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 "check.h"
  11#include "elf.h"
  12#include "special.h"
  13#include "arch.h"
  14#include "warn.h"
 
  15
 
  16#include <linux/hashtable.h>
  17#include <linux/kernel.h>
  18
  19#define FAKE_JUMP_OFFSET -1
  20
  21#define C_JUMP_TABLE_SECTION ".rodata..c_jump_table"
  22
  23struct alternative {
  24	struct list_head list;
  25	struct instruction *insn;
  26	bool skip_orig;
  27};
  28
  29const char *objname;
  30struct cfi_state initial_func_cfi;
 
 
 
 
  31
  32struct instruction *find_insn(struct objtool_file *file,
  33			      struct section *sec, unsigned long offset)
  34{
  35	struct instruction *insn;
  36
  37	hash_for_each_possible(file->insn_hash, insn, hash, offset)
  38		if (insn->sec == sec && insn->offset == offset)
  39			return insn;
 
  40
  41	return NULL;
  42}
  43
  44static struct instruction *next_insn_same_sec(struct objtool_file *file,
  45					      struct instruction *insn)
  46{
  47	struct instruction *next = list_next_entry(insn, list);
 
  48
  49	if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
 
  50		return NULL;
  51
  52	return next;
  53}
  54
  55static struct instruction *next_insn_same_func(struct objtool_file *file,
  56					       struct instruction *insn)
  57{
  58	struct instruction *next = list_next_entry(insn, list);
  59	struct symbol *func = insn->func;
  60
  61	if (!func)
  62		return NULL;
  63
  64	if (&next->list != &file->insn_list && next->func == func)
  65		return next;
  66
  67	/* Check if we're already in the subfunction: */
  68	if (func == func->cfunc)
  69		return NULL;
  70
  71	/* Move to the subfunction: */
  72	return find_insn(file, func->cfunc->sec, func->cfunc->offset);
  73}
  74
  75#define func_for_each_insn_all(file, func, insn)			\
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  76	for (insn = find_insn(file, func->sec, func->offset);		\
  77	     insn;							\
  78	     insn = next_insn_same_func(file, insn))
  79
  80#define func_for_each_insn(file, func, insn)				\
  81	for (insn = find_insn(file, func->sec, func->offset);		\
  82	     insn && &insn->list != &file->insn_list &&			\
  83		insn->sec == func->sec &&				\
  84		insn->offset < func->offset + func->len;		\
  85	     insn = list_next_entry(insn, list))
  86
  87#define func_for_each_insn_continue_reverse(file, func, insn)		\
  88	for (insn = list_prev_entry(insn, list);			\
  89	     &insn->list != &file->insn_list &&				\
  90		insn->sec == func->sec && insn->offset >= func->offset;	\
  91	     insn = list_prev_entry(insn, list))
  92
  93#define sec_for_each_insn_from(file, insn)				\
  94	for (; insn; insn = next_insn_same_sec(file, insn))
  95
  96#define sec_for_each_insn_continue(file, insn)				\
  97	for (insn = next_insn_same_sec(file, insn); insn;		\
  98	     insn = next_insn_same_sec(file, insn))
  99
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 100static bool is_sibling_call(struct instruction *insn)
 101{
 102	/* An indirect jump is either a sibling call or a jump to a table. */
 103	if (insn->type == INSN_JUMP_DYNAMIC)
 104		return list_empty(&insn->alts);
 
 
 
 
 
 
 
 
 
 105
 106	if (insn->type != INSN_JUMP_CONDITIONAL &&
 107	    insn->type != INSN_JUMP_UNCONDITIONAL)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 108		return false;
 109
 110	/* add_jump_destinations() sets insn->call_dest for sibling calls. */
 111	return !!insn->call_dest;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 112}
 113
 114/*
 115 * This checks to see if the given function is a "noreturn" function.
 116 *
 117 * For global functions which are outside the scope of this object file, we
 118 * have to keep a manual list of them.
 119 *
 120 * For local functions, we have to detect them manually by simply looking for
 121 * the lack of a return instruction.
 122 */
 123static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 124				int recursion)
 125{
 126	int i;
 127	struct instruction *insn;
 128	bool empty = true;
 129
 130	/*
 131	 * Unfortunately these have to be hard coded because the noreturn
 132	 * attribute isn't provided in ELF data.
 133	 */
 134	static const char * const global_noreturns[] = {
 135		"__stack_chk_fail",
 136		"panic",
 137		"do_exit",
 138		"do_task_dead",
 139		"__module_put_and_exit",
 140		"complete_and_exit",
 141		"__reiserfs_panic",
 142		"lbug_with_loc",
 143		"fortify_panic",
 144		"usercopy_abort",
 145		"machine_real_restart",
 146		"rewind_stack_do_exit",
 147	};
 
 148
 149	if (!func)
 150		return false;
 151
 152	if (func->bind == STB_WEAK)
 153		return false;
 
 154
 155	if (func->bind == STB_GLOBAL)
 156		for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 157			if (!strcmp(func->name, global_noreturns[i]))
 158				return true;
 
 
 
 
 159
 160	if (!func->len)
 161		return false;
 162
 163	insn = find_insn(file, func->sec, func->offset);
 164	if (!insn->func)
 165		return false;
 166
 167	func_for_each_insn_all(file, func, insn) {
 168		empty = false;
 169
 170		if (insn->type == INSN_RETURN)
 171			return false;
 172	}
 173
 174	if (empty)
 175		return false;
 176
 177	/*
 178	 * A function can have a sibling call instead of a return.  In that
 179	 * case, the function's dead-end status depends on whether the target
 180	 * of the sibling call returns.
 181	 */
 182	func_for_each_insn_all(file, func, insn) {
 183		if (is_sibling_call(insn)) {
 184			struct instruction *dest = insn->jump_dest;
 185
 186			if (!dest)
 187				/* sibling call to another file */
 188				return false;
 189
 190			/* local sibling call */
 191			if (recursion == 5) {
 192				/*
 193				 * Infinite recursion: two functions have
 194				 * sibling calls to each other.  This is a very
 195				 * rare case.  It means they aren't dead ends.
 196				 */
 197				return false;
 198			}
 199
 200			return __dead_end_function(file, dest->func, recursion+1);
 201		}
 202	}
 203
 204	return true;
 205}
 206
 207static bool dead_end_function(struct objtool_file *file, struct symbol *func)
 208{
 209	return __dead_end_function(file, func, 0);
 210}
 211
 212static void clear_insn_state(struct insn_state *state)
 213{
 214	int i;
 215
 216	memset(state, 0, sizeof(*state));
 217	state->cfa.base = CFI_UNDEFINED;
 218	for (i = 0; i < CFI_NUM_REGS; i++) {
 219		state->regs[i].base = CFI_UNDEFINED;
 220		state->vals[i].base = CFI_UNDEFINED;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 221	}
 222	state->drap_reg = CFI_UNDEFINED;
 223	state->drap_offset = -1;
 
 
 
 
 
 
 
 
 
 
 
 224}
 225
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 226/*
 227 * Call the arch-specific instruction decoder for all the instructions and add
 228 * them to the global instruction list.
 229 */
 230static int decode_instructions(struct objtool_file *file)
 231{
 232	struct section *sec;
 233	struct symbol *func;
 234	unsigned long offset;
 235	struct instruction *insn;
 236	int ret;
 237
 238	for_each_sec(file, sec) {
 
 
 
 239
 240		if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 241			continue;
 242
 243		if (strcmp(sec->name, ".altinstr_replacement") &&
 244		    strcmp(sec->name, ".altinstr_aux") &&
 245		    strncmp(sec->name, ".discard.", 9))
 246			sec->text = true;
 247
 248		for (offset = 0; offset < sec->len; offset += insn->len) {
 249			insn = malloc(sizeof(*insn));
 250			if (!insn) {
 251				WARN("malloc failed");
 252				return -1;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 253			}
 254			memset(insn, 0, sizeof(*insn));
 255			INIT_LIST_HEAD(&insn->alts);
 256			clear_insn_state(&insn->state);
 257
 
 258			insn->sec = sec;
 259			insn->offset = offset;
 
 260
 261			ret = arch_decode_instruction(file->elf, sec, offset,
 262						      sec->len - offset,
 263						      &insn->len, &insn->type,
 264						      &insn->immediate,
 265						      &insn->stack_op);
 266			if (ret)
 267				goto err;
 268
 269			hash_add(file->insn_hash, &insn->hash, insn->offset);
 270			list_add_tail(&insn->list, &file->insn_list);
 
 
 
 
 
 
 
 
 
 
 271		}
 272
 273		list_for_each_entry(func, &sec->symbol_list, list) {
 274			if (func->type != STT_FUNC || func->alias != func)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 275				continue;
 276
 277			if (!find_insn(file, sec, func->offset)) {
 278				WARN("%s(): can't find starting instruction",
 279				     func->name);
 280				return -1;
 281			}
 282
 283			func_for_each_insn(file, func, insn)
 284				insn->func = func;
 
 
 
 
 
 
 
 
 
 
 
 285		}
 286	}
 287
 
 
 
 288	return 0;
 
 289
 290err:
 291	free(insn);
 292	return ret;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 293}
 294
 295/*
 296 * Mark "ud2" instructions and manually annotated dead ends.
 297 */
 298static int add_dead_ends(struct objtool_file *file)
 299{
 300	struct section *sec;
 301	struct rela *rela;
 302	struct instruction *insn;
 303	bool found;
 304
 305	/*
 306	 * By default, "ud2" is a dead end unless otherwise annotated, because
 307	 * GCC 7 inserts it for certain divide-by-zero cases.
 308	 */
 309	for_each_insn(file, insn)
 310		if (insn->type == INSN_BUG)
 311			insn->dead_end = true;
 312
 313	/*
 314	 * Check for manually annotated dead ends.
 
