1// SPDX-License-Identifier: GPL-2.0-or-later
   2/*
   3 * Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
   4 */
   5
   6#include <string.h>
   7#include <stdlib.h>
   8
   9#include "builtin.h"
  10#include "cfi.h"
  11#include "arch.h"
  12#include "check.h"
  13#include "special.h"
  14#include "warn.h"
  15#include "arch_elf.h"
  16
  17#include <linux/hashtable.h>
  18#include <linux/kernel.h>
  19
  20#define FAKE_JUMP_OFFSET -1
  21
  22#define C_JUMP_TABLE_SECTION ".rodata..c_jump_table"
  23
  24struct alternative {
  25	struct list_head list;
  26	struct instruction *insn;
  27	bool skip_orig;
  28};
  29
  30const char *objname;
  31struct cfi_init_state initial_func_cfi;
  32
  33struct instruction *find_insn(struct objtool_file *file,
  34			      struct section *sec, unsigned long offset)
  35{
  36	struct instruction *insn;
  37
  38	hash_for_each_possible(file->insn_hash, insn, hash, sec_offset_hash(sec, offset)) {
  39		if (insn->sec == sec && insn->offset == offset)
  40			return insn;
  41	}
  42
  43	return NULL;
  44}
  45
  46static struct instruction *next_insn_same_sec(struct objtool_file *file,
  47					      struct instruction *insn)
  48{
  49	struct instruction *next = list_next_entry(insn, list);
  50
  51	if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
  52		return NULL;
  53
  54	return next;
  55}
  56
  57static struct instruction *next_insn_same_func(struct objtool_file *file,
  58					       struct instruction *insn)
  59{
  60	struct instruction *next = list_next_entry(insn, list);
  61	struct symbol *func = insn->func;
  62
  63	if (!func)
  64		return NULL;
  65
  66	if (&next->list != &file->insn_list && next->func == func)
  67		return next;
  68
  69	/* Check if we're already in the subfunction: */
  70	if (func == func->cfunc)
  71		return NULL;
  72
  73	/* Move to the subfunction: */
  74	return find_insn(file, func->cfunc->sec, func->cfunc->offset);
  75}
  76
  77static struct instruction *prev_insn_same_sym(struct objtool_file *file,
  78					       struct instruction *insn)
  79{
  80	struct instruction *prev = list_prev_entry(insn, list);
  81
  82	if (&prev->list != &file->insn_list && prev->func == insn->func)
  83		return prev;
  84
  85	return NULL;
  86}
  87
  88#define func_for_each_insn(file, func, insn)				\
  89	for (insn = find_insn(file, func->sec, func->offset);		\
  90	     insn;							\
  91	     insn = next_insn_same_func(file, insn))
  92
  93#define sym_for_each_insn(file, sym, insn)				\
  94	for (insn = find_insn(file, sym->sec, sym->offset);		\
  95	     insn && &insn->list != &file->insn_list &&			\
  96		insn->sec == sym->sec &&				\
  97		insn->offset < sym->offset + sym->len;			\
  98	     insn = list_next_entry(insn, list))
  99
 100#define sym_for_each_insn_continue_reverse(file, sym, insn)		\
 101	for (insn = list_prev_entry(insn, list);			\
 102	     &insn->list != &file->insn_list &&				\
 103		insn->sec == sym->sec && insn->offset >= sym->offset;	\
 104	     insn = list_prev_entry(insn, list))
 105
 106#define sec_for_each_insn_from(file, insn)				\
 107	for (; insn; insn = next_insn_same_sec(file, insn))
 108
 109#define sec_for_each_insn_continue(file, insn)				\
 110	for (insn = next_insn_same_sec(file, insn); insn;		\
 111	     insn = next_insn_same_sec(file, insn))
 112
 113static bool is_static_jump(struct instruction *insn)
 114{
 115	return insn->type == INSN_JUMP_CONDITIONAL ||
 116	       insn->type == INSN_JUMP_UNCONDITIONAL;
 117}
 118
 119static bool is_sibling_call(struct instruction *insn)
 120{
 121	/* An indirect jump is either a sibling call or a jump to a table. */
 122	if (insn->type == INSN_JUMP_DYNAMIC)
 123		return list_empty(&insn->alts);
 124
 125	if (!is_static_jump(insn))
 126		return false;
 127
 128	/* add_jump_destinations() sets insn->call_dest for sibling calls. */
 129	return !!insn->call_dest;
 130}
 131
 132/*
 133 * This checks to see if the given function is a "noreturn" function.
 134 *
 135 * For global functions which are outside the scope of this object file, we
 136 * have to keep a manual list of them.
 137 *
 138 * For local functions, we have to detect them manually by simply looking for
 139 * the lack of a return instruction.
 140 */
 141static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 142				int recursion)
 143{
 144	int i;
 145	struct instruction *insn;
 146	bool empty = true;
 147
 148	/*
 149	 * Unfortunately these have to be hard coded because the noreturn
 150	 * attribute isn't provided in ELF data.
 151	 */
 152	static const char * const global_noreturns[] = {
 153		"__stack_chk_fail",
 154		"panic",
 155		"do_exit",
 156		"do_task_dead",
 157		"__module_put_and_exit",
 158		"complete_and_exit",
 159		"__reiserfs_panic",
 160		"lbug_with_loc",
 161		"fortify_panic",
 162		"usercopy_abort",
 163		"machine_real_restart",
 164		"rewind_stack_do_exit",
 165		"kunit_try_catch_throw",
 166	};
 167
 168	if (!func)
 169		return false;
 170
 171	if (func->bind == STB_WEAK)
 172		return false;
 173
 174	if (func->bind == STB_GLOBAL)
 175		for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 176			if (!strcmp(func->name, global_noreturns[i]))
 177				return true;
 178
 179	if (!func->len)
 180		return false;
 181
 182	insn = find_insn(file, func->sec, func->offset);
 183	if (!insn->func)
 184		return false;
 185
 186	func_for_each_insn(file, func, insn) {
 187		empty = false;
 188
 189		if (insn->type == INSN_RETURN)
 190			return false;
 191	}
 192
 193	if (empty)
 194		return false;
 195
 196	/*
 197	 * A function can have a sibling call instead of a return.  In that
 198	 * case, the function's dead-end status depends on whether the target
 199	 * of the sibling call returns.
 200	 */
 201	func_for_each_insn(file, func, insn) {
 202		if (is_sibling_call(insn)) {
 203			struct instruction *dest = insn->jump_dest;
 204
 205			if (!dest)
 206				/* sibling call to another file */
 207				return false;
 208
 209			/* local sibling call */
 210			if (recursion == 5) {
 211				/*
 212				 * Infinite recursion: two functions have
 213				 * sibling calls to each other.  This is a very
 214				 * rare case.  It means they aren't dead ends.
 215				 */
 216				return false;
 217			}
 218
 219			return __dead_end_function(file, dest->func, recursion+1);
 220		}
 221	}
 222
 223	return true;
 224}
 225
 226static bool dead_end_function(struct objtool_file *file, struct symbol *func)
 227{
 228	return __dead_end_function(file, func, 0);
 229}
 230
 231static void init_cfi_state(struct cfi_state *cfi)
 232{
 233	int i;
 234
 235	for (i = 0; i < CFI_NUM_REGS; i++) {
 236		cfi->regs[i].base = CFI_UNDEFINED;
 237		cfi->vals[i].base = CFI_UNDEFINED;
 238	}
 239	cfi->cfa.base = CFI_UNDEFINED;
 240	cfi->drap_reg = CFI_UNDEFINED;
 241	cfi->drap_offset = -1;
 242}
 243
 244static void init_insn_state(struct insn_state *state, struct section *sec)
 245{
 246	memset(state, 0, sizeof(*state));
 247	init_cfi_state(&state->cfi);
 248
 249	/*
 250	 * We need the full vmlinux for noinstr validation, otherwise we can
 251	 * not correctly determine insn->call_dest->sec (external symbols do
 252	 * not have a section).
 253	 */
 254	if (vmlinux && sec)
 255		state->noinstr = sec->noinstr;
 256}
 257
 258/*
 259 * Call the arch-specific instruction decoder for all the instructions and add
 260 * them to the global instruction list.
 261 */
 262static int decode_instructions(struct objtool_file *file)
 263{
 264	struct section *sec;
 265	struct symbol *func;
 266	unsigned long offset;
 267	struct instruction *insn;
 268	unsigned long nr_insns = 0;
 269	int ret;
 270
 271	for_each_sec(file, sec) {
 272
 273		if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 274			continue;
 275
 276		if (strcmp(sec->name, ".altinstr_replacement") &&
 277		    strcmp(sec->name, ".altinstr_aux") &&
 278		    strncmp(sec->name, ".discard.", 9))
 279			sec->text = true;
 280
 281		if (!strcmp(sec->name, ".noinstr.text") ||
 282		    !strcmp(sec->name, ".entry.text"))
 283			sec->noinstr = true;
 284
 285		for (offset = 0; offset < sec->len; offset += insn->len) {
 286			insn = malloc(sizeof(*insn));
 287			if (!insn) {
 288				WARN("malloc failed");
 289				return -1;
 290			}
 291			memset(insn, 0, sizeof(*insn));
 292			INIT_LIST_HEAD(&insn->alts);
 293			INIT_LIST_HEAD(&insn->stack_ops);
 294			init_cfi_state(&insn->cfi);
 295
 296			insn->sec = sec;
 297			insn->offset = offset;
 298
 299			ret = arch_decode_instruction(file->elf, sec, offset,
 300						      sec->len - offset,
 301						      &insn->len, &insn->type,
 302						      &insn->immediate,
 303						      &insn->stack_ops);
 304			if (ret)
 305				goto err;
 306
 307			hash_add(file->insn_hash, &insn->hash, sec_offset_hash(sec, insn->offset));
 308			list_add_tail(&insn->list, &file->insn_list);
 309			nr_insns++;
 310		}
 311
 312		list_for_each_entry(func, &sec->symbol_list, list) {
 313			if (func->type != STT_FUNC || func->alias != func)
 314				continue;
 315
 316			if (!find_insn(file, sec, func->offset)) {
 317				WARN("%s(): can't find starting instruction",
 318				     func->name);
 319				return -1;
 320			}
 321
 322			sym_for_each_insn(file, func, insn)
 323				insn->func = func;
 324		}
 325	}
 326
 327	if (stats)
 328		printf("nr_insns: %lu\n", nr_insns);
 329
 330	return 0;
 331
 332err:
 333	free(insn);
 334	return ret;
 335}
 336
 337static struct instruction *find_last_insn(struct objtool_file *file,
 338					  struct section *sec)
 339{
 340	struct instruction *insn = NULL;
 341	unsigned int offset;
 342	unsigned int end = (sec->len > 10) ? sec->len - 10 : 0;
 343
 344	for (offset = sec->len - 1; offset >= end && !insn; offset--)
 345		insn = find_insn(file, sec, offset);
 346
 347	return insn;
 348}
 349
 350/*
 351 * Mark "ud2" instructions and manually annotated dead ends.
 352 */
 353static int add_dead_ends(struct objtool_file *file)
 354{
 355	struct section *sec;
 356	struct reloc *reloc;
 357	struct instruction *insn;
 358
 359	/*
 360	 * By default, "ud2" is a dead end unless otherwise annotated, because
 361	 * GCC 7 inserts it for certain divide-by-zero cases.
 362	 */
 363	for_each_insn(file, insn)
 364		if (insn->type == INSN_BUG)
 365			insn->dead_end = true;
 366
 367	/*
 368	 * Check for manually annotated dead ends.
