1 // SPDX-License-Identifier: GPL-2.0-or-later
3 * Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
16 #include <linux/hashtable.h>
17 #include <linux/kernel.h>
19 #define FAKE_JUMP_OFFSET -1
21 #define C_JUMP_TABLE_SECTION ".rodata..c_jump_table"
24 struct list_head list;
25 struct instruction *insn;
30 struct cfi_state initial_func_cfi;
32 struct instruction *find_insn(struct objtool_file *file,
33 struct section *sec, unsigned long offset)
35 struct instruction *insn;
37 hash_for_each_possible(file->insn_hash, insn, hash, offset)
38 if (insn->sec == sec && insn->offset == offset)
44 static struct instruction *next_insn_same_sec(struct objtool_file *file,
45 struct instruction *insn)
47 struct instruction *next = list_next_entry(insn, list);
49 if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
55 static struct instruction *next_insn_same_func(struct objtool_file *file,
56 struct instruction *insn)
58 struct instruction *next = list_next_entry(insn, list);
59 struct symbol *func = insn->func;
64 if (&next->list != &file->insn_list && next->func == func)
67 /* Check if we're already in the subfunction: */
68 if (func == func->cfunc)
71 /* Move to the subfunction: */
72 return find_insn(file, func->cfunc->sec, func->cfunc->offset);
75 #define func_for_each_insn_all(file, func, insn) \
76 for (insn = find_insn(file, func->sec, func->offset); \
78 insn = next_insn_same_func(file, insn))
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))
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))
93 #define sec_for_each_insn_from(file, insn) \
94 for (; insn; insn = next_insn_same_sec(file, insn))
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))
100 static bool is_sibling_call(struct instruction *insn)
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);
106 if (insn->type != INSN_JUMP_CONDITIONAL &&
107 insn->type != INSN_JUMP_UNCONDITIONAL)
110 /* add_jump_destinations() sets insn->call_dest for sibling calls. */
111 return !!insn->call_dest;
115 * This checks to see if the given function is a "noreturn" function.
117 * For global functions which are outside the scope of this object file, we
118 * have to keep a manual list of them.
120 * For local functions, we have to detect them manually by simply looking for
121 * the lack of a return instruction.
123 static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
127 struct instruction *insn;
131 * Unfortunately these have to be hard coded because the noreturn
132 * attribute isn't provided in ELF data.
134 static const char * const global_noreturns[] = {
139 "__module_put_and_exit",
141 "kvm_spurious_fault",
146 "machine_real_restart",
147 "rewind_stack_do_exit",
153 if (func->bind == STB_WEAK)
156 if (func->bind == STB_GLOBAL)
157 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
158 if (!strcmp(func->name, global_noreturns[i]))
164 insn = find_insn(file, func->sec, func->offset);
168 func_for_each_insn_all(file, func, insn) {
171 if (insn->type == INSN_RETURN)
179 * A function can have a sibling call instead of a return. In that
180 * case, the function's dead-end status depends on whether the target
181 * of the sibling call returns.
183 func_for_each_insn_all(file, func, insn) {
184 if (is_sibling_call(insn)) {
185 struct instruction *dest = insn->jump_dest;
188 /* sibling call to another file */
191 /* local sibling call */
192 if (recursion == 5) {
194 * Infinite recursion: two functions have
195 * sibling calls to each other. This is a very
196 * rare case. It means they aren't dead ends.
201 return __dead_end_function(file, dest->func, recursion+1);
208 static bool dead_end_function(struct objtool_file *file, struct symbol *func)
210 return __dead_end_function(file, func, 0);
213 static void clear_insn_state(struct insn_state *state)
217 memset(state, 0, sizeof(*state));
218 state->cfa.base = CFI_UNDEFINED;
219 for (i = 0; i < CFI_NUM_REGS; i++) {
220 state->regs[i].base = CFI_UNDEFINED;
221 state->vals[i].base = CFI_UNDEFINED;
223 state->drap_reg = CFI_UNDEFINED;
224 state->drap_offset = -1;
228 * Call the arch-specific instruction decoder for all the instructions and add
229 * them to the global instruction list.
231 static int decode_instructions(struct objtool_file *file)
235 unsigned long offset;
236 struct instruction *insn;
239 for_each_sec(file, sec) {
241 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
244 if (strcmp(sec->name, ".altinstr_replacement") &&
245 strcmp(sec->name, ".altinstr_aux") &&
246 strncmp(sec->name, ".discard.", 9))
249 for (offset = 0; offset < sec->len; offset += insn->len) {
250 insn = malloc(sizeof(*insn));
252 WARN("malloc failed");
255 memset(insn, 0, sizeof(*insn));
256 INIT_LIST_HEAD(&insn->alts);
257 clear_insn_state(&insn->state);
260 insn->offset = offset;
262 ret = arch_decode_instruction(file->elf, sec, offset,
264 &insn->len, &insn->type,
270 hash_add(file->insn_hash, &insn->hash, insn->offset);
271 list_add_tail(&insn->list, &file->insn_list);
274 list_for_each_entry(func, &sec->symbol_list, list) {
275 if (func->type != STT_FUNC || func->alias != func)
278 if (!find_insn(file, sec, func->offset)) {
279 WARN("%s(): can't find starting instruction",
284 func_for_each_insn(file, func, insn)
297 * Mark "ud2" instructions and manually annotated dead ends.
299 static int add_dead_ends(struct objtool_file *file)
303 struct instruction *insn;
307 * By default, "ud2" is a dead end unless otherwise annotated, because
308 * GCC 7 inserts it for certain divide-by-zero cases.
310 for_each_insn(file, insn)
311 if (insn->type == INSN_BUG)
312 insn->dead_end = true;
315 * Check for manually annotated dead ends.