 315	 */
 316	sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
 317	if (!sec)
 318		goto reachable;
 319
 320	list_for_each_entry(rela, &sec->rela_list, list) {
 321		if (rela->sym->type != STT_SECTION) {
 322			WARN("unexpected relocation symbol type in %s", sec->name);
 
 
 
 
 323			return -1;
 324		}
 325		insn = find_insn(file, rela->sym->sec, rela->addend);
 326		if (insn)
 327			insn = list_prev_entry(insn, list);
 328		else if (rela->addend == rela->sym->sec->len) {
 329			found = false;
 330			list_for_each_entry_reverse(insn, &file->insn_list, list) {
 331				if (insn->sec == rela->sym->sec) {
 332					found = true;
 333					break;
 334				}
 335			}
 336
 337			if (!found) {
 338				WARN("can't find unreachable insn at %s+0x%x",
 339				     rela->sym->sec->name, rela->addend);
 
 
 
 
 
 340				return -1;
 341			}
 342		} else {
 343			WARN("can't find unreachable insn at %s+0x%x",
 344			     rela->sym->sec->name, rela->addend);
 345			return -1;
 346		}
 347
 348		insn->dead_end = true;
 349	}
 350
 351reachable:
 352	/*
 353	 * These manually annotated reachable checks are needed for GCC 4.4,
 354	 * where the Linux unreachable() macro isn't supported.  In that case
 355	 * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
 356	 * not a dead end.
 357	 */
 358	sec = find_section_by_name(file->elf, ".rela.discard.reachable");
 359	if (!sec)
 
 
 
 
 
 
 
 
 
 
 
 360		return 0;
 361
 362	list_for_each_entry(rela, &sec->rela_list, list) {
 363		if (rela->sym->type != STT_SECTION) {
 364			WARN("unexpected relocation symbol type in %s", sec->name);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 365			return -1;
 366		}
 367		insn = find_insn(file, rela->sym->sec, rela->addend);
 368		if (insn)
 369			insn = list_prev_entry(insn, list);
 370		else if (rela->addend == rela->sym->sec->len) {
 371			found = false;
 372			list_for_each_entry_reverse(insn, &file->insn_list, list) {
 373				if (insn->sec == rela->sym->sec) {
 374					found = true;
 375					break;
 376				}
 377			}
 378
 379			if (!found) {
 380				WARN("can't find reachable insn at %s+0x%x",
 381				     rela->sym->sec->name, rela->addend);
 
 
 382				return -1;
 383			}
 384		} else {
 385			WARN("can't find reachable insn at %s+0x%x",
 386			     rela->sym->sec->name, rela->addend);
 387			return -1;
 
 
 
 
 
 
 
 388		}
 
 389
 390		insn->dead_end = false;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 391	}
 392
 393	return 0;
 394}
 395
 396/*
 397 * Warnings shouldn't be reported for ignored functions.
 398 */
 399static void add_ignores(struct objtool_file *file)
 400{
 401	struct instruction *insn;
 402	struct section *sec;
 403	struct symbol *func;
 404	struct rela *rela;
 405
 406	sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
 407	if (!sec)
 408		return;
 409
 410	list_for_each_entry(rela, &sec->rela_list, list) {
 411		switch (rela->sym->type) {
 412		case STT_FUNC:
 413			func = rela->sym;
 414			break;
 415
 416		case STT_SECTION:
 417			func = find_symbol_by_offset(rela->sym->sec, rela->addend);
 418			if (!func || func->type != STT_FUNC)
 419				continue;
 420			break;
 421
 422		default:
 423			WARN("unexpected relocation symbol type in %s: %d", sec->name, rela->sym->type);
 
 424			continue;
 425		}
 426
 427		func_for_each_insn_all(file, func, insn)
 428			insn->ignore = true;
 429	}
 430}
 431
 432/*
 433 * This is a whitelist of functions that is allowed to be called with AC set.
 434 * The list is meant to be minimal and only contains compiler instrumentation
 435 * ABI and a few functions used to implement *_{to,from}_user() functions.
 436 *
 437 * These functions must not directly change AC, but may PUSHF/POPF.
 438 */
 439static const char *uaccess_safe_builtin[] = {
 440	/* KASAN */
 441	"kasan_report",
 442	"check_memory_region",
 443	/* KASAN out-of-line */
 444	"__asan_loadN_noabort",
 445	"__asan_load1_noabort",
 446	"__asan_load2_noabort",
 447	"__asan_load4_noabort",
 448	"__asan_load8_noabort",
 449	"__asan_load16_noabort",
 450	"__asan_storeN_noabort",
 451	"__asan_store1_noabort",
 452	"__asan_store2_noabort",
 453	"__asan_store4_noabort",
 454	"__asan_store8_noabort",
 455	"__asan_store16_noabort",
 
 
 456	/* KASAN in-line */
 457	"__asan_report_load_n_noabort",
 458	"__asan_report_load1_noabort",
 459	"__asan_report_load2_noabort",
 460	"__asan_report_load4_noabort",
 461	"__asan_report_load8_noabort",
 462	"__asan_report_load16_noabort",
 463	"__asan_report_store_n_noabort",
 464	"__asan_report_store1_noabort",
 465	"__asan_report_store2_noabort",
 466	"__asan_report_store4_noabort",
 467	"__asan_report_store8_noabort",
 468	"__asan_report_store16_noabort",
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 469	/* KCOV */
 470	"write_comp_data",
 
 471	"__sanitizer_cov_trace_pc",
 472	"__sanitizer_cov_trace_const_cmp1",
 473	"__sanitizer_cov_trace_const_cmp2",
 474	"__sanitizer_cov_trace_const_cmp4",
 475	"__sanitizer_cov_trace_const_cmp8",
 476	"__sanitizer_cov_trace_cmp1",
 477	"__sanitizer_cov_trace_cmp2",
 478	"__sanitizer_cov_trace_cmp4",
 479	"__sanitizer_cov_trace_cmp8",
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 480	/* UBSAN */
 481	"ubsan_type_mismatch_common",
 482	"__ubsan_handle_type_mismatch",
 483	"__ubsan_handle_type_mismatch_v1",
 
 
 
 
 484	/* misc */
 485	"csum_partial_copy_generic",
 486	"__memcpy_mcsafe",
 487	"mcsafe_handle_tail",
 
 488	"ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
 
 
 
 489	NULL
 490};
 491
 492static void add_uaccess_safe(struct objtool_file *file)
 493{
 494	struct symbol *func;
 495	const char **name;
 496
 497	if (!uaccess)
 498		return;
 499
 500	for (name = uaccess_safe_builtin; *name; name++) {
 501		func = find_symbol_by_name(file->elf, *name);
 502		if (!func)
 503			continue;
 504
 505		func->uaccess_safe = true;
 506	}
 507}
 508
 509/*
 510 * FIXME: For now, just ignore any alternatives which add retpolines.  This is
 511 * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
 512 * But it at least allows objtool to understand the control flow *around* the
 513 * retpoline.
 514 */
 515static int add_ignore_alternatives(struct objtool_file *file)
 516{
 517	struct section *sec;
 518	struct rela *rela;
 519	struct instruction *insn;
 520
 521	sec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
 522	if (!sec)
 523		return 0;
 524
 525	list_for_each_entry(rela, &sec->rela_list, list) {
 526		if (rela->sym->type != STT_SECTION) {
 527			WARN("unexpected relocation symbol type in %s", sec->name);
 528			return -1;
 529		}
 530
 531		insn = find_insn(file, rela->sym->sec, rela->addend);
 532		if (!insn) {
 533			WARN("bad .discard.ignore_alts entry");
 534			return -1;
 535		}
 536
 537		insn->ignore_alts = true;
 538	}
 539
 540	return 0;
 541}
 542
 543/*
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 544 * Find the destination instructions for all jumps.
 545 */
 546static int add_jump_destinations(struct objtool_file *file)
 547{
 548	struct instruction *insn;
 549	struct rela *rela;
 550	struct section *dest_sec;
 551	unsigned long dest_off;
 552
 553	for_each_insn(file, insn) {
 554		if (insn->type != INSN_JUMP_CONDITIONAL &&
 555		    insn->type != INSN_JUMP_UNCONDITIONAL)
 
 
 
 556			continue;
 557
 558		if (insn->ignore || insn->offset == FAKE_JUMP_OFFSET)
 559			continue;
 560
 561		rela = find_rela_by_dest_range(insn->sec, insn->offset,
 562					       insn->len);
 563		if (!rela) {
 564			dest_sec = insn->sec;
 565			dest_off = insn->offset + insn->len + insn->immediate;
 566		} else if (rela->sym->type == STT_SECTION) {
 567			dest_sec = rela->sym->sec;
 568			dest_off = rela->addend + 4;
 569		} else if (rela->sym->sec->idx) {
 570			dest_sec = rela->sym->sec;
 571			dest_off = rela->sym->sym.st_value + rela->addend + 4;
 572		} else if (strstr(rela->sym->name, "_indirect_thunk_")) {
 
 
 
 573			/*
 574			 * Retpoline jumps are really dynamic jumps in
 575			 * disguise, so convert them accordingly.
 576			 */
 577			if (insn->type == INSN_JUMP_UNCONDITIONAL)
 578				insn->type = INSN_JUMP_DYNAMIC;
 579			else
 580				insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;
 581
 582			insn->retpoline_safe = true;
 583			continue;
 
 
 
 
 584		} else {
 585			/* external sibling call */
 586			insn->call_dest = rela->sym;
 587			continue;
 588		}
 589
 590		insn->jump_dest = find_insn(file, dest_sec, dest_off);
 591		if (!insn->jump_dest) {
 
 592
 593			/*
 594			 * This is a special case where an alt instruction
 595			 * jumps past the end of the section.  These are
 596			 * handled later in handle_group_alt().
 