 369	 */
 370	sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
 371	if (!sec)
 372		goto reachable;
 373
 374	list_for_each_entry(reloc, &sec->reloc_list, list) {
 375		if (reloc->sym->type != STT_SECTION) {
 376			WARN("unexpected relocation symbol type in %s", sec->name);
 377			return -1;
 378		}
 379		insn = find_insn(file, reloc->sym->sec, reloc->addend);
 380		if (insn)
 381			insn = list_prev_entry(insn, list);
 382		else if (reloc->addend == reloc->sym->sec->len) {
 383			insn = find_last_insn(file, reloc->sym->sec);
 384			if (!insn) {
 385				WARN("can't find unreachable insn at %s+0x%x",
 386				     reloc->sym->sec->name, reloc->addend);
 387				return -1;
 388			}
 389		} else {
 390			WARN("can't find unreachable insn at %s+0x%x",
 391			     reloc->sym->sec->name, reloc->addend);
 392			return -1;
 393		}
 394
 395		insn->dead_end = true;
 396	}
 397
 398reachable:
 399	/*
 400	 * These manually annotated reachable checks are needed for GCC 4.4,
 401	 * where the Linux unreachable() macro isn't supported.  In that case
 402	 * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
 403	 * not a dead end.
 404	 */
 405	sec = find_section_by_name(file->elf, ".rela.discard.reachable");
 406	if (!sec)
 407		return 0;
 408
 409	list_for_each_entry(reloc, &sec->reloc_list, list) {
 410		if (reloc->sym->type != STT_SECTION) {
 411			WARN("unexpected relocation symbol type in %s", sec->name);
 412			return -1;
 413		}
 414		insn = find_insn(file, reloc->sym->sec, reloc->addend);
 415		if (insn)
 416			insn = list_prev_entry(insn, list);
 417		else if (reloc->addend == reloc->sym->sec->len) {
 418			insn = find_last_insn(file, reloc->sym->sec);
 419			if (!insn) {
 420				WARN("can't find reachable insn at %s+0x%x",
 421				     reloc->sym->sec->name, reloc->addend);
 422				return -1;
 423			}
 424		} else {
 425			WARN("can't find reachable insn at %s+0x%x",
 426			     reloc->sym->sec->name, reloc->addend);
 427			return -1;
 428		}
 429
 430		insn->dead_end = false;
 431	}
 432
 433	return 0;
 434}
 435
 436/*
 437 * Warnings shouldn't be reported for ignored functions.
 438 */
 439static void add_ignores(struct objtool_file *file)
 440{
 441	struct instruction *insn;
 442	struct section *sec;
 443	struct symbol *func;
 444	struct reloc *reloc;
 445
 446	sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
 447	if (!sec)
 448		return;
 449
 450	list_for_each_entry(reloc, &sec->reloc_list, list) {
 451		switch (reloc->sym->type) {
 452		case STT_FUNC:
 453			func = reloc->sym;
 454			break;
 455
 456		case STT_SECTION:
 457			func = find_func_by_offset(reloc->sym->sec, reloc->addend);
 458			if (!func)
 459				continue;
 460			break;
 461
 462		default:
 463			WARN("unexpected relocation symbol type in %s: %d", sec->name, reloc->sym->type);
 464			continue;
 465		}
 466
 467		func_for_each_insn(file, func, insn)
 468			insn->ignore = true;
 469	}
 470}
 471
 472/*
 473 * This is a whitelist of functions that is allowed to be called with AC set.
 474 * The list is meant to be minimal and only contains compiler instrumentation
 475 * ABI and a few functions used to implement *_{to,from}_user() functions.
 476 *
 477 * These functions must not directly change AC, but may PUSHF/POPF.
 478 */
 479static const char *uaccess_safe_builtin[] = {
 480	/* KASAN */
 481	"kasan_report",
 482	"check_memory_region",
 483	/* KASAN out-of-line */
 484	"__asan_loadN_noabort",
 485	"__asan_load1_noabort",
 486	"__asan_load2_noabort",
 487	"__asan_load4_noabort",
 488	"__asan_load8_noabort",
 489	"__asan_load16_noabort",
 490	"__asan_storeN_noabort",
 491	"__asan_store1_noabort",
 492	"__asan_store2_noabort",
 493	"__asan_store4_noabort",
 494	"__asan_store8_noabort",
 495	"__asan_store16_noabort",
 496	/* KASAN in-line */
 497	"__asan_report_load_n_noabort",
 498	"__asan_report_load1_noabort",
 499	"__asan_report_load2_noabort",
 500	"__asan_report_load4_noabort",
 501	"__asan_report_load8_noabort",
 502	"__asan_report_load16_noabort",
 503	"__asan_report_store_n_noabort",
 504	"__asan_report_store1_noabort",
 505	"__asan_report_store2_noabort",
 506	"__asan_report_store4_noabort",
 507	"__asan_report_store8_noabort",
 508	"__asan_report_store16_noabort",
 509	/* KCSAN */
 510	"__kcsan_check_access",
 511	"kcsan_found_watchpoint",
 512	"kcsan_setup_watchpoint",
 513	"kcsan_check_scoped_accesses",
 514	"kcsan_disable_current",
 515	"kcsan_enable_current_nowarn",
 516	/* KCSAN/TSAN */
 517	"__tsan_func_entry",
 518	"__tsan_func_exit",
 519	"__tsan_read_range",
 520	"__tsan_write_range",
 521	"__tsan_read1",
 522	"__tsan_read2",
 523	"__tsan_read4",
 524	"__tsan_read8",
 525	"__tsan_read16",
 526	"__tsan_write1",
 527	"__tsan_write2",
 528	"__tsan_write4",
 529	"__tsan_write8",
 530	"__tsan_write16",
 531	/* KCOV */
 532	"write_comp_data",
 533	"check_kcov_mode",
 534	"__sanitizer_cov_trace_pc",
 535	"__sanitizer_cov_trace_const_cmp1",
 536	"__sanitizer_cov_trace_const_cmp2",
 537	"__sanitizer_cov_trace_const_cmp4",
 538	"__sanitizer_cov_trace_const_cmp8",
 539	"__sanitizer_cov_trace_cmp1",
 540	"__sanitizer_cov_trace_cmp2",
 541	"__sanitizer_cov_trace_cmp4",
 542	"__sanitizer_cov_trace_cmp8",
 543	"__sanitizer_cov_trace_switch",
 544	/* UBSAN */
 545	"ubsan_type_mismatch_common",
 546	"__ubsan_handle_type_mismatch",
 547	"__ubsan_handle_type_mismatch_v1",
 548	"__ubsan_handle_shift_out_of_bounds",
 549	/* misc */
 550	"csum_partial_copy_generic",
 551	"__memcpy_mcsafe",
 552	"mcsafe_handle_tail",
 553	"ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
 554	NULL
 555};
 556
 557static void add_uaccess_safe(struct objtool_file *file)
 558{
 559	struct symbol *func;
 560	const char **name;
 561
 562	if (!uaccess)
 563		return;
 564
 565	for (name = uaccess_safe_builtin; *name; name++) {
 566		func = find_symbol_by_name(file->elf, *name);
 567		if (!func)
 568			continue;
 569
 570		func->uaccess_safe = true;
 571	}
 572}
 573
 574/*
 575 * FIXME: For now, just ignore any alternatives which add retpolines.  This is
 576 * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
 577 * But it at least allows objtool to understand the control flow *around* the
 578 * retpoline.
 579 */
 580static int add_ignore_alternatives(struct objtool_file *file)
 581{
 582	struct section *sec;
 583	struct reloc *reloc;
 584	struct instruction *insn;
 585
 586	sec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
 587	if (!sec)
 588		return 0;
 589
 590	list_for_each_entry(reloc, &sec->reloc_list, list) {
 591		if (reloc->sym->type != STT_SECTION) {
 592			WARN("unexpected relocation symbol type in %s", sec->name);
 593			return -1;
 594		}
 595
 596		insn = find_insn(file, reloc->sym->sec, reloc->addend);
 597		if (!insn) {
 598			WARN("bad .discard.ignore_alts entry");
 599			return -1;
 600		}
 601
 602		insn->ignore_alts = true;
 603	}
 604
 605	return 0;
 606}
 607
 608/*
 609 * Find the destination instructions for all jumps.
 610 */
 611static int add_jump_destinations(struct objtool_file *file)
 612{
 613	struct instruction *insn;
 614	struct reloc *reloc;
 615	struct section *dest_sec;
 616	unsigned long dest_off;
 617
 618	for_each_insn(file, insn) {
 619		if (!is_static_jump(insn))
 620			continue;
 621
 622		if (insn->offset == FAKE_JUMP_OFFSET)
 623			continue;
 624
 625		reloc = find_reloc_by_dest_range(file->elf, insn->sec,
 626					       insn->offset, insn->len);
 627		if (!reloc) {
 628			dest_sec = insn->sec;
 629			dest_off = arch_jump_destination(insn);
 630		} else if (reloc->sym->type == STT_SECTION) {
 631			dest_sec = reloc->sym->sec;
 632			dest_off = arch_dest_reloc_offset(reloc->addend);
 633		} else if (reloc->sym->sec->idx) {
 634			dest_sec = reloc->sym->sec;
 635			dest_off = reloc->sym->sym.st_value +
 636				   arch_dest_reloc_offset(reloc->addend);
 637		} else if (strstr(reloc->sym->name, "_indirect_thunk_")) {
 638			/*
 639			 * Retpoline jumps are really dynamic jumps in
 640			 * disguise, so convert them accordingly.
 641			 */
 642			if (insn->type == INSN_JUMP_UNCONDITIONAL)
 643				insn->type = INSN_JUMP_DYNAMIC;
 644			else
 645				insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;
 646
 647			insn->retpoline_safe = true;
 648			continue;
 649		} else {
 650			/* external sibling call */
 651			insn->call_dest = reloc->sym;
 652			continue;
 653		}
 654
 655		insn->jump_dest = find_insn(file, dest_sec, dest_off);
 656		if (!insn->jump_dest) {
 657
 658			/*
 659			 * This is a special case where an alt instruction
 660			 * jumps past the end of the section.  These are
 661			 * handled later in handle_group_alt().
 662			 */
 663			if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 664				continue;
 665
 666			WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 667				  insn->sec, insn->offset, dest_sec->name,
 668				  dest_off);
 669			return -1;
 670		}
 671
 672		/*
 673		 * Cross-function jump.
 674		 */
 675		if (insn->func && insn->jump_dest->func &&
 676		    insn->func != insn->jump_dest->func) {
 677
 678			/*
 679			 * For GCC 8+, create parent/child links for any cold
 680			 * subfunctions.  This is _mostly_ redundant with a
 681			 * similar initialization in read_symbols().
 682			 *
 683			 * If a function has aliases, we want the *first* such
 684			 * function in the symbol table to be the subfunction's
 685			 * parent.  In that case we overwrite the
 686			 * initialization done in read_symbols().
 687			 *
 688			 * However this code can't completely replace the
 689			 * read_symbols() code because this doesn't detect the
 690			 * case where the parent function's only reference to a
 691			 * subfunction is through a jump table.
 692			 */
 693			if (!strstr(insn->func->name, ".cold.") &&
 694			    strstr(insn->jump_dest->func->name, ".cold.")) {
 695				insn->func->cfunc = insn->jump_dest->func;
 696				insn->jump_dest->func->pfunc = insn->func;
 697
 698			} else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
 699				   insn->jump_dest->offset == insn->jump_dest->func->offset) {
 700
 701				/* internal sibling call */
 702				insn->call_dest = insn->jump_dest->func;
 703			}
 704		}
 705	}
 706
 707	return 0;
 708}
 709
 710static void remove_insn_ops(struct instruction *insn)
 711{
 712	struct stack_op *op, *tmp;
 713
 714	list_for_each_entry_safe(op, tmp, &insn->stack_ops, list) {
 715		list_del(&op->list);
 716		free(op);
 717	}
 718}
 719
 720/*
 721 * Find the destination instructions for all calls.
