core.c

   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 */
  38DEFINE_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 */
  45LIST_HEAD(klp_patches);
  46
  47static struct kobject *klp_root_kobj;
  48
  49static 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 */
  55static 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	guard(rcu)();
  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
  80static bool klp_initialized(void)
  81{
  82	return !!klp_root_kobj;
  83}
  84
  85static struct klp_func *klp_find_func(struct klp_object *obj,
  86				      struct klp_func *old_func)
  87{
  88	struct klp_func *func;
  89
  90	klp_for_each_func(obj, func) {
  91		/*
  92		 * Besides identical old_sympos, also consider old_sympos
  93		 * of 0 and 1 are identical.
  94		 */
  95		if ((strcmp(old_func->old_name, func->old_name) == 0) &&
  96		    ((old_func->old_sympos == func->old_sympos) ||
  97		     (old_func->old_sympos == 0 && func->old_sympos == 1) ||
  98		     (old_func->old_sympos == 1 && func->old_sympos == 0))) {
  99			return func;
 100		}
 101	}
 102
 103	return NULL;
 104}
 105
 106static struct klp_object *klp_find_object(struct klp_patch *patch,
 107					  struct klp_object *old_obj)
 108{
 109	struct klp_object *obj;
 110
 111	klp_for_each_object(patch, obj) {
 112		if (klp_is_module(old_obj)) {
 113			if (klp_is_module(obj) &&
 114			    strcmp(old_obj->name, obj->name) == 0) {
 115				return obj;
 116			}
 117		} else if (!klp_is_module(obj)) {
 118			return obj;
 119		}
 120	}
 121
 122	return NULL;
 123}
 124
 125struct klp_find_arg {
 126	const char *name;
 127	unsigned long addr;
 128	unsigned long count;
 129	unsigned long pos;
 130};
 131
 132static int klp_match_callback(void *data, unsigned long addr)
 133{
 134	struct klp_find_arg *args = data;
 135
 136	args->addr = addr;
 137	args->count++;
 138
 139	/*
 140	 * Finish the search when the symbol is found for the desired position
 141	 * or the position is not defined for a non-unique symbol.
 142	 */
 143	if ((args->pos && (args->count == args->pos)) ||
 144	    (!args->pos && (args->count > 1)))
 145		return 1;
 146
 147	return 0;
 148}
 149
 150static int klp_find_callback(void *data, const char *name, unsigned long addr)
 151{
 152	struct klp_find_arg *args = data;
 153
 154	if (strcmp(args->name, name))
 155		return 0;
 156
 157	return klp_match_callback(data, addr);
 158}
 159
 160static int klp_find_object_symbol(const char *objname, const char *name,
 161				  unsigned long sympos, unsigned long *addr)
 162{
 163	struct klp_find_arg args = {
 164		.name = name,
 165		.addr = 0,
 166		.count = 0,
 167		.pos = sympos,
 168	};
 169
 170	if (objname)
 171		module_kallsyms_on_each_symbol(objname, klp_find_callback, &args);
 172	else
 173		kallsyms_on_each_match_symbol(klp_match_callback, name, &args);
 174
 175	/*
 176	 * Ensure an address was found. If sympos is 0, ensure symbol is unique;
 177	 * otherwise ensure the symbol position count matches sympos.
 178	 */
 179	if (args.addr == 0)
 180		pr_err("symbol '%s' not found in symbol table\n", name);
 181	else if (args.count > 1 && sympos == 0) {
 182		pr_err("unresolvable ambiguity for symbol '%s' in object '%s'\n",
 183		       name, objname);
 184	} else if (sympos != args.count && sympos > 0) {
 185		pr_err("symbol position %lu for symbol '%s' in object '%s' not found\n",
 186		       sympos, name, objname ? objname : "vmlinux");
 187	} else {
 188		*addr = args.addr;
 189		return 0;
 190	}
 191
 192	*addr = 0;
 193	return -EINVAL;
 194}
 195
 196static int klp_resolve_symbols(Elf_Shdr *sechdrs, const char *strtab,
 197			       unsigned int symndx, Elf_Shdr *relasec,
 198			       const char *sec_objname)
 199{
 200	int i, cnt, ret;
 201	char sym_objname[MODULE_NAME_LEN];
 202	char sym_name[KSYM_NAME_LEN];
 203	Elf_Rela *relas;
 204	Elf_Sym *sym;
 205	unsigned long sympos, addr;
 206	bool sym_vmlinux;
 207	bool sec_vmlinux = !strcmp(sec_objname, "vmlinux");
 208
 209	/*
 210	 * Since the field widths for sym_objname and sym_name in the sscanf()
 211	 * call are hard-coded and correspond to MODULE_NAME_LEN and
 212	 * KSYM_NAME_LEN respectively, we must make sure that MODULE_NAME_LEN
 213	 * and KSYM_NAME_LEN have the values we expect them to have.
 214	 *
 215	 * Because the value of MODULE_NAME_LEN can differ among architectures,
 216	 * we use the smallest/strictest upper bound possible (56, based on
 217	 * the current definition of MODULE_NAME_LEN) to prevent overflows.