 
 
 597			 */
 598			if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 
 599				continue;
 
 600
 601			WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 602				  insn->sec, insn->offset, dest_sec->name,
 603				  dest_off);
 604			return -1;
 605		}
 606
 607		/*
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 608		 * Cross-function jump.
 609		 */
 610		if (insn->func && insn->jump_dest->func &&
 611		    insn->func != insn->jump_dest->func) {
 612
 613			/*
 614			 * For GCC 8+, create parent/child links for any cold
 615			 * subfunctions.  This is _mostly_ redundant with a
 616			 * similar initialization in read_symbols().
 617			 *
 618			 * If a function has aliases, we want the *first* such
 619			 * function in the symbol table to be the subfunction's
 620			 * parent.  In that case we overwrite the
 621			 * initialization done in read_symbols().
 622			 *
 623			 * However this code can't completely replace the
 624			 * read_symbols() code because this doesn't detect the
 625			 * case where the parent function's only reference to a
 626			 * subfunction is through a jump table.
 627			 */
 628			if (!strstr(insn->func->name, ".cold.") &&
 629			    strstr(insn->jump_dest->func->name, ".cold.")) {
 630				insn->func->cfunc = insn->jump_dest->func;
 631				insn->jump_dest->func->pfunc = insn->func;
 632
 633			} else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
 634				   insn->jump_dest->offset == insn->jump_dest->func->offset) {
 635
 636				/* internal sibling call */
 637				insn->call_dest = insn->jump_dest->func;
 638			}
 639		}
 
 
 
 
 
 
 
 
 
 
 
 640	}
 641
 642	return 0;
 643}
 644
 
 
 
 
 
 
 
 
 
 
 
 645/*
 646 * Find the destination instructions for all calls.
 647 */
 648static int add_call_destinations(struct objtool_file *file)
 649{
 650	struct instruction *insn;
 651	unsigned long dest_off;
 652	struct rela *rela;
 
 653
 654	for_each_insn(file, insn) {
 655		if (insn->type != INSN_CALL)
 656			continue;
 657
 658		rela = find_rela_by_dest_range(insn->sec, insn->offset,
 659					       insn->len);
 660		if (!rela) {
 661			dest_off = insn->offset + insn->len + insn->immediate;
 662			insn->call_dest = find_symbol_by_offset(insn->sec,
 663								dest_off);
 664
 665			if (!insn->call_dest && !insn->ignore) {
 666				WARN_FUNC("unsupported intra-function call",
 667					  insn->sec, insn->offset);
 668				if (retpoline)
 669					WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
 670				return -1;
 671			}
 672
 673		} else if (rela->sym->type == STT_SECTION) {
 674			insn->call_dest = find_symbol_by_offset(rela->sym->sec,
 675								rela->addend+4);
 676			if (!insn->call_dest ||
 677			    insn->call_dest->type != STT_FUNC) {
 678				WARN_FUNC("can't find call dest symbol at %s+0x%x",
 679					  insn->sec, insn->offset,
 680					  rela->sym->sec->name,
 681					  rela->addend + 4);
 682				return -1;
 683			}
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 684		} else
 685			insn->call_dest = rela->sym;
 686	}
 687
 688	return 0;
 689}
 690
 691/*
 692 * The .alternatives section requires some extra special care, over and above
 693 * what other special sections require:
 694 *
 695 * 1. Because alternatives are patched in-place, we need to insert a fake jump
 696 *    instruction at the end so that validate_branch() skips all the original
 697 *    replaced instructions when validating the new instruction path.
 698 *
 699 * 2. An added wrinkle is that the new instruction length might be zero.  In
 700 *    that case the old instructions are replaced with noops.  We simulate that
 701 *    by creating a fake jump as the only new instruction.
 702 *
 703 * 3. In some cases, the alternative section includes an instruction which
 704 *    conditionally jumps to the _end_ of the entry.  We have to modify these
 705 *    jumps' destinations to point back to .text rather than the end of the
 706 *    entry in .altinstr_replacement.
 707 */
 708static int handle_group_alt(struct objtool_file *file,
 709			    struct special_alt *special_alt,
 710			    struct instruction *orig_insn,
 711			    struct instruction **new_insn)
 712{
 713	struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
 
 714	unsigned long dest_off;
 715
 716	last_orig_insn = NULL;
 717	insn = orig_insn;
 718	sec_for_each_insn_from(file, insn) {
 719		if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 720			break;
 721
 722		insn->alt_group = true;
 723		last_orig_insn = insn;
 724	}
 725
 726	if (next_insn_same_sec(file, last_orig_insn)) {
 727		fake_jump = malloc(sizeof(*fake_jump));
 728		if (!fake_jump) {
 729			WARN("malloc failed");
 730			return -1;
 731		}
 732		memset(fake_jump, 0, sizeof(*fake_jump));
 733		INIT_LIST_HEAD(&fake_jump->alts);
 734		clear_insn_state(&fake_jump->state);
 735
 736		fake_jump->sec = special_alt->new_sec;
 737		fake_jump->offset = FAKE_JUMP_OFFSET;
 738		fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 739		fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 740		fake_jump->func = orig_insn->func;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 741	}
 742
 743	if (!special_alt->new_len) {
 744		if (!fake_jump) {
 745			WARN("%s: empty alternative at end of section",
 746			     special_alt->orig_sec->name);
 
 
 
 
 
 
 
 
 
 
 
 
 
 747			return -1;
 748		}
 
 749
 750		*new_insn = fake_jump;
 751		return 0;
 
 
 
 
 
 
 
 
 
 
 752	}
 753
 754	last_new_insn = NULL;
 755	insn = *new_insn;
 756	sec_for_each_insn_from(file, insn) {
 
 
 757		if (insn->offset >= special_alt->new_off + special_alt->new_len)
 758			break;
 759
 760		last_new_insn = insn;
 761
 762		insn->ignore = orig_insn->ignore_alts;
 763		insn->func = orig_insn->func;
 
 
 
 
 
 
 
 
 
 
 
 
 
 764
 765		if (insn->type != INSN_JUMP_CONDITIONAL &&
 766		    insn->type != INSN_JUMP_UNCONDITIONAL)
 
 
 
 767			continue;
 768
 769		if (!insn->immediate)
 770			continue;
 771
 772		dest_off = insn->offset + insn->len + insn->immediate;
 773		if (dest_off == special_alt->new_off + special_alt->new_len) {
 774			if (!fake_jump) {
 775				WARN("%s: alternative jump to end of section",
 776				     special_alt->orig_sec->name);
 777				return -1;
 778			}
 779			insn->jump_dest = fake_jump;
 780		}
 781
 782		if (!insn->jump_dest) {
 783			WARN_FUNC("can't find alternative jump destination",
 784				  insn->sec, insn->offset);
 785			return -1;
 786		}
 787	}
 788
 789	if (!last_new_insn) {
 790		WARN_FUNC("can't find last new alternative instruction",
 791			  special_alt->new_sec, special_alt->new_off);
 792		return -1;
 793	}
 794
 795	if (fake_jump)
 796		list_add(&fake_jump->list, &last_new_insn->list);
 797
 
 
 
 798	return 0;
 799}
 800
 801/*
 802 * A jump table entry can either convert a nop to a jump or a jump to a nop.
 803 * If the original instruction is a jump, make the alt entry an effective nop
 804 * by just skipping the original instruction.
 805 */
 806static int handle_jump_alt(struct objtool_file *file,
 807			   struct special_alt *special_alt,
 808			   struct instruction *orig_insn,
 809			   struct instruction **new_insn)
 810{
 811	if (orig_insn->type == INSN_NOP)
 812		return 0;
 813
 814	if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 815		WARN_FUNC("unsupported instruction at jump label",
 816			  orig_insn->sec, orig_insn->offset);
 817		return -1;
 818	}
 819
 820	*new_insn = list_next_entry(orig_insn, list);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 821	return 0;
 822}
 823
 824/*
 825 * Read all the special sections which have alternate instructions which can be
 826 * patched in or redirected to at runtime.  Each instruction having alternate
 827 * instruction(s) has them added to its insn->alts list, which will be
 828 * traversed in validate_branch().
 829 */
 830static int add_special_section_alts(struct objtool_file *file)
 831{
 832	struct list_head special_alts;
 833	struct instruction *orig_insn, *new_insn;
 834	struct special_alt *special_alt, *tmp;
 835	struct alternative *alt;
 836	int ret;
 837
 838	ret = special_get_alts(file->elf, &special_alts);
 839	if (ret)
 840		return ret;
 841
 842	list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 843
 844		orig_insn = find_insn(file, special_alt->orig_sec,
 845				      special_alt->orig_off);
 846		if (!orig_insn) {
 847			WARN_FUNC("special: can't find orig instruction",
 848				  special_alt->orig_sec, special_alt->orig_off);
 849			ret = -1;
 850			goto out;
 851		}
 852
 853		new_insn = NULL;
 854		if (!special_alt->group || special_alt->new_len) {
 855			new_insn = find_insn(file, special_alt->new_sec,
 856					     special_alt->new_off);
 857			if (!new_insn) {
 858				WARN_FUNC("special: can't find new instruction",
 859					  special_alt->new_sec,
 860					  special_alt->new_off);
 861				ret = -1;
 862				goto out;
 863			}
 864		}
 865
 866		if (special_alt->group) {
 
 
 
 
 
 867			ret = handle_group_alt(file, special_alt, orig_insn,
 868					       &new_insn);
 869			if (ret)
 870				goto out;
 871		} else if (special_alt->jump_or_nop) {
 872			ret = handle_jump_alt(file, special_alt, orig_insn,
 873					      &new_insn);
 874			if (ret)
 875				goto out;
 876		}
 877
 878		alt = malloc(sizeof(*alt));
 879		if (!alt) {
 880			WARN("malloc failed");
 881			ret = -1;
 882			goto out;
 883		}
 884
 885		alt->insn = new_insn;
 886		alt->skip_orig = special_alt->skip_orig;
 887		orig_insn->ignore_alts |= special_alt->skip_alt;
 888		list_add_tail(&alt->list, &orig_insn->alts);
 