 722 */
 723static int add_call_destinations(struct objtool_file *file)
 724{
 725	struct instruction *insn;
 726	unsigned long dest_off;
 727	struct reloc *reloc;
 728
 729	for_each_insn(file, insn) {
 730		if (insn->type != INSN_CALL)
 731			continue;
 732
 733		reloc = find_reloc_by_dest_range(file->elf, insn->sec,
 734					       insn->offset, insn->len);
 735		if (!reloc) {
 736			dest_off = arch_jump_destination(insn);
 737			insn->call_dest = find_func_by_offset(insn->sec, dest_off);
 738			if (!insn->call_dest)
 739				insn->call_dest = find_symbol_by_offset(insn->sec, dest_off);
 740
 741			if (insn->ignore)
 742				continue;
 743
 744			if (!insn->call_dest) {
 745				WARN_FUNC("unannotated intra-function call", insn->sec, insn->offset);
 746				return -1;
 747			}
 748
 749			if (insn->func && insn->call_dest->type != STT_FUNC) {
 750				WARN_FUNC("unsupported call to non-function",
 751					  insn->sec, insn->offset);
 752				return -1;
 753			}
 754
 755		} else if (reloc->sym->type == STT_SECTION) {
 756			dest_off = arch_dest_reloc_offset(reloc->addend);
 757			insn->call_dest = find_func_by_offset(reloc->sym->sec,
 758							      dest_off);
 759			if (!insn->call_dest) {
 760				WARN_FUNC("can't find call dest symbol at %s+0x%lx",
 761					  insn->sec, insn->offset,
 762					  reloc->sym->sec->name,
 763					  dest_off);
 764				return -1;
 765			}
 766		} else
 767			insn->call_dest = reloc->sym;
 768
 769		/*
 770		 * Many compilers cannot disable KCOV with a function attribute
 771		 * so they need a little help, NOP out any KCOV calls from noinstr
 772		 * text.
 773		 */
 774		if (insn->sec->noinstr &&
 775		    !strncmp(insn->call_dest->name, "__sanitizer_cov_", 16)) {
 776			if (reloc) {
 777				reloc->type = R_NONE;
 778				elf_write_reloc(file->elf, reloc);
 779			}
 780
 781			elf_write_insn(file->elf, insn->sec,
 782				       insn->offset, insn->len,
 783				       arch_nop_insn(insn->len));
 784			insn->type = INSN_NOP;
 785		}
 786
 787		/*
 788		 * Whatever stack impact regular CALLs have, should be undone
 789		 * by the RETURN of the called function.
 790		 *
 791		 * Annotated intra-function calls retain the stack_ops but
 792		 * are converted to JUMP, see read_intra_function_calls().
 793		 */
 794		remove_insn_ops(insn);
 795	}
 796
 797	return 0;
 798}
 799
 800/*
 801 * The .alternatives section requires some extra special care, over and above
 802 * what other special sections require:
 803 *
 804 * 1. Because alternatives are patched in-place, we need to insert a fake jump
 805 *    instruction at the end so that validate_branch() skips all the original
 806 *    replaced instructions when validating the new instruction path.
 807 *
 808 * 2. An added wrinkle is that the new instruction length might be zero.  In
 809 *    that case the old instructions are replaced with noops.  We simulate that
 810 *    by creating a fake jump as the only new instruction.
 811 *
 812 * 3. In some cases, the alternative section includes an instruction which
 813 *    conditionally jumps to the _end_ of the entry.  We have to modify these
 814 *    jumps' destinations to point back to .text rather than the end of the
 815 *    entry in .altinstr_replacement.
 816 */
 817static int handle_group_alt(struct objtool_file *file,
 818			    struct special_alt *special_alt,
 819			    struct instruction *orig_insn,
 820			    struct instruction **new_insn)
 821{
 822	static unsigned int alt_group_next_index = 1;
 823	struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
 824	unsigned int alt_group = alt_group_next_index++;
 825	unsigned long dest_off;
 826
 827	last_orig_insn = NULL;
 828	insn = orig_insn;
 829	sec_for_each_insn_from(file, insn) {
 830		if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 831			break;
 832
 833		insn->alt_group = alt_group;
 834		last_orig_insn = insn;
 835	}
 836
 837	if (next_insn_same_sec(file, last_orig_insn)) {
 838		fake_jump = malloc(sizeof(*fake_jump));
 839		if (!fake_jump) {
 840			WARN("malloc failed");
 841			return -1;
 842		}
 843		memset(fake_jump, 0, sizeof(*fake_jump));
 844		INIT_LIST_HEAD(&fake_jump->alts);
 845		INIT_LIST_HEAD(&fake_jump->stack_ops);
 846		init_cfi_state(&fake_jump->cfi);
 847
 848		fake_jump->sec = special_alt->new_sec;
 849		fake_jump->offset = FAKE_JUMP_OFFSET;
 850		fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 851		fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 852		fake_jump->func = orig_insn->func;
 853	}
 854
 855	if (!special_alt->new_len) {
 856		if (!fake_jump) {
 857			WARN("%s: empty alternative at end of section",
 858			     special_alt->orig_sec->name);
 859			return -1;
 860		}
 861
 862		*new_insn = fake_jump;
 863		return 0;
 864	}
 865
 866	last_new_insn = NULL;
 867	alt_group = alt_group_next_index++;
 868	insn = *new_insn;
 869	sec_for_each_insn_from(file, insn) {
 870		if (insn->offset >= special_alt->new_off + special_alt->new_len)
 871			break;
 872
 873		last_new_insn = insn;
 874
 875		insn->ignore = orig_insn->ignore_alts;
 876		insn->func = orig_insn->func;
 877		insn->alt_group = alt_group;
 878
 879		/*
 880		 * Since alternative replacement code is copy/pasted by the
 881		 * kernel after applying relocations, generally such code can't
 882		 * have relative-address relocation references to outside the
 883		 * .altinstr_replacement section, unless the arch's
 884		 * alternatives code can adjust the relative offsets
 885		 * accordingly.
 886		 *
 887		 * The x86 alternatives code adjusts the offsets only when it
 888		 * encounters a branch instruction at the very beginning of the
 889		 * replacement group.
 890		 */
 891		if ((insn->offset != special_alt->new_off ||
 892		    (insn->type != INSN_CALL && !is_static_jump(insn))) &&
 893		    find_reloc_by_dest_range(file->elf, insn->sec, insn->offset, insn->len)) {
 894
 895			WARN_FUNC("unsupported relocation in alternatives section",
 896				  insn->sec, insn->offset);
 897			return -1;
 898		}
 899
 900		if (!is_static_jump(insn))
 901			continue;
 902
 903		if (!insn->immediate)
 904			continue;
 905
 906		dest_off = arch_jump_destination(insn);
 907		if (dest_off == special_alt->new_off + special_alt->new_len) {
 908			if (!fake_jump) {
 909				WARN("%s: alternative jump to end of section",
 910				     special_alt->orig_sec->name);
 911				return -1;
 912			}
 913			insn->jump_dest = fake_jump;
 914		}
 915
 916		if (!insn->jump_dest) {
 917			WARN_FUNC("can't find alternative jump destination",
 918				  insn->sec, insn->offset);
 919			return -1;
 920		}
 921	}
 922
 923	if (!last_new_insn) {
 924		WARN_FUNC("can't find last new alternative instruction",
 925			  special_alt->new_sec, special_alt->new_off);
 926		return -1;
 927	}
 928
 929	if (fake_jump)
 930		list_add(&fake_jump->list, &last_new_insn->list);
 931
 932	return 0;
 933}
 934
 935/*
 936 * A jump table entry can either convert a nop to a jump or a jump to a nop.
 937 * If the original instruction is a jump, make the alt entry an effective nop
 938 * by just skipping the original instruction.
 939 */
 940static int handle_jump_alt(struct objtool_file *file,
 941			   struct special_alt *special_alt,
 942			   struct instruction *orig_insn,
 943			   struct instruction **new_insn)
 944{
 945	if (orig_insn->type == INSN_NOP)
 946		return 0;
 947
 948	if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 949		WARN_FUNC("unsupported instruction at jump label",
 950			  orig_insn->sec, orig_insn->offset);
 951		return -1;
 952	}
 953
 954	*new_insn = list_next_entry(orig_insn, list);
 955	return 0;
 956}
 957
 958/*
 959 * Read all the special sections which have alternate instructions which can be
 960 * patched in or redirected to at runtime.  Each instruction having alternate
 961 * instruction(s) has them added to its insn->alts list, which will be
 962 * traversed in validate_branch().
 963 */
 964static int add_special_section_alts(struct objtool_file *file)
 965{
 966	struct list_head special_alts;
 967	struct instruction *orig_insn, *new_insn;
 968	struct special_alt *special_alt, *tmp;
 969	struct alternative *alt;
 970	int ret;
 971
 972	ret = special_get_alts(file->elf, &special_alts);
 973	if (ret)
 974		return ret;
 975
 976	list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 977
 978		orig_insn = find_insn(file, special_alt->orig_sec,
 979				      special_alt->orig_off);
 980		if (!orig_insn) {
 981			WARN_FUNC("special: can't find orig instruction",
 982				  special_alt->orig_sec, special_alt->orig_off);
 983			ret = -1;
 984			goto out;
 985		}
 986
 987		new_insn = NULL;
 988		if (!special_alt->group || special_alt->new_len) {
 989			new_insn = find_insn(file, special_alt->new_sec,
 990					     special_alt->new_off);
 991			if (!new_insn) {
 992				WARN_FUNC("special: can't find new instruction",
 993					  special_alt->new_sec,
 994					  special_alt->new_off);
 995				ret = -1;
 996				goto out;
 997			}
 998		}
 999
1000		if (special_alt->group) {
1001			if (!special_alt->orig_len) {
1002				WARN_FUNC("empty alternative entry",
1003					  orig_insn->sec, orig_insn->offset);
1004				continue;
1005			}
1006
1007			ret = handle_group_alt(file, special_alt, orig_insn,
1008					       &new_insn);
1009			if (ret)
1010				goto out;
1011		} else if (special_alt->jump_or_nop) {
1012			ret = handle_jump_alt(file, special_alt, orig_insn,
1013					      &new_insn);
1014			if (ret)
1015				goto out;
1016		}
1017
1018		alt = malloc(sizeof(*alt));
1019		if (!alt) {
1020			WARN("malloc failed");
1021			ret = -1;
1022			goto out;
1023		}
1024
1025		alt->insn = new_insn;
1026		alt->skip_orig = special_alt->skip_orig;
1027		orig_insn->ignore_alts |= special_alt->skip_alt;
1028		list_add_tail(&alt->list, &orig_insn->alts);
1029
1030		list_del(&special_alt->list);
1031		free(special_alt);
1032	}
1033
1034out:
1035	return ret;
1036}
1037
1038static int add_jump_table(struct objtool_file *file, struct instruction *insn,
1039			    struct reloc *table)
1040{
1041	struct reloc *reloc = table;
1042	struct instruction *dest_insn;
1043	struct alternative *alt;
1044	struct symbol *pfunc = insn->func->pfunc;
1045	unsigned int prev_offset = 0;
1046
1047	/*
1048	 * Each @reloc is a switch table relocation which points to the target
1049	 * instruction.