 218	 */
 219	BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 512);
 220
 221	relas = (Elf_Rela *) relasec->sh_addr;
 222	/* For each rela in this klp relocation section */
 223	for (i = 0; i < relasec->sh_size / sizeof(Elf_Rela); i++) {
 224		sym = (Elf_Sym *)sechdrs[symndx].sh_addr + ELF_R_SYM(relas[i].r_info);
 225		if (sym->st_shndx != SHN_LIVEPATCH) {
 226			pr_err("symbol %s at rela sec %u idx %d is not marked as a livepatch symbol\n",
 227			       strtab + sym->st_name, symndx, i);
 228			return -EINVAL;
 229		}
 230
 231		/* Format: .klp.sym.sym_objname.sym_name,sympos */
 232		cnt = sscanf(strtab + sym->st_name,
 233			     KLP_SYM_PREFIX "%55[^.].%511[^,],%lu",
 234			     sym_objname, sym_name, &sympos);
 235		if (cnt != 3) {
 236			pr_err("symbol %s has an incorrectly formatted name\n",
 237			       strtab + sym->st_name);
 238			return -EINVAL;
 239		}
 240
 241		sym_vmlinux = !strcmp(sym_objname, "vmlinux");
 242
 243		/*
 244		 * Prevent module-specific KLP rela sections from referencing
 245		 * vmlinux symbols.  This helps prevent ordering issues with
 246		 * module special section initializations.  Presumably such
 247		 * symbols are exported and normal relas can be used instead.
 248		 */
 249		if (!sec_vmlinux && sym_vmlinux) {
 250			pr_err("invalid access to vmlinux symbol '%s' from module-specific livepatch relocation section\n",
 251			       sym_name);
 252			return -EINVAL;
 253		}
 254
 255		/* klp_find_object_symbol() treats a NULL objname as vmlinux */
 256		ret = klp_find_object_symbol(sym_vmlinux ? NULL : sym_objname,
 257					     sym_name, sympos, &addr);
 258		if (ret)
 259			return ret;
 260
 261		sym->st_value = addr;
 262	}
 263
 264	return 0;
 265}
 266
 267void __weak clear_relocate_add(Elf_Shdr *sechdrs,
 268		   const char *strtab,
 269		   unsigned int symindex,
 270		   unsigned int relsec,
 271		   struct module *me)
 272{
 273}
 274
 275/*
 276 * At a high-level, there are two types of klp relocation sections: those which
 277 * reference symbols which live in vmlinux; and those which reference symbols
 278 * which live in other modules.  This function is called for both types:
 279 *
 280 * 1) When a klp module itself loads, the module code calls this function to
 281 *    write vmlinux-specific klp relocations (.klp.rela.vmlinux.* sections).
 282 *    These relocations are written to the klp module text to allow the patched
 283 *    code/data to reference unexported vmlinux symbols.  They're written as
 284 *    early as possible to ensure that other module init code (.e.g.,
 285 *    jump_label_apply_nops) can access any unexported vmlinux symbols which
 286 *    might be referenced by the klp module's special sections.
 287 *
 288 * 2) When a to-be-patched module loads -- or is already loaded when a
 289 *    corresponding klp module loads -- klp code calls this function to write
 290 *    module-specific klp relocations (.klp.rela.{module}.* sections).  These
 291 *    are written to the klp module text to allow the patched code/data to
 292 *    reference symbols which live in the to-be-patched module or one of its
 293 *    module dependencies.  Exported symbols are supported, in addition to
 294 *    unexported symbols, in order to enable late module patching, which allows
 295 *    the to-be-patched module to be loaded and patched sometime *after* the
 296 *    klp module is loaded.
 297 */
 298static int klp_write_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
 299				    const char *shstrtab, const char *strtab,
 300				    unsigned int symndx, unsigned int secndx,
 301				    const char *objname, bool apply)
 302{
 303	int cnt, ret;
 304	char sec_objname[MODULE_NAME_LEN];
 305	Elf_Shdr *sec = sechdrs + secndx;
 306
 307	/*
 308	 * Format: .klp.rela.sec_objname.section_name
 309	 * See comment in klp_resolve_symbols() for an explanation
 310	 * of the selected field width value.
 311	 */
 312	cnt = sscanf(shstrtab + sec->sh_name, KLP_RELOC_SEC_PREFIX "%55[^.]",
 313		     sec_objname);
 314	if (cnt != 1) {
 315		pr_err("section %s has an incorrectly formatted name\n",
 316		       shstrtab + sec->sh_name);
 317		return -EINVAL;
 318	}
 319
 320	if (strcmp(objname ? objname : "vmlinux", sec_objname))
 321		return 0;
 322
 323	if (apply) {
 324		ret = klp_resolve_symbols(sechdrs, strtab, symndx,
 325					  sec, sec_objname);
 326		if (ret)
 327			return ret;
 328
 329		return apply_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
 330	}
 331
 332	clear_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
 333	return 0;
 334}
 335
 336int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
 337			     const char *shstrtab, const char *strtab,
 338			     unsigned int symndx, unsigned int secndx,
 339			     const char *objname)
 340{
 341	return klp_write_section_relocs(pmod, sechdrs, shstrtab, strtab, symndx,
 342					secndx, objname, true);
 343}
 344
 345/*
 346 * Sysfs Interface
 347 *
 348 * /sys/kernel/livepatch
 349 * /sys/kernel/livepatch/<patch>
 350 * /sys/kernel/livepatch/<patch>/enabled
 351 * /sys/kernel/livepatch/<patch>/transition
 352 * /sys/kernel/livepatch/<patch>/force
 353 * /sys/kernel/livepatch/<patch>/replace
 354 * /sys/kernel/livepatch/<patch>/stack_order
 355 * /sys/kernel/livepatch/<patch>/<object>
 356 * /sys/kernel/livepatch/<patch>/<object>/patched
 357 * /sys/kernel/livepatch/<patch>/<object>/<function,sympos>
 358 */
 359static int __klp_disable_patch(struct klp_patch *patch);
 360
 361static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
 362			     const char *buf, size_t count)
 363{
 364	struct klp_patch *patch;
 365	int ret;
 366	bool enabled;
 367
 368	ret = kstrtobool(buf, &enabled);
 369	if (ret)
 370		return ret;
 371
 372	patch = container_of(kobj, struct klp_patch, kobj);
 373
 374	mutex_lock(&klp_mutex);
 375
 376	if (patch->enabled == enabled) {
 377		/* already in requested state */
 378		ret = -EINVAL;
 379		goto out;
 380	}
 381
 382	/*
 383	 * Allow to reverse a pending transition in both ways. It might be
 384	 * necessary to complete the transition without forcing and breaking
 385	 * the system integrity.
