * patch)696 static void klp_free_patch_start(struct klp_patch *patch)
697 {
698 	if (!list_empty(&patch->list))
699 		list_del(&patch->list);
700 
701 	klp_free_objects(patch);
702 }
703 
704 /*
705  * This function implements the free part that must be called outside
706  * klp_mutex.
707  *
708  * It must be called after klp_free_patch_start(). And it has to be
709  * the last function accessing the livepatch structures when the patch
710  * gets disabled.
711  */
klp_free_patch_finish(struct klp_patch * patch)712 static void klp_free_patch_finish(struct klp_patch *patch)
713 {
714 	/*
715 	 * Avoid deadlock with enabled_store() sysfs callback by
716 	 * calling this outside klp_mutex. It is safe because
717 	 * this is called when the patch gets disabled and it
718 	 * cannot get enabled again.
719 	 */
720 	kobject_put(&patch->kobj);
721 	wait_for_completion(&patch->finish);
722 
723 	/* Put the module after the last access to struct klp_patch. */
724 	if (!patch->forced)
725 		module_put(patch->mod);
726 }
727 
728 /*
729  * The livepatch might be freed from sysfs interface created by the patch.
730  * This work allows to wait until the interface is destroyed in a separate
731  * context.
732  */
klp_free_patch_work_fn(struct work_struct * work)733 static void klp_free_patch_work_fn(struct work_struct *work)
734 {
735 	struct klp_patch *patch =
736 		container_of(work, struct klp_patch, free_work);
737 
738 	klp_free_patch_finish(patch);
739 }
740 
klp_free_patch_async(struct klp_patch * patch)741 void klp_free_patch_async(struct klp_patch *patch)
742 {
743 	klp_free_patch_start(patch);
744 	schedule_work(&patch->free_work);
745 }
746 
klp_free_replaced_patches_async(struct klp_patch * new_patch)747 void klp_free_replaced_patches_async(struct klp_patch *new_patch)
748 {
749 	struct klp_patch *old_patch, *tmp_patch;
750 
751 	klp_for_each_patch_safe(old_patch, tmp_patch) {
752 		if (old_patch == new_patch)
753 			return;
754 		klp_free_patch_async(old_patch);
755 	}
756 }
757 
klp_init_func(struct klp_object * obj,struct klp_func * func)758 static int klp_init_func(struct klp_object *obj, struct klp_func *func)
759 {
760 	if (!func->old_name)
761 		return -EINVAL;
762 
763 	/*
764 	 * NOPs get the address later. The patched module must be loaded,
765 	 * see klp_init_object_loaded().
766 	 */
767 	if (!func->new_func && !func->nop)
768 		return -EINVAL;
769 
770 	if (strlen(func->old_name) >= KSYM_NAME_LEN)
771 		return -EINVAL;
772 
773 	INIT_LIST_HEAD(&func->stack_node);
774 	func->patched = false;
775 	func->transition = false;
776 
777 	/* The format for the sysfs directory is <function,sympos> where sympos
778 	 * is the nth occurrence of this symbol in kallsyms for the patched
779 	 * object. If the user selects 0 for old_sympos, then 1 will be used
780 	 * since a unique symbol will be the first occurrence.
781 	 */
782 	return kobject_add(&func->kobj, &obj->kobj, "%s,%lu",
783 			   func->old_name,
784 			   func->old_sympos ? func->old_sympos : 1);
785 }
786 
klp_write_object_relocs(struct klp_patch * patch,struct klp_object * obj,bool apply)787 static int klp_write_object_relocs(struct klp_patch *patch,
788 				   struct klp_object *obj,
789 				   bool apply)
790 {
791 	int i, ret;
792 	struct klp_modinfo *info = patch->mod->klp_info;
793 
794 	for (i = 1; i < info->hdr.e_shnum; i++) {
795 		Elf_Shdr *sec = info->sechdrs + i;
796 
797 		if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
798 			continue;
799 
800 		ret = klp_write_section_relocs(patch->mod, info->sechdrs,
801 					       info->secstrings,
802 					       patch->mod->core_kallsyms.strtab,
803 					       info->symndx, i, obj->name, apply);
804 		if (ret)
805 			return ret;
806 	}
807 
808 	return 0;
809 }
810 
klp_apply_object_relocs(struct klp_patch * patch,struct klp_object * obj)811 static int klp_apply_object_relocs(struct klp_patch *patch,
812 				   struct klp_object *obj)
813 {
814 	return klp_write_object_relocs(patch, obj, true);
815 }
816 
klp_clear_object_relocs(struct klp_patch * patch,struct klp_object * obj)817 static void klp_clear_object_relocs(struct klp_patch *patch,
818 				    struct klp_object *obj)
819 {
820 	klp_write_object_relocs(patch, obj, false);
821 }
822 
823 /* 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)824 static int klp_init_object_loaded(struct klp_patch *patch,
825 				  struct klp_object *obj)
826 {
827 	struct klp_func *func;
828 	int ret;
829 
830 	if (klp_is_module(obj)) {
831 		/*
832 		 * Only write module-specific relocations here
833 		 * (.klp.rela.{module}.*).  vmlinux-specific relocations were
834 		 * written earlier during the initialization of the klp module
835 		 * itself.