1050	 */
1051	list_for_each_entry_from(reloc, &table->sec->reloc_list, list) {
1052
1053		/* Check for the end of the table: */
1054		if (reloc != table && reloc->jump_table_start)
1055			break;
1056
1057		/* Make sure the table entries are consecutive: */
1058		if (prev_offset && reloc->offset != prev_offset + 8)
1059			break;
1060
1061		/* Detect function pointers from contiguous objects: */
1062		if (reloc->sym->sec == pfunc->sec &&
1063		    reloc->addend == pfunc->offset)
1064			break;
1065
1066		dest_insn = find_insn(file, reloc->sym->sec, reloc->addend);
1067		if (!dest_insn)
1068			break;
1069
1070		/* Make sure the destination is in the same function: */
1071		if (!dest_insn->func || dest_insn->func->pfunc != pfunc)
1072			break;
1073
1074		alt = malloc(sizeof(*alt));
1075		if (!alt) {
1076			WARN("malloc failed");
1077			return -1;
1078		}
1079
1080		alt->insn = dest_insn;
1081		list_add_tail(&alt->list, &insn->alts);
1082		prev_offset = reloc->offset;
1083	}
1084
1085	if (!prev_offset) {
1086		WARN_FUNC("can't find switch jump table",
1087			  insn->sec, insn->offset);
1088		return -1;
1089	}
1090
1091	return 0;
1092}
1093
1094/*
1095 * find_jump_table() - Given a dynamic jump, find the switch jump table in
1096 * .rodata associated with it.
1097 *
1098 * There are 3 basic patterns:
1099 *
1100 * 1. jmpq *[rodata addr](,%reg,8)
1101 *
1102 *    This is the most common case by far.  It jumps to an address in a simple
1103 *    jump table which is stored in .rodata.
1104 *
1105 * 2. jmpq *[rodata addr](%rip)
1106 *
1107 *    This is caused by a rare GCC quirk, currently only seen in three driver
1108 *    functions in the kernel, only with certain obscure non-distro configs.
1109 *
1110 *    As part of an optimization, GCC makes a copy of an existing switch jump
1111 *    table, modifies it, and then hard-codes the jump (albeit with an indirect
1112 *    jump) to use a single entry in the table.  The rest of the jump table and
1113 *    some of its jump targets remain as dead code.
1114 *
1115 *    In such a case we can just crudely ignore all unreachable instruction
1116 *    warnings for the entire object file.  Ideally we would just ignore them
1117 *    for the function, but that would require redesigning the code quite a
1118 *    bit.  And honestly that's just not worth doing: unreachable instruction
1119 *    warnings are of questionable value anyway, and this is such a rare issue.
1120 *
1121 * 3. mov [rodata addr],%reg1
1122 *    ... some instructions ...
1123 *    jmpq *(%reg1,%reg2,8)
1124 *
1125 *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
1126 *    writing, there are 11 occurrences of it in the allmodconfig kernel.
1127 *
1128 *    As of GCC 7 there are quite a few more of these and the 'in between' code
1129 *    is significant. Esp. with KASAN enabled some of the code between the mov
1130 *    and jmpq uses .rodata itself, which can confuse things.
1131 *
1132 *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
1133 *    ensure the same register is used in the mov and jump instructions.
1134 *
1135 *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
1136 */
1137static struct reloc *find_jump_table(struct objtool_file *file,
1138				      struct symbol *func,
1139				      struct instruction *insn)
1140{
1141	struct reloc *text_reloc, *table_reloc;
1142	struct instruction *dest_insn, *orig_insn = insn;
1143	struct section *table_sec;
1144	unsigned long table_offset;
1145
1146	/*
1147	 * Backward search using the @first_jump_src links, these help avoid
1148	 * much of the 'in between' code. Which avoids us getting confused by
1149	 * it.
1150	 */
1151	for (;
1152	     insn && insn->func && insn->func->pfunc == func;
1153	     insn = insn->first_jump_src ?: prev_insn_same_sym(file, insn)) {
1154
1155		if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
1156			break;
1157
1158		/* allow small jumps within the range */
1159		if (insn->type == INSN_JUMP_UNCONDITIONAL &&
1160		    insn->jump_dest &&
1161		    (insn->jump_dest->offset <= insn->offset ||
1162		     insn->jump_dest->offset > orig_insn->offset))
1163		    break;
1164
1165		/* look for a relocation which references .rodata */
1166		text_reloc = find_reloc_by_dest_range(file->elf, insn->sec,
1167						    insn->offset, insn->len);
1168		if (!text_reloc || text_reloc->sym->type != STT_SECTION ||
1169		    !text_reloc->sym->sec->rodata)
1170			continue;
1171
1172		table_offset = text_reloc->addend;
1173		table_sec = text_reloc->sym->sec;
1174
1175		if (text_reloc->type == R_X86_64_PC32)
1176			table_offset += 4;
1177
1178		/*
1179		 * Make sure the .rodata address isn't associated with a
1180		 * symbol.  GCC jump tables are anonymous data.
1181		 *
1182		 * Also support C jump tables which are in the same format as
1183		 * switch jump tables.  For objtool to recognize them, they
1184		 * need to be placed in the C_JUMP_TABLE_SECTION section.  They
1185		 * have symbols associated with them.
1186		 */
1187		if (find_symbol_containing(table_sec, table_offset) &&
1188		    strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
1189			continue;
1190
1191		/*
1192		 * Each table entry has a reloc associated with it.  The reloc
1193		 * should reference text in the same function as the original
1194		 * instruction.
1195		 */
1196		table_reloc = find_reloc_by_dest(file->elf, table_sec, table_offset);
1197		if (!table_reloc)
1198			continue;
1199		dest_insn = find_insn(file, table_reloc->sym->sec, table_reloc->addend);
1200		if (!dest_insn || !dest_insn->func || dest_insn->func->pfunc != func)
1201			continue;
1202
1203		/*
1204		 * Use of RIP-relative switch jumps is quite rare, and
1205		 * indicates a rare GCC quirk/bug which can leave dead code
1206		 * behind.
1207		 */
1208		if (text_reloc->type == R_X86_64_PC32)
1209			file->ignore_unreachables = true;
1210
1211		return table_reloc;
1212	}
1213
1214	return NULL;
1215}
1216
1217/*
1218 * First pass: Mark the head of each jump table so that in the next pass,
1219 * we know when a given jump table ends and the next one starts.
1220 */
1221static void mark_func_jump_tables(struct objtool_file *file,
1222				    struct symbol *func)
1223{
1224	struct instruction *insn, *last = NULL;
1225	struct reloc *reloc;
1226
1227	func_for_each_insn(file, func, insn) {
1228		if (!last)
1229			last = insn;
1230
1231		/*
1232		 * Store back-pointers for unconditional forward jumps such
1233		 * that find_jump_table() can back-track using those and
1234		 * avoid some potentially confusing code.
1235		 */
1236		if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
1237		    insn->offset > last->offset &&
1238		    insn->jump_dest->offset > insn->offset &&
1239		    !insn->jump_dest->first_jump_src) {
1240
1241			insn->jump_dest->first_jump_src = insn;
1242			last = insn->jump_dest;
1243		}
1244
1245		if (insn->type != INSN_JUMP_DYNAMIC)
1246			continue;
1247
1248		reloc = find_jump_table(file, func, insn);
1249		if (reloc) {
1250			reloc->jump_table_start = true;
1251			insn->jump_table = reloc;
1252		}
1253	}
1254}
1255
1256static int add_func_jump_tables(struct objtool_file *file,
1257				  struct symbol *func)
1258{
1259	struct instruction *insn;
1260	int ret;
1261
1262	func_for_each_insn(file, func, insn) {
1263		if (!insn->jump_table)
1264			continue;
1265
1266		ret = add_jump_table(file, insn, insn->jump_table);
1267		if (ret)
1268			return ret;
1269	}
1270
1271	return 0;
1272}
1273
1274/*
1275 * For some switch statements, gcc generates a jump table in the .rodata
1276 * section which contains a list of addresses within the function to jump to.
1277 * This finds these jump tables and adds them to the insn->alts lists.