 386	 *
 387	 * Do not allow to re-enable a disabled patch.
 388	 */
 389	if (patch == klp_transition_patch)
 390		klp_reverse_transition();
 391	else if (!enabled)
 392		ret = __klp_disable_patch(patch);
 393	else
 394		ret = -EINVAL;
 395
 396out:
 397	mutex_unlock(&klp_mutex);
 398
 399	if (ret)
 400		return ret;
 401	return count;
 402}
 403
 404static ssize_t enabled_show(struct kobject *kobj,
 405			    struct kobj_attribute *attr, char *buf)
 406{
 407	struct klp_patch *patch;
 408
 409	patch = container_of(kobj, struct klp_patch, kobj);
 410	return sysfs_emit(buf, "%d\n", patch->enabled);
 411}
 412
 413static ssize_t transition_show(struct kobject *kobj,
 414			       struct kobj_attribute *attr, char *buf)
 415{
 416	struct klp_patch *patch;
 417
 418	patch = container_of(kobj, struct klp_patch, kobj);
 419	return sysfs_emit(buf, "%d\n", patch == klp_transition_patch);
 420}
 421
 422static ssize_t force_store(struct kobject *kobj, struct kobj_attribute *attr,
 423			   const char *buf, size_t count)
 424{
 425	struct klp_patch *patch;
 426	int ret;
 427	bool val;
 428
 429	ret = kstrtobool(buf, &val);
 430	if (ret)
 431		return ret;
 432
 433	if (!val)
 434		return count;
 435
 436	mutex_lock(&klp_mutex);
 437
 438	patch = container_of(kobj, struct klp_patch, kobj);
 439	if (patch != klp_transition_patch) {
 440		mutex_unlock(&klp_mutex);
 441		return -EINVAL;
 442	}
 443
 444	klp_force_transition();
 445
 446	mutex_unlock(&klp_mutex);
 447
 448	return count;
 449}
 450
 451static ssize_t replace_show(struct kobject *kobj,
 452			    struct kobj_attribute *attr, char *buf)
 453{
 454	struct klp_patch *patch;
 455
 456	patch = container_of(kobj, struct klp_patch, kobj);
 457	return sysfs_emit(buf, "%d\n", patch->replace);
 458}
 459
 460static ssize_t stack_order_show(struct kobject *kobj,
 461				struct kobj_attribute *attr, char *buf)
 462{
 463	struct klp_patch *patch, *this_patch;
 464	int stack_order = 0;
 465
 466	this_patch = container_of(kobj, struct klp_patch, kobj);
 467
 468	mutex_lock(&klp_mutex);
 469
 470	klp_for_each_patch(patch) {
 471		stack_order++;
 472		if (patch == this_patch)
 473			break;
 474	}
 475
 476	mutex_unlock(&klp_mutex);
 477
 478	return sysfs_emit(buf, "%d\n", stack_order);
 479}
 480
 481static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled);
 482static struct kobj_attribute transition_kobj_attr = __ATTR_RO(transition);
 483static struct kobj_attribute force_kobj_attr = __ATTR_WO(force);
 484static struct kobj_attribute replace_kobj_attr = __ATTR_RO(replace);
 485static struct kobj_attribute stack_order_kobj_attr = __ATTR_RO(stack_order);
 486static struct attribute *klp_patch_attrs[] = {
 487	&enabled_kobj_attr.attr,
 488	&transition_kobj_attr.attr,
 489	&force_kobj_attr.attr,
 490	&replace_kobj_attr.attr,
 491	&stack_order_kobj_attr.attr,
 492	NULL
 493};
 494ATTRIBUTE_GROUPS(klp_patch);
 495
 496static ssize_t patched_show(struct kobject *kobj,
 497			    struct kobj_attribute *attr, char *buf)
 498{
 499	struct klp_object *obj;
 500
 501	obj = container_of(kobj, struct klp_object, kobj);
 502	return sysfs_emit(buf, "%d\n", obj->patched);
 503}
 504
 505static struct kobj_attribute patched_kobj_attr = __ATTR_RO(patched);
 506static struct attribute *klp_object_attrs[] = {
 507	&patched_kobj_attr.attr,
 508	NULL,
 509};
 510ATTRIBUTE_GROUPS(klp_object);
 511
 512static void klp_free_object_dynamic(struct klp_object *obj)
 513{
 514	kfree(obj->name);
 515	kfree(obj);
 516}
 517
 518static void klp_init_func_early(struct klp_object *obj,
 519				struct klp_func *func);
 520static void klp_init_object_early(struct klp_patch *patch,
 521				  struct klp_object *obj);
 522
 523static struct klp_object *klp_alloc_object_dynamic(const char *name,
 524						   struct klp_patch *patch)
 525{
 526	struct klp_object *obj;
 527
 528	obj = kzalloc(sizeof(*obj), GFP_KERNEL);
 529	if (!obj)
 530		return NULL;
 531
 532	if (name) {
 533		obj->name = kstrdup(name, GFP_KERNEL);
 534		if (!obj->name) {
 535			kfree(obj);
 536			return NULL;
 537		}
 538	}
 539
 540	klp_init_object_early(patch, obj);
 541	obj->dynamic = true;
 542
 543	return obj;
 544}
 545
 546static void klp_free_func_nop(struct klp_func *func)
 547{
 548	kfree(func->old_name);
 549	kfree(func);
 550}
 551
 552static struct klp_func *klp_alloc_func_nop(struct klp_func *old_func,
 553					   struct klp_object *obj)
 554{
 555	struct klp_func *func;
 556
 557	func = kzalloc(sizeof(*func), GFP_KERNEL);
 558	if (!func)
 559		return NULL;
 560
 561	if (old_func->old_name) {
 562		func->old_name = kstrdup(old_func->old_name, GFP_KERNEL);
 563		if (!func->old_name) {
 564			kfree(func);
 565			return NULL;
 566		}
 567	}
 568
 569	klp_init_func_early(obj, func);
 570	/*
 571	 * func->new_func is same as func->old_func. These addresses are
 572	 * set when the object is loaded, see klp_init_object_loaded().