836 		 */
837 		ret = klp_apply_object_relocs(patch, obj);
838 		if (ret)
839 			return ret;
840 	}
841 
842 	klp_for_each_func(obj, func) {
843 		ret = klp_find_object_symbol(obj->name, func->old_name,
844 					     func->old_sympos,
845 					     (unsigned long *)&func->old_func);
846 		if (ret)
847 			return ret;
848 
849 		ret = kallsyms_lookup_size_offset((unsigned long)func->old_func,
850 						  &func->old_size, NULL);
851 		if (!ret) {
852 			pr_err("kallsyms size lookup failed for '%s'\n",
853 			       func->old_name);
854 			return -ENOENT;
855 		}
856 
857 		if (func->nop)
858 			func->new_func = func->old_func;
859 
860 		ret = kallsyms_lookup_size_offset((unsigned long)func->new_func,
861 						  &func->new_size, NULL);
862 		if (!ret) {
863 			pr_err("kallsyms size lookup failed for '%s' replacement\n",
864 			       func->old_name);
865 			return -ENOENT;
866 		}
867 	}
868 
869 	return 0;
870 }
871 
klp_init_object(struct klp_patch * patch,struct klp_object * obj)872 static int klp_init_object(struct klp_patch *patch, struct klp_object *obj)
873 {
874 	struct klp_func *func;
875 	int ret;
876 	const char *name;
877 
878 	if (klp_is_module(obj) && strlen(obj->name) >= MODULE_NAME_LEN)
879 		return -EINVAL;
880 
881 	obj->patched = false;
882 	obj->mod = NULL;
883 
884 	klp_find_object_module(obj);
885 
886 	name = klp_is_module(obj) ? obj->name : "vmlinux";
887 	ret = kobject_add(&obj->kobj, &patch->kobj, "%s", name);
888 	if (ret)
889 		return ret;
890 
891 	klp_for_each_func(obj, func) {
892 		ret = klp_init_func(obj, func);
893 		if (ret)
894 			return ret;
895 	}
896 
897 	if (klp_is_object_loaded(obj))
898 		ret = klp_init_object_loaded(patch, obj);
899 
900 	return ret;
901 }
902 
klp_init_func_early(struct klp_object * obj,struct klp_func * func)903 static void klp_init_func_early(struct klp_object *obj,
904 				struct klp_func *func)
905 {
906 	kobject_init(&func->kobj, &klp_ktype_func);
907 	list_add_tail(&func->node, &obj->func_list);
908 }
909 
klp_init_object_early(struct klp_patch * patch,struct klp_object * obj)910 static void klp_init_object_early(struct klp_patch *patch,
911 				  struct klp_object *obj)
912 {
913 	INIT_LIST_HEAD(&obj->func_list);
914 	kobject_init(&obj->kobj, &klp_ktype_object);
915 	list_add_tail(&obj->node, &patch->obj_list);
916 }
917 
klp_init_patch_early(struct klp_patch * patch)918 static void klp_init_patch_early(struct klp_patch *patch)
919 {
920 	struct klp_object *obj;
921 	struct klp_func *func;
922 
923 	INIT_LIST_HEAD(&patch->list);
924 	INIT_LIST_HEAD(&patch->obj_list);
925 	kobject_init(&patch->kobj, &klp_ktype_patch);
926 	patch->enabled = false;
927 	patch->forced = false;
928 	INIT_WORK(&patch->free_work, klp_free_patch_work_fn);
929 	init_completion(&patch->finish);
930 
931 	klp_for_each_object_static(patch, obj) {
932 		klp_init_object_early(patch, obj);
933 
934 		klp_for_each_func_static(obj, func) {
935 			klp_init_func_early(obj, func);
936 		}
937 	}
938 }
939 
klp_init_patch(struct klp_patch * patch)940 static int klp_init_patch(struct klp_patch *patch)
941 {
942 	struct klp_object *obj;
943 	int ret;
944 
945 	ret = kobject_add(&patch->kobj, klp_root_kobj, "%s", patch->mod->name);
946 	if (ret)