1278 */
1279static int add_jump_table_alts(struct objtool_file *file)
1280{
1281	struct section *sec;
1282	struct symbol *func;
1283	int ret;
1284
1285	if (!file->rodata)
1286		return 0;
1287
1288	for_each_sec(file, sec) {
1289		list_for_each_entry(func, &sec->symbol_list, list) {
1290			if (func->type != STT_FUNC)
1291				continue;
1292
1293			mark_func_jump_tables(file, func);
1294			ret = add_func_jump_tables(file, func);
1295			if (ret)
1296				return ret;
1297		}
1298	}
1299
1300	return 0;
1301}
1302
1303static int read_unwind_hints(struct objtool_file *file)
1304{
1305	struct section *sec, *relocsec;
1306	struct reloc *reloc;
1307	struct unwind_hint *hint;
1308	struct instruction *insn;
1309	struct cfi_reg *cfa;
1310	int i;
1311
1312	sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1313	if (!sec)
1314		return 0;
1315
1316	relocsec = sec->reloc;
1317	if (!relocsec) {
1318		WARN("missing .rela.discard.unwind_hints section");
1319		return -1;
1320	}
1321
1322	if (sec->len % sizeof(struct unwind_hint)) {
1323		WARN("struct unwind_hint size mismatch");
1324		return -1;
1325	}
1326
1327	file->hints = true;
1328
1329	for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1330		hint = (struct unwind_hint *)sec->data->d_buf + i;
1331
1332		reloc = find_reloc_by_dest(file->elf, sec, i * sizeof(*hint));
1333		if (!reloc) {
1334			WARN("can't find reloc for unwind_hints[%d]", i);
1335			return -1;
1336		}
1337
1338		insn = find_insn(file, reloc->sym->sec, reloc->addend);
1339		if (!insn) {
1340			WARN("can't find insn for unwind_hints[%d]", i);
1341			return -1;
1342		}
1343
1344		cfa = &insn->cfi.cfa;
1345
1346		if (hint->type == UNWIND_HINT_TYPE_RET_OFFSET) {
1347			insn->ret_offset = hint->sp_offset;
1348			continue;
1349		}
1350
1351		insn->hint = true;
1352
1353		switch (hint->sp_reg) {
1354		case ORC_REG_UNDEFINED:
1355			cfa->base = CFI_UNDEFINED;
1356			break;
1357		case ORC_REG_SP:
1358			cfa->base = CFI_SP;
1359			break;
1360		case ORC_REG_BP:
1361			cfa->base = CFI_BP;
1362			break;
1363		case ORC_REG_SP_INDIRECT:
1364			cfa->base = CFI_SP_INDIRECT;
1365			break;
1366		case ORC_REG_R10:
1367			cfa->base = CFI_R10;
1368			break;
1369		case ORC_REG_R13:
1370			cfa->base = CFI_R13;
1371			break;
1372		case ORC_REG_DI:
1373			cfa->base = CFI_DI;
1374			break;
1375		case ORC_REG_DX:
1376			cfa->base = CFI_DX;
1377			break;
1378		default:
1379			WARN_FUNC("unsupported unwind_hint sp base reg %d",
1380				  insn->sec, insn->offset, hint->sp_reg);
1381			return -1;
1382		}
1383
1384		cfa->offset = hint->sp_offset;
1385		insn->cfi.type = hint->type;
1386		insn->cfi.end = hint->end;
1387	}
1388
1389	return 0;
1390}
1391
1392static int read_retpoline_hints(struct objtool_file *file)
1393{
1394	struct section *sec;
1395	struct instruction *insn;
1396	struct reloc *reloc;
1397
1398	sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1399	if (!sec)
1400		return 0;
1401
1402	list_for_each_entry(reloc, &sec->reloc_list, list) {
1403		if (reloc->sym->type != STT_SECTION) {
1404			WARN("unexpected relocation symbol type in %s", sec->name);
1405			return -1;
1406		}
1407
1408		insn = find_insn(file, reloc->sym->sec, reloc->addend);
1409		if (!insn) {
1410			WARN("bad .discard.retpoline_safe entry");
1411			return -1;
1412		}
1413
1414		if (insn->type != INSN_JUMP_DYNAMIC &&
1415		    insn->type != INSN_CALL_DYNAMIC) {
1416			WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1417				  insn->sec, insn->offset);
1418			return -1;
1419		}
1420
1421		insn->retpoline_safe = true;
1422	}
1423
1424	return 0;
1425}
1426
1427static int read_instr_hints(struct objtool_file *file)
1428{
1429	struct section *sec;
1430	struct instruction *insn;
1431	struct reloc *reloc;
1432
1433	sec = find_section_by_name(file->elf, ".rela.discard.instr_end");
1434	if (!sec)
1435		return 0;
1436
1437	list_for_each_entry(reloc, &sec->reloc_list, list) {
1438		if (reloc->sym->type != STT_SECTION) {
1439			WARN("unexpected relocation symbol type in %s", sec->name);
1440			return -1;
1441		}
1442
1443		insn = find_insn(file, reloc->sym->sec, reloc->addend);
1444		if (!insn) {
1445			WARN("bad .discard.instr_end entry");
1446			return -1;
1447		}
1448
1449		insn->instr--;
1450	}
1451
1452	sec = find_section_by_name(file->elf, ".rela.discard.instr_begin");
1453	if (!sec)
1454		return 0;
1455
1456	list_for_each_entry(reloc, &sec->reloc_list, list) {
1457		if (reloc->sym->type != STT_SECTION) {
1458			WARN("unexpected relocation symbol type in %s", sec->name);
1459			return -1;
1460		}
1461
1462		insn = find_insn(file, reloc->sym->sec, reloc->addend);
1463		if (!insn) {
1464			WARN("bad .discard.instr_begin entry");
1465			return -1;
1466		}
1467
1468		insn->instr++;
1469	}
1470
1471	return 0;
1472}
1473
1474static int read_intra_function_calls(struct objtool_file *file)
1475{
1476	struct instruction *insn;
1477	struct section *sec;
1478	struct reloc *reloc;
1479
1480	sec = find_section_by_name(file->elf, ".rela.discard.intra_function_calls");
1481	if (!sec)
1482		return 0;
1483
1484	list_for_each_entry(reloc, &sec->reloc_list, list) {
1485		unsigned long dest_off;
1486
1487		if (reloc->sym->type != STT_SECTION) {
1488			WARN("unexpected relocation symbol type in %s",
1489			     sec->name);
1490			return -1;
1491		}
1492
1493		insn = find_insn(file, reloc->sym->sec, reloc->addend);
1494		if (!insn) {
1495			WARN("bad .discard.intra_function_call entry");
1496			return -1;
1497		}
1498
1499		if (insn->type != INSN_CALL) {
1500			WARN_FUNC("intra_function_call not a direct call",
1501				  insn->sec, insn->offset);
1502			return -1;
1503		}
1504
1505		/*
1506		 * Treat intra-function CALLs as JMPs, but with a stack_op.
1507		 * See add_call_destinations(), which strips stack_ops from
1508		 * normal CALLs.
1509		 */
1510		insn->type = INSN_JUMP_UNCONDITIONAL;
1511
1512		dest_off = insn->offset + insn->len + insn->immediate;
1513		insn->jump_dest = find_insn(file, insn->sec, dest_off);
1514		if (!insn->jump_dest) {
1515			WARN_FUNC("can't find call dest at %s+0x%lx",
1516				  insn->sec, insn->offset,
1517				  insn->sec->name, dest_off);
1518			return -1;
1519		}
1520	}
1521
1522	return 0;
1523}
1524
1525static void mark_rodata(struct objtool_file *file)
1526{
1527	struct section *sec;
1528	bool found = false;
1529
1530	/*
1531	 * Search for the following rodata sections, each of which can
1532	 * potentially contain jump tables:
1533	 *
1534	 * - .rodata: can contain GCC switch tables
1535	 * - .rodata.<func>: same, if -fdata-sections is being used
1536	 * - .rodata..c_jump_table: contains C annotated jump tables
1537	 *
1538	 * .rodata.str1.* sections are ignored; they don't contain jump tables.
1539	 */
1540	for_each_sec(file, sec) {
1541		if (!strncmp(sec->name, ".rodata", 7) &&
1542		    !strstr(sec->name, ".str1.")) {
1543			sec->rodata = true;
1544			found = true;
1545		}
1546	}
1547
1548	file->rodata = found;
1549}
1550
1551static int decode_sections(struct objtool_file *file)
1552{
1553	int ret;
1554
1555	mark_rodata(file);
1556
1557	ret = decode_instructions(file);
1558	if (ret)
1559		return ret;
1560
1561	ret = add_dead_ends(file);
1562	if (ret)
1563		return ret;
1564
1565	add_ignores(file);
1566	add_uaccess_safe(file);
1567
1568	ret = add_ignore_alternatives(file);
1569	if (ret)
1570		return ret;
1571
1572	ret = add_jump_destinations(file);
1573	if (ret)
1574		return ret;
1575
1576	ret = add_special_section_alts(file);
1577	if (ret)
1578		return ret;
1579
1580	ret = read_intra_function_calls(file);
1581	if (ret)
1582		return ret;
1583
1584	ret = add_call_destinations(file);
1585	if (ret)
1586		return ret;
1587
1588	ret = add_jump_table_alts(file);
1589	if (ret)
1590		return ret;
1591
1592	ret = read_unwind_hints(file);
1593	if (ret)
1594		return ret;
1595
1596	ret = read_retpoline_hints(file);
1597	if (ret)
1598		return ret;
1599
1600	ret = read_instr_hints(file);
1601	if (ret)
1602		return ret;
1603
1604	return 0;
1605}
1606
1607static bool is_fentry_call(struct instruction *insn)
1608{
1609	if (insn->type == INSN_CALL && insn->call_dest &&
1610	    insn->call_dest->type == STT_NOTYPE &&
1611	    !strcmp(insn->call_dest->name, "__fentry__"))
1612		return true;
1613
1614	return false;
1615}
1616
1617static bool has_modified_stack_frame(struct instruction *insn, struct insn_state *state)
1618{
1619	u8 ret_offset = insn->ret_offset;
1620	struct cfi_state *cfi = &state->cfi;
1621	int i;
1622
1623	if (cfi->cfa.base != initial_func_cfi.cfa.base || cfi->drap)
1624		return true;
1625
1626	if (cfi->cfa.offset != initial_func_cfi.cfa.offset + ret_offset)
1627		return true;
1628
1629	if (cfi->stack_size != initial_func_cfi.cfa.offset + ret_offset)
1630		return true;
1631
1632	/*
1633	 * If there is a ret offset hint then don't check registers
1634	 * because a callee-saved register might have been pushed on
1635	 * the stack.
1636	 */
1637	if (ret_offset)
1638		return false;
1639
1640	for (i = 0; i < CFI_NUM_REGS; i++) {
1641		if (cfi->regs[i].base != initial_func_cfi.regs[i].base ||
1642		    cfi->regs[i].offset != initial_func_cfi.regs[i].offset)
1643			return true;
1644	}
1645
1646	return false;
1647}
1648
1649static bool has_valid_stack_frame(struct insn_state *state)
1650{
1651	struct cfi_state *cfi = &state->cfi;
1652
1653	if (cfi->cfa.base == CFI_BP && cfi->regs[CFI_BP].base == CFI_CFA &&
1654	    cfi->regs[CFI_BP].offset == -16)
1655		return true;
1656
1657	if (cfi->drap && cfi->regs[CFI_BP].base == CFI_BP)
1658		return true;
1659
1660	return false;
1661}
1662
1663static int update_cfi_state_regs(struct instruction *insn,
1664				  struct cfi_state *cfi,
1665				  struct stack_op *op)
1666{
1667	struct cfi_reg *cfa = &cfi->cfa;
1668
1669	if (cfa->base != CFI_SP && cfa->base != CFI_SP_INDIRECT)
1670		return 0;
1671
1672	/* push */
1673	if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
1674		cfa->offset += 8;
1675
1676	/* pop */
1677	if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
1678		cfa->offset -= 8;
1679
1680	/* add immediate to sp */
1681	if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1682	    op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1683		cfa->offset -= op->src.offset;
1684
1685	return 0;
1686}
1687
1688static void save_reg(struct cfi_state *cfi, unsigned char reg, int base, int offset)
1689{
1690	if (arch_callee_saved_reg(reg) &&
1691	    cfi->regs[reg].base == CFI_UNDEFINED) {
1692		cfi->regs[reg].base = base;
1693		cfi->regs[reg].offset = offset;
1694	}
1695}
1696
1697static void restore_reg(struct cfi_state *cfi, unsigned char reg)
1698{
1699	cfi->regs[reg].base = initial_func_cfi.regs[reg].base;
1700	cfi->regs[reg].offset = initial_func_cfi.regs[reg].offset;
1701}
1702
1703/*
1704 * A note about DRAP stack alignment:
1705 *
1706 * GCC has the concept of a DRAP register, which is used to help keep track of
1707 * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
1708 * register.  The typical DRAP pattern is:
1709 *
1710 *   4c 8d 54 24 08		lea    0x8(%rsp),%r10
1711 *   48 83 e4 c0		and    $0xffffffffffffffc0,%rsp
1712 *   41 ff 72 f8		pushq  -0x8(%r10)
1713 *   55				push   %rbp
1714 *   48 89 e5			mov    %rsp,%rbp
1715 *				(more pushes)
1716 *   41 52			push   %r10
1717 *				...
1718 *   41 5a			pop    %r10
1719 *				(more pops)
1720 *   5d				pop    %rbp
1721 *   49 8d 62 f8		lea    -0x8(%r10),%rsp
1722 *   c3				retq
1723 *
1724 * There are some variations in the epilogues, like:
1725 *
1726 *   5b				pop    %rbx
1727 *   41 5a			pop    %r10
1728 *   41 5c			pop    %r12
1729 *   41 5d			pop    %r13
1730 *   41 5e			pop    %r14
1731 *   c9				leaveq
1732 *   49 8d 62 f8		lea    -0x8(%r10),%rsp
1733 *   c3				retq
1734 *
1735 * and:
1736 *
1737 *   4c 8b 55 e8		mov    -0x18(%rbp),%r10
1738 *   48 8b 5d e0		mov    -0x20(%rbp),%rbx
1739 *   4c 8b 65 f0		mov    -0x10(%rbp),%r12
1740 *   4c 8b 6d f8		mov    -0x8(%rbp),%r13
1741 *   c9				leaveq
1742 *   49 8d 62 f8		lea    -0x8(%r10),%rsp
1743 *   c3				retq
1744 *
1745 * Sometimes r13 is used as the DRAP register, in which case it's saved and
1746 * restored beforehand:
1747 *
1748 *   41 55			push   %r13
1749 *   4c 8d 6c 24 10		lea    0x10(%rsp),%r13
1750 *   48 83 e4 f0		and    $0xfffffffffffffff0,%rsp
1751 *				...