317 sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
321 list_for_each_entry(rela, &sec->rela_list, list) {
322 if (rela->sym->type != STT_SECTION) {
323 WARN("unexpected relocation symbol type in %s", sec->name);
326 insn = find_insn(file, rela->sym->sec, rela->addend);
328 insn = list_prev_entry(insn, list);
329 else if (rela->addend == rela->sym->sec->len) {
331 list_for_each_entry_reverse(insn, &file->insn_list, list) {
332 if (insn->sec == rela->sym->sec) {
339 WARN("can't find unreachable insn at %s+0x%x",
340 rela->sym->sec->name, rela->addend);
344 WARN("can't find unreachable insn at %s+0x%x",
345 rela->sym->sec->name, rela->addend);
349 insn->dead_end = true;
354 * These manually annotated reachable checks are needed for GCC 4.4,
355 * where the Linux unreachable() macro isn't supported. In that case
356 * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
359 sec = find_section_by_name(file->elf, ".rela.discard.reachable");
363 list_for_each_entry(rela, &sec->rela_list, list) {
364 if (rela->sym->type != STT_SECTION) {
365 WARN("unexpected relocation symbol type in %s", sec->name);
368 insn = find_insn(file, rela->sym->sec, rela->addend);
370 insn = list_prev_entry(insn, list);
371 else if (rela->addend == rela->sym->sec->len) {
373 list_for_each_entry_reverse(insn, &file->insn_list, list) {
374 if (insn->sec == rela->sym->sec) {
381 WARN("can't find reachable insn at %s+0x%x",
382 rela->sym->sec->name, rela->addend);
386 WARN("can't find reachable insn at %s+0x%x",
387 rela->sym->sec->name, rela->addend);
391 insn->dead_end = false;
398 * Warnings shouldn't be reported for ignored functions.
400 static void add_ignores(struct objtool_file *file)
402 struct instruction *insn;
407 sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
411 list_for_each_entry(rela, &sec->rela_list, list) {
412 switch (rela->sym->type) {
418 func = find_symbol_by_offset(rela->sym->sec, rela->addend);
419 if (!func || func->type != STT_FUNC)
424 WARN("unexpected relocation symbol type in %s: %d", sec->name, rela->sym->type);
428 func_for_each_insn_all(file, func, insn)
434 * This is a whitelist of functions that is allowed to be called with AC set.
435 * The list is meant to be minimal and only contains compiler instrumentation
436 * ABI and a few functions used to implement *_{to,from}_user() functions.
438 * These functions must not directly change AC, but may PUSHF/POPF.
440 static const char *uaccess_safe_builtin[] = {
443 "check_memory_region",
444 /* KASAN out-of-line */
445 "__asan_loadN_noabort",
446 "__asan_load1_noabort",
447 "__asan_load2_noabort",
448 "__asan_load4_noabort",
449 "__asan_load8_noabort",
450 "__asan_load16_noabort",
451 "__asan_storeN_noabort",
452 "__asan_store1_noabort",
453 "__asan_store2_noabort",
454 "__asan_store4_noabort",
455 "__asan_store8_noabort",
456 "__asan_store16_noabort",
458 "__asan_report_load_n_noabort",
459 "__asan_report_load1_noabort",
460 "__asan_report_load2_noabort",
461 "__asan_report_load4_noabort",
462 "__asan_report_load8_noabort",
463 "__asan_report_load16_noabort",
464 "__asan_report_store_n_noabort",
465 "__asan_report_store1_noabort",
466 "__asan_report_store2_noabort",
467 "__asan_report_store4_noabort",
468 "__asan_report_store8_noabort",
469 "__asan_report_store16_noabort",
472 "__sanitizer_cov_trace_pc",
473 "__sanitizer_cov_trace_const_cmp1",
474 "__sanitizer_cov_trace_const_cmp2",
475 "__sanitizer_cov_trace_const_cmp4",
476 "__sanitizer_cov_trace_const_cmp8",
477 "__sanitizer_cov_trace_cmp1",
478 "__sanitizer_cov_trace_cmp2",
479 "__sanitizer_cov_trace_cmp4",
480 "__sanitizer_cov_trace_cmp8",
482 "ubsan_type_mismatch_common",
483 "__ubsan_handle_type_mismatch",
484 "__ubsan_handle_type_mismatch_v1",
486 "csum_partial_copy_generic",
488 "mcsafe_handle_tail",
489 "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
493 static void add_uaccess_safe(struct objtool_file *file)
501 for (name = uaccess_safe_builtin; *name; name++) {
502 func = find_symbol_by_name(file->elf, *name);
506 func->uaccess_safe = true;
511 * FIXME: For now, just ignore any alternatives which add retpolines. This is
512 * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
513 * But it at least allows objtool to understand the control flow *around* the
516 static int add_ignore_alternatives(struct objtool_file *file)
520 struct instruction *insn;
522 sec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
526 list_for_each_entry(rela, &sec->rela_list, list) {
527 if (rela->sym->type != STT_SECTION) {
528 WARN("unexpected relocation symbol type in %s", sec->name);
532 insn = find_insn(file, rela->sym->sec, rela->addend);
534 WARN("bad .discard.ignore_alts entry");
538 insn->ignore_alts = true;
545 * Find the destination instructions for all jumps.
547 static int add_jump_destinations(struct objtool_file *file)
549 struct instruction *insn;
551 struct section *dest_sec;
552 unsigned long dest_off;
554 for_each_insn(file, insn) {
555 if (insn->type != INSN_JUMP_CONDITIONAL &&
556 insn->type != INSN_JUMP_UNCONDITIONAL)
559 if (insn->ignore || insn->offset == FAKE_JUMP_OFFSET)
562 rela = find_rela_by_dest_range(insn->sec, insn->offset,
565 dest_sec = insn->sec;
566 dest_off = insn->offset + insn->len + insn->immediate;
567 } else if (rela->sym->type == STT_SECTION) {
568 dest_sec = rela->sym->sec;
569 dest_off = rela->addend + 4;
570 } else if (rela->sym->sec->idx) {
571 dest_sec = rela->sym->sec;
572 dest_off = rela->sym->sym.st_value + rela->addend + 4;
573 } else if (strstr(rela->sym->name, "_indirect_thunk_")) {
575 * Retpoline jumps are really dynamic jumps in
576 * disguise, so convert them accordingly.
578 insn->type = INSN_JUMP_DYNAMIC;
579 insn->retpoline_safe = true;
582 /* external sibling call */
583 insn->call_dest = rela->sym;
587 insn->jump_dest = find_insn(file, dest_sec, dest_off);
588 if (!insn->jump_dest) {
591 * This is a special case where an alt instruction
592 * jumps past the end of the section. These are
593 * handled later in handle_group_alt().
595 if (!strcmp(insn->sec->name, ".altinstr_replacement"))
598 WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
599 insn->sec, insn->offset, dest_sec->name,
605 * Cross-function jump.
607 if (insn->func && insn->jump_dest->func &&
608 insn->func != insn->jump_dest->func) {
611 * For GCC 8+, create parent/child links for any cold
612 * subfunctions. This is _mostly_ redundant with a
613 * similar initialization in read_symbols().
615 * If a function has aliases, we want the *first* such
616 * function in the symbol table to be the subfunction's
617 * parent. In that case we overwrite the
618 * initialization done in read_symbols().