 889
 890		list_del(&special_alt->list);
 891		free(special_alt);
 892	}
 893
 
 
 
 
 
 
 894out:
 895	return ret;
 896}
 897
 898static int add_jump_table(struct objtool_file *file, struct instruction *insn,
 899			    struct rela *table)
 900{
 901	struct rela *rela = table;
 
 902	struct instruction *dest_insn;
 903	struct alternative *alt;
 904	struct symbol *pfunc = insn->func->pfunc;
 905	unsigned int prev_offset = 0;
 
 
 906
 907	/*
 908	 * Each @rela is a switch table relocation which points to the target
 909	 * instruction.
 910	 */
 911	list_for_each_entry_from(rela, &table->sec->rela_list, list) {
 912
 913		/* Check for the end of the table: */
 914		if (rela != table && rela->jump_table_start)
 915			break;
 916
 917		/* Make sure the table entries are consecutive: */
 918		if (prev_offset && rela->offset != prev_offset + 8)
 919			break;
 920
 921		/* Detect function pointers from contiguous objects: */
 922		if (rela->sym->sec == pfunc->sec &&
 923		    rela->addend == pfunc->offset)
 924			break;
 925
 926		dest_insn = find_insn(file, rela->sym->sec, rela->addend);
 927		if (!dest_insn)
 928			break;
 929
 930		/* Make sure the destination is in the same function: */
 931		if (!dest_insn->func || dest_insn->func->pfunc != pfunc)
 932			break;
 933
 934		alt = malloc(sizeof(*alt));
 935		if (!alt) {
 936			WARN("malloc failed");
 937			return -1;
 938		}
 939
 940		alt->insn = dest_insn;
 941		list_add_tail(&alt->list, &insn->alts);
 942		prev_offset = rela->offset;
 
 943	}
 944
 945	if (!prev_offset) {
 946		WARN_FUNC("can't find switch jump table",
 947			  insn->sec, insn->offset);
 948		return -1;
 949	}
 950
 951	return 0;
 952}
 953
 954/*
 955 * find_jump_table() - Given a dynamic jump, find the switch jump table in
 956 * .rodata associated with it.
 957 *
 958 * There are 3 basic patterns:
 959 *
 960 * 1. jmpq *[rodata addr](,%reg,8)
 961 *
 962 *    This is the most common case by far.  It jumps to an address in a simple
 963 *    jump table which is stored in .rodata.
 964 *
 965 * 2. jmpq *[rodata addr](%rip)
 966 *
 967 *    This is caused by a rare GCC quirk, currently only seen in three driver
 968 *    functions in the kernel, only with certain obscure non-distro configs.
 969 *
 970 *    As part of an optimization, GCC makes a copy of an existing switch jump
 971 *    table, modifies it, and then hard-codes the jump (albeit with an indirect
 972 *    jump) to use a single entry in the table.  The rest of the jump table and
 973 *    some of its jump targets remain as dead code.
 974 *
 975 *    In such a case we can just crudely ignore all unreachable instruction
 976 *    warnings for the entire object file.  Ideally we would just ignore them
 977 *    for the function, but that would require redesigning the code quite a
 978 *    bit.  And honestly that's just not worth doing: unreachable instruction
 979 *    warnings are of questionable value anyway, and this is such a rare issue.
 980 *
 981 * 3. mov [rodata addr],%reg1
 982 *    ... some instructions ...
 983 *    jmpq *(%reg1,%reg2,8)
 984 *
 985 *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
 986 *    writing, there are 11 occurrences of it in the allmodconfig kernel.
 987 *
 988 *    As of GCC 7 there are quite a few more of these and the 'in between' code
 989 *    is significant. Esp. with KASAN enabled some of the code between the mov
 990 *    and jmpq uses .rodata itself, which can confuse things.
 991 *
 992 *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
 993 *    ensure the same register is used in the mov and jump instructions.
 994 *
 995 *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
 996 */
 997static struct rela *find_jump_table(struct objtool_file *file,
 998				      struct symbol *func,
 999				      struct instruction *insn)
1000{
1001	struct rela *text_rela, *table_rela;
1002	struct instruction *orig_insn = insn;
1003	struct section *table_sec;
1004	unsigned long table_offset;
1005
1006	/*
1007	 * Backward search using the @first_jump_src links, these help avoid
1008	 * much of the 'in between' code. Which avoids us getting confused by
1009	 * it.
1010	 */
1011	for (;
1012	     &insn->list != &file->insn_list &&
1013	     insn->sec == func->sec &&
1014	     insn->offset >= func->offset;
1015
1016	     insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
1017
1018		if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
1019			break;
1020
1021		/* allow small jumps within the range */
1022		if (insn->type == INSN_JUMP_UNCONDITIONAL &&
1023		    insn->jump_dest &&
1024		    (insn->jump_dest->offset <= insn->offset ||
1025		     insn->jump_dest->offset > orig_insn->offset))
1026		    break;
1027
1028		/* look for a relocation which references .rodata */
1029		text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
1030						    insn->len);
1031		if (!text_rela || text_rela->sym->type != STT_SECTION ||
1032		    !text_rela->sym->sec->rodata)
1033			continue;
1034
1035		table_offset = text_rela->addend;
1036		table_sec = text_rela->sym->sec;
1037
1038		if (text_rela->type == R_X86_64_PC32)
1039			table_offset += 4;
1040
1041		/*
1042		 * Make sure the .rodata address isn't associated with a
1043		 * symbol.  GCC jump tables are anonymous data.
1044		 *
1045		 * Also support C jump tables which are in the same format as
1046		 * switch jump tables.  For objtool to recognize them, they
1047		 * need to be placed in the C_JUMP_TABLE_SECTION section.  They
1048		 * have symbols associated with them.
1049		 */
1050		if (find_symbol_containing(table_sec, table_offset) &&
1051		    strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
1052			continue;
1053
1054		/* Each table entry has a rela associated with it. */
1055		table_rela = find_rela_by_dest(table_sec, table_offset);
1056		if (!table_rela)
1057			continue;
1058
1059		/*
1060		 * Use of RIP-relative switch jumps is quite rare, and
1061		 * indicates a rare GCC quirk/bug which can leave dead code
1062		 * behind.
1063		 */
1064		if (text_rela->type == R_X86_64_PC32)
1065			file->ignore_unreachables = true;
1066
1067		return table_rela;
1068	}
1069
1070	return NULL;
1071}
1072
1073/*
1074 * First pass: Mark the head of each jump table so that in the next pass,
1075 * we know when a given jump table ends and the next one starts.
1076 */
1077static void mark_func_jump_tables(struct objtool_file *file,
1078				    struct symbol *func)
1079{
1080	struct instruction *insn, *last = NULL;
1081	struct rela *rela;
1082
1083	func_for_each_insn_all(file, func, insn) {
1084		if (!last)
1085			last = insn;
1086
1087		/*
1088		 * Store back-pointers for unconditional forward jumps such
1089		 * that find_jump_table() can back-track using those and
1090		 * avoid some potentially confusing code.
1091		 */
1092		if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
1093		    insn->offset > last->offset &&
1094		    insn->jump_dest->offset > insn->offset &&
1095		    !insn->jump_dest->first_jump_src) {
1096
1097			insn->jump_dest->first_jump_src = insn;
1098			last = insn->jump_dest;
1099		}
1100
1101		if (insn->type != INSN_JUMP_DYNAMIC)
1102			continue;
1103
1104		rela = find_jump_table(file, func, insn);
1105		if (rela) {
1106			rela->jump_table_start = true;
1107			insn->jump_table = rela;
1108		}
1109	}
1110}
1111
1112static int add_func_jump_tables(struct objtool_file *file,
1113				  struct symbol *func)
1114{
1115	struct instruction *insn;
1116	int ret;
 
 
 
 
1117
1118	func_for_each_insn_all(file, func, insn) {
1119		if (!insn->jump_table)
1120			continue;
 
 
 
1121
1122		ret = add_jump_table(file, insn, insn->jump_table);
1123		if (ret)
1124			return ret;
 
 
1125	}
1126
1127	return 0;
 
 
 
1128}
1129
1130/*
1131 * For some switch statements, gcc generates a jump table in the .rodata
1132 * section which contains a list of addresses within the function to jump to.
1133 * This finds these jump tables and adds them to the insn->alts lists.
1134 */
1135static int add_jump_table_alts(struct objtool_file *file)
1136{
1137	struct section *sec;
1138	struct symbol *func;
1139	int ret;
1140
1141	if (!file->rodata)
1142		return 0;
1143
1144	for_each_sec(file, sec) {
1145		list_for_each_entry(func, &sec->symbol_list, list) {
1146			if (func->type != STT_FUNC)
1147				continue;
1148
1149			mark_func_jump_tables(file, func);
1150			ret = add_func_jump_tables(file, func);
1151			if (ret)
1152				return ret;
1153		}
1154	}
1155
1156	return 0;
1157}
1158
 
 
 
 
 
 
 
 
 
1159static int read_unwind_hints(struct objtool_file *file)
1160{
1161	struct section *sec, *relasec;
1162	struct rela *rela;
1163	struct unwind_hint *hint;
1164	struct instruction *insn;
1165	struct cfi_reg *cfa;
 
1166	int i;
1167
1168	sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1169	if (!sec)
1170		return 0;
1171
1172	relasec = sec->rela;
1173	if (!relasec) {
1174		WARN("missing .rela.discard.unwind_hints section");
1175		return -1;
1176	}
1177
1178	if (sec->len % sizeof(struct unwind_hint)) {
1179		WARN("struct unwind_hint size mismatch");
1180		return -1;
1181	}
1182
1183	file->hints = true;
1184
1185	for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1186		hint = (struct unwind_hint *)sec->data->d_buf + i;
1187
1188		rela = find_rela_by_dest(sec, i * sizeof(*hint));
1189		if (!rela) {
1190			WARN("can't find rela for unwind_hints[%d]", i);
 