1752 *   49 8d 65 f0		lea    -0x10(%r13),%rsp
1753 *   41 5d			pop    %r13
1754 *   c3				retq
1755 */
1756static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi,
1757			     struct stack_op *op)
1758{
1759	struct cfi_reg *cfa = &cfi->cfa;
1760	struct cfi_reg *regs = cfi->regs;
1761
1762	/* stack operations don't make sense with an undefined CFA */
1763	if (cfa->base == CFI_UNDEFINED) {
1764		if (insn->func) {
1765			WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1766			return -1;
1767		}
1768		return 0;
1769	}
1770
1771	if (cfi->type == ORC_TYPE_REGS || cfi->type == ORC_TYPE_REGS_IRET)
1772		return update_cfi_state_regs(insn, cfi, op);
1773
1774	switch (op->dest.type) {
1775
1776	case OP_DEST_REG:
1777		switch (op->src.type) {
1778
1779		case OP_SRC_REG:
1780			if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1781			    cfa->base == CFI_SP &&
1782			    regs[CFI_BP].base == CFI_CFA &&
1783			    regs[CFI_BP].offset == -cfa->offset) {
1784
1785				/* mov %rsp, %rbp */
1786				cfa->base = op->dest.reg;
1787				cfi->bp_scratch = false;
1788			}
1789
1790			else if (op->src.reg == CFI_SP &&
1791				 op->dest.reg == CFI_BP && cfi->drap) {
1792
1793				/* drap: mov %rsp, %rbp */
1794				regs[CFI_BP].base = CFI_BP;
1795				regs[CFI_BP].offset = -cfi->stack_size;
1796				cfi->bp_scratch = false;
1797			}
1798
1799			else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1800
1801				/*
1802				 * mov %rsp, %reg
1803				 *
1804				 * This is needed for the rare case where GCC
1805				 * does:
1806				 *
1807				 *   mov    %rsp, %rax
1808				 *   ...
1809				 *   mov    %rax, %rsp
1810				 */
1811				cfi->vals[op->dest.reg].base = CFI_CFA;
1812				cfi->vals[op->dest.reg].offset = -cfi->stack_size;
1813			}
1814
1815			else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
1816				 cfa->base == CFI_BP) {
1817
1818				/*
1819				 * mov %rbp, %rsp
1820				 *
1821				 * Restore the original stack pointer (Clang).
1822				 */
1823				cfi->stack_size = -cfi->regs[CFI_BP].offset;
1824			}
1825
1826			else if (op->dest.reg == cfa->base) {
1827
1828				/* mov %reg, %rsp */
1829				if (cfa->base == CFI_SP &&
1830				    cfi->vals[op->src.reg].base == CFI_CFA) {
1831
1832					/*
1833					 * This is needed for the rare case
1834					 * where GCC does something dumb like:
1835					 *
1836					 *   lea    0x8(%rsp), %rcx
1837					 *   ...
1838					 *   mov    %rcx, %rsp
1839					 */
1840					cfa->offset = -cfi->vals[op->src.reg].offset;
1841					cfi->stack_size = cfa->offset;
1842
1843				} else {
1844					cfa->base = CFI_UNDEFINED;
1845					cfa->offset = 0;
1846				}
1847			}
1848
1849			break;
1850
1851		case OP_SRC_ADD:
1852			if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1853
1854				/* add imm, %rsp */
1855				cfi->stack_size -= op->src.offset;
1856				if (cfa->base == CFI_SP)
1857					cfa->offset -= op->src.offset;
1858				break;
1859			}
1860
1861			if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1862
1863				/* lea disp(%rbp), %rsp */
1864				cfi->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1865				break;
1866			}
1867
1868			if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1869
1870				/* drap: lea disp(%rsp), %drap */
1871				cfi->drap_reg = op->dest.reg;
1872
1873				/*
1874				 * lea disp(%rsp), %reg
1875				 *
1876				 * This is needed for the rare case where GCC
1877				 * does something dumb like:
1878				 *
1879				 *   lea    0x8(%rsp), %rcx
1880				 *   ...
1881				 *   mov    %rcx, %rsp
1882				 */
1883				cfi->vals[op->dest.reg].base = CFI_CFA;
1884				cfi->vals[op->dest.reg].offset = \
1885					-cfi->stack_size + op->src.offset;
1886
1887				break;
1888			}
1889
1890			if (cfi->drap && op->dest.reg == CFI_SP &&
1891			    op->src.reg == cfi->drap_reg) {
1892
1893				 /* drap: lea disp(%drap), %rsp */
1894				cfa->base = CFI_SP;
1895				cfa->offset = cfi->stack_size = -op->src.offset;
1896				cfi->drap_reg = CFI_UNDEFINED;
1897				cfi->drap = false;
1898				break;
1899			}
1900
1901			if (op->dest.reg == cfi->cfa.base) {
1902				WARN_FUNC("unsupported stack register modification",
1903					  insn->sec, insn->offset);
1904				return -1;
1905			}
1906
1907			break;
1908
1909		case OP_SRC_AND:
1910			if (op->dest.reg != CFI_SP ||
1911			    (cfi->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1912			    (cfi->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1913				WARN_FUNC("unsupported stack pointer realignment",
1914					  insn->sec, insn->offset);
1915				return -1;
1916			}
1917
1918			if (cfi->drap_reg != CFI_UNDEFINED) {
1919				/* drap: and imm, %rsp */
1920				cfa->base = cfi->drap_reg;
1921				cfa->offset = cfi->stack_size = 0;
1922				cfi->drap = true;
1923			}
1924
1925			/*
1926			 * Older versions of GCC (4.8ish) realign the stack
1927			 * without DRAP, with a frame pointer.
1928			 */
1929
1930			break;
1931
1932		case OP_SRC_POP:
1933		case OP_SRC_POPF:
1934			if (!cfi->drap && op->dest.reg == cfa->base) {
1935
1936				/* pop %rbp */
1937				cfa->base = CFI_SP;
1938			}
1939
1940			if (cfi->drap && cfa->base == CFI_BP_INDIRECT &&
1941			    op->dest.reg == cfi->drap_reg &&
1942			    cfi->drap_offset == -cfi->stack_size) {
1943
1944				/* drap: pop %drap */
1945				cfa->base = cfi->drap_reg;
1946				cfa->offset = 0;
1947				cfi->drap_offset = -1;
1948
1949			} else if (regs[op->dest.reg].offset == -cfi->stack_size) {
1950
1951				/* pop %reg */
1952				restore_reg(cfi, op->dest.reg);
1953			}
1954
1955			cfi->stack_size -= 8;
1956			if (cfa->base == CFI_SP)
1957				cfa->offset -= 8;
1958
1959			break;
1960
1961		case OP_SRC_REG_INDIRECT:
1962			if (cfi->drap && op->src.reg == CFI_BP &&
1963			    op->src.offset == cfi->drap_offset) {
1964
1965				/* drap: mov disp(%rbp), %drap */
1966				cfa->base = cfi->drap_reg;
1967				cfa->offset = 0;
1968				cfi->drap_offset = -1;
1969			}
1970
1971			if (cfi->drap && op->src.reg == CFI_BP &&
1972			    op->src.offset == regs[op->dest.reg].offset) {
1973
1974				/* drap: mov disp(%rbp), %reg */
1975				restore_reg(cfi, op->dest.reg);
1976
1977			} else if (op->src.reg == cfa->base &&
1978			    op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1979
1980				/* mov disp(%rbp), %reg */
1981				/* mov disp(%rsp), %reg */
1982				restore_reg(cfi, op->dest.reg);
1983			}
1984
1985			break;
1986
1987		default:
1988			WARN_FUNC("unknown stack-related instruction",
1989				  insn->sec, insn->offset);
1990			return -1;
1991		}
1992
1993		break;
1994
1995	case OP_DEST_PUSH:
1996	case OP_DEST_PUSHF:
1997		cfi->stack_size += 8;
1998		if (cfa->base == CFI_SP)
1999			cfa->offset += 8;
2000
2001		if (op->src.type != OP_SRC_REG)
2002			break;
2003
2004		if (cfi->drap) {
2005			if (op->src.reg == cfa->base && op->src.reg == cfi->drap_reg) {
2006
2007				/* drap: push %drap */
2008				cfa->base = CFI_BP_INDIRECT;
2009				cfa->offset = -cfi->stack_size;
2010
2011				/* save drap so we know when to restore it */
2012				cfi->drap_offset = -cfi->stack_size;
2013
2014			} else if (op->src.reg == CFI_BP && cfa->base == cfi->drap_reg) {
2015
2016				/* drap: push %rbp */
2017				cfi->stack_size = 0;
2018
2019			} else if (regs[op->src.reg].base == CFI_UNDEFINED) {
2020
2021				/* drap: push %reg */
2022				save_reg(cfi, op->src.reg, CFI_BP, -cfi->stack_size);
2023			}
2024
2025		} else {
2026
2027			/* push %reg */
2028			save_reg(cfi, op->src.reg, CFI_CFA, -cfi->stack_size);
2029		}
2030
2031		/* detect when asm code uses rbp as a scratch register */
2032		if (!no_fp && insn->func && op->src.reg == CFI_BP &&
2033		    cfa->base != CFI_BP)
2034			cfi->bp_scratch = true;
2035		break;
2036
2037	case OP_DEST_REG_INDIRECT:
2038
2039		if (cfi->drap) {
2040			if (op->src.reg == cfa->base && op->src.reg == cfi->drap_reg) {
2041
2042				/* drap: mov %drap, disp(%rbp) */
2043				cfa->base = CFI_BP_INDIRECT;
2044				cfa->offset = op->dest.offset;
2045
2046				/* save drap offset so we know when to restore it */
2047				cfi->drap_offset = op->dest.offset;
2048			}
2049
2050			else if (regs[op->src.reg].base == CFI_UNDEFINED) {
2051
2052				/* drap: mov reg, disp(%rbp) */
2053				save_reg(cfi, op->src.reg, CFI_BP, op->dest.offset);
2054			}
2055
2056		} else if (op->dest.reg == cfa->base) {
2057
2058			/* mov reg, disp(%rbp) */
2059			/* mov reg, disp(%rsp) */
2060			save_reg(cfi, op->src.reg, CFI_CFA,
2061				 op->dest.offset - cfi->cfa.offset);
2062		}
2063
2064		break;
2065
2066	case OP_DEST_LEAVE:
2067		if ((!cfi->drap && cfa->base != CFI_BP) ||
2068		    (cfi->drap && cfa->base != cfi->drap_reg)) {
2069			WARN_FUNC("leave instruction with modified stack frame",
2070				  insn->sec, insn->offset);
2071			return -1;
2072		}
2073
2074		/* leave (mov %rbp, %rsp; pop %rbp) */
2075
2076		cfi->stack_size = -cfi->regs[CFI_BP].offset - 8;
2077		restore_reg(cfi, CFI_BP);
2078
2079		if (!cfi->drap) {
2080			cfa->base = CFI_SP;
2081			cfa->offset -= 8;
2082		}
2083
2084		break;
2085
2086	case OP_DEST_MEM:
2087		if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
2088			WARN_FUNC("unknown stack-related memory operation",
2089				  insn->sec, insn->offset);
2090			return -1;
2091		}
2092
2093		/* pop mem */
2094		cfi->stack_size -= 8;
2095		if (cfa->base == CFI_SP)
2096			cfa->offset -= 8;
2097
2098		break;
2099
2100	default:
2101		WARN_FUNC("unknown stack-related instruction",
2102			  insn->sec, insn->offset);
2103		return -1;
2104	}
2105
2106	return 0;
2107}
2108
2109static int handle_insn_ops(struct instruction *insn, struct insn_state *state)
2110{
2111	struct stack_op *op;
2112
2113	list_for_each_entry(op, &insn->stack_ops, list) {
2114		struct cfi_state old_cfi = state->cfi;
2115		int res;
2116
2117		res = update_cfi_state(insn, &state->cfi, op);
2118		if (res)
2119			return res;
2120
2121		if (insn->alt_group && memcmp(&state->cfi, &old_cfi, sizeof(struct cfi_state))) {