620 * However this code can't completely replace the
621 * read_symbols() code because this doesn't detect the
622 * case where the parent function's only reference to a
623 * subfunction is through a jump table.
625 if (!strstr(insn->func->name, ".cold.") &&
626 strstr(insn->jump_dest->func->name, ".cold.")) {
627 insn->func->cfunc = insn->jump_dest->func;
628 insn->jump_dest->func->pfunc = insn->func;
630 } else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
631 insn->jump_dest->offset == insn->jump_dest->func->offset) {
633 /* internal sibling call */
634 insn->call_dest = insn->jump_dest->func;
643 * Find the destination instructions for all calls.
645 static int add_call_destinations(struct objtool_file *file)
647 struct instruction *insn;
648 unsigned long dest_off;
651 for_each_insn(file, insn) {
652 if (insn->type != INSN_CALL)
655 rela = find_rela_by_dest_range(insn->sec, insn->offset,
658 dest_off = insn->offset + insn->len + insn->immediate;
659 insn->call_dest = find_symbol_by_offset(insn->sec,
662 if (!insn->call_dest && !insn->ignore) {
663 WARN_FUNC("unsupported intra-function call",
664 insn->sec, insn->offset);
666 WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
670 } else if (rela->sym->type == STT_SECTION) {
671 insn->call_dest = find_symbol_by_offset(rela->sym->sec,
673 if (!insn->call_dest ||
674 insn->call_dest->type != STT_FUNC) {
675 WARN_FUNC("can't find call dest symbol at %s+0x%x",
676 insn->sec, insn->offset,
677 rela->sym->sec->name,
682 insn->call_dest = rela->sym;
689 * The .alternatives section requires some extra special care, over and above
690 * what other special sections require:
692 * 1. Because alternatives are patched in-place, we need to insert a fake jump
693 * instruction at the end so that validate_branch() skips all the original
694 * replaced instructions when validating the new instruction path.
696 * 2. An added wrinkle is that the new instruction length might be zero. In
697 * that case the old instructions are replaced with noops. We simulate that
698 * by creating a fake jump as the only new instruction.
700 * 3. In some cases, the alternative section includes an instruction which
701 * conditionally jumps to the _end_ of the entry. We have to modify these
702 * jumps' destinations to point back to .text rather than the end of the
703 * entry in .altinstr_replacement.
705 static int handle_group_alt(struct objtool_file *file,
706 struct special_alt *special_alt,
707 struct instruction *orig_insn,
708 struct instruction **new_insn)
710 struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
711 unsigned long dest_off;
713 last_orig_insn = NULL;
715 sec_for_each_insn_from(file, insn) {
716 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
719 insn->alt_group = true;
720 last_orig_insn = insn;
723 if (next_insn_same_sec(file, last_orig_insn)) {
724 fake_jump = malloc(sizeof(*fake_jump));
726 WARN("malloc failed");
729 memset(fake_jump, 0, sizeof(*fake_jump));
730 INIT_LIST_HEAD(&fake_jump->alts);
731 clear_insn_state(&fake_jump->state);
733 fake_jump->sec = special_alt->new_sec;
734 fake_jump->offset = FAKE_JUMP_OFFSET;
735 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
736 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
737 fake_jump->func = orig_insn->func;
740 if (!special_alt->new_len) {
742 WARN("%s: empty alternative at end of section",
743 special_alt->orig_sec->name);
747 *new_insn = fake_jump;
751 last_new_insn = NULL;
753 sec_for_each_insn_from(file, insn) {
754 if (insn->offset >= special_alt->new_off + special_alt->new_len)
757 last_new_insn = insn;
759 insn->ignore = orig_insn->ignore_alts;
760 insn->func = orig_insn->func;
762 if (insn->type != INSN_JUMP_CONDITIONAL &&
763 insn->type != INSN_JUMP_UNCONDITIONAL)
766 if (!insn->immediate)
769 dest_off = insn->offset + insn->len + insn->immediate;
770 if (dest_off == special_alt->new_off + special_alt->new_len) {
772 WARN("%s: alternative jump to end of section",
773 special_alt->orig_sec->name);
776 insn->jump_dest = fake_jump;
779 if (!insn->jump_dest) {
780 WARN_FUNC("can't find alternative jump destination",
781 insn->sec, insn->offset);
786 if (!last_new_insn) {
787 WARN_FUNC("can't find last new alternative instruction",
788 special_alt->new_sec, special_alt->new_off);
793 list_add(&fake_jump->list, &last_new_insn->list);
799 * A jump table entry can either convert a nop to a jump or a jump to a nop.
800 * If the original instruction is a jump, make the alt entry an effective nop
801 * by just skipping the original instruction.
803 static int handle_jump_alt(struct objtool_file *file,
804 struct special_alt *special_alt,
805 struct instruction *orig_insn,
806 struct instruction **new_insn)
808 if (orig_insn->type == INSN_NOP)
811 if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
812 WARN_FUNC("unsupported instruction at jump label",
813 orig_insn->sec, orig_insn->offset);
817 *new_insn = list_next_entry(orig_insn, list);
822 * Read all the special sections which have alternate instructions which can be
823 * patched in or redirected to at runtime. Each instruction having alternate
824 * instruction(s) has them added to its insn->alts list, which will be
825 * traversed in validate_branch().