 573	 */
 574	func->old_sympos = old_func->old_sympos;
 575	func->nop = true;
 576
 577	return func;
 578}
 579
 580static int klp_add_object_nops(struct klp_patch *patch,
 581			       struct klp_object *old_obj)
 582{
 583	struct klp_object *obj;
 584	struct klp_func *func, *old_func;
 585
 586	obj = klp_find_object(patch, old_obj);
 587
 588	if (!obj) {
 589		obj = klp_alloc_object_dynamic(old_obj->name, patch);
 590		if (!obj)
 591			return -ENOMEM;
 592	}
 593
 594	klp_for_each_func(old_obj, old_func) {
 595		func = klp_find_func(obj, old_func);
 596		if (func)
 597			continue;
 598
 599		func = klp_alloc_func_nop(old_func, obj);
 600		if (!func)
 601			return -ENOMEM;
 602	}
 603
 604	return 0;
 605}
 606
 607/*
 608 * Add 'nop' functions which simply return to the caller to run the
 609 * original function.
 610 *
 611 * They are added only when the atomic replace mode is used and only for
 612 * functions which are currently livepatched but are no longer included
 613 * in the new livepatch.
 614 */
 615static int klp_add_nops(struct klp_patch *patch)
 616{
 617	struct klp_patch *old_patch;
 618	struct klp_object *old_obj;
 619
 620	klp_for_each_patch(old_patch) {
 621		klp_for_each_object(old_patch, old_obj) {
 622			int err;
 623
 624			err = klp_add_object_nops(patch, old_obj);
 625			if (err)
 626				return err;
 627		}
 628	}
 629
 630	return 0;
 631}
 632
 633static void klp_kobj_release_patch(struct kobject *kobj)
 634{
 635	struct klp_patch *patch;
 636
 637	patch = container_of(kobj, struct klp_patch, kobj);
 638	complete(&patch->finish);
 639}
 640
 641static const struct kobj_type klp_ktype_patch = {
 642	.release = klp_kobj_release_patch,
 643	.sysfs_ops = &kobj_sysfs_ops,
 644	.default_groups = klp_patch_groups,
 645};
 646
 647static void klp_kobj_release_object(struct kobject *kobj)
 648{
 649	struct klp_object *obj;
 650
 651	obj = container_of(kobj, struct klp_object, kobj);
 652
 653	if (obj->dynamic)
 654		klp_free_object_dynamic(obj);
 655}
 656
 657static const struct kobj_type klp_ktype_object = {
 658	.release = klp_kobj_release_object,
 659	.sysfs_ops = &kobj_sysfs_ops,
 660	.default_groups = klp_object_groups,
 661};
 662
 663static void klp_kobj_release_func(struct kobject *kobj)
 664{
 665	struct klp_func *func;
 666
 667	func = container_of(kobj, struct klp_func, kobj);
 668
 669	if (func->nop)
 670		klp_free_func_nop(func);
 671}
 672
 673static const struct kobj_type klp_ktype_func = {
 674	.release = klp_kobj_release_func,
 675	.sysfs_ops = &kobj_sysfs_ops,
 676};
 677
 678static void __klp_free_funcs(struct klp_object *obj, bool nops_only)
 679{
 680	struct klp_func *func, *tmp_func;
 681
 682	klp_for_each_func_safe(obj, func, tmp_func) {
 683		if (nops_only && !func->nop)
 684			continue;
 685
 686		list_del(&func->node);
 687		kobject_put(&func->kobj);
 688	}
 689}
 690
 691/* Clean up when a patched object is unloaded */
 692static void klp_free_object_loaded(struct klp_object *obj)
 693{
 694	struct klp_func *func;
 695
 696	obj->mod = NULL;
 697
 698	klp_for_each_func(obj, func) {
 699		func->old_func = NULL;
 700
 701		if (func->nop)
 702			func->new_func = NULL;
 703	}
 704}
 705
 706static void __klp_free_objects(struct klp_patch *patch, bool nops_only)
 707{
 708	struct klp_object *obj, *tmp_obj;
 709
 710	klp_for_each_object_safe(patch, obj, tmp_obj) {
 711		__klp_free_funcs(obj, nops_only);
 712
 713		if (nops_only && !obj->dynamic)
 714			continue;
 715
 716		list_del(&obj->node);
 717		kobject_put(&obj->kobj);
 718	}
 719}
 720
 721static void klp_free_objects(struct klp_patch *patch)
 722{
 723	__klp_free_objects(patch, false);
 724}
 725
 726static void klp_free_objects_dynamic(struct klp_patch *patch)
 727{
 728	__klp_free_objects(patch, true);
 729}
 730
 731/*
 732 * This function implements the free operations that can be called safely
 733 * under klp_mutex.