 
 
 
 
 
 
 
 
1191			return -1;
1192		}
1193
1194		insn = find_insn(file, rela->sym->sec, rela->addend);
1195		if (!insn) {
1196			WARN("can't find insn for unwind_hints[%d]", i);
1197			return -1;
1198		}
1199
1200		cfa = &insn->state.cfa;
 
 
 
 
 
1201
1202		if (hint->type == UNWIND_HINT_TYPE_SAVE) {
 
1203			insn->save = true;
1204			continue;
 
1205
1206		} else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1207			insn->restore = true;
1208			insn->hint = true;
1209			continue;
1210		}
1211
1212		insn->hint = true;
 
1213
1214		switch (hint->sp_reg) {
1215		case ORC_REG_UNDEFINED:
1216			cfa->base = CFI_UNDEFINED;
1217			break;
1218		case ORC_REG_SP:
1219			cfa->base = CFI_SP;
1220			break;
1221		case ORC_REG_BP:
1222			cfa->base = CFI_BP;
1223			break;
1224		case ORC_REG_SP_INDIRECT:
1225			cfa->base = CFI_SP_INDIRECT;
1226			break;
1227		case ORC_REG_R10:
1228			cfa->base = CFI_R10;
1229			break;
1230		case ORC_REG_R13:
1231			cfa->base = CFI_R13;
1232			break;
1233		case ORC_REG_DI:
1234			cfa->base = CFI_DI;
1235			break;
1236		case ORC_REG_DX:
1237			cfa->base = CFI_DX;
1238			break;
1239		default:
1240			WARN_FUNC("unsupported unwind_hint sp base reg %d",
1241				  insn->sec, insn->offset, hint->sp_reg);
1242			return -1;
1243		}
1244
1245		cfa->offset = hint->sp_offset;
1246		insn->state.type = hint->type;
1247		insn->state.end = hint->end;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1248	}
1249
1250	return 0;
1251}
1252
1253static int read_retpoline_hints(struct objtool_file *file)
1254{
1255	struct section *sec;
1256	struct instruction *insn;
1257	struct rela *rela;
1258
1259	sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1260	if (!sec)
1261		return 0;
1262
1263	list_for_each_entry(rela, &sec->rela_list, list) {
1264		if (rela->sym->type != STT_SECTION) {
1265			WARN("unexpected relocation symbol type in %s", sec->name);
1266			return -1;
1267		}
1268
1269		insn = find_insn(file, rela->sym->sec, rela->addend);
1270		if (!insn) {
1271			WARN("bad .discard.retpoline_safe entry");
1272			return -1;
1273		}
1274
1275		if (insn->type != INSN_JUMP_DYNAMIC &&
1276		    insn->type != INSN_CALL_DYNAMIC) {
1277			WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1278				  insn->sec, insn->offset);
 
1279			return -1;
1280		}
1281
1282		insn->retpoline_safe = true;
1283	}
1284
1285	return 0;
1286}
1287
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1288static void mark_rodata(struct objtool_file *file)
1289{
1290	struct section *sec;
1291	bool found = false;
1292
1293	/*
1294	 * Search for the following rodata sections, each of which can
1295	 * potentially contain jump tables:
1296	 *
1297	 * - .rodata: can contain GCC switch tables
1298	 * - .rodata.<func>: same, if -fdata-sections is being used
1299	 * - .rodata..c_jump_table: contains C annotated jump tables
1300	 *
1301	 * .rodata.str1.* sections are ignored; they don't contain jump tables.
1302	 */
1303	for_each_sec(file, sec) {
1304		if ((!strncmp(sec->name, ".rodata", 7) && !strstr(sec->name, ".str1.")) ||
1305		    !strcmp(sec->name, C_JUMP_TABLE_SECTION)) {
 
1306			sec->rodata = true;
1307			found = true;
1308		}
1309	}
1310
1311	file->rodata = found;
1312}
1313
1314static int decode_sections(struct objtool_file *file)
1315{
1316	int ret;
1317
1318	mark_rodata(file);
1319
1320	ret = decode_instructions(file);
1321	if (ret)
1322		return ret;
1323
1324	ret = add_dead_ends(file);
 
 
 
 
 
 
 
1325	if (ret)
1326		return ret;
1327
1328	add_ignores(file);
1329	add_uaccess_safe(file);
1330
1331	ret = add_ignore_alternatives(file);
1332	if (ret)
1333		return ret;
1334
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1335	ret = add_jump_destinations(file);
1336	if (ret)
1337		return ret;
1338
1339	ret = add_special_section_alts(file);
 
 
 
 
1340	if (ret)
1341		return ret;
1342
1343	ret = add_call_destinations(file);
1344	if (ret)
1345		return ret;
1346
 
 
 
 
 
 
 
 
1347	ret = add_jump_table_alts(file);
1348	if (ret)
1349		return ret;
1350
1351	ret = read_unwind_hints(file);
1352	if (ret)
1353		return ret;
1354
1355	ret = read_retpoline_hints(file);
1356	if (ret)
1357		return ret;
1358
 
 
 
 
 
 
 
 
1359	return 0;
1360}
1361
1362static bool is_fentry_call(struct instruction *insn)
1363{
1364	if (insn->type == INSN_CALL &&
1365	    insn->call_dest->type == STT_NOTYPE &&
1366	    !strcmp(insn->call_dest->name, "__fentry__"))
1367		return true;
 
 
 
 
 
1368
1369	return false;
1370}
1371
1372static bool has_modified_stack_frame(struct insn_state *state)
1373{
 
1374	int i;
1375
1376	if (state->cfa.base != initial_func_cfi.cfa.base ||
1377	    state->cfa.offset != initial_func_cfi.cfa.offset ||
1378	    state->stack_size != initial_func_cfi.cfa.offset ||
1379	    state->drap)
1380		return true;
1381
1382	for (i = 0; i < CFI_NUM_REGS; i++)
1383		if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1384		    state->regs[i].offset != initial_func_cfi.regs[i].offset)
 
 
 
1385			return true;
 
1386
1387	return false;
1388}
1389
 
 
 
 
 
 
 
1390static bool has_valid_stack_frame(struct insn_state *state)
1391{
1392	if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1393	    state->regs[CFI_BP].offset == -16)
 
 
 
1394		return true;
1395
1396	if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1397		return true;
1398
1399	return false;
1400}
1401
1402static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
 
 
1403{
1404	struct cfi_reg *cfa = &state->cfa;
1405	struct stack_op *op = &insn->stack_op;
1406
1407	if (cfa->base != CFI_SP)
1408		return 0;
1409
1410	/* push */
1411	if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
1412		cfa->offset += 8;
1413
1414	/* pop */
1415	if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
1416		cfa->offset -= 8;
1417
1418	/* add immediate to sp */
1419	if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1420	    op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1421		cfa->offset -= op->src.offset;
1422
1423	return 0;
1424}
1425
1426static void save_reg(struct insn_state *state, unsigned char reg, int base,
1427		     int offset)
1428{
1429	if (arch_callee_saved_reg(reg) &&
1430	    state->regs[reg].base == CFI_UNDEFINED) {
1431		state->regs[reg].base = base;
1432		state->regs[reg].offset = offset;
1433	}
1434}
1435
1436static void restore_reg(struct insn_state *state, unsigned char reg)
1437{
1438	state->regs[reg].base = CFI_UNDEFINED;
1439	state->regs[reg].offset = 0;
1440}
1441
1442/*
1443 * A note about DRAP stack alignment:
1444 *
1445 * GCC has the concept of a DRAP register, which is used to help keep track of
1446 * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
1447 * register.  The typical DRAP pattern is:
1448 *
1449 *   4c 8d 54 24 08		lea    0x8(%rsp),%r10
1450 *   48 83 e4 c0		and    $0xffffffffffffffc0,%rsp
1451 *   41 ff 72 f8		pushq  -0x8(%r10)
1452 *   55				push   %rbp
1453 *   48 89 e5			mov    %rsp,%rbp
1454 *				(more pushes)
1455 *   41 52			push   %r10
1456 *				...
1457 *   41 5a			pop    %r10
1458 *				(more pops)
1459 *   5d				pop    %rbp
1460 *   49 8d 62 f8		lea    -0x8(%r10),%rsp
1461 *   c3				retq
1462 *
1463 * There are some variations in the epilogues, like:
1464 *
1465 *   5b				pop    %rbx
1466 *   41 5a			pop    %r10
1467 *   41 5c			pop    %r12
1468 *   41 5d			pop    %r13
1469 *   41 5e			pop    %r14
1470 *   c9				leaveq
1471 *   49 8d 62 f8		lea    -0x8(%r10),%rsp
1472 *   c3				retq
1473 *
1474 * and:
1475 *
1476 *   4c 8b 55 e8		mov    -0x18(%rbp),%r10
1477 *   48 8b 5d e0		mov    -0x20(%rbp),%rbx
1478 *   4c 8b 65 f0		mov    -0x10(%rbp),%r12
1479 *   4c 8b 6d f8		mov    -0x8(%rbp),%r13
1480 *   c9				leaveq
1481 *   49 8d 62 f8		lea    -0x8(%r10),%rsp
1482 *   c3				retq
1483 *
1484 * Sometimes r13 is used as the DRAP register, in which case it's saved and
1485 * restored beforehand:
1486 *
1487 *   41 55			push   %r13
1488 *   4c 8d 6c 24 10		lea    0x10(%rsp),%r13
1489 *   48 83 e4 f0		and    $0xfffffffffffffff0,%rsp
1490 *				...
1491 *   49 8d 65 f0		lea    -0x10(%r13),%rsp
1492 *   41 5d			pop    %r13
1493 *   c3				retq
1494 */
1495static int update_insn_state(struct instruction *insn, struct insn_state *state)
 
 
1496{
1497	struct stack_op *op = &insn->stack_op;
1498	struct cfi_reg *cfa = &state->cfa;
1499	struct cfi_reg *regs = state->regs;
 