827 static int add_special_section_alts(struct objtool_file *file)
829 struct list_head special_alts;
830 struct instruction *orig_insn, *new_insn;
831 struct special_alt *special_alt, *tmp;
832 struct alternative *alt;
835 ret = special_get_alts(file->elf, &special_alts);
839 list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
841 orig_insn = find_insn(file, special_alt->orig_sec,
842 special_alt->orig_off);
844 WARN_FUNC("special: can't find orig instruction",
845 special_alt->orig_sec, special_alt->orig_off);
851 if (!special_alt->group || special_alt->new_len) {
852 new_insn = find_insn(file, special_alt->new_sec,
853 special_alt->new_off);
855 WARN_FUNC("special: can't find new instruction",
856 special_alt->new_sec,
857 special_alt->new_off);
863 if (special_alt->group) {
864 ret = handle_group_alt(file, special_alt, orig_insn,
868 } else if (special_alt->jump_or_nop) {
869 ret = handle_jump_alt(file, special_alt, orig_insn,
875 alt = malloc(sizeof(*alt));
877 WARN("malloc failed");
882 alt->insn = new_insn;
883 alt->skip_orig = special_alt->skip_orig;
884 orig_insn->ignore_alts |= special_alt->skip_alt;
885 list_add_tail(&alt->list, &orig_insn->alts);
887 list_del(&special_alt->list);
895 static int add_jump_table(struct objtool_file *file, struct instruction *insn,
898 struct rela *rela = table;
899 struct instruction *dest_insn;
900 struct alternative *alt;
901 struct symbol *pfunc = insn->func->pfunc;
902 unsigned int prev_offset = 0;
905 * Each @rela is a switch table relocation which points to the target
908 list_for_each_entry_from(rela, &table->sec->rela_list, list) {
910 /* Check for the end of the table: */
911 if (rela != table && rela->jump_table_start)
914 /* Make sure the table entries are consecutive: */
915 if (prev_offset && rela->offset != prev_offset + 8)
918 /* Detect function pointers from contiguous objects: */
919 if (rela->sym->sec == pfunc->sec &&
920 rela->addend == pfunc->offset)
923 dest_insn = find_insn(file, rela->sym->sec, rela->addend);
927 /* Make sure the destination is in the same function: */
928 if (!dest_insn->func || dest_insn->func->pfunc != pfunc)
931 alt = malloc(sizeof(*alt));
933 WARN("malloc failed");
937 alt->insn = dest_insn;
938 list_add_tail(&alt->list, &insn->alts);
939 prev_offset = rela->offset;
943 WARN_FUNC("can't find switch jump table",
944 insn->sec, insn->offset);
952 * find_jump_table() - Given a dynamic jump, find the switch jump table in
953 * .rodata associated with it.
955 * There are 3 basic patterns:
957 * 1. jmpq *[rodata addr](,%reg,8)
959 * This is the most common case by far. It jumps to an address in a simple
960 * jump table which is stored in .rodata.
962 * 2. jmpq *[rodata addr](%rip)
964 * This is caused by a rare GCC quirk, currently only seen in three driver
965 * functions in the kernel, only with certain obscure non-distro configs.
967 * As part of an optimization, GCC makes a copy of an existing switch jump
968 * table, modifies it, and then hard-codes the jump (albeit with an indirect
969 * jump) to use a single entry in the table. The rest of the jump table and
970 * some of its jump targets remain as dead code.
972 * In such a case we can just crudely ignore all unreachable instruction
973 * warnings for the entire object file. Ideally we would just ignore them
974 * for the function, but that would require redesigning the code quite a
975 * bit. And honestly that's just not worth doing: unreachable instruction
976 * warnings are of questionable value anyway, and this is such a rare issue.
978 * 3. mov [rodata addr],%reg1
979 * ... some instructions ...
980 * jmpq *(%reg1,%reg2,8)
982 * This is a fairly uncommon pattern which is new for GCC 6. As of this
983 * writing, there are 11 occurrences of it in the allmodconfig kernel.
985 * As of GCC 7 there are quite a few more of these and the 'in between' code
986 * is significant. Esp. with KASAN enabled some of the code between the mov
987 * and jmpq uses .rodata itself, which can confuse things.
989 * TODO: Once we have DWARF CFI and smarter instruction decoding logic,
990 * ensure the same register is used in the mov and jump instructions.
992 * NOTE: RETPOLINE made it harder still to decode dynamic jumps.
994 static struct rela *find_jump_table(struct objtool_file *file,
996 struct instruction *insn)
998 struct rela *text_rela, *table_rela;
999 struct instruction *orig_insn = insn;
1000 struct section *table_sec;
1001 unsigned long table_offset;
1004 * Backward search using the @first_jump_src links, these help avoid
1005 * much of the 'in between' code. Which avoids us getting confused by
1009 &insn->list != &file->insn_list &&
1010 insn->sec == func->sec &&
1011 insn->offset >= func->offset;
1013 insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
1015 if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
1018 /* allow small jumps within the range */
1019 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
1021 (insn->jump_dest->offset <= insn->offset ||
1022 insn->jump_dest->offset > orig_insn->offset))
1025 /* look for a relocation which references .rodata */
1026 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
1028 if (!text_rela || text_rela->sym->type != STT_SECTION ||
1029 !text_rela->sym->sec->rodata)
1032 table_offset = text_rela->addend;
1033 table_sec = text_rela->sym->sec;
1035 if (text_rela->type == R_X86_64_PC32)
1039 * Make sure the .rodata address isn't associated with a
1040 * symbol. GCC jump tables are anonymous data.
1042 * Also support C jump tables which are in the same format as
1043 * switch jump tables. For objtool to recognize them, they
1044 * need to be placed in the C_JUMP_TABLE_SECTION section. They
1045 * have symbols associated with them.
1047 if (find_symbol_containing(table_sec, table_offset) &&
1048 strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
1051 /* Each table entry has a rela associated with it. */
1052 table_rela = find_rela_by_dest(table_sec, table_offset);
1057 * Use of RIP-relative switch jumps is quite rare, and
1058 * indicates a rare GCC quirk/bug which can leave dead code
1061 if (text_rela->type == R_X86_64_PC32)
1062 file->ignore_unreachables = true;
1071 * First pass: Mark the head of each jump table so that in the next pass,
1072 * we know when a given jump table ends and the next one starts.
1074 static void mark_func_jump_tables(struct objtool_file *file,
1075 struct symbol *func)
1077 struct instruction *insn, *last = NULL;
1080 func_for_each_insn_all(file, func, insn) {
1085 * Store back-pointers for unconditional forward jumps such
1086 * that find_jump_table() can back-track using those and
1087 * avoid some potentially confusing code.
1089 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
1090 insn->offset > last->offset &&
1091 insn->jump_dest->offset > insn->offset &&
1092 !insn->jump_dest->first_jump_src) {
1094 insn->jump_dest->first_jump_src = insn;
1095 last = insn->jump_dest;
1098 if (insn->type != INSN_JUMP_DYNAMIC)
1101 rela = find_jump_table(file, func, insn);
1103 rela->jump_table_start = true;
1104 insn->jump_table = rela;
1109 static int add_func_jump_tables(struct objtool_file *file,
1110 struct symbol *func)
1112 struct instruction *insn;
1115 func_for_each_insn_all(file, func, insn) {
1116 if (!insn->jump_table)
1119 ret = add_jump_table(file, insn, insn->jump_table);
1128 * For some switch statements, gcc generates a jump table in the .rodata
1129 * section which contains a list of addresses within the function to jump to.
1130 * This finds these jump tables and adds them to the insn->alts lists.
1132 static int add_jump_table_alts(struct objtool_file *file)
1134 struct section *sec;
1135 struct symbol *func;
1141 for_each_sec(file, sec) {
1142 list_for_each_entry(func, &sec->symbol_list, list) {
1143 if (func->type != STT_FUNC)
1146 mark_func_jump_tables(file, func);
1147 ret = add_func_jump_tables(file, func);
1156 static int read_unwind_hints(struct objtool_file *file)
1158 struct section *sec, *relasec;
1160 struct unwind_hint *hint;
1161 struct instruction *insn;
1162 struct cfi_reg *cfa;
1165 sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1169 relasec = sec->rela;
1171 WARN("missing .rela.discard.unwind_hints section");
1175 if (sec->len % sizeof(struct unwind_hint)) {
1176 WARN("struct unwind_hint size mismatch");
1182 for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1183 hint = (struct unwind_hint *)sec->data->d_buf + i;
1185 rela = find_rela_by_dest(sec, i * sizeof(*hint));
1187 WARN("can't find rela for unwind_hints[%d]", i);
1191 insn = find_insn(file, rela->sym->sec, rela->addend);
1193 WARN("can't find insn for unwind_hints[%d]", i);
1197 cfa = &insn->state.cfa;
1199 if (hint->type == UNWIND_HINT_TYPE_SAVE) {
1203 } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1204 insn->restore = true;
1211 switch (hint->sp_reg) {
1212 case ORC_REG_UNDEFINED:
1213 cfa->base = CFI_UNDEFINED;
1221 case ORC_REG_SP_INDIRECT:
1222 cfa->base = CFI_SP_INDIRECT;
1225 cfa->base = CFI_R10;
1228 cfa->base = CFI_R13;
1237 WARN_FUNC("unsupported unwind_hint sp base reg %d",
1238 insn->sec, insn->offset, hint->sp_reg);
1242 cfa->offset = hint->sp_offset;
1243 insn->state.type = hint->type;
1244 insn->state.end = hint->end;
1250 static int read_retpoline_hints(struct objtool_file *file)
1252 struct section *sec;
1253 struct instruction *insn;
1256 sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1260 list_for_each_entry(rela, &sec->rela_list, list) {
1261 if (rela->sym->type != STT_SECTION) {
1262 WARN("unexpected relocation symbol type in %s", sec->name);
1266 insn = find_insn(file, rela->sym->sec, rela->addend);
1268 WARN("bad .discard.retpoline_safe entry");
1272 if (insn->type != INSN_JUMP_DYNAMIC &&
1273 insn->type != INSN_CALL_DYNAMIC) {
1274 WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1275 insn->sec, insn->offset);
1279 insn->retpoline_safe = true;
1285 static void mark_rodata(struct objtool_file *file)
1287 struct section *sec;
1291 * Search for the following rodata sections, each of which can
1292 * potentially contain jump tables:
1294 * - .rodata: can contain GCC switch tables
1295 * - .rodata.<func>: same, if -fdata-sections is being used
1296 * - .rodata..c_jump_table: contains C annotated jump tables
1298 * .rodata.str1.* sections are ignored; they don't contain jump tables.
1300 for_each_sec(file, sec) {
1301 if ((!strncmp(sec->name, ".rodata", 7) && !strstr(sec->name, ".str1.")) ||
1302 !strcmp(sec->name, C_JUMP_TABLE_SECTION)) {
1308 file->rodata = found;
1311 static int decode_sections(struct objtool_file *file)
1317 ret = decode_instructions(file);
1321 ret = add_dead_ends(file);
1326 add_uaccess_safe(file);
1328 ret = add_ignore_alternatives(file);
1332 ret = add_jump_destinations(file);
1336 ret = add_special_section_alts(file);
1340 ret = add_call_destinations(file);
1344 ret = add_jump_table_alts(file);
1348 ret = read_unwind_hints(file);
1352 ret = read_retpoline_hints(file);
1359 static bool is_fentry_call(struct instruction *insn)
1361 if (insn->type == INSN_CALL &&
1362 insn->call_dest->type == STT_NOTYPE &&
1363 !strcmp(insn->call_dest->name, "__fentry__"))
1369 static bool has_modified_stack_frame(struct insn_state *state)
1373 if (state->cfa.base != initial_func_cfi.cfa.base ||
1374 state->cfa.offset != initial_func_cfi.cfa.offset ||
1375 state->stack_size != initial_func_cfi.cfa.offset ||
1379 for (i = 0; i < CFI_NUM_REGS; i++)
1380 if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1381 state->regs[i].offset != initial_func_cfi.regs[i].offset)
1387 static bool has_valid_stack_frame(struct insn_state *state)
1389 if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1390 state->regs[CFI_BP].offset == -16)
1393 if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1399 static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
1401 struct cfi_reg *cfa = &state->cfa;
1402 struct stack_op *op = &insn->stack_op;
1404 if (cfa->base != CFI_SP)
1408 if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
1412 if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
1415 /* add immediate to sp */
1416 if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1417 op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1418 cfa->offset -= op->src.offset;
1423 static void save_reg(struct insn_state *state, unsigned char reg, int base,
1426 if (arch_callee_saved_reg(reg) &&
1427 state->regs[reg].base == CFI_UNDEFINED) {
1428 state->regs[reg].base = base;
1429 state->regs[reg].offset = offset;
1433 static void restore_reg(struct insn_state *state, unsigned char reg)
1435 state->regs[reg].base = CFI_UNDEFINED;
1436 state->regs[reg].offset = 0;
1440 * A note about DRAP stack alignment:
1442 * GCC has the concept of a DRAP register, which is used to help keep track of
1443 * the stack pointer when aligning the stack. r10 or r13 is used as the DRAP
1444 * register. The typical DRAP pattern is:
1446 * 4c 8d 54 24 08 lea 0x8(%rsp),%r10
1447 * 48 83 e4 c0 and $0xffffffffffffffc0,%rsp
1448 * 41 ff 72 f8 pushq -0x8(%r10)
1450 * 48 89 e5 mov %rsp,%rbp
1457 * 49 8d 62 f8 lea -0x8(%r10),%rsp
1460 * There are some variations in the epilogues, like:
1468 * 49 8d 62 f8 lea -0x8(%r10),%rsp
1473 * 4c 8b 55 e8 mov -0x18(%rbp),%r10
1474 * 48 8b 5d e0 mov -0x20(%rbp),%rbx
1475 * 4c 8b 65 f0 mov -0x10(%rbp),%r12
1476 * 4c 8b 6d f8 mov -0x8(%rbp),%r13
1478 * 49 8d 62 f8 lea -0x8(%r10),%rsp
1481 * Sometimes r13 is used as the DRAP register, in which case it's saved and
1482 * restored beforehand:
1485 * 4c 8d 6c 24 10 lea 0x10(%rsp),%r13
1486 * 48 83 e4 f0 and $0xfffffffffffffff0,%rsp
1488 * 49 8d 65 f0 lea -0x10(%r13),%rsp
1492 static int update_insn_state(struct instruction *insn, struct insn_state *state)
1494 struct stack_op *op = &insn->stack_op;
1495 struct cfi_reg *cfa = &state->cfa;
1496 struct cfi_reg *regs = state->regs;
1498 /* stack operations don't make sense with an undefined CFA */
1499 if (cfa->base == CFI_UNDEFINED) {
1501 WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1507 if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1508 return update_insn_state_regs(insn, state);
1510 switch (op->dest.type) {
1513 switch (op->src.type) {
1516 if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1517 cfa->base == CFI_SP &&
1518 regs[CFI_BP].base == CFI_CFA &&
1519 regs[CFI_BP].offset == -cfa->offset) {
1521 /* mov %rsp, %rbp */
1522 cfa->base = op->dest.reg;
1523 state->bp_scratch = false;
1526 else if (op->src.reg == CFI_SP &&
1527 op->dest.reg == CFI_BP && state->drap) {
1529 /* drap: mov %rsp, %rbp */
1530 regs[CFI_BP].base = CFI_BP;
1531 regs[CFI_BP].offset = -state->stack_size;
1532 state->bp_scratch = false;
1535 else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1540 * This is needed for the rare case where GCC
1547 state->vals[op->dest.reg].base = CFI_CFA;
1548 state->vals[op->dest.reg].offset = -state->stack_size;
1551 else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
1552 cfa->base == CFI_BP) {
1557 * Restore the original stack pointer (Clang).
1559 state->stack_size = -state->regs[CFI_BP].offset;
1562 else if (op->dest.reg == cfa->base) {
1564 /* mov %reg, %rsp */
1565 if (cfa->base == CFI_SP &&
1566 state->vals[op->src.reg].base == CFI_CFA) {
1569 * This is needed for the rare case
1570 * where GCC does something dumb like:
1572 * lea 0x8(%rsp), %rcx
1576 cfa->offset = -state->vals[op->src.reg].offset;
1577 state->stack_size = cfa->offset;
1580 cfa->base = CFI_UNDEFINED;
1588 if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1591 state->stack_size -= op->src.offset;
1592 if (cfa->base == CFI_SP)
1593 cfa->offset -= op->src.offset;
1597 if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1599 /* lea disp(%rbp), %rsp */
1600 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1604 if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1606 /* drap: lea disp(%rsp), %drap */
1607 state->drap_reg = op->dest.reg;
1610 * lea disp(%rsp), %reg
1612 * This is needed for the rare case where GCC
1613 * does something dumb like:
1615 * lea 0x8(%rsp), %rcx
1619 state->vals[op->dest.reg].base = CFI_CFA;
1620 state->vals[op->dest.reg].offset = \
1621 -state->stack_size + op->src.offset;
1626 if (state->drap && op->dest.reg == CFI_SP &&
1627 op->src.reg == state->drap_reg) {
1629 /* drap: lea disp(%drap), %rsp */
1631 cfa->offset = state->stack_size = -op->src.offset;
1632 state->drap_reg = CFI_UNDEFINED;
1633 state->drap = false;
1637 if (op->dest.reg == state->cfa.base) {
1638 WARN_FUNC("unsupported stack register modification",
1639 insn->sec, insn->offset);
1646 if (op->dest.reg != CFI_SP ||
1647 (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1648 (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1649 WARN_FUNC("unsupported stack pointer realignment",
1650 insn->sec, insn->offset);
1654 if (state->drap_reg != CFI_UNDEFINED) {
1655 /* drap: and imm, %rsp */
1656 cfa->base = state->drap_reg;
1657 cfa->offset = state->stack_size = 0;
1662 * Older versions of GCC (4.8ish) realign the stack
1663 * without DRAP, with a frame pointer.
1670 if (!state->drap && op->dest.type == OP_DEST_REG &&
1671 op->dest.reg == cfa->base) {
1677 if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1678 op->dest.type == OP_DEST_REG &&
1679 op->dest.reg == state->drap_reg &&
1680 state->drap_offset == -state->stack_size) {
1682 /* drap: pop %drap */
1683 cfa->base = state->drap_reg;
1685 state->drap_offset = -1;
1687 } else if (regs[op->dest.reg].offset == -state->stack_size) {
1690 restore_reg(state, op->dest.reg);
1693 state->stack_size -= 8;
1694 if (cfa->base == CFI_SP)
1699 case OP_SRC_REG_INDIRECT:
1700 if (state->drap && op->src.reg == CFI_BP &&
1701 op->src.offset == state->drap_offset) {
1703 /* drap: mov disp(%rbp), %drap */
1704 cfa->base = state->drap_reg;
1706 state->drap_offset = -1;
1709 if (state->drap && op->src.reg == CFI_BP &&
1710 op->src.offset == regs[op->dest.reg].offset) {
1712 /* drap: mov disp(%rbp), %reg */
1713 restore_reg(state, op->dest.reg);
1715 } else if (op->src.reg == cfa->base &&
1716 op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1718 /* mov disp(%rbp), %reg */
1719 /* mov disp(%rsp), %reg */
1720 restore_reg(state, op->dest.reg);
1726 WARN_FUNC("unknown stack-related instruction",
1727 insn->sec, insn->offset);
1735 state->stack_size += 8;
1736 if (cfa->base == CFI_SP)
1739 if (op->src.type != OP_SRC_REG)
1743 if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1745 /* drap: push %drap */
1746 cfa->base = CFI_BP_INDIRECT;
1747 cfa->offset = -state->stack_size;
1749 /* save drap so we know when to restore it */
1750 state->drap_offset = -state->stack_size;
1752 } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1754 /* drap: push %rbp */
1755 state->stack_size = 0;
1757 } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1759 /* drap: push %reg */
1760 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1766 save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1769 /* detect when asm code uses rbp as a scratch register */
1770 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1771 cfa->base != CFI_BP)
1772 state->bp_scratch = true;
1775 case OP_DEST_REG_INDIRECT:
1778 if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1780 /* drap: mov %drap, disp(%rbp) */
1781 cfa->base = CFI_BP_INDIRECT;
1782 cfa->offset = op->dest.offset;
1784 /* save drap offset so we know when to restore it */
1785 state->drap_offset = op->dest.offset;
1788 else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1790 /* drap: mov reg, disp(%rbp) */
1791 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1794 } else if (op->dest.reg == cfa->base) {
1796 /* mov reg, disp(%rbp) */
1797 /* mov reg, disp(%rsp) */
1798 save_reg(state, op->src.reg, CFI_CFA,
1799 op->dest.offset - state->cfa.offset);
1805 if ((!state->drap && cfa->base != CFI_BP) ||
1806 (state->drap && cfa->base != state->drap_reg)) {
1807 WARN_FUNC("leave instruction with modified stack frame",
1808 insn->sec, insn->offset);
1812 /* leave (mov %rbp, %rsp; pop %rbp) */
1814 state->stack_size = -state->regs[CFI_BP].offset - 8;
1815 restore_reg(state, CFI_BP);
1825 if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
1826 WARN_FUNC("unknown stack-related memory operation",
1827 insn->sec, insn->offset);
1832 state->stack_size -= 8;
1833 if (cfa->base == CFI_SP)
1839 WARN_FUNC("unknown stack-related instruction",
1840 insn->sec, insn->offset);
1847 static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1849 struct insn_state *state1 = &insn->state, *state2 = state;
1852 if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1853 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1854 insn->sec, insn->offset,
1855 state1->cfa.base, state1->cfa.offset,
1856 state2->cfa.base, state2->cfa.offset);
1858 } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1859 for (i = 0; i < CFI_NUM_REGS; i++) {
1860 if (!memcmp(&state1->regs[i], &state2->regs[i],
1861 sizeof(struct cfi_reg)))
1864 WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1865 insn->sec, insn->offset,
1866 i, state1->regs[i].base, state1->regs[i].offset,
1867 i, state2->regs[i].base, state2->regs[i].offset);
1871 } else if (state1->type != state2->type) {
1872 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1873 insn->sec, insn->offset, state1->type, state2->type);
1875 } else if (state1->drap != state2->drap ||
1876 (state1->drap && state1->drap_reg != state2->drap_reg) ||
1877 (state1->drap && state1->drap_offset != state2->drap_offset)) {
1878 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1879 insn->sec, insn->offset,
1880 state1->drap, state1->drap_reg, state1->drap_offset,
1881 state2->drap, state2->drap_reg, state2->drap_offset);
1889 static inline bool func_uaccess_safe(struct symbol *func)
1892 return func->uaccess_safe;
1897 static inline const char *call_dest_name(struct instruction *insn)
1899 if (insn->call_dest)
1900 return insn->call_dest->name;
1905 static int validate_call(struct instruction *insn, struct insn_state *state)
1907 if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
1908 WARN_FUNC("call to %s() with UACCESS enabled",
1909 insn->sec, insn->offset, call_dest_name(insn));
1914 WARN_FUNC("call to %s() with DF set",
1915 insn->sec, insn->offset, call_dest_name(insn));
1922 static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
1924 if (has_modified_stack_frame(state)) {
1925 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1926 insn->sec, insn->offset);
1930 return validate_call(insn, state);
1934 * Follow the branch starting at the given instruction, and recursively follow
1935 * any other branches (jumps). Meanwhile, track the frame pointer state at
1936 * each instruction and validate all the rules described in
1937 * tools/objtool/Documentation/stack-validation.txt.
1939 static int validate_branch(struct objtool_file *file, struct symbol *func,
1940 struct instruction *first, struct insn_state state)
1942 struct alternative *alt;
1943 struct instruction *insn, *next_insn;
1944 struct section *sec;
1950 if (insn->alt_group && list_empty(&insn->alts)) {
1951 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
1957 next_insn = next_insn_same_sec(file, insn);
1959 if (file->c_file && func && insn->func && func != insn->func->pfunc) {
1960 WARN("%s() falls through to next function %s()",
1961 func->name, insn->func->name);
1965 if (func && insn->ignore) {
1966 WARN_FUNC("BUG: why am I validating an ignored function?",
1971 if (insn->visited) {
1972 if (!insn->hint && !insn_state_match(insn, &state))
1975 /* If we were here with AC=0, but now have AC=1, go again */
1976 if (insn->state.uaccess || !state.uaccess)
1981 if (insn->restore) {
1982 struct instruction *save_insn, *i;
1986 func_for_each_insn_continue_reverse(file, func, i) {
1994 WARN_FUNC("no corresponding CFI save for CFI restore",
1999 if (!save_insn->visited) {
2001 * Oops, no state to copy yet.
2002 * Hopefully we can reach this
2003 * instruction from another branch
2004 * after the save insn has been
2010 WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
2015 insn->state = save_insn->state;
2018 state = insn->state;
2021 insn->state = state;
2023 insn->visited = true;
2025 if (!insn->ignore_alts) {
2026 bool skip_orig = false;
2028 list_for_each_entry(alt, &insn->alts, list) {
2032 ret = validate_branch(file, func, alt->insn, state);
2035 BT_FUNC("(alt)", insn);
2044 switch (insn->type) {
2047 if (state.uaccess && !func_uaccess_safe(func)) {
2048 WARN_FUNC("return with UACCESS enabled", sec, insn->offset);
2052 if (!state.uaccess && func_uaccess_safe(func)) {
2053 WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function", sec, insn->offset);
2058 WARN_FUNC("return with DF set", sec, insn->offset);
2062 if (func && has_modified_stack_frame(&state)) {
2063 WARN_FUNC("return with modified stack frame",
2068 if (state.bp_scratch) {
2069 WARN("%s uses BP as a scratch register",
2077 case INSN_CALL_DYNAMIC:
2078 ret = validate_call(insn, &state);
2082 if (!no_fp && func && !is_fentry_call(insn) &&
2083 !has_valid_stack_frame(&state)) {
2084 WARN_FUNC("call without frame pointer save/setup",
2089 if (dead_end_function(file, insn->call_dest))
2094 case INSN_JUMP_CONDITIONAL:
2095 case INSN_JUMP_UNCONDITIONAL:
2096 if (func && is_sibling_call(insn)) {
2097 ret = validate_sibling_call(insn, &state);
2101 } else if (insn->jump_dest) {
2102 ret = validate_branch(file, func,
2103 insn->jump_dest, state);
2106 BT_FUNC("(branch)", insn);
2111 if (insn->type == INSN_JUMP_UNCONDITIONAL)
2116 case INSN_JUMP_DYNAMIC:
2117 if (func && is_sibling_call(insn)) {
2118 ret = validate_sibling_call(insn, &state);
2125 case INSN_CONTEXT_SWITCH:
2126 if (func && (!next_insn || !next_insn->hint)) {
2127 WARN_FUNC("unsupported instruction in callable function",
2134 if (update_insn_state(insn, &state))
2137 if (insn->stack_op.dest.type == OP_DEST_PUSHF) {
2138 if (!state.uaccess_stack) {
2139 state.uaccess_stack = 1;
2140 } else if (state.uaccess_stack >> 31) {
2141 WARN_FUNC("PUSHF stack exhausted", sec, insn->offset);
2144 state.uaccess_stack <<= 1;
2145 state.uaccess_stack |= state.uaccess;
2148 if (insn->stack_op.src.type == OP_SRC_POPF) {
2149 if (state.uaccess_stack) {
2150 state.uaccess = state.uaccess_stack & 1;
2151 state.uaccess_stack >>= 1;
2152 if (state.uaccess_stack == 1)
2153 state.uaccess_stack = 0;
2160 if (state.uaccess) {
2161 WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
2165 state.uaccess = true;
2169 if (!state.uaccess && func) {
2170 WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
2174 if (func_uaccess_safe(func) && !state.uaccess_stack) {
2175 WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
2179 state.uaccess = false;
2184 WARN_FUNC("recursive STD", sec, insn->offset);
2190 if (!state.df && func)
2191 WARN_FUNC("redundant CLD", sec, insn->offset);
2204 if (state.cfa.base == CFI_UNDEFINED)
2206 WARN("%s: unexpected end of section", sec->name);
2216 static int validate_unwind_hints(struct objtool_file *file)
2218 struct instruction *insn;
2219 int ret, warnings = 0;
2220 struct insn_state state;
2225 clear_insn_state(&state);
2227 for_each_insn(file, insn) {
2228 if (insn->hint && !insn->visited) {
2229 ret = validate_branch(file, insn->func, insn, state);
2230 if (ret && backtrace)
2231 BT_FUNC("<=== (hint)", insn);
2239 static int validate_retpoline(struct objtool_file *file)
2241 struct instruction *insn;
2244 for_each_insn(file, insn) {
2245 if (insn->type != INSN_JUMP_DYNAMIC &&
2246 insn->type != INSN_CALL_DYNAMIC)
2249 if (insn->retpoline_safe)
2253 * .init.text code is ran before userspace and thus doesn't
2254 * strictly need retpolines, except for modules which are
2255 * loaded late, they very much do need retpoline in their
2258 if (!strcmp(insn->sec->name, ".init.text") && !module)
2261 WARN_FUNC("indirect %s found in RETPOLINE build",
2262 insn->sec, insn->offset,
2263 insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
2271 static bool is_kasan_insn(struct instruction *insn)
2273 return (insn->type == INSN_CALL &&
2274 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
2277 static bool is_ubsan_insn(struct instruction *insn)
2279 return (insn->type == INSN_CALL &&
2280 !strcmp(insn->call_dest->name,
2281 "__ubsan_handle_builtin_unreachable"));
2284 static bool ignore_unreachable_insn(struct instruction *insn)
2288 if (insn->ignore || insn->type == INSN_NOP)
2292 * Ignore any unused exceptions. This can happen when a whitelisted
2293 * function has an exception table entry.
2295 * Also ignore alternative replacement instructions. This can happen
2296 * when a whitelisted function uses one of the ALTERNATIVE macros.
2298 if (!strcmp(insn->sec->name, ".fixup") ||
2299 !strcmp(insn->sec->name, ".altinstr_replacement") ||
2300 !strcmp(insn->sec->name, ".altinstr_aux"))
2304 * Check if this (or a subsequent) instruction is related to
2305 * CONFIG_UBSAN or CONFIG_KASAN.
2307 * End the search at 5 instructions to avoid going into the weeds.
2311 for (i = 0; i < 5; i++) {
2313 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2316 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2317 if (insn->jump_dest &&
2318 insn->jump_dest->func == insn->func) {
2319 insn = insn->jump_dest;
2326 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2329 insn = list_next_entry(insn, list);
2335 static int validate_functions(struct objtool_file *file)
2337 struct section *sec;
2338 struct symbol *func;
2339 struct instruction *insn;
2340 struct insn_state state;
2341 int ret, warnings = 0;
2343 clear_insn_state(&state);
2345 state.cfa = initial_func_cfi.cfa;
2346 memcpy(&state.regs, &initial_func_cfi.regs,
2347 CFI_NUM_REGS * sizeof(struct cfi_reg));
2348 state.stack_size = initial_func_cfi.cfa.offset;
2350 for_each_sec(file, sec) {
2351 list_for_each_entry(func, &sec->symbol_list, list) {
2352 if (func->type != STT_FUNC)
2356 WARN("%s() is missing an ELF size annotation",
2361 if (func->pfunc != func || func->alias != func)
2364 insn = find_insn(file, sec, func->offset);
2365 if (!insn || insn->ignore || insn->visited)
2368 state.uaccess = func->uaccess_safe;
2370 ret = validate_branch(file, func, insn, state);
2371 if (ret && backtrace)
2372 BT_FUNC("<=== (func)", insn);
2380 static int validate_reachable_instructions(struct objtool_file *file)
2382 struct instruction *insn;
2384 if (file->ignore_unreachables)
2387 for_each_insn(file, insn) {
2388 if (insn->visited || ignore_unreachable_insn(insn))
2391 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2398 static void cleanup(struct objtool_file *file)
2400 struct instruction *insn, *tmpinsn;
2401 struct alternative *alt, *tmpalt;
2403 list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
2404 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
2405 list_del(&alt->list);
2408 list_del(&insn->list);
2409 hash_del(&insn->hash);
2412 elf_close(file->elf);
2415 static struct objtool_file file;
2417 int check(const char *_objname, bool orc)
2419 int ret, warnings = 0;
2423 file.elf = elf_read(objname, orc ? O_RDWR : O_RDONLY);
2427 INIT_LIST_HEAD(&file.insn_list);
2428 hash_init(file.insn_hash);
2429 file.c_file = find_section_by_name(file.elf, ".comment");
2430 file.ignore_unreachables = no_unreachable;
2433 arch_initial_func_cfi_state(&initial_func_cfi);
2435 ret = decode_sections(&file);
2440 if (list_empty(&file.insn_list))
2444 ret = validate_retpoline(&file);
2450 ret = validate_functions(&file);
2455 ret = validate_unwind_hints(&file);
2461 ret = validate_reachable_instructions(&file);
2468 ret = create_orc(&file);
2472 ret = create_orc_sections(&file);
2476 ret = elf_write(file.elf);
2484 /* ignore warnings for now until we get all the code cleaned up */
2485 if (ret || warnings)