 734 *
 735 * The operation must be completed by calling klp_free_patch_finish()
 736 * outside klp_mutex.
 737 */
 738static void klp_free_patch_start(struct klp_patch *patch)
 739{
 740	if (!list_empty(&patch->list))
 741		list_del(&patch->list);
 742
 743	klp_free_objects(patch);
 744}
 745
 746/*
 747 * This function implements the free part that must be called outside
 748 * klp_mutex.
 749 *
 750 * It must be called after klp_free_patch_start(). And it has to be
 751 * the last function accessing the livepatch structures when the patch
 752 * gets disabled.
 753 */
 754static void klp_free_patch_finish(struct klp_patch *patch)
 755{
 756	/*
 757	 * Avoid deadlock with enabled_store() sysfs callback by
 758	 * calling this outside klp_mutex. It is safe because
 759	 * this is called when the patch gets disabled and it
 760	 * cannot get enabled again.
 761	 */
 762	kobject_put(&patch->kobj);
 763	wait_for_completion(&patch->finish);
 764
 765	/* Put the module after the last access to struct klp_patch. */
 766	if (!patch->forced)
 767		module_put(patch->mod);
 768}
 769
 770/*
 771 * The livepatch might be freed from sysfs interface created by the patch.
 772 * This work allows to wait until the interface is destroyed in a separate
 773 * context.
 774 */
 775static void klp_free_patch_work_fn(struct work_struct *work)
 776{
 777	struct klp_patch *patch =
 778		container_of(work, struct klp_patch, free_work);
 779
 780	klp_free_patch_finish(patch);
 781}
 782
 783void klp_free_patch_async(struct klp_patch *patch)
 784{
 785	klp_free_patch_start(patch);
 786	schedule_work(&patch->free_work);
 787}
 788
 789void klp_free_replaced_patches_async(struct klp_patch *new_patch)
 790{
 791	struct klp_patch *old_patch, *tmp_patch;
 792
 793	klp_for_each_patch_safe(old_patch, tmp_patch) {
 794		if (old_patch == new_patch)
 795			return;
 796		klp_free_patch_async(old_patch);
 797	}
 798}
 799
 800static int klp_init_func(struct klp_object *obj, struct klp_func *func)
 801{
 802	if (!func->old_name)
 803		return -EINVAL;
 804
 805	/*
 806	 * NOPs get the address later. The patched module must be loaded,
 807	 * see klp_init_object_loaded().
 808	 */
 809	if (!func->new_func && !func->nop)
 810		return -EINVAL;
 811
 812	if (strlen(func->old_name) >= KSYM_NAME_LEN)
 813		return -EINVAL;
 814
 815	INIT_LIST_HEAD(&func->stack_node);
 816	func->patched = false;
 817	func->transition = false;
 818
 819	/* The format for the sysfs directory is <function,sympos> where sympos
 820	 * is the nth occurrence of this symbol in kallsyms for the patched
 821	 * object. If the user selects 0 for old_sympos, then 1 will be used
 822	 * since a unique symbol will be the first occurrence.
 823	 */
 824	return kobject_add(&func->kobj, &obj->kobj, "%s,%lu",
 825			   func->old_name,
 826			   func->old_sympos ? func->old_sympos : 1);
 827}
 828
 829static int klp_write_object_relocs(struct klp_patch *patch,
 830				   struct klp_object *obj,
 831				   bool apply)
 832{
 833	int i, ret;
 834	struct klp_modinfo *info = patch->mod->klp_info;
 835
 836	for (i = 1; i < info->hdr.e_shnum; i++) {
 837		Elf_Shdr *sec = info->sechdrs + i;
 838
 839		if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
 840			continue;
 841
 842		ret = klp_write_section_relocs(patch->mod, info->sechdrs,
 843					       info->secstrings,
 844					       patch->mod->core_kallsyms.strtab,
 845					       info->symndx, i, obj->name, apply);
 846		if (ret)
 847			return ret;
 848	}
 849
 850	return 0;
 851}
 852
 853static int klp_apply_object_relocs(struct klp_patch *patch,
 854				   struct klp_object *obj)
 855{
 856	return klp_write_object_relocs(patch, obj, true);
 857}
 858
 859static void klp_clear_object_relocs(struct klp_patch *patch,
 860				    struct klp_object *obj)
 861{
 862	klp_write_object_relocs(patch, obj, false);
 863}
 864
 865/* parts of the initialization that is done only when the object is loaded */
 866static int klp_init_object_loaded(struct klp_patch *patch,
 867				  struct klp_object *obj)
 868{
 869	struct klp_func *func;
 870	int ret;
 871
 872	if (klp_is_module(obj)) {
 873		/*
 874		 * Only write module-specific relocations here
 875		 * (.klp.rela.{module}.*).  vmlinux-specific relocations were
 876		 * written earlier during the initialization of the klp module
 877		 * itself.