 
 
1500
1501	/* stack operations don't make sense with an undefined CFA */
1502	if (cfa->base == CFI_UNDEFINED) {
1503		if (insn->func) {
1504			WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1505			return -1;
1506		}
1507		return 0;
1508	}
1509
1510	if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1511		return update_insn_state_regs(insn, state);
 
1512
1513	switch (op->dest.type) {
1514
1515	case OP_DEST_REG:
1516		switch (op->src.type) {
1517
1518		case OP_SRC_REG:
1519			if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1520			    cfa->base == CFI_SP &&
1521			    regs[CFI_BP].base == CFI_CFA &&
1522			    regs[CFI_BP].offset == -cfa->offset) {
1523
1524				/* mov %rsp, %rbp */
1525				cfa->base = op->dest.reg;
1526				state->bp_scratch = false;
1527			}
1528
1529			else if (op->src.reg == CFI_SP &&
1530				 op->dest.reg == CFI_BP && state->drap) {
1531
1532				/* drap: mov %rsp, %rbp */
1533				regs[CFI_BP].base = CFI_BP;
1534				regs[CFI_BP].offset = -state->stack_size;
1535				state->bp_scratch = false;
1536			}
1537
1538			else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1539
1540				/*
1541				 * mov %rsp, %reg
1542				 *
1543				 * This is needed for the rare case where GCC
1544				 * does:
1545				 *
1546				 *   mov    %rsp, %rax
1547				 *   ...
1548				 *   mov    %rax, %rsp
1549				 */
1550				state->vals[op->dest.reg].base = CFI_CFA;
1551				state->vals[op->dest.reg].offset = -state->stack_size;
1552			}
1553
1554			else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
1555				 cfa->base == CFI_BP) {
1556
1557				/*
1558				 * mov %rbp, %rsp
1559				 *
1560				 * Restore the original stack pointer (Clang).
1561				 */
1562				state->stack_size = -state->regs[CFI_BP].offset;
1563			}
1564
1565			else if (op->dest.reg == cfa->base) {
1566
1567				/* mov %reg, %rsp */
1568				if (cfa->base == CFI_SP &&
1569				    state->vals[op->src.reg].base == CFI_CFA) {
1570
1571					/*
1572					 * This is needed for the rare case
1573					 * where GCC does something dumb like:
1574					 *
1575					 *   lea    0x8(%rsp), %rcx
1576					 *   ...
1577					 *   mov    %rcx, %rsp
1578					 */
1579					cfa->offset = -state->vals[op->src.reg].offset;
1580					state->stack_size = cfa->offset;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1581
1582				} else {
1583					cfa->base = CFI_UNDEFINED;
1584					cfa->offset = 0;
1585				}
1586			}
1587
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1588			break;
1589
1590		case OP_SRC_ADD:
1591			if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1592
1593				/* add imm, %rsp */
1594				state->stack_size -= op->src.offset;
1595				if (cfa->base == CFI_SP)
1596					cfa->offset -= op->src.offset;
1597				break;
1598			}
1599
1600			if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
 
 
 
 
 
 
 
 
1601
1602				/* lea disp(%rbp), %rsp */
1603				state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
 
 
 
 
 
 
 
 
 
1604				break;
1605			}
1606
1607			if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1608
1609				/* drap: lea disp(%rsp), %drap */
1610				state->drap_reg = op->dest.reg;
1611
1612				/*
1613				 * lea disp(%rsp), %reg
1614				 *
1615				 * This is needed for the rare case where GCC
1616				 * does something dumb like:
1617				 *
1618				 *   lea    0x8(%rsp), %rcx
1619				 *   ...
1620				 *   mov    %rcx, %rsp
1621				 */
1622				state->vals[op->dest.reg].base = CFI_CFA;
1623				state->vals[op->dest.reg].offset = \
1624					-state->stack_size + op->src.offset;
1625
1626				break;
1627			}
1628
1629			if (state->drap && op->dest.reg == CFI_SP &&
1630			    op->src.reg == state->drap_reg) {
1631
1632				 /* drap: lea disp(%drap), %rsp */
1633				cfa->base = CFI_SP;
1634				cfa->offset = state->stack_size = -op->src.offset;
1635				state->drap_reg = CFI_UNDEFINED;
1636				state->drap = false;
1637				break;
1638			}
1639
1640			if (op->dest.reg == state->cfa.base) {
1641				WARN_FUNC("unsupported stack register modification",
1642					  insn->sec, insn->offset);
1643				return -1;
1644			}
1645
1646			break;
1647
1648		case OP_SRC_AND:
1649			if (op->dest.reg != CFI_SP ||
1650			    (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1651			    (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1652				WARN_FUNC("unsupported stack pointer realignment",
1653					  insn->sec, insn->offset);
1654				return -1;
1655			}
1656
1657			if (state->drap_reg != CFI_UNDEFINED) {
1658				/* drap: and imm, %rsp */
1659				cfa->base = state->drap_reg;
1660				cfa->offset = state->stack_size = 0;
1661				state->drap = true;
1662			}
1663
1664			/*
1665			 * Older versions of GCC (4.8ish) realign the stack
1666			 * without DRAP, with a frame pointer.
1667			 */
1668
1669			break;
1670
1671		case OP_SRC_POP:
1672		case OP_SRC_POPF:
1673			if (!state->drap && op->dest.type == OP_DEST_REG &&
1674			    op->dest.reg == cfa->base) {
 
 
 
 
 
 
1675
1676				/* pop %rbp */
1677				cfa->base = CFI_SP;
1678			}
1679
1680			if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1681			    op->dest.type == OP_DEST_REG &&
1682			    op->dest.reg == state->drap_reg &&
1683			    state->drap_offset == -state->stack_size) {
1684
1685				/* drap: pop %drap */
1686				cfa->base = state->drap_reg;
1687				cfa->offset = 0;
1688				state->drap_offset = -1;
1689
1690			} else if (regs[op->dest.reg].offset == -state->stack_size) {
1691
1692				/* pop %reg */
1693				restore_reg(state, op->dest.reg);
1694			}
1695
1696			state->stack_size -= 8;
1697			if (cfa->base == CFI_SP)
1698				cfa->offset -= 8;
1699
1700			break;
1701
1702		case OP_SRC_REG_INDIRECT:
1703			if (state->drap && op->src.reg == CFI_BP &&
1704			    op->src.offset == state->drap_offset) {
 
 
 
 
 
 
 
 
1705
1706				/* drap: mov disp(%rbp), %drap */
1707				cfa->base = state->drap_reg;
1708				cfa->offset = 0;
1709				state->drap_offset = -1;
1710			}
1711
1712			if (state->drap && op->src.reg == CFI_BP &&
1713			    op->src.offset == regs[op->dest.reg].offset) {
1714
1715				/* drap: mov disp(%rbp), %reg */
1716				restore_reg(state, op->dest.reg);
1717
1718			} else if (op->src.reg == cfa->base &&
1719			    op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1720
1721				/* mov disp(%rbp), %reg */
1722				/* mov disp(%rsp), %reg */
1723				restore_reg(state, op->dest.reg);
 
 
 
 
 
 
1724			}
1725
1726			break;
1727
1728		default:
1729			WARN_FUNC("unknown stack-related instruction",
1730				  insn->sec, insn->offset);
1731			return -1;
1732		}
1733
1734		break;
1735
1736	case OP_DEST_PUSH:
1737	case OP_DEST_PUSHF:
1738		state->stack_size += 8;
1739		if (cfa->base == CFI_SP)
1740			cfa->offset += 8;
1741
1742		if (op->src.type != OP_SRC_REG)
1743			break;
1744
1745		if (state->drap) {
1746			if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1747
1748				/* drap: push %drap */
1749				cfa->base = CFI_BP_INDIRECT;
1750				cfa->offset = -state->stack_size;
1751
1752				/* save drap so we know when to restore it */
1753				state->drap_offset = -state->stack_size;
1754
1755			} else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1756
1757				/* drap: push %rbp */
1758				state->stack_size = 0;
1759
1760			} else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1761
1762				/* drap: push %reg */
1763				save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1764			}
1765
1766		} else {
1767
1768			/* push %reg */
1769			save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1770		}
1771
1772		/* detect when asm code uses rbp as a scratch register */
1773		if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1774		    cfa->base != CFI_BP)
1775			state->bp_scratch = true;
1776		break;
1777
1778	case OP_DEST_REG_INDIRECT:
1779
1780		if (state->drap) {
1781			if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1782
1783				/* drap: mov %drap, disp(%rbp) */
1784				cfa->base = CFI_BP_INDIRECT;
1785				cfa->offset = op->dest.offset;
1786
1787				/* save drap offset so we know when to restore it */
1788				state->drap_offset = op->dest.offset;
1789			}
1790
1791			else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1792
1793				/* drap: mov reg, disp(%rbp) */
1794				save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1795			}
1796
1797		} else if (op->dest.reg == cfa->base) {
1798
1799			/* mov reg, disp(%rbp) */
1800			/* mov reg, disp(%rsp) */
1801			save_reg(state, op->src.reg, CFI_CFA,
1802				 op->dest.offset - state->cfa.offset);
1803		}
1804
1805		break;
1806
1807	case OP_DEST_LEAVE:
1808		if ((!state->drap && cfa->base != CFI_BP) ||
1809		    (state->drap && cfa->base != state->drap_reg)) {
1810			WARN_FUNC("leave instruction with modified stack frame",
1811				  insn->sec, insn->offset);
1812			return -1;
1813		}
1814
1815		/* leave (mov %rbp, %rsp; pop %rbp) */
 