947 		return ret;
948 
949 	if (patch->replace) {
950 		ret = klp_add_nops(patch);
951 		if (ret)
952 			return ret;
953 	}
954 
955 	klp_for_each_object(patch, obj) {
956 		ret = klp_init_object(patch, obj);
957 		if (ret)
958 			return ret;
959 	}
960 
961 	list_add_tail(&patch->list, &klp_patches);
962 
963 	return 0;
964 }
965 
__klp_disable_patch(struct klp_patch * patch)966 static int __klp_disable_patch(struct klp_patch *patch)
967 {
968 	struct klp_object *obj;
969 
970 	if (WARN_ON(!patch->enabled))
971 		return -EINVAL;
972 
973 	if (klp_transition_patch)
974 		return -EBUSY;
975 
976 	klp_init_transition(patch, KLP_UNPATCHED);
977 
978 	klp_for_each_object(patch, obj)
979 		if (obj->patched)
980 			klp_pre_unpatch_callback(obj);
981 
982 	/*
983 	 * Enforce the order of the func->transition writes in
984 	 * klp_init_transition() and the TIF_PATCH_PENDING writes in
985 	 * klp_start_transition().  In the rare case where klp_ftrace_handler()
986 	 * is called shortly after klp_update_patch_state() switches the task,
987 	 * this ensures the handler sees that func->transition is set.
988 	 */
989 	smp_wmb();
990 
991 	klp_start_transition();
992 	patch->enabled = false;
993 	klp_try_complete_transition();
994 
995 	return 0;
996 }
997 
__klp_enable_patch(struct klp_patch * patch)998 static int __klp_enable_patch(struct klp_patch *patch)
999 {
1000 	struct klp_object *obj;
1001 	int ret;
1002 
1003 	if (klp_transition_patch)
1004 		return -EBUSY;
1005 
1006 	if (WARN_ON(patch->enabled))
1007 		return -EINVAL;
1008 
1009 	pr_notice("enabling patch '%s'\n", patch->mod->name);
1010 
1011 	klp_init_transition(patch, KLP_PATCHED);
1012 
1013 	/*
1014 	 * Enforce the order of the func->transition writes in
1015 	 * klp_init_transition() and the ops->func_stack writes in
1016 	 * klp_patch_object(), so that klp_ftrace_handler() will see the
1017 	 * func->transition updates before the handler is registered and the
1018 	 * new funcs become visible to the handler.
1019 	 */
1020 	smp_wmb();
1021 
1022 	klp_for_each_object(patch, obj) {
1023 		if (!klp_is_object_loaded(obj))
1024 			continue;
1025 
1026 		ret = klp_pre_patch_callback(obj);
1027 		if (ret) {
1028 			pr_warn("pre-patch callback failed for object '%s'\n",
1029 				klp_is_module(obj) ? obj->name : "vmlinux");
1030 			goto err;
1031 		}
1032 
1033 		ret = klp_patch_object(obj);
1034 		if (ret) {
1035 			pr_warn("failed to patch object '%s'\n",
1036 				klp_is_module(obj) ? obj->name : "vmlinux");
1037 			goto err;
1038 		}
1039 	}
1040 
1041 	klp_start_transition();
1042 	patch->enabled = true;
1043 	klp_try_complete_transition();
1044 
1045 	return 0;
1046 err:
1047 	pr_warn("failed to enable patch '%s'\n", patch->mod->name);
1048 
1049 	klp_cancel_transition();
1050 	return ret;
1051 }
1052 
1053 /**
1054  * klp_enable_patch() - enable the livepatch
1055  * @patch:	patch to be enabled
1056  *
1057  * Initializes the data structure associated with the patch, creates the sysfs
1058  * interface, performs the needed symbol lookups and code relocations,
1059  * registers the patched functions with ftrace.
1060  *
1061  * This function is supposed to be called from the livepatch module_init()
1062  * callback.