 878		 */
 879		ret = klp_apply_object_relocs(patch, obj);
 880		if (ret)
 881			return ret;
 882	}
 883
 884	klp_for_each_func(obj, func) {
 885		ret = klp_find_object_symbol(obj->name, func->old_name,
 886					     func->old_sympos,
 887					     (unsigned long *)&func->old_func);
 888		if (ret)
 889			return ret;
 890
 891		ret = kallsyms_lookup_size_offset((unsigned long)func->old_func,
 892						  &func->old_size, NULL);
 893		if (!ret) {
 894			pr_err("kallsyms size lookup failed for '%s'\n",
 895			       func->old_name);
 896			return -ENOENT;
 897		}
 898
 899		if (func->nop)
 900			func->new_func = func->old_func;
 901
 902		ret = kallsyms_lookup_size_offset((unsigned long)func->new_func,
 903						  &func->new_size, NULL);
 904		if (!ret) {
 905			pr_err("kallsyms size lookup failed for '%s' replacement\n",
 906			       func->old_name);
 907			return -ENOENT;
 908		}
 909	}
 910
 911	return 0;
 912}
 913
 914static int klp_init_object(struct klp_patch *patch, struct klp_object *obj)
 915{
 916	struct klp_func *func;
 917	int ret;
 918	const char *name;
 919
 920	if (klp_is_module(obj) && strlen(obj->name) >= MODULE_NAME_LEN)
 921		return -EINVAL;
 922
 923	obj->patched = false;
 924	obj->mod = NULL;
 925
 926	klp_find_object_module(obj);
 927
 928	name = klp_is_module(obj) ? obj->name : "vmlinux";
 929	ret = kobject_add(&obj->kobj, &patch->kobj, "%s", name);
 930	if (ret)
 931		return ret;
 932
 933	klp_for_each_func(obj, func) {
 934		ret = klp_init_func(obj, func);
 935		if (ret)
 936			return ret;
 937	}
 938
 939	if (klp_is_object_loaded(obj))
 940		ret = klp_init_object_loaded(patch, obj);
 941
 942	return ret;
 943}
 944
 945static void klp_init_func_early(struct klp_object *obj,
 946				struct klp_func *func)
 947{
 948	kobject_init(&func->kobj, &klp_ktype_func);
 949	list_add_tail(&func->node, &obj->func_list);
 950}
 951
 952static void klp_init_object_early(struct klp_patch *patch,
 953				  struct klp_object *obj)
 954{
 955	INIT_LIST_HEAD(&obj->func_list);
 956	kobject_init(&obj->kobj, &klp_ktype_object);
 957	list_add_tail(&obj->node, &patch->obj_list);
 958}
 959
 960static void klp_init_patch_early(struct klp_patch *patch)
 961{
 962	struct klp_object *obj;
 963	struct klp_func *func;
 964
 965	INIT_LIST_HEAD(&patch->list);
 966	INIT_LIST_HEAD(&patch->obj_list);
 967	kobject_init(&patch->kobj, &klp_ktype_patch);
 968	patch->enabled = false;
 969	patch->forced = false;
 970	INIT_WORK(&patch->free_work, klp_free_patch_work_fn);
 971	init_completion(&patch->finish);
 972
 973	klp_for_each_object_static(patch, obj) {
 974		klp_init_object_early(patch, obj);
 975
 976		klp_for_each_func_static(obj, func) {
 977			klp_init_func_early(obj, func);
 978		}
 979	}
 980}
 981
 982static int klp_init_patch(struct klp_patch *patch)
 983{
 984	struct klp_object *obj;
 985	int ret;
 986
 987	ret = kobject_add(&patch->kobj, klp_root_kobj, "%s", patch->mod->name);
 988	if (ret)
 989		return ret;
 990
 991	if (patch->replace) {
 992		ret = klp_add_nops(patch);
 993		if (ret)
 994			return ret;
 995	}
 996
 997	klp_for_each_object(patch, obj) {
 998		ret = klp_init_object(patch, obj);
 999		if (ret)
1000			return ret;
1001	}
1002
1003	list_add_tail(&patch->list, &klp_patches);
1004
1005	return 0;
1006}
1007
1008static int __klp_disable_patch(struct klp_patch *patch)
1009{
1010	struct klp_object *obj;
1011
1012	if (WARN_ON(!patch->enabled))
1013		return -EINVAL;
1014
1015	if (klp_transition_patch)
1016		return -EBUSY;
1017
1018	klp_init_transition(patch, KLP_TRANSITION_UNPATCHED);
1019
1020	klp_for_each_object(patch, obj)
1021		if (obj->patched)
1022			klp_pre_unpatch_callback(obj);
1023
1024	/*
1025	 * Enforce the order of the func->transition writes in
1026	 * klp_init_transition() and the TIF_PATCH_PENDING writes in
1027	 * klp_start_transition().  In the rare case where klp_ftrace_handler()
1028	 * is called shortly after klp_update_patch_state() switches the task,
1029	 * this ensures the handler sees that func->transition is set.
1030	 */
1031	smp_wmb();
1032
1033	klp_start_transition();
1034	patch->enabled = false;
1035	klp_try_complete_transition();
1036
1037	return 0;
1038}
1039
1040static int __klp_enable_patch(struct klp_patch *patch)
1041{
1042	struct klp_object *obj;
1043	int ret;
1044
1045	if (klp_transition_patch)
1046		return -EBUSY;
1047
1048	if (WARN_ON(patch->enabled))
1049		return -EINVAL;
1050
1051	pr_notice("enabling patch '%s'\n", patch->mod->name);
1052
1053	klp_init_transition(patch, KLP_TRANSITION_PATCHED);
1054
1055	/*
1056	 * Enforce the order of the func->transition writes in
1057	 * klp_init_transition() and the ops->func_stack writes in
1058	 * klp_patch_object(), so that klp_ftrace_handler() will see the
1059	 * func->transition updates before the handler is registered and the
1060	 * new funcs become visible to the handler.