 
1816
1817		state->stack_size = -state->regs[CFI_BP].offset - 8;
1818		restore_reg(state, CFI_BP);
1819
1820		if (!state->drap) {
1821			cfa->base = CFI_SP;
1822			cfa->offset -= 8;
1823		}
1824
1825		break;
1826
1827	case OP_DEST_MEM:
1828		if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
1829			WARN_FUNC("unknown stack-related memory operation",
1830				  insn->sec, insn->offset);
1831			return -1;
1832		}
1833
1834		/* pop mem */
1835		state->stack_size -= 8;
1836		if (cfa->base == CFI_SP)
1837			cfa->offset -= 8;
1838
1839		break;
1840
1841	default:
1842		WARN_FUNC("unknown stack-related instruction",
1843			  insn->sec, insn->offset);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1844		return -1;
1845	}
1846
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1847	return 0;
1848}
1849
1850static bool insn_state_match(struct instruction *insn, struct insn_state *state)
 
 
1851{
1852	struct insn_state *state1 = &insn->state, *state2 = state;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1853	int i;
1854
1855	if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1856		WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1857			  insn->sec, insn->offset,
1858			  state1->cfa.base, state1->cfa.offset,
1859			  state2->cfa.base, state2->cfa.offset);
 
1860
1861	} else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
 
 
 
 
1862		for (i = 0; i < CFI_NUM_REGS; i++) {
1863			if (!memcmp(&state1->regs[i], &state2->regs[i],
1864				    sizeof(struct cfi_reg)))
1865				continue;
1866
1867			WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1868				  insn->sec, insn->offset,
1869				  i, state1->regs[i].base, state1->regs[i].offset,
1870				  i, state2->regs[i].base, state2->regs[i].offset);
1871			break;
1872		}
1873
1874	} else if (state1->type != state2->type) {
1875		WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1876			  insn->sec, insn->offset, state1->type, state2->type);
1877
1878	} else if (state1->drap != state2->drap ||
1879		 (state1->drap && state1->drap_reg != state2->drap_reg) ||
1880		 (state1->drap && state1->drap_offset != state2->drap_offset)) {
1881		WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1882			  insn->sec, insn->offset,
1883			  state1->drap, state1->drap_reg, state1->drap_offset,
1884			  state2->drap, state2->drap_reg, state2->drap_offset);
 
1885
1886	} else
1887		return true;
1888
1889	return false;
1890}
1891
1892static inline bool func_uaccess_safe(struct symbol *func)
1893{
1894	if (func)
1895		return func->uaccess_safe;
1896
1897	return false;
1898}
1899
1900static inline const char *call_dest_name(struct instruction *insn)
1901{
1902	if (insn->call_dest)
1903		return insn->call_dest->name;
 
 
 
 
 
 
 
 
 
 
 
1904
1905	return "{dynamic}";
1906}
1907
1908static int validate_call(struct instruction *insn, struct insn_state *state)
1909{
1910	if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
1911		WARN_FUNC("call to %s() with UACCESS enabled",
1912				insn->sec, insn->offset, call_dest_name(insn));
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1913		return 1;
1914	}
1915
1916	if (state->df) {
1917		WARN_FUNC("call to %s() with DF set",
1918				insn->sec, insn->offset, call_dest_name(insn));
1919		return 1;
1920	}
1921
1922	return 0;
1923}
1924
1925static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
 
 
 
 
 
 
 
 
 
 
 
 
1926{
1927	if (has_modified_stack_frame(state)) {
1928		WARN_FUNC("sibling call from callable instruction with modified stack frame",
1929				insn->sec, insn->offset);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1930		return 1;
1931	}
1932
1933	return validate_call(insn, state);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1934}
1935
1936/*
1937 * Follow the branch starting at the given instruction, and recursively follow
1938 * any other branches (jumps).  Meanwhile, track the frame pointer state at
1939 * each instruction and validate all the rules described in
1940 * tools/objtool/Documentation/stack-validation.txt.
1941 */
1942static int validate_branch(struct objtool_file *file, struct symbol *func,
1943			   struct instruction *first, struct insn_state state)
1944{
1945	struct alternative *alt;
1946	struct instruction *insn, *next_insn;
1947	struct section *sec;
1948	u8 visited;
1949	int ret;
1950
1951	insn = first;
1952	sec = insn->sec;
1953
1954	if (insn->alt_group && list_empty(&insn->alts)) {
1955		WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
1956			  sec, insn->offset);
1957		return 1;
1958	}
1959
1960	while (1) {
1961		next_insn = next_insn_same_sec(file, insn);
 
 
 
 
 
 
1962
1963		if (file->c_file && func && insn->func && func != insn->func->pfunc) {
1964			WARN("%s() falls through to next function %s()",
1965			     func->name, insn->func->name);
1966			return 1;
1967		}
1968
1969		if (func && insn->ignore) {
1970			WARN_FUNC("BUG: why am I validating an ignored function?",
1971				  sec, insn->offset);
1972			return 1;
1973		}
1974
1975		visited = 1 << state.uaccess;
1976		if (insn->visited) {
1977			if (!insn->hint && !insn_state_match(insn, &state))
1978				return 1;
1979
1980			if (insn->visited & visited)
1981				return 0;
 
 
1982		}
1983
 
 
 
1984		if (insn->hint) {
1985			if (insn->restore) {
1986				struct instruction *save_insn, *i;
1987
1988				i = insn;
1989				save_insn = NULL;
1990				func_for_each_insn_continue_reverse(file, func, i) {
 
1991					if (i->save) {
1992						save_insn = i;
1993						break;
1994					}
1995				}
1996
1997				if (!save_insn) {
1998					WARN_FUNC("no corresponding CFI save for CFI restore",
1999						  sec, insn->offset);
2000					return 1;
2001				}
2002
2003				if (!save_insn->visited) {
2004					/*
2005					 * Oops, no state to copy yet.
2006					 * Hopefully we can reach this
2007					 * instruction from another branch
2008					 * after the save insn has been
2009					 * visited.
 
 
2010					 */
2011					if (insn == first)
2012						return 0;
2013
2014					WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
2015						  sec, insn->offset);
2016					return 1;
2017				}
2018
2019				insn->state = save_insn->state;
 
2020			}
2021
2022			state = insn->state;
 
 
2023
2024		} else
2025			insn->state = state;
 
 
 
 
 
2026
2027		insn->visited |= visited;
2028
2029		if (!insn->ignore_alts) {
 
 
 
2030			bool skip_orig = false;
2031
2032			list_for_each_entry(alt, &insn->alts, list) {
2033				if (alt->skip_orig)
2034					skip_orig = true;
2035
2036				ret = validate_branch(file, func, alt->insn, state);
2037				if (ret) {
2038					if (backtrace)
2039						BT_FUNC("(alt)", insn);
2040					return ret;
2041				}
2042			}
2043
2044			if (skip_orig)
2045				return 0;
2046		}
2047
 
 
 
2048		switch (insn->type) {
2049
2050		case INSN_RETURN:
2051			if (state.uaccess && !func_uaccess_safe(func)) {
2052				WARN_FUNC("return with UACCESS enabled", sec, insn->offset);
2053				return 1;
2054			}
2055
2056			if (!state.uaccess && func_uaccess_safe(func)) {
2057				WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function", sec, insn->offset);
2058				return 1;
2059			}
2060
2061			if (state.df) {
2062				WARN_FUNC("return with DF set", sec, insn->offset);
2063				return 1;
2064			}
2065
2066			if (func && has_modified_stack_frame(&state)) {
2067				WARN_FUNC("return with modified stack frame",
2068					  sec, insn->offset);
2069				return 1;
2070			}
2071
2072			if (state.bp_scratch) {
2073				WARN("%s uses BP as a scratch register",
2074				     func->name);
2075				return 1;
2076			}
2077
2078			return 0;
2079
2080		case INSN_CALL:
2081		case INSN_CALL_DYNAMIC:
2082			ret = validate_call(insn, &state);
2083			if (ret)
2084				return ret;
2085
2086			if (!no_fp && func && !is_fentry_call(insn) &&
2087			    !has_valid_stack_frame(&state)) {
2088				WARN_FUNC("call without frame pointer save/setup",
2089					  sec, insn->offset);
2090				return 1;
2091			}
2092
2093			if (dead_end_function(file, insn->call_dest))
2094				return 0;
2095
2096			break;
2097
2098		case INSN_JUMP_CONDITIONAL:
2099		case INSN_JUMP_UNCONDITIONAL:
2100			if (func && is_sibling_call(insn)) {
2101				ret = validate_sibling_call(insn, &state);
2102				if (ret)
2103					return ret;
2104
2105			} else if (insn->jump_dest) {
2106				ret = validate_branch(file, func,
2107						      insn->jump_dest, state);
2108				if (ret) {
2109					if (backtrace)
2110						BT_FUNC("(branch)", insn);
2111					return ret;
2112				}
2113			}
2114
2115			if (insn->type == INSN_JUMP_UNCONDITIONAL)
2116				return 0;
2117
2118			break;
2119
2120		case INSN_JUMP_DYNAMIC:
2121		case INSN_JUMP_DYNAMIC_CONDITIONAL:
2122			if (func && is_sibling_call(insn)) {
2123				ret = validate_sibling_call(insn, &state);
2124				if (ret)
2125					return ret;
2126			}
2127
2128			if (insn->type == INSN_JUMP_DYNAMIC)
2129				return 0;
2130
2131			break;
2132
2133		case INSN_CONTEXT_SWITCH:
2134			if (func && (!next_insn || !next_insn->hint)) {
2135				WARN_FUNC("unsupported instruction in callable function",
2136					  sec, insn->offset);
2137				return 1;
2138			}
2139			return 0;
2140
2141		case INSN_STACK:
2142			if (update_insn_state(insn, &state))
2143				return 1;
2144
2145			if (insn->stack_op.dest.type == OP_DEST_PUSHF) {
2146				if (!state.uaccess_stack) {
2147					state.uaccess_stack = 1;
2148				} else if (state.uaccess_stack >> 31) {
2149					WARN_FUNC("PUSHF stack exhausted", sec, insn->offset);
2150					return 1;
2151				}
2152				state.uaccess_stack <<= 1;
2153				state.uaccess_stack  |= state.uaccess;
2154			}
2155
2156			if (insn->stack_op.src.type == OP_SRC_POPF) {
2157				if (state.uaccess_stack) {
2158					state.uaccess = state.uaccess_stack & 1;
2159					state.uaccess_stack >>= 1;
2160					if (state.uaccess_stack == 1)
2161						state.uaccess_stack = 0;
2162				}
2163			}
2164
2165			break;
2166
2167		case INSN_STAC:
2168			if (state.uaccess) {
2169				WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
2170				return 1;
2171			}
2172
2173			state.uaccess = true;
2174			break;
2175
2176		case INSN_CLAC:
2177			if (!state.uaccess && func) {
2178				WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
2179				return 1;
2180			}
2181
2182			if (func_uaccess_safe(func) && !state.uaccess_stack) {
2183				WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
2184				return 1;
2185			}
2186
2187			state.uaccess = false;
2188			break;
2189
2190		case INSN_STD:
2191			if (state.df)
2192				WARN_FUNC("recursive STD", sec, insn->offset);
 