1063  *
1064  * Return: 0 on success, otherwise error
1065  */
klp_enable_patch(struct klp_patch * patch)1066 int klp_enable_patch(struct klp_patch *patch)
1067 {
1068 	int ret;
1069 	struct klp_object *obj;
1070 
1071 	if (!patch || !patch->mod || !patch->objs)
1072 		return -EINVAL;
1073 
1074 	klp_for_each_object_static(patch, obj) {
1075 		if (!obj->funcs)
1076 			return -EINVAL;
1077 	}
1078 
1079 
1080 	if (!is_livepatch_module(patch->mod)) {
1081 		pr_err("module %s is not marked as a livepatch module\n",
1082 		       patch->mod->name);
1083 		return -EINVAL;
1084 	}
1085 
1086 	if (!klp_initialized())
1087 		return -ENODEV;
1088 
1089 	if (!klp_have_reliable_stack()) {
1090 		pr_warn("This architecture doesn't have support for the livepatch consistency model.\n");
1091 		pr_warn("The livepatch transition may never complete.\n");
1092 	}
1093 
1094 	mutex_lock(&klp_mutex);
1095 
1096 	if (!klp_is_patch_compatible(patch)) {
1097 		pr_err("Livepatch patch (%s) is not compatible with the already installed livepatches.\n",
1098 			patch->mod->name);
1099 		mutex_unlock(&klp_mutex);
1100 		return -EINVAL;
1101 	}
1102 
1103 	if (!try_module_get(patch->mod)) {
1104 		mutex_unlock(&klp_mutex);
1105 		return -ENODEV;
1106 	}
1107 
1108 	klp_init_patch_early(patch);
1109 
1110 	ret = klp_init_patch(patch);
1111 	if (ret)
1112 		goto err;
1113 
1114 	ret = __klp_enable_patch(patch);
1115 	if (ret)
1116 		goto err;
1117 
1118 	mutex_unlock(&klp_mutex);
1119 
1120 	return 0;
1121 
1122 err:
1123 	klp_free_patch_start(patch);
1124 
1125 	mutex_unlock(&klp_mutex);
1126 
1127 	klp_free_patch_finish(patch);
1128 
1129 	return ret;
1130 }
1131 EXPORT_SYMBOL_GPL(klp_enable_patch);
1132 
1133 /*
1134  * This function unpatches objects from the replaced livepatches.
1135  *
1136  * We could be pretty aggressive here. It is called in the situation where
1137  * these structures are no longer accessed from the ftrace handler.
1138  * All functions are redirected by the klp_transition_patch. They
1139  * use either a new code or they are in the original code because
1140  * of the special nop function patches.
1141  *
1142  * The only exception is when the transition was forced. In this case,
1143  * klp_ftrace_handler() might still see the replaced patch on the stack.
1144  * Fortunately, it is carefully designed to work with removed functions
1145  * thanks to RCU. We only have to keep the patches on the system. Also
1146  * this is handled transparently by patch->module_put.
1147  */
klp_unpatch_replaced_patches(struct klp_patch * new_patch)1148 void klp_unpatch_replaced_patches(struct klp_patch *new_patch)
1149 {
1150 	struct klp_patch *old_patch;
1151 
1152 	klp_for_each_patch(old_patch) {
1153 		if (old_patch == new_patch)
1154 			return;
1155 
1156 		old_patch->enabled = false;
1157 		klp_unpatch_objects(old_patch);
1158 	}
1159 }
1160 
1161 /*
1162  * This function removes the dynamically allocated 'nop' functions.
1163  *
1164  * We could be pretty aggressive. NOPs do not change the existing
1165  * behavior except for adding unnecessary delay by the ftrace handler.
1166  *
1167  * It is safe even when the transition was forced. The ftrace handler
1168  * will see a valid ops->func_stack entry thanks to RCU.
1169  *
1170  * We could even free the NOPs structures. They must be the last entry
1171  * in ops->func_stack. Therefore unregister_ftrace_function() is called.
1172  * It does the same as klp_synchronize_transition() to make sure that
1173  * nobody is inside the ftrace handler once the operation finishes.
1174  *
1175  * IMPORTANT: It must be called right after removing the replaced patches!
1176  */
klp_discard_nops(struct klp_patch * new_patch)1177 void klp_discard_nops(struct klp_patch *new_patch)
1178 {
1179 	klp_unpatch_objects_dynamic(klp_transition_patch);
1180 	klp_free_objects_dynamic(klp_transition_patch);
1181 }
1182 
1183 /*
1184  * Remove parts of patches that touch a given kernel module. The list of
1185  * patches processed might be limited. When limit is NULL, all patches
1186  * will be handled.