1061	 */
1062	smp_wmb();
1063
1064	klp_for_each_object(patch, obj) {
1065		if (!klp_is_object_loaded(obj))
1066			continue;
1067
1068		ret = klp_pre_patch_callback(obj);
1069		if (ret) {
1070			pr_warn("pre-patch callback failed for object '%s'\n",
1071				klp_is_module(obj) ? obj->name : "vmlinux");
1072			goto err;
1073		}
1074
1075		ret = klp_patch_object(obj);
1076		if (ret) {
1077			pr_warn("failed to patch object '%s'\n",
1078				klp_is_module(obj) ? obj->name : "vmlinux");
1079			goto err;
1080		}
1081	}
1082
1083	klp_start_transition();
1084	patch->enabled = true;
1085	klp_try_complete_transition();
1086
1087	return 0;
1088err:
1089	pr_warn("failed to enable patch '%s'\n", patch->mod->name);
1090
1091	klp_cancel_transition();
1092	return ret;
1093}
1094
1095/**
1096 * klp_enable_patch() - enable the livepatch
1097 * @patch:	patch to be enabled
1098 *
1099 * Initializes the data structure associated with the patch, creates the sysfs
1100 * interface, performs the needed symbol lookups and code relocations,
1101 * registers the patched functions with ftrace.
1102 *
1103 * This function is supposed to be called from the livepatch module_init()
1104 * callback.
1105 *
1106 * Return: 0 on success, otherwise error
1107 */
1108int klp_enable_patch(struct klp_patch *patch)
1109{
1110	int ret;
1111	struct klp_object *obj;
1112
1113	if (!patch || !patch->mod || !patch->objs)
1114		return -EINVAL;
1115
1116	klp_for_each_object_static(patch, obj) {
1117		if (!obj->funcs)
1118			return -EINVAL;
1119	}
1120
1121
1122	if (!is_livepatch_module(patch->mod)) {
1123		pr_err("module %s is not marked as a livepatch module\n",
1124		       patch->mod->name);
1125		return -EINVAL;
1126	}
1127
1128	if (!klp_initialized())
1129		return -ENODEV;
1130
1131	if (!klp_have_reliable_stack()) {
1132		pr_warn("This architecture doesn't have support for the livepatch consistency model.\n");
1133		pr_warn("The livepatch transition may never complete.\n");
1134	}
1135
1136	mutex_lock(&klp_mutex);
1137
1138	if (!klp_is_patch_compatible(patch)) {
1139		pr_err("Livepatch patch (%s) is not compatible with the already installed livepatches.\n",
1140			patch->mod->name);
1141		mutex_unlock(&klp_mutex);
1142		return -EINVAL;
1143	}
1144
1145	if (!try_module_get(patch->mod)) {
1146		mutex_unlock(&klp_mutex);
1147		return -ENODEV;
1148	}
1149
1150	klp_init_patch_early(patch);
1151
1152	ret = klp_init_patch(patch);
1153	if (ret)
1154		goto err;
1155
1156	ret = __klp_enable_patch(patch);
1157	if (ret)
1158		goto err;
1159
1160	mutex_unlock(&klp_mutex);
1161
1162	return 0;
1163
1164err:
1165	klp_free_patch_start(patch);
1166
1167	mutex_unlock(&klp_mutex);
1168
1169	klp_free_patch_finish(patch);
1170
1171	return ret;
1172}
1173EXPORT_SYMBOL_GPL(klp_enable_patch);
1174
1175/*
1176 * This function unpatches objects from the replaced livepatches.
1177 *
1178 * We could be pretty aggressive here. It is called in the situation where
1179 * these structures are no longer accessed from the ftrace handler.
1180 * All functions are redirected by the klp_transition_patch. They
1181 * use either a new code or they are in the original code because
1182 * of the special nop function patches.
1183 *
1184 * The only exception is when the transition was forced. In this case,
1185 * klp_ftrace_handler() might still see the replaced patch on the stack.
1186 * Fortunately, it is carefully designed to work with removed functions
1187 * thanks to RCU. We only have to keep the patches on the system. Also
1188 * this is handled transparently by patch->module_put.
1189 */
1190void klp_unpatch_replaced_patches(struct klp_patch *new_patch)
1191{
1192	struct klp_patch *old_patch;
1193
1194	klp_for_each_patch(old_patch) {
1195		if (old_patch == new_patch)
1196			return;
1197
1198		old_patch->enabled = false;
1199		klp_unpatch_objects(old_patch);
1200	}
1201}
1202
1203/*
1204 * This function removes the dynamically allocated 'nop' functions.
1205 *
1206 * We could be pretty aggressive. NOPs do not change the existing
1207 * behavior except for adding unnecessary delay by the ftrace handler.
1208 *
1209 * It is safe even when the transition was forced. The ftrace handler
1210 * will see a valid ops->func_stack entry thanks to RCU.
1211 *
1212 * We could even free the NOPs structures. They must be the last entry
1213 * in ops->func_stack. Therefore unregister_ftrace_function() is called.
1214 * It does the same as klp_synchronize_transition() to make sure that
1215 * nobody is inside the ftrace handler once the operation finishes.