 
2193
2194			state.df = true;
2195			break;
2196
2197		case INSN_CLD:
2198			if (!state.df && func)
2199				WARN_FUNC("redundant CLD", sec, insn->offset);
 
 
2200
2201			state.df = false;
2202			break;
2203
2204		default:
2205			break;
2206		}
2207
2208		if (insn->dead_end)
2209			return 0;
2210
2211		if (!next_insn) {
2212			if (state.cfa.base == CFI_UNDEFINED)
2213				return 0;
2214			WARN("%s: unexpected end of section", sec->name);
2215			return 1;
2216		}
2217
 
2218		insn = next_insn;
2219	}
2220
2221	return 0;
2222}
2223
2224static int validate_unwind_hints(struct objtool_file *file)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2225{
2226	struct instruction *insn;
2227	int ret, warnings = 0;
2228	struct insn_state state;
 
2229
2230	if (!file->hints)
2231		return 0;
2232
2233	clear_insn_state(&state);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2234
2235	for_each_insn(file, insn) {
2236		if (insn->hint && !insn->visited) {
2237			ret = validate_branch(file, insn->func, insn, state);
2238			if (ret && backtrace)
2239				BT_FUNC("<=== (hint)", insn);
2240			warnings += ret;
 
 
2241		}
 
2242	}
2243
2244	return warnings;
2245}
2246
2247static int validate_retpoline(struct objtool_file *file)
2248{
2249	struct instruction *insn;
2250	int warnings = 0;
2251
2252	for_each_insn(file, insn) {
2253		if (insn->type != INSN_JUMP_DYNAMIC &&
2254		    insn->type != INSN_CALL_DYNAMIC)
 
2255			continue;
2256
2257		if (insn->retpoline_safe)
2258			continue;
2259
2260		/*
2261		 * .init.text code is ran before userspace and thus doesn't
2262		 * strictly need retpolines, except for modules which are
2263		 * loaded late, they very much do need retpoline in their
2264		 * .init.text
2265		 */
2266		if (!strcmp(insn->sec->name, ".init.text") && !module)
2267			continue;
2268
2269		WARN_FUNC("indirect %s found in RETPOLINE build",
2270			  insn->sec, insn->offset,
2271			  insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
 
 
 
 
 
 
2272
2273		warnings++;
2274	}
2275
2276	return warnings;
2277}
2278
2279static bool is_kasan_insn(struct instruction *insn)
2280{
2281	return (insn->type == INSN_CALL &&
2282		!strcmp(insn->call_dest->name, "__asan_handle_no_return"));
2283}
2284
2285static bool is_ubsan_insn(struct instruction *insn)
2286{
2287	return (insn->type == INSN_CALL &&
2288		!strcmp(insn->call_dest->name,
2289			"__ubsan_handle_builtin_unreachable"));
2290}
2291
2292static bool ignore_unreachable_insn(struct instruction *insn)
2293{
2294	int i;
 
2295
2296	if (insn->ignore || insn->type == INSN_NOP)
2297		return true;
2298
2299	/*
2300	 * Ignore any unused exceptions.  This can happen when a whitelisted
2301	 * function has an exception table entry.
2302	 *
2303	 * Also ignore alternative replacement instructions.  This can happen
2304	 * when a whitelisted function uses one of the ALTERNATIVE macros.
2305	 */
2306	if (!strcmp(insn->sec->name, ".fixup") ||
2307	    !strcmp(insn->sec->name, ".altinstr_replacement") ||
2308	    !strcmp(insn->sec->name, ".altinstr_aux"))
2309		return true;
2310
2311	/*
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2312	 * Check if this (or a subsequent) instruction is related to
2313	 * CONFIG_UBSAN or CONFIG_KASAN.
2314	 *
2315	 * End the search at 5 instructions to avoid going into the weeds.
2316	 */
2317	if (!insn->func)
2318		return false;
2319	for (i = 0; i < 5; i++) {
2320
2321		if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2322			return true;
2323
2324		if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2325			if (insn->jump_dest &&
2326			    insn->jump_dest->func == insn->func) {
2327				insn = insn->jump_dest;
2328				continue;
2329			}
2330
2331			break;
2332		}
2333
2334		if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2335			break;
2336
2337		insn = list_next_entry(insn, list);
2338	}
2339
2340	return false;
2341}
2342
2343static int validate_functions(struct objtool_file *file)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2344{
2345	struct section *sec;
2346	struct symbol *func;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2347	struct instruction *insn;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2348	struct insn_state state;
2349	int ret, warnings = 0;
 
2350
2351	clear_insn_state(&state);
 
 
2352
2353	state.cfa = initial_func_cfi.cfa;
2354	memcpy(&state.regs, &initial_func_cfi.regs,
2355	       CFI_NUM_REGS * sizeof(struct cfi_reg));
2356	state.stack_size = initial_func_cfi.cfa.offset;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2357
2358	for_each_sec(file, sec) {
2359		list_for_each_entry(func, &sec->symbol_list, list) {
2360			if (func->type != STT_FUNC)
2361				continue;
2362
2363			if (!func->len) {
2364				WARN("%s() is missing an ELF size annotation",
2365				     func->name);
2366				warnings++;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2367			}
2368
2369			if (func->pfunc != func || func->alias != func)
2370				continue;
 
2371
2372			insn = find_insn(file, sec, func->offset);
2373			if (!insn || insn->ignore || insn->visited)
2374				continue;
2375
2376			state.uaccess = func->uaccess_safe;
 
 
 
 
 
 
 
 
 
 
 
2377
2378			ret = validate_branch(file, func, insn, state);
2379			if (ret && backtrace)
2380				BT_FUNC("<=== (func)", insn);
2381			warnings += ret;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2382		}
2383	}
2384
2385	return warnings;
2386}
2387
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2388static int validate_reachable_instructions(struct objtool_file *file)
2389{
2390	struct instruction *insn;
 
 
2391
2392	if (file->ignore_unreachables)
2393		return 0;
2394
2395	for_each_insn(file, insn) {
2396		if (insn->visited || ignore_unreachable_insn(insn))
2397			continue;
2398
2399		WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2400		return 1;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2401	}
2402
2403	return 0;
2404}
2405
2406static void cleanup(struct objtool_file *file)
2407{
2408	struct instruction *insn, *tmpinsn;
2409	struct alternative *alt, *tmpalt;
2410
2411	list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
2412		list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
2413			list_del(&alt->list);
2414			free(alt);
 
 
 
 
 
 
 
2415		}
2416		list_del(&insn->list);
2417		hash_del(&insn->hash);
2418		free(insn);
2419	}
2420	elf_close(file->elf);
 
 
 
 
2421}
2422
2423static struct objtool_file file;
 
 
 
2424
2425int check(const char *_objname, bool orc)
 
 
 
 
 
2426{
2427	int ret, warnings = 0;
 
2428
2429	objname = _objname;
 
 
 
 
 
 
 
2430
2431	file.elf = elf_read(objname, orc ? O_RDWR : O_RDONLY);
2432	if (!file.elf)
2433		return 1;
2434
2435	INIT_LIST_HEAD(&file.insn_list);
2436	hash_init(file.insn_hash);
2437	file.c_file = find_section_by_name(file.elf, ".comment");
2438	file.ignore_unreachables = no_unreachable;
2439	file.hints = false;
2440
2441	arch_initial_func_cfi_state(&initial_func_cfi);
 
 
 
 
 
 
 
 
 
 
 
2442
2443	ret = decode_sections(&file);
2444	if (ret < 0)
2445		goto out;
 
2446	warnings += ret;
2447
2448	if (list_empty(&file.insn_list))
2449		goto out;
2450
2451	if (retpoline) {
2452		ret = validate_retpoline(&file);
2453		if (ret < 0)
2454			return ret;
2455		warnings += ret;
2456	}
2457
2458	ret = validate_functions(&file);
2459	if (ret < 0)
2460		goto out;
2461	warnings += ret;
 
2462
2463	ret = validate_unwind_hints(&file);
2464	if (ret < 0)
2465		goto out;
2466	warnings += ret;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2467
2468	if (!warnings) {
2469		ret = validate_reachable_instructions(&file);
2470		if (ret < 0)
2471			goto out;
2472		warnings += ret;
2473	}
2474
2475	if (orc) {
2476		ret = create_orc(&file);
2477		if (ret < 0)
2478			goto out;
 
 
2479
2480		ret = create_orc_sections(&file);
 
2481		if (ret < 0)
2482			goto out;
 
 
2483
2484		ret = elf_write(file.elf);
 
2485		if (ret < 0)
2486			goto out;
 
2487	}
2488
2489out:
2490	cleanup(&file);
 
 
 
 
2491
2492	/* ignore warnings for now until we get all the code cleaned up */
2493	if (ret || warnings)
2494		return 0;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2495	return 0;
2496}