1187  */
klp_cleanup_module_patches_limited(struct module * mod,struct klp_patch * limit)1188 static void klp_cleanup_module_patches_limited(struct module *mod,
1189 					       struct klp_patch *limit)
1190 {
1191 	struct klp_patch *patch;
1192 	struct klp_object *obj;
1193 
1194 	klp_for_each_patch(patch) {
1195 		if (patch == limit)
1196 			break;
1197 
1198 		klp_for_each_object(patch, obj) {
1199 			if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
1200 				continue;
1201 
1202 			if (patch != klp_transition_patch)
1203 				klp_pre_unpatch_callback(obj);
1204 
1205 			pr_notice("reverting patch '%s' on unloading module '%s'\n",
1206 				  patch->mod->name, obj->mod->name);
1207 			klp_unpatch_object(obj);
1208 
1209 			klp_post_unpatch_callback(obj);
1210 			klp_clear_object_relocs(patch, obj);
1211 			klp_free_object_loaded(obj);
1212 			break;
1213 		}
1214 	}
1215 }
1216 
klp_module_coming(struct module * mod)1217 int klp_module_coming(struct module *mod)
1218 {
1219 	int ret;
1220 	struct klp_patch *patch;
1221 	struct klp_object *obj;
1222 
1223 	if (WARN_ON(mod->state != MODULE_STATE_COMING))
1224 		return -EINVAL;
1225 
1226 	if (!strcmp(mod->name, "vmlinux")) {
1227 		pr_err("vmlinux.ko: invalid module name\n");
1228 		return -EINVAL;
1229 	}
1230 
1231 	mutex_lock(&klp_mutex);
1232 	/*
1233 	 * Each module has to know that klp_module_coming()
1234 	 * has been called. We never know what module will
1235 	 * get patched by a new patch.
1236 	 */
1237 	mod->klp_alive = true;
1238 
1239 	klp_for_each_patch(patch) {
1240 		klp_for_each_object(patch, obj) {
1241 			if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
1242 				continue;
1243 
1244 			obj->mod = mod;
1245 
1246 			ret = klp_init_object_loaded(patch, obj);
1247 			if (ret) {
1248 				pr_warn("failed to initialize patch '%s' for module '%s' (%d)\n",
1249 					patch->mod->name, obj->mod->name, ret);
1250 				goto err;
1251 			}
1252 
1253 			pr_notice("applying patch '%s' to loading module '%s'\n",
1254 				  patch->mod->name, obj->mod->name);
1255 
1256 			ret = klp_pre_patch_callback(obj);
1257 			if (ret) {
1258 				pr_warn("pre-patch callback failed for object '%s'\n",
1259 					obj->name);
1260 				goto err;
1261 			}
1262 
1263 			ret = klp_patch_object(obj);
1264 			if (ret) {
1265 				pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
1266 					patch->mod->name, obj->mod->name, ret);
1267 
1268 				klp_post_unpatch_callback(obj);
1269 				goto err;
1270 			}
1271 
1272 			if (patch != klp_transition_patch)
1273 				klp_post_patch_callback(obj);
1274 
1275 			break;
1276 		}
1277 	}
1278 
1279 	mutex_unlock(&klp_mutex);
1280 
1281 	return 0;
1282 
1283 err:
1284 	/*
1285 	 * If a patch is unsuccessfully applied, return
1286 	 * error to the module loader.
1287 	 */
1288 	pr_warn("patch '%s' failed for module '%s', refusing to load module '%s'\n",
1289 		patch->mod->name, obj->mod->name, obj->mod->name);
1290 	mod->klp_alive = false;
1291 	obj->mod = NULL;
1292 	klp_cleanup_module_patches_limited(mod, patch);
1293 	mutex_unlock(&klp_mutex);
1294 
1295 	return ret;
1296 }
1297 
klp_module_going(struct module * mod)1298 void klp_module_going(struct module *mod)
1299 {
1300 	if (WARN_ON(mod->state != MODULE_STATE_GOING &&
1301 		    mod->state != MODULE_STATE_COMING))
1302 		return;
1303 
1304 	mutex_lock(&klp_mutex);
1305 	/*
1306 	 * Each module has to know that klp_module_going()
1307 	 * has been called. We never know what module will
1308 	 * get patched by a new patch.
1309 	 */
1310 	mod->klp_alive = false;
1311 
1312 	klp_cleanup_module_patches_limited(mod, NULL);
1313 
1314 	mutex_unlock(&klp_mutex);
1315 }
1316 
klp_init(void)1317 static int __init klp_init(void)
1318 {
1319 	klp_root_kobj = kobject_create_and_add("livepatch", kernel_kobj);
1320 	if (!klp_root_kobj)
1321 		return -ENOMEM;
1322 
1323 	return 0;
1324 }
1325 
1326 module_init(klp_init);
1327