2122			WARN_FUNC("alternative modifies stack", insn->sec, insn->offset);
2123			return -1;
2124		}
2125
2126		if (op->dest.type == OP_DEST_PUSHF) {
2127			if (!state->uaccess_stack) {
2128				state->uaccess_stack = 1;
2129			} else if (state->uaccess_stack >> 31) {
2130				WARN_FUNC("PUSHF stack exhausted",
2131					  insn->sec, insn->offset);
2132				return 1;
2133			}
2134			state->uaccess_stack <<= 1;
2135			state->uaccess_stack  |= state->uaccess;
2136		}
2137
2138		if (op->src.type == OP_SRC_POPF) {
2139			if (state->uaccess_stack) {
2140				state->uaccess = state->uaccess_stack & 1;
2141				state->uaccess_stack >>= 1;
2142				if (state->uaccess_stack == 1)
2143					state->uaccess_stack = 0;
2144			}
2145		}
2146	}
2147
2148	return 0;
2149}
2150
2151static bool insn_cfi_match(struct instruction *insn, struct cfi_state *cfi2)
2152{
2153	struct cfi_state *cfi1 = &insn->cfi;
2154	int i;
2155
2156	if (memcmp(&cfi1->cfa, &cfi2->cfa, sizeof(cfi1->cfa))) {
2157
2158		WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
2159			  insn->sec, insn->offset,
2160			  cfi1->cfa.base, cfi1->cfa.offset,
2161			  cfi2->cfa.base, cfi2->cfa.offset);
2162
2163	} else if (memcmp(&cfi1->regs, &cfi2->regs, sizeof(cfi1->regs))) {
2164		for (i = 0; i < CFI_NUM_REGS; i++) {
2165			if (!memcmp(&cfi1->regs[i], &cfi2->regs[i],
2166				    sizeof(struct cfi_reg)))
2167				continue;
2168
2169			WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
2170				  insn->sec, insn->offset,
2171				  i, cfi1->regs[i].base, cfi1->regs[i].offset,
2172				  i, cfi2->regs[i].base, cfi2->regs[i].offset);
2173			break;
2174		}
2175
2176	} else if (cfi1->type != cfi2->type) {
2177
2178		WARN_FUNC("stack state mismatch: type1=%d type2=%d",
2179			  insn->sec, insn->offset, cfi1->type, cfi2->type);
2180
2181	} else if (cfi1->drap != cfi2->drap ||
2182		   (cfi1->drap && cfi1->drap_reg != cfi2->drap_reg) ||
2183		   (cfi1->drap && cfi1->drap_offset != cfi2->drap_offset)) {
2184
2185		WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
2186			  insn->sec, insn->offset,
2187			  cfi1->drap, cfi1->drap_reg, cfi1->drap_offset,
2188			  cfi2->drap, cfi2->drap_reg, cfi2->drap_offset);
2189
2190	} else
2191		return true;
2192
2193	return false;
2194}
2195
2196static inline bool func_uaccess_safe(struct symbol *func)
2197{
2198	if (func)
2199		return func->uaccess_safe;
2200
2201	return false;
2202}
2203
2204static inline const char *call_dest_name(struct instruction *insn)
2205{
2206	if (insn->call_dest)
2207		return insn->call_dest->name;
2208
2209	return "{dynamic}";
2210}
2211
2212static inline bool noinstr_call_dest(struct symbol *func)
2213{
2214	/*
2215	 * We can't deal with indirect function calls at present;
2216	 * assume they're instrumented.
2217	 */
2218	if (!func)
2219		return false;
2220
2221	/*
2222	 * If the symbol is from a noinstr section; we good.
2223	 */
2224	if (func->sec->noinstr)
2225		return true;
2226
2227	/*
2228	 * The __ubsan_handle_*() calls are like WARN(), they only happen when
2229	 * something 'BAD' happened. At the risk of taking the machine down,
2230	 * let them proceed to get the message out.
2231	 */
2232	if (!strncmp(func->name, "__ubsan_handle_", 15))
2233		return true;
2234
2235	return false;
2236}
2237
2238static int validate_call(struct instruction *insn, struct insn_state *state)
2239{
2240	if (state->noinstr && state->instr <= 0 &&
2241	    !noinstr_call_dest(insn->call_dest)) {
2242		WARN_FUNC("call to %s() leaves .noinstr.text section",
2243				insn->sec, insn->offset, call_dest_name(insn));
2244		return 1;
2245	}
2246
2247	if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
2248		WARN_FUNC("call to %s() with UACCESS enabled",
2249				insn->sec, insn->offset, call_dest_name(insn));
2250		return 1;
2251	}
2252
2253	if (state->df) {
2254		WARN_FUNC("call to %s() with DF set",
2255				insn->sec, insn->offset, call_dest_name(insn));
2256		return 1;
2257	}
2258
2259	return 0;
2260}
2261
2262static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
2263{
2264	if (has_modified_stack_frame(insn, state)) {
2265		WARN_FUNC("sibling call from callable instruction with modified stack frame",
2266				insn->sec, insn->offset);
2267		return 1;
2268	}
2269
2270	return validate_call(insn, state);
2271}
2272
2273static int validate_return(struct symbol *func, struct instruction *insn, struct insn_state *state)
2274{
2275	if (state->noinstr && state->instr > 0) {
2276		WARN_FUNC("return with instrumentation enabled",
2277			  insn->sec, insn->offset);
2278		return 1;
2279	}
2280
2281	if (state->uaccess && !func_uaccess_safe(func)) {
2282		WARN_FUNC("return with UACCESS enabled",
2283			  insn->sec, insn->offset);
2284		return 1;
2285	}
2286
2287	if (!state->uaccess && func_uaccess_safe(func)) {
2288		WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function",
2289			  insn->sec, insn->offset);
2290		return 1;
2291	}
2292
2293	if (state->df) {
2294		WARN_FUNC("return with DF set",
2295			  insn->sec, insn->offset);
2296		return 1;
2297	}
2298
2299	if (func && has_modified_stack_frame(insn, state)) {
2300		WARN_FUNC("return with modified stack frame",
2301			  insn->sec, insn->offset);
2302		return 1;
2303	}
2304
2305	if (state->cfi.bp_scratch) {
2306		WARN_FUNC("BP used as a scratch register",
2307			  insn->sec, insn->offset);
2308		return 1;
2309	}
2310
2311	return 0;
2312}
2313
2314/*
2315 * Alternatives should not contain any ORC entries, this in turn means they
2316 * should not contain any CFI ops, which implies all instructions should have
2317 * the same same CFI state.
2318 *
2319 * It is possible to constuct alternatives that have unreachable holes that go
2320 * unreported (because they're NOPs), such holes would result in CFI_UNDEFINED
2321 * states which then results in ORC entries, which we just said we didn't want.
2322 *
2323 * Avoid them by copying the CFI entry of the first instruction into the whole
2324 * alternative.
2325 */
2326static void fill_alternative_cfi(struct objtool_file *file, struct instruction *insn)
2327{
2328	struct instruction *first_insn = insn;
2329	int alt_group = insn->alt_group;
2330
2331	sec_for_each_insn_continue(file, insn) {
2332		if (insn->alt_group != alt_group)
2333			break;
2334		insn->cfi = first_insn->cfi;
2335	}
2336}
2337
2338/*
2339 * Follow the branch starting at the given instruction, and recursively follow
2340 * any other branches (jumps).  Meanwhile, track the frame pointer state at
2341 * each instruction and validate all the rules described in
2342 * tools/objtool/Documentation/stack-validation.txt.
2343 */
2344static int validate_branch(struct objtool_file *file, struct symbol *func,
2345			   struct instruction *insn, struct insn_state state)
2346{
2347	struct alternative *alt;
2348	struct instruction *next_insn;
2349	struct section *sec;
2350	u8 visited;
2351	int ret;
2352
2353	sec = insn->sec;
2354
2355	while (1) {
2356		next_insn = next_insn_same_sec(file, insn);
2357
2358		if (file->c_file && func && insn->func && func != insn->func->pfunc) {
2359			WARN("%s() falls through to next function %s()",
2360			     func->name, insn->func->name);
2361			return 1;
2362		}
2363
2364		if (func && insn->ignore) {
2365			WARN_FUNC("BUG: why am I validating an ignored function?",
2366				  sec, insn->offset);
2367			return 1;
2368		}
2369
2370		visited = 1 << state.uaccess;
2371		if (insn->visited) {
2372			if (!insn->hint && !insn_cfi_match(insn, &state.cfi))
2373				return 1;
2374
2375			if (insn->visited & visited)
2376				return 0;
2377		}
2378
2379		if (state.noinstr)
2380			state.instr += insn->instr;
2381
2382		if (insn->hint)
2383			state.cfi = insn->cfi;
2384		else
2385			insn->cfi = state.cfi;
2386
2387		insn->visited |= visited;
2388
2389		if (!insn->ignore_alts && !list_empty(&insn->alts)) {
2390			bool skip_orig = false;
2391
2392			list_for_each_entry(alt, &insn->alts, list) {
2393				if (alt->skip_orig)
2394					skip_orig = true;
2395
2396				ret = validate_branch(file, func, alt->insn, state);
2397				if (ret) {
2398					if (backtrace)
2399						BT_FUNC("(alt)", insn);
2400					return ret;
2401				}
2402			}
2403
2404			if (insn->alt_group)
2405				fill_alternative_cfi(file, insn);
2406
2407			if (skip_orig)
2408				return 0;
2409		}
2410
2411		if (handle_insn_ops(insn, &state))
2412			return 1;
2413
2414		switch (insn->type) {
2415
2416		case INSN_RETURN:
2417			return validate_return(func, insn, &state);
2418
2419		case INSN_CALL:
2420		case INSN_CALL_DYNAMIC:
2421			ret = validate_call(insn, &state);
2422			if (ret)
2423				return ret;
2424
2425			if (!no_fp && func && !is_fentry_call(insn) &&
2426			    !has_valid_stack_frame(&state)) {
2427				WARN_FUNC("call without frame pointer save/setup",
2428					  sec, insn->offset);
2429				return 1;
2430			}
2431
2432			if (dead_end_function(file, insn->call_dest))
2433				return 0;
2434
2435			break;
2436
2437		case INSN_JUMP_CONDITIONAL:
2438		case INSN_JUMP_UNCONDITIONAL:
2439			if (func && is_sibling_call(insn)) {
2440				ret = validate_sibling_call(insn, &state);
2441				if (ret)
2442					return ret;
2443
2444			} else if (insn->jump_dest) {
2445				ret = validate_branch(file, func,
2446						      insn->jump_dest, state);
2447				if (ret) {
2448					if (backtrace)
2449						BT_FUNC("(branch)", insn);
2450					return ret;
2451				}
2452			}
2453
2454			if (insn->type == INSN_JUMP_UNCONDITIONAL)
2455				return 0;
2456
2457			break;
2458
2459		case INSN_JUMP_DYNAMIC:
2460		case INSN_JUMP_DYNAMIC_CONDITIONAL:
2461			if (func && is_sibling_call(insn)) {
2462				ret = validate_sibling_call(insn, &state);
2463				if (ret)
2464					return ret;
2465			}
2466
2467			if (insn->type == INSN_JUMP_DYNAMIC)
2468				return 0;
2469
2470			break;
2471
2472		case INSN_CONTEXT_SWITCH:
2473			if (func && (!next_insn || !next_insn->hint)) {
2474				WARN_FUNC("unsupported instruction in callable function",
2475					  sec, insn->offset);
2476				return 1;
2477			}
2478			return 0;
2479
2480		case INSN_STAC:
2481			if (state.uaccess) {
2482				WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
2483				return 1;
2484			}
2485
2486			state.uaccess = true;
2487			break;
2488
2489		case INSN_CLAC:
2490			if (!state.uaccess && func) {
2491				WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
2492				return 1;
2493			}
2494
2495			if (func_uaccess_safe(func) && !state.uaccess_stack) {
2496				WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
2497				return 1;
2498			}
2499
2500			state.uaccess = false;
2501			break;
2502
2503		case INSN_STD:
2504			if (state.df)
2505				WARN_FUNC("recursive STD", sec, insn->offset);
2506
2507			state.df = true;
2508			break;
2509
2510		case INSN_CLD:
2511			if (!state.df && func)
2512				WARN_FUNC("redundant CLD", sec, insn->offset);
2513
2514			state.df = false;
2515			break;
2516
2517		default:
2518			break;
2519		}
2520
2521		if (insn->dead_end)
2522			return 0;
2523
2524		if (!next_insn) {
2525			if (state.cfi.cfa.base == CFI_UNDEFINED)
2526				return 0;
2527			WARN("%s: unexpected end of section", sec->name);
2528			return 1;
2529		}
2530
2531		insn = next_insn;
2532	}
2533
2534	return 0;
2535}
2536
2537static int validate_unwind_hints(struct objtool_file *file, struct section *sec)
2538{
2539	struct instruction *insn;
2540	struct insn_state state;
2541	int ret, warnings = 0;
2542
2543	if (!file->hints)
2544		return 0;
2545
2546	init_insn_state(&state, sec);
2547
2548	if (sec) {
2549		insn = find_insn(file, sec, 0);
2550		if (!insn)
2551			return 0;
2552	} else {
2553		insn = list_first_entry(&file->insn_list, typeof(*insn), list);
2554	}
2555
2556	while (&insn->list != &file->insn_list && (!sec || insn->sec == sec)) {
2557		if (insn->hint && !insn->visited) {
2558			ret = validate_branch(file, insn->func, insn, state);
2559			if (ret && backtrace)
2560				BT_FUNC("<=== (hint)", insn);
2561			warnings += ret;
2562		}
2563
2564		insn = list_next_entry(insn, list);
2565	}
2566
2567	return warnings;
2568}
2569
2570static int validate_retpoline(struct objtool_file *file)
2571{
2572	struct instruction *insn;
2573	int warnings = 0;
2574
2575	for_each_insn(file, insn) {
2576		if (insn->type != INSN_JUMP_DYNAMIC &&
2577		    insn->type != INSN_CALL_DYNAMIC)
2578			continue;
2579
2580		if (insn->retpoline_safe)
2581			continue;
2582
2583		/*
2584		 * .init.text code is ran before userspace and thus doesn't
2585		 * strictly need retpolines, except for modules which are
2586		 * loaded late, they very much do need retpoline in their
2587		 * .init.text
2588		 */
2589		if (!strcmp(insn->sec->name, ".init.text") && !module)
2590			continue;
2591
2592		WARN_FUNC("indirect %s found in RETPOLINE build",
2593			  insn->sec, insn->offset,
2594			  insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
2595
2596		warnings++;
2597	}
2598
2599	return warnings;
2600}
2601
2602static bool is_kasan_insn(struct instruction *insn)
2603{
2604	return (insn->type == INSN_CALL &&
2605		!strcmp(insn->call_dest->name, "__asan_handle_no_return"));
2606}
2607
2608static bool is_ubsan_insn(struct instruction *insn)
2609{
2610	return (insn->type == INSN_CALL &&
2611		!strcmp(insn->call_dest->name,
2612			"__ubsan_handle_builtin_unreachable"));
2613}
2614
2615static bool ignore_unreachable_insn(struct instruction *insn)
2616{
2617	int i;
2618
2619	if (insn->ignore || insn->type == INSN_NOP)
2620		return true;
2621
2622	/*
2623	 * Ignore any unused exceptions.  This can happen when a whitelisted
2624	 * function has an exception table entry.
2625	 *
2626	 * Also ignore alternative replacement instructions.  This can happen
2627	 * when a whitelisted function uses one of the ALTERNATIVE macros.
2628	 */
2629	if (!strcmp(insn->sec->name, ".fixup") ||
2630	    !strcmp(insn->sec->name, ".altinstr_replacement") ||
2631	    !strcmp(insn->sec->name, ".altinstr_aux"))
2632		return true;
2633
2634	if (!insn->func)
2635		return false;
2636
2637	/*
2638	 * CONFIG_UBSAN_TRAP inserts a UD2 when it sees
2639	 * __builtin_unreachable().  The BUG() macro has an unreachable() after
2640	 * the UD2, which causes GCC's undefined trap logic to emit another UD2
2641	 * (or occasionally a JMP to UD2).
2642	 */
2643	if (list_prev_entry(insn, list)->dead_end &&
2644	    (insn->type == INSN_BUG ||
2645	     (insn->type == INSN_JUMP_UNCONDITIONAL &&
2646	      insn->jump_dest && insn->jump_dest->type == INSN_BUG)))
2647		return true;
2648
2649	/*
2650	 * Check if this (or a subsequent) instruction is related to
2651	 * CONFIG_UBSAN or CONFIG_KASAN.
2652	 *
2653	 * End the search at 5 instructions to avoid going into the weeds.
2654	 */
2655	for (i = 0; i < 5; i++) {
2656
2657		if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2658			return true;
2659
2660		if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2661			if (insn->jump_dest &&
2662			    insn->jump_dest->func == insn->func) {
2663				insn = insn->jump_dest;
2664				continue;
2665			}
2666
2667			break;
2668		}
2669
2670		if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2671			break;
2672
2673		insn = list_next_entry(insn, list);
2674	}
2675
2676	return false;
2677}
2678
2679static int validate_symbol(struct objtool_file *file, struct section *sec,
2680			   struct symbol *sym, struct insn_state *state)
2681{
2682	struct instruction *insn;
2683	int ret;
2684
2685	if (!sym->len) {
2686		WARN("%s() is missing an ELF size annotation", sym->name);
2687		return 1;
2688	}
2689
2690	if (sym->pfunc != sym || sym->alias != sym)
2691		return 0;
2692
2693	insn = find_insn(file, sec, sym->offset);
2694	if (!insn || insn->ignore || insn->visited)
2695		return 0;
2696
2697	state->uaccess = sym->uaccess_safe;
2698
2699	ret = validate_branch(file, insn->func, insn, *state);
2700	if (ret && backtrace)
2701		BT_FUNC("<=== (sym)", insn);
2702	return ret;
2703}
2704
2705static int validate_section(struct objtool_file *file, struct section *sec)
2706{
2707	struct insn_state state;
2708	struct symbol *func;
2709	int warnings = 0;
2710
2711	list_for_each_entry(func, &sec->symbol_list, list) {
2712		if (func->type != STT_FUNC)
2713			continue;
2714
2715		init_insn_state(&state, sec);
2716		state.cfi.cfa = initial_func_cfi.cfa;
2717		memcpy(&state.cfi.regs, &initial_func_cfi.regs,
2718		       CFI_NUM_REGS * sizeof(struct cfi_reg));
2719		state.cfi.stack_size = initial_func_cfi.cfa.offset;
2720
2721		warnings += validate_symbol(file, sec, func, &state);
2722	}
2723
2724	return warnings;
2725}
2726
2727static int validate_vmlinux_functions(struct objtool_file *file)
2728{
2729	struct section *sec;
2730	int warnings = 0;
2731
2732	sec = find_section_by_name(file->elf, ".noinstr.text");
2733	if (sec) {
2734		warnings += validate_section(file, sec);
2735		warnings += validate_unwind_hints(file, sec);
2736	}
2737
2738	sec = find_section_by_name(file->elf, ".entry.text");
2739	if (sec) {
2740		warnings += validate_section(file, sec);
2741		warnings += validate_unwind_hints(file, sec);
2742	}
2743
2744	return warnings;
2745}
2746
2747static int validate_functions(struct objtool_file *file)
2748{
2749	struct section *sec;
2750	int warnings = 0;
2751
2752	for_each_sec(file, sec) {
2753		if (!(sec->sh.sh_flags & SHF_EXECINSTR))
2754			continue;
2755
2756		warnings += validate_section(file, sec);
2757	}
2758
2759	return warnings;
2760}
2761
2762static int validate_reachable_instructions(struct objtool_file *file)
2763{
2764	struct instruction *insn;
2765
2766	if (file->ignore_unreachables)
2767		return 0;
2768
2769	for_each_insn(file, insn) {
2770		if (insn->visited || ignore_unreachable_insn(insn))
2771			continue;
2772
2773		WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2774		return 1;
2775	}
2776
2777	return 0;
2778}
2779
2780static struct objtool_file file;
2781
2782int check(const char *_objname, bool orc)
2783{
2784	int ret, warnings = 0;
2785
2786	objname = _objname;
2787
2788	file.elf = elf_open_read(objname, O_RDWR);
2789	if (!file.elf)
2790		return 1;
2791
2792	INIT_LIST_HEAD(&file.insn_list);
2793	hash_init(file.insn_hash);
2794	file.c_file = !vmlinux && find_section_by_name(file.elf, ".comment");
2795	file.ignore_unreachables = no_unreachable;
2796	file.hints = false;
2797
2798	arch_initial_func_cfi_state(&initial_func_cfi);
2799
2800	ret = decode_sections(&file);
2801	if (ret < 0)
2802		goto out;
2803	warnings += ret;
2804
2805	if (list_empty(&file.insn_list))
2806		goto out;
2807
2808	if (vmlinux && !validate_dup) {
2809		ret = validate_vmlinux_functions(&file);
2810		if (ret < 0)
2811			goto out;
2812
2813		warnings += ret;
2814		goto out;
2815	}
2816
2817	if (retpoline) {
2818		ret = validate_retpoline(&file);
2819		if (ret < 0)
2820			return ret;
2821		warnings += ret;
2822	}
2823
2824	ret = validate_functions(&file);
2825	if (ret < 0)
2826		goto out;
2827	warnings += ret;
2828
2829	ret = validate_unwind_hints(&file, NULL);
2830	if (ret < 0)
2831		goto out;
2832	warnings += ret;
2833
2834	if (!warnings) {
2835		ret = validate_reachable_instructions(&file);
2836		if (ret < 0)
2837			goto out;
2838		warnings += ret;
2839	}
2840
2841	if (orc) {
2842		ret = create_orc(&file);
2843		if (ret < 0)
2844			goto out;
2845
2846		ret = create_orc_sections(&file);
2847		if (ret < 0)
2848			goto out;
2849	}
2850
2851	if (file.elf->changed) {
2852		ret = elf_write(file.elf);
2853		if (ret < 0)
2854			goto out;
2855	}
2856
2857out:
2858	if (ret < 0) {
2859		/*
2860		 *  Fatal error.  The binary is corrupt or otherwise broken in
2861		 *  some way, or objtool itself is broken.  Fail the kernel
2862		 *  build.
2863		 */
2864		return ret;
2865	}
2866
2867	return 0;
2868}