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
22 struct list_head list
;
23 struct instruction
*insn
;
28 struct cfi_state initial_func_cfi
;
30 struct instruction
*find_insn(struct objtool_file
*file
,
31 struct section
*sec
, unsigned long offset
)
33 struct instruction
*insn
;
35 hash_for_each_possible(file
->insn_hash
, insn
, hash
, offset
)
36 if (insn
->sec
== sec
&& insn
->offset
== offset
)
42 static struct instruction
*next_insn_same_sec(struct objtool_file
*file
,
43 struct instruction
*insn
)
45 struct instruction
*next
= list_next_entry(insn
, list
);
47 if (!next
|| &next
->list
== &file
->insn_list
|| next
->sec
!= insn
->sec
)
53 static struct instruction
*next_insn_same_func(struct objtool_file
*file
,
54 struct instruction
*insn
)
56 struct instruction
*next
= list_next_entry(insn
, list
);
57 struct symbol
*func
= insn
->func
;
62 if (&next
->list
!= &file
->insn_list
&& next
->func
== func
)
65 /* Check if we're already in the subfunction: */
66 if (func
== func
->cfunc
)
69 /* Move to the subfunction: */
70 return find_insn(file
, func
->cfunc
->sec
, func
->cfunc
->offset
);
73 #define func_for_each_insn_all(file, func, insn) \
74 for (insn = find_insn(file, func->sec, func->offset); \
76 insn = next_insn_same_func(file, insn))
78 #define func_for_each_insn(file, func, insn) \
79 for (insn = find_insn(file, func->sec, func->offset); \
80 insn && &insn->list != &file->insn_list && \
81 insn->sec == func->sec && \
82 insn->offset < func->offset + func->len; \
83 insn = list_next_entry(insn, list))
85 #define func_for_each_insn_continue_reverse(file, func, insn) \
86 for (insn = list_prev_entry(insn, list); \
87 &insn->list != &file->insn_list && \
88 insn->sec == func->sec && insn->offset >= func->offset; \
89 insn = list_prev_entry(insn, list))
91 #define sec_for_each_insn_from(file, insn) \
92 for (; insn; insn = next_insn_same_sec(file, insn))
94 #define sec_for_each_insn_continue(file, insn) \
95 for (insn = next_insn_same_sec(file, insn); insn; \
96 insn = next_insn_same_sec(file, insn))
99 * This checks to see if the given function is a "noreturn" function.
101 * For global functions which are outside the scope of this object file, we
102 * have to keep a manual list of them.
104 * For local functions, we have to detect them manually by simply looking for
105 * the lack of a return instruction.
112 static int __dead_end_function(struct objtool_file
*file
, struct symbol
*func
,
116 struct instruction
*insn
;
120 * Unfortunately these have to be hard coded because the noreturn
121 * attribute isn't provided in ELF data.
123 static const char * const global_noreturns
[] = {
128 "__module_put_and_exit",
130 "kvm_spurious_fault",
135 "machine_real_restart",
136 "rewind_stack_do_exit",
139 if (func
->bind
== STB_WEAK
)
142 if (func
->bind
== STB_GLOBAL
)
143 for (i
= 0; i
< ARRAY_SIZE(global_noreturns
); i
++)
144 if (!strcmp(func
->name
, global_noreturns
[i
]))
150 insn
= find_insn(file
, func
->sec
, func
->offset
);
154 func_for_each_insn_all(file
, func
, insn
) {
157 if (insn
->type
== INSN_RETURN
)
165 * A function can have a sibling call instead of a return. In that
166 * case, the function's dead-end status depends on whether the target
167 * of the sibling call returns.
169 func_for_each_insn_all(file
, func
, insn
) {
170 if (insn
->type
== INSN_JUMP_UNCONDITIONAL
) {
171 struct instruction
*dest
= insn
->jump_dest
;
174 /* sibling call to another file */
177 if (dest
->func
&& dest
->func
->pfunc
!= insn
->func
->pfunc
) {
179 /* local sibling call */
180 if (recursion
== 5) {
182 * Infinite recursion: two functions
183 * have sibling calls to each other.
184 * This is a very rare case. It means
185 * they aren't dead ends.