1216 *
1217 * IMPORTANT: It must be called right after removing the replaced patches!
1218 */
1219void klp_discard_nops(struct klp_patch *new_patch)
1220{
1221	klp_unpatch_objects_dynamic(klp_transition_patch);
1222	klp_free_objects_dynamic(klp_transition_patch);
1223}
1224
1225/*
1226 * Remove parts of patches that touch a given kernel module. The list of
1227 * patches processed might be limited. When limit is NULL, all patches
1228 * will be handled.
1229 */
1230static void klp_cleanup_module_patches_limited(struct module *mod,
1231					       struct klp_patch *limit)
1232{
1233	struct klp_patch *patch;
1234	struct klp_object *obj;
1235
1236	klp_for_each_patch(patch) {
1237		if (patch == limit)
1238			break;
1239
1240		klp_for_each_object(patch, obj) {
1241			if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
1242				continue;
1243
1244			if (patch != klp_transition_patch)
1245				klp_pre_unpatch_callback(obj);
1246
1247			pr_notice("reverting patch '%s' on unloading module '%s'\n",
1248				  patch->mod->name, obj->mod->name);
1249			klp_unpatch_object(obj);
1250
1251			klp_post_unpatch_callback(obj);
1252			klp_clear_object_relocs(patch, obj);
1253			klp_free_object_loaded(obj);
1254			break;
1255		}
1256	}
1257}
1258
1259int klp_module_coming(struct module *mod)
1260{
1261	int ret;
1262	struct klp_patch *patch;
1263	struct klp_object *obj;
1264
1265	if (WARN_ON(mod->state != MODULE_STATE_COMING))
1266		return -EINVAL;
1267
1268	if (!strcmp(mod->name, "vmlinux")) {
1269		pr_err("vmlinux.ko: invalid module name\n");
1270		return -EINVAL;
1271	}
1272
1273	mutex_lock(&klp_mutex);
1274	/*
1275	 * Each module has to know that klp_module_coming()
1276	 * has been called. We never know what module will
1277	 * get patched by a new patch.
1278	 */
1279	mod->klp_alive = true;
1280
1281	klp_for_each_patch(patch) {
1282		klp_for_each_object(patch, obj) {
1283			if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
1284				continue;
1285
1286			obj->mod = mod;
1287
1288			ret = klp_init_object_loaded(patch, obj);
1289			if (ret) {
1290				pr_warn("failed to initialize patch '%s' for module '%s' (%d)\n",
1291					patch->mod->name, obj->mod->name, ret);
1292				goto err;
1293			}
1294
1295			pr_notice("applying patch '%s' to loading module '%s'\n",
1296				  patch->mod->name, obj->mod->name);
1297
1298			ret = klp_pre_patch_callback(obj);
1299			if (ret) {
1300				pr_warn("pre-patch callback failed for object '%s'\n",
1301					obj->name);
1302				goto err;
1303			}
1304
1305			ret = klp_patch_object(obj);
1306			if (ret) {
1307				pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
1308					patch->mod->name, obj->mod->name, ret);
1309
1310				klp_post_unpatch_callback(obj);
1311				goto err;
1312			}
1313
1314			if (patch != klp_transition_patch)
1315				klp_post_patch_callback(obj);
1316
1317			break;
1318		}
1319	}
1320
1321	mutex_unlock(&klp_mutex);
1322
1323	return 0;
1324
1325err:
1326	/*
1327	 * If a patch is unsuccessfully applied, return
1328	 * error to the module loader.
1329	 */
1330	pr_warn("patch '%s' failed for module '%s', refusing to load module '%s'\n",
1331		patch->mod->name, obj->mod->name, obj->mod->name);
1332	mod->klp_alive = false;
1333	obj->mod = NULL;
1334	klp_cleanup_module_patches_limited(mod, patch);
1335	mutex_unlock(&klp_mutex);
1336
1337	return ret;
1338}
1339
1340void klp_module_going(struct module *mod)
1341{
1342	if (WARN_ON(mod->state != MODULE_STATE_GOING &&
1343		    mod->state != MODULE_STATE_COMING))
1344		return;
1345
1346	mutex_lock(&klp_mutex);
1347	/*
1348	 * Each module has to know that klp_module_going()
1349	 * has been called. We never know what module will
1350	 * get patched by a new patch.
1351	 */
1352	mod->klp_alive = false;
1353
1354	klp_cleanup_module_patches_limited(mod, NULL);
1355
1356	mutex_unlock(&klp_mutex);
1357}
1358
1359void *klp_find_section_by_name(const struct module *mod, const char *name,
1360			       size_t *sec_size)
1361{
1362	struct klp_modinfo *info = mod->klp_info;
1363
1364	for (int i = 1; i < info->hdr.e_shnum; i++) {
1365		Elf_Shdr *shdr = &info->sechdrs[i];
1366
1367		if (!strcmp(info->secstrings + shdr->sh_name, name)) {
1368			*sec_size = shdr->sh_size;
1369			return (void *)shdr->sh_addr;
1370		}
1371	}
1372
1373	*sec_size = 0;
1374	return NULL;
1375}
1376EXPORT_SYMBOL_GPL(klp_find_section_by_name);
1377
1378static int __init klp_init(void)
1379{
1380	klp_root_kobj = kobject_create_and_add("livepatch", kernel_kobj);
1381	if (!klp_root_kobj)
1382		return -ENOMEM;
1383
1384	return 0;
1385}
1386
1387module_init(klp_init);