190 return __dead_end_function(file
, dest
->func
,
195 if (insn
->type
== INSN_JUMP_DYNAMIC
&& list_empty(&insn
->alts
))
203 static int dead_end_function(struct objtool_file
*file
, struct symbol
*func
)
205 return __dead_end_function(file
, func
, 0);
208 static void clear_insn_state(struct insn_state
*state
)
212 memset(state
, 0, sizeof(*state
));
213 state
->cfa
.base
= CFI_UNDEFINED
;
214 for (i
= 0; i
< CFI_NUM_REGS
; i
++) {
215 state
->regs
[i
].base
= CFI_UNDEFINED
;
216 state
->vals
[i
].base
= CFI_UNDEFINED
;
218 state
->drap_reg
= CFI_UNDEFINED
;
219 state
->drap_offset
= -1;
223 * Call the arch-specific instruction decoder for all the instructions and add
224 * them to the global instruction list.
226 static int decode_instructions(struct objtool_file
*file
)
230 unsigned long offset
;
231 struct instruction
*insn
;
234 for_each_sec(file
, sec
) {
236 if (!(sec
->sh
.sh_flags
& SHF_EXECINSTR
))
239 if (strcmp(sec
->name
, ".altinstr_replacement") &&
240 strcmp(sec
->name
, ".altinstr_aux") &&
241 strncmp(sec
->name
, ".discard.", 9))
244 for (offset
= 0; offset
< sec
->len
; offset
+= insn
->len
) {
245 insn
= malloc(sizeof(*insn
));
247 WARN("malloc failed");
250 memset(insn
, 0, sizeof(*insn
));
251 INIT_LIST_HEAD(&insn
->alts
);
252 clear_insn_state(&insn
->state
);
255 insn
->offset
= offset
;
257 ret
= arch_decode_instruction(file
->elf
, sec
, offset
,
259 &insn
->len
, &insn
->type
,
265 if (!insn
->type
|| insn
->type
> INSN_LAST
) {
266 WARN_FUNC("invalid instruction type %d",
267 insn
->sec
, insn
->offset
, insn
->type
);
272 hash_add(file
->insn_hash
, &insn
->hash
, insn
->offset
);
273 list_add_tail(&insn
->list
, &file
->insn_list
);
276 list_for_each_entry(func
, &sec
->symbol_list
, list
) {
277 if (func
->type
!= STT_FUNC
)
280 if (!find_insn(file
, sec
, func
->offset
)) {
281 WARN("%s(): can't find starting instruction",
286 func_for_each_insn(file
, func
, insn
)
300 * Mark "ud2" instructions and manually annotated dead ends.
302 static int add_dead_ends(struct objtool_file
*file
)
306 struct instruction
*insn
;
310 * By default, "ud2" is a dead end unless otherwise annotated, because
311 * GCC 7 inserts it for certain divide-by-zero cases.
313 for_each_insn(file
, insn
)
314 if (insn
->type
== INSN_BUG
)
315 insn
->dead_end
= true;
318 * Check for manually annotated dead ends.
320 sec
= find_section_by_name(file
->elf
, ".rela.discard.unreachable");
324 list_for_each_entry(rela
, &sec
->rela_list
, list
) {
325 if (rela
->sym
->type
!= STT_SECTION
) {
326 WARN("unexpected relocation symbol type in %s", sec
->name
);
329 insn
= find_insn(file
, rela
->sym
->sec
, rela
->addend
);
331 insn
= list_prev_entry(insn
, list
);
332 else if (rela
->addend
== rela
->sym
->sec
->len
) {
334 list_for_each_entry_reverse(insn
, &file
->insn_list
, list
) {
335 if (insn
->sec
== rela
->sym
->sec
) {
342 WARN("can't find unreachable insn at %s+0x%x",
343 rela
->sym
->sec
->name
, rela
->addend
);
347 WARN("can't find unreachable insn at %s+0x%x",
348 rela
->sym
->sec
->name
, rela
->addend
);
352 insn
->dead_end
= true;
357 * These manually annotated reachable checks are needed for GCC 4.4,
358 * where the Linux unreachable() macro isn't supported. In that case
359 * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
362 sec
= find_section_by_name(file
->elf
, ".rela.discard.reachable");
366 list_for_each_entry(rela
, &sec
->rela_list
, list
) {
367 if (rela
->sym
->type
!= STT_SECTION
) {
368 WARN("unexpected relocation symbol type in %s", sec
->name
);
371 insn
= find_insn(file
, rela
->sym
->sec
, rela
->addend
);
373 insn
= list_prev_entry(insn
, list
);
374 else if (rela
->addend
== rela
->sym
->sec
->len
) {
376 list_for_each_entry_reverse(insn
, &file
->insn_list
, list
) {
377 if (insn
->sec
== rela
->sym
->sec
) {
384 WARN("can't find reachable insn at %s+0x%x",
385 rela
->sym
->sec
->name
, rela
->addend
);
389 WARN("can't find reachable insn at %s+0x%x",
390 rela
->sym
->sec
->name
, rela
->addend
);
394 insn
->dead_end
= false;
401 * Warnings shouldn't be reported for ignored functions.
403 static void add_ignores(struct objtool_file
*file
)
405 struct instruction
*insn
;
410 sec
= find_section_by_name(file
->elf
, ".rela.discard.func_stack_frame_non_standard");
414 list_for_each_entry(rela
, &sec
->rela_list
, list
) {
415 switch (rela
->sym
->type
) {
421 func
= find_symbol_by_offset(rela
->sym
->sec
, rela
->addend
);
422 if (!func
|| func
->type
!= STT_FUNC
)
427 WARN("unexpected relocation symbol type in %s: %d", sec
->name
, rela
->sym
->type
);
431 func_for_each_insn_all(file
, func
, insn
)
437 * This is a whitelist of functions that is allowed to be called with AC set.
438 * The list is meant to be minimal and only contains compiler instrumentation
439 * ABI and a few functions used to implement *_{to,from}_user() functions.
441 * These functions must not directly change AC, but may PUSHF/POPF.
443 static const char *uaccess_safe_builtin
[] = {
446 "check_memory_region",
447 /* KASAN out-of-line */
448 "__asan_loadN_noabort",
449 "__asan_load1_noabort",
450 "__asan_load2_noabort",
451 "__asan_load4_noabort",
452 "__asan_load8_noabort",
453 "__asan_load16_noabort",
454 "__asan_storeN_noabort",
455 "__asan_store1_noabort",
456 "__asan_store2_noabort",
457 "__asan_store4_noabort",
458 "__asan_store8_noabort",
459 "__asan_store16_noabort",
461 "__asan_report_load_n_noabort",
462 "__asan_report_load1_noabort",
463 "__asan_report_load2_noabort",
464 "__asan_report_load4_noabort",
465 "__asan_report_load8_noabort",
466 "__asan_report_load16_noabort",
467 "__asan_report_store_n_noabort",
468 "__asan_report_store1_noabort",
469 "__asan_report_store2_noabort",
470 "__asan_report_store4_noabort",
471 "__asan_report_store8_noabort",
472 "__asan_report_store16_noabort",
475 "__sanitizer_cov_trace_pc",
476 "__sanitizer_cov_trace_const_cmp1",
477 "__sanitizer_cov_trace_const_cmp2",
478 "__sanitizer_cov_trace_const_cmp4",
479 "__sanitizer_cov_trace_const_cmp8",
480 "__sanitizer_cov_trace_cmp1",
481 "__sanitizer_cov_trace_cmp2",
482 "__sanitizer_cov_trace_cmp4",
483 "__sanitizer_cov_trace_cmp8",
485 "ubsan_type_mismatch_common",
486 "__ubsan_handle_type_mismatch",
487 "__ubsan_handle_type_mismatch_v1",
489 "csum_partial_copy_generic",
491 "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
495 static void add_uaccess_safe(struct objtool_file
*file
)
503 for (name
= uaccess_safe_builtin
; *name
; name
++) {
504 func
= find_symbol_by_name(file
->elf
, *name
);
508 func
->alias
->uaccess_safe
= true;
513 * FIXME: For now, just ignore any alternatives which add retpolines. This is
514 * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
515 * But it at least allows objtool to understand the control flow *around* the
518 static int add_ignore_alternatives(struct objtool_file
*file
)
522 struct instruction
*insn
;
524 sec
= find_section_by_name(file
->elf
, ".rela.discard.ignore_alts");
528 list_for_each_entry(rela
, &sec
->rela_list
, list
) {
529 if (rela
->sym
->type
!= STT_SECTION
) {
530 WARN("unexpected relocation symbol type in %s", sec
->name
);
534 insn
= find_insn(file
, rela
->sym
->sec
, rela
->addend
);
536 WARN("bad .discard.ignore_alts entry");
540 insn
->ignore_alts
= true;
547 * Find the destination instructions for all jumps.
549 static int add_jump_destinations(struct objtool_file
*file
)
551 struct instruction
*insn
;
553 struct section
*dest_sec
;
554 unsigned long dest_off
;
556 for_each_insn(file
, insn
) {
557 if (insn
->type
!= INSN_JUMP_CONDITIONAL
&&
558 insn
->type
!= INSN_JUMP_UNCONDITIONAL
)
561 if (insn
->ignore
|| insn
->offset
== FAKE_JUMP_OFFSET
)
564 rela
= find_rela_by_dest_range(insn
->sec
, insn
->offset
,
567 dest_sec
= insn
->sec
;
568 dest_off
= insn
->offset
+ insn
->len
+ insn
->immediate
;
569 } else if (rela
->sym
->type
== STT_SECTION
) {
570 dest_sec
= rela
->sym
->sec
;
571 dest_off
= rela
->addend
+ 4;
572 } else if (rela
->sym
->sec
->idx
) {
573 dest_sec
= rela
->sym
->sec
;
574 dest_off
= rela
->sym
->sym
.st_value
+ rela
->addend
+ 4;
575 } else if (strstr(rela
->sym
->name
, "_indirect_thunk_")) {
577 * Retpoline jumps are really dynamic jumps in
578 * disguise, so convert them accordingly.
580 insn
->type
= INSN_JUMP_DYNAMIC
;
581 insn
->retpoline_safe
= true;
585 insn
->call_dest
= rela
->sym
;
586 insn
->jump_dest
= NULL
;
590 insn
->jump_dest
= find_insn(file
, dest_sec
, dest_off
);
591 if (!insn
->jump_dest
) {
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().
598 if (!strcmp(insn
->sec
->name
, ".altinstr_replacement"))
601 WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
602 insn
->sec
, insn
->offset
, dest_sec
->name
,
608 * Cross-function jump.
610 if (insn
->func
&& insn
->jump_dest
->func
&&
611 insn
->func
!= insn
->jump_dest
->func
) {
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().
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().
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 switch table.
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
;
633 } else if (insn
->jump_dest
->func
->pfunc
!= insn
->func
->pfunc
&&
634 insn
->jump_dest
->offset
== insn
->jump_dest
->func
->offset
) {
637 insn
->call_dest
= insn
->jump_dest
->func
;
638 insn
->jump_dest
= NULL
;
647 * Find the destination instructions for all calls.
649 static int add_call_destinations(struct objtool_file
*file
)
651 struct instruction
*insn
;
652 unsigned long dest_off
;
655 for_each_insn(file
, insn
) {
656 if (insn
->type
!= INSN_CALL
)
659 rela
= find_rela_by_dest_range(insn
->sec
, insn
->offset
,
662 dest_off
= insn
->offset
+ insn
->len
+ insn
->immediate
;
663 insn
->call_dest
= find_symbol_by_offset(insn
->sec
,
666 if (!insn
->call_dest
&& !insn
->ignore
) {
667 WARN_FUNC("unsupported intra-function call",
668 insn
->sec
, insn
->offset
);
670 WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
674 } else if (rela
->sym
->type
== STT_SECTION
) {
675 insn
->call_dest
= find_symbol_by_offset(rela
->sym
->sec
,
677 if (!insn
->call_dest
||
678 insn
->call_dest
->type
!= STT_FUNC
) {
679 WARN_FUNC("can't find call dest symbol at %s+0x%x",
680 insn
->sec
, insn
->offset
,
681 rela
->sym
->sec
->name
,
686 insn
->call_dest
= rela
->sym
;
693 * The .alternatives section requires some extra special care, over and above
694 * what other special sections require:
696 * 1. Because alternatives are patched in-place, we need to insert a fake jump
697 * instruction at the end so that validate_branch() skips all the original
698 * replaced instructions when validating the new instruction path.
700 * 2. An added wrinkle is that the new instruction length might be zero. In
701 * that case the old instructions are replaced with noops. We simulate that
702 * by creating a fake jump as the only new instruction.
704 * 3. In some cases, the alternative section includes an instruction which
705 * conditionally jumps to the _end_ of the entry. We have to modify these
706 * jumps' destinations to point back to .text rather than the end of the
707 * entry in .altinstr_replacement.
709 static int handle_group_alt(struct objtool_file
*file
,
710 struct special_alt
*special_alt
,
711 struct instruction
*orig_insn
,
712 struct instruction
**new_insn
)
714 struct instruction
*last_orig_insn
, *last_new_insn
, *insn
, *fake_jump
= NULL
;
715 unsigned long dest_off
;
717 last_orig_insn
= NULL
;
719 sec_for_each_insn_from(file
, insn
) {
720 if (insn
->offset
>= special_alt
->orig_off
+ special_alt
->orig_len
)
723 insn
->alt_group
= true;
724 last_orig_insn
= insn
;
727 if (next_insn_same_sec(file
, last_orig_insn
)) {
728 fake_jump
= malloc(sizeof(*fake_jump
));
730 WARN("malloc failed");
733 memset(fake_jump
, 0, sizeof(*fake_jump
));
734 INIT_LIST_HEAD(&fake_jump
->alts
);
735 clear_insn_state(&fake_jump
->state
);
737 fake_jump
->sec
= special_alt
->new_sec
;
738 fake_jump
->offset
= FAKE_JUMP_OFFSET
;
739 fake_jump
->type
= INSN_JUMP_UNCONDITIONAL
;
740 fake_jump
->jump_dest
= list_next_entry(last_orig_insn
, list
);
741 fake_jump
->func
= orig_insn
->func
;
744 if (!special_alt
->new_len
) {
746 WARN("%s: empty alternative at end of section",
747 special_alt
->orig_sec
->name
);
751 *new_insn
= fake_jump
;
755 last_new_insn
= NULL
;
757 sec_for_each_insn_from(file
, insn
) {
758 if (insn
->offset
>= special_alt
->new_off
+ special_alt
->new_len
)
761 last_new_insn
= insn
;
763 insn
->ignore
= orig_insn
->ignore_alts
;
764 insn
->func
= orig_insn
->func
;
766 if (insn
->type
!= INSN_JUMP_CONDITIONAL
&&
767 insn
->type
!= INSN_JUMP_UNCONDITIONAL
)
770 if (!insn
->immediate
)
773 dest_off
= insn
->offset
+ insn
->len
+ insn
->immediate
;
774 if (dest_off
== special_alt
->new_off
+ special_alt
->new_len
) {
776 WARN("%s: alternative jump to end of section",
777 special_alt
->orig_sec
->name
);
780 insn
->jump_dest
= fake_jump
;
783 if (!insn
->jump_dest
) {
784 WARN_FUNC("can't find alternative jump destination",
785 insn
->sec
, insn
->offset
);
790 if (!last_new_insn
) {
791 WARN_FUNC("can't find last new alternative instruction",
792 special_alt
->new_sec
, special_alt
->new_off
);
797 list_add(&fake_jump
->list
, &last_new_insn
->list
);
803 * A jump table entry can either convert a nop to a jump or a jump to a nop.
804 * If the original instruction is a jump, make the alt entry an effective nop
805 * by just skipping the original instruction.
807 static int handle_jump_alt(struct objtool_file
*file
,
808 struct special_alt
*special_alt
,
809 struct instruction
*orig_insn
,
810 struct instruction
**new_insn
)
812 if (orig_insn
->type
== INSN_NOP
)
815 if (orig_insn
->type
!= INSN_JUMP_UNCONDITIONAL
) {
816 WARN_FUNC("unsupported instruction at jump label",
817 orig_insn
->sec
, orig_insn
->offset
);
821 *new_insn
= list_next_entry(orig_insn
, list
);
826 * Read all the special sections which have alternate instructions which can be
827 * patched in or redirected to at runtime. Each instruction having alternate
828 * instruction(s) has them added to its insn->alts list, which will be
829 * traversed in validate_branch().
831 static int add_special_section_alts(struct objtool_file
*file
)
833 struct list_head special_alts
;
834 struct instruction
*orig_insn
, *new_insn
;
835 struct special_alt
*special_alt
, *tmp
;
836 struct alternative
*alt
;
839 ret
= special_get_alts(file
->elf
, &special_alts
);
843 list_for_each_entry_safe(special_alt
, tmp
, &special_alts
, list
) {
845 orig_insn
= find_insn(file
, special_alt
->orig_sec
,
846 special_alt
->orig_off
);
848 WARN_FUNC("special: can't find orig instruction",
849 special_alt
->orig_sec
, special_alt
->orig_off
);
855 if (!special_alt
->group
|| special_alt
->new_len
) {
856 new_insn
= find_insn(file
, special_alt
->new_sec
,
857 special_alt
->new_off
);
859 WARN_FUNC("special: can't find new instruction",
860 special_alt
->new_sec
,
861 special_alt
->new_off
);
867 if (special_alt
->group
) {
868 ret
= handle_group_alt(file
, special_alt
, orig_insn
,
872 } else if (special_alt
->jump_or_nop
) {
873 ret
= handle_jump_alt(file
, special_alt
, orig_insn
,
879 alt
= malloc(sizeof(*alt
));
881 WARN("malloc failed");
886 alt
->insn
= new_insn
;
887 alt
->skip_orig
= special_alt
->skip_orig
;
888 orig_insn
->ignore_alts
|= special_alt
->skip_alt
;
889 list_add_tail(&alt
->list
, &orig_insn
->alts
);
891 list_del(&special_alt
->list
);
899 static int add_switch_table(struct objtool_file
*file
, struct instruction
*insn
,
900 struct rela
*table
, struct rela
*next_table
)
902 struct rela
*rela
= table
;
903 struct instruction
*alt_insn
;
904 struct alternative
*alt
;
905 struct symbol
*pfunc
= insn
->func
->pfunc
;
906 unsigned int prev_offset
= 0;
908 list_for_each_entry_from(rela
, &table
->rela_sec
->rela_list
, list
) {
909 if (rela
== next_table
)
912 /* Make sure the switch table entries are consecutive: */
913 if (prev_offset
&& rela
->offset
!= prev_offset
+ 8)
916 /* Detect function pointers from contiguous objects: */
917 if (rela
->sym
->sec
== pfunc
->sec
&&
918 rela
->addend
== pfunc
->offset
)
921 alt_insn
= find_insn(file
, rela
->sym
->sec
, rela
->addend
);
925 /* Make sure the jmp dest is in the function or subfunction: */
926 if (alt_insn
->func
->pfunc
!= pfunc
)
929 alt
= malloc(sizeof(*alt
));
931 WARN("malloc failed");
935 alt
->insn
= alt_insn
;
936 list_add_tail(&alt
->list
, &insn
->alts
);
937 prev_offset
= rela
->offset
;
941 WARN_FUNC("can't find switch jump table",
942 insn
->sec
, insn
->offset
);
950 * find_switch_table() - Given a dynamic jump, find the switch jump table in
951 * .rodata associated with it.
953 * There are 3 basic patterns:
955 * 1. jmpq *[rodata addr](,%reg,8)
957 * This is the most common case by far. It jumps to an address in a simple
958 * jump table which is stored in .rodata.
960 * 2. jmpq *[rodata addr](%rip)
962 * This is caused by a rare GCC quirk, currently only seen in three driver
963 * functions in the kernel, only with certain obscure non-distro configs.
965 * As part of an optimization, GCC makes a copy of an existing switch jump
966 * table, modifies it, and then hard-codes the jump (albeit with an indirect
967 * jump) to use a single entry in the table. The rest of the jump table and
968 * some of its jump targets remain as dead code.
970 * In such a case we can just crudely ignore all unreachable instruction
971 * warnings for the entire object file. Ideally we would just ignore them
972 * for the function, but that would require redesigning the code quite a
973 * bit. And honestly that's just not worth doing: unreachable instruction
974 * warnings are of questionable value anyway, and this is such a rare issue.
976 * 3. mov [rodata addr],%reg1
977 * ... some instructions ...
978 * jmpq *(%reg1,%reg2,8)
980 * This is a fairly uncommon pattern which is new for GCC 6. As of this
981 * writing, there are 11 occurrences of it in the allmodconfig kernel.
983 * As of GCC 7 there are quite a few more of these and the 'in between' code
984 * is significant. Esp. with KASAN enabled some of the code between the mov
985 * and jmpq uses .rodata itself, which can confuse things.
987 * TODO: Once we have DWARF CFI and smarter instruction decoding logic,
988 * ensure the same register is used in the mov and jump instructions.
990 * NOTE: RETPOLINE made it harder still to decode dynamic jumps.
992 static struct rela
*find_switch_table(struct objtool_file
*file
,
994 struct instruction
*insn
)
996 struct rela
*text_rela
, *rodata_rela
;
997 struct instruction
*orig_insn
= insn
;
998 struct section
*rodata_sec
;
999 unsigned long table_offset
;
1002 * Backward search using the @first_jump_src links, these help avoid
1003 * much of the 'in between' code. Which avoids us getting confused by
1007 &insn
->list
!= &file
->insn_list
&&
1008 insn
->sec
== func
->sec
&&
1009 insn
->offset
>= func
->offset
;
1011 insn
= insn
->first_jump_src
?: list_prev_entry(insn
, list
)) {
1013 if (insn
!= orig_insn
&& insn
->type
== INSN_JUMP_DYNAMIC
)
1016 /* allow small jumps within the range */
1017 if (insn
->type
== INSN_JUMP_UNCONDITIONAL
&&
1019 (insn
->jump_dest
->offset
<= insn
->offset
||
1020 insn
->jump_dest
->offset
> orig_insn
->offset
))
1023 /* look for a relocation which references .rodata */
1024 text_rela
= find_rela_by_dest_range(insn
->sec
, insn
->offset
,
1026 if (!text_rela
|| text_rela
->sym
->type
!= STT_SECTION
||
1027 !text_rela
->sym
->sec
->rodata
)
1030 table_offset
= text_rela
->addend
;
1031 rodata_sec
= text_rela
->sym
->sec
;
1033 if (text_rela
->type
== R_X86_64_PC32
)
1037 * Make sure the .rodata address isn't associated with a
1038 * symbol. gcc jump tables are anonymous data.
1040 if (find_symbol_containing(rodata_sec
, table_offset
))
1043 rodata_rela
= find_rela_by_dest(rodata_sec
, table_offset
);
1046 * Use of RIP-relative switch jumps is quite rare, and
1047 * indicates a rare GCC quirk/bug which can leave dead
1050 if (text_rela
->type
== R_X86_64_PC32
)
1051 file
->ignore_unreachables
= true;
1061 static int add_func_switch_tables(struct objtool_file
*file
,
1062 struct symbol
*func
)
1064 struct instruction
*insn
, *last
= NULL
, *prev_jump
= NULL
;
1065 struct rela
*rela
, *prev_rela
= NULL
;
1068 func_for_each_insn_all(file
, func
, insn
) {
1073 * Store back-pointers for unconditional forward jumps such
1074 * that find_switch_table() can back-track using those and
1075 * avoid some potentially confusing code.
1077 if (insn
->type
== INSN_JUMP_UNCONDITIONAL
&& insn
->jump_dest
&&
1078 insn
->offset
> last
->offset
&&
1079 insn
->jump_dest
->offset
> insn
->offset
&&
1080 !insn
->jump_dest
->first_jump_src
) {
1082 insn
->jump_dest
->first_jump_src
= insn
;
1083 last
= insn
->jump_dest
;
1086 if (insn
->type
!= INSN_JUMP_DYNAMIC
)
1089 rela
= find_switch_table(file
, func
, insn
);
1094 * We found a switch table, but we don't know yet how big it
1095 * is. Don't add it until we reach the end of the function or
1096 * the beginning of another switch table in the same function.
1099 ret
= add_switch_table(file
, prev_jump
, prev_rela
, rela
);
1109 ret
= add_switch_table(file
, prev_jump
, prev_rela
, NULL
);
1118 * For some switch statements, gcc generates a jump table in the .rodata
1119 * section which contains a list of addresses within the function to jump to.
1120 * This finds these jump tables and adds them to the insn->alts lists.
1122 static int add_switch_table_alts(struct objtool_file
*file
)
1124 struct section
*sec
;
1125 struct symbol
*func
;
1131 for_each_sec(file
, sec
) {
1132 list_for_each_entry(func
, &sec
->symbol_list
, list
) {
1133 if (func
->type
!= STT_FUNC
)
1136 ret
= add_func_switch_tables(file
, func
);
1145 static int read_unwind_hints(struct objtool_file
*file
)
1147 struct section
*sec
, *relasec
;
1149 struct unwind_hint
*hint
;
1150 struct instruction
*insn
;
1151 struct cfi_reg
*cfa
;
1154 sec
= find_section_by_name(file
->elf
, ".discard.unwind_hints");
1158 relasec
= sec
->rela
;
1160 WARN("missing .rela.discard.unwind_hints section");
1164 if (sec
->len
% sizeof(struct unwind_hint
)) {
1165 WARN("struct unwind_hint size mismatch");
1171 for (i
= 0; i
< sec
->len
/ sizeof(struct unwind_hint
); i
++) {
1172 hint
= (struct unwind_hint
*)sec
->data
->d_buf
+ i
;
1174 rela
= find_rela_by_dest(sec
, i
* sizeof(*hint
));
1176 WARN("can't find rela for unwind_hints[%d]", i
);
1180 insn
= find_insn(file
, rela
->sym
->sec
, rela
->addend
);
1182 WARN("can't find insn for unwind_hints[%d]", i
);
1186 cfa
= &insn
->state
.cfa
;
1188 if (hint
->type
== UNWIND_HINT_TYPE_SAVE
) {
1192 } else if (hint
->type
== UNWIND_HINT_TYPE_RESTORE
) {
1193 insn
->restore
= true;
1200 switch (hint
->sp_reg
) {
1201 case ORC_REG_UNDEFINED
:
1202 cfa
->base
= CFI_UNDEFINED
;
1210 case ORC_REG_SP_INDIRECT
:
1211 cfa
->base
= CFI_SP_INDIRECT
;
1214 cfa
->base
= CFI_R10
;
1217 cfa
->base
= CFI_R13
;
1226 WARN_FUNC("unsupported unwind_hint sp base reg %d",
1227 insn
->sec
, insn
->offset
, hint
->sp_reg
);
1231 cfa
->offset
= hint
->sp_offset
;
1232 insn
->state
.type
= hint
->type
;
1233 insn
->state
.end
= hint
->end
;
1239 static int read_retpoline_hints(struct objtool_file
*file
)
1241 struct section
*sec
;
1242 struct instruction
*insn
;
1245 sec
= find_section_by_name(file
->elf
, ".rela.discard.retpoline_safe");
1249 list_for_each_entry(rela
, &sec
->rela_list
, list
) {
1250 if (rela
->sym
->type
!= STT_SECTION
) {
1251 WARN("unexpected relocation symbol type in %s", sec
->name
);
1255 insn
= find_insn(file
, rela
->sym
->sec
, rela
->addend
);
1257 WARN("bad .discard.retpoline_safe entry");
1261 if (insn
->type
!= INSN_JUMP_DYNAMIC
&&
1262 insn
->type
!= INSN_CALL_DYNAMIC
) {
1263 WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1264 insn
->sec
, insn
->offset
);
1268 insn
->retpoline_safe
= true;
1274 static void mark_rodata(struct objtool_file
*file
)
1276 struct section
*sec
;
1280 * This searches for the .rodata section or multiple .rodata.func_name
1281 * sections if -fdata-sections is being used. The .str.1.1 and .str.1.8
1282 * rodata sections are ignored as they don't contain jump tables.
1284 for_each_sec(file
, sec
) {
1285 if (!strncmp(sec
->name
, ".rodata", 7) &&
1286 !strstr(sec
->name
, ".str1.")) {
1292 file
->rodata
= found
;
1295 static int decode_sections(struct objtool_file
*file
)
1301 ret
= decode_instructions(file
);
1305 ret
= add_dead_ends(file
);
1310 add_uaccess_safe(file
);
1312 ret
= add_ignore_alternatives(file
);
1316 ret
= add_jump_destinations(file
);
1320 ret
= add_special_section_alts(file
);
1324 ret
= add_call_destinations(file
);
1328 ret
= add_switch_table_alts(file
);
1332 ret
= read_unwind_hints(file
);
1336 ret
= read_retpoline_hints(file
);
1343 static bool is_fentry_call(struct instruction
*insn
)
1345 if (insn
->type
== INSN_CALL
&&
1346 insn
->call_dest
->type
== STT_NOTYPE
&&
1347 !strcmp(insn
->call_dest
->name
, "__fentry__"))
1353 static bool has_modified_stack_frame(struct insn_state
*state
)
1357 if (state
->cfa
.base
!= initial_func_cfi
.cfa
.base
||
1358 state
->cfa
.offset
!= initial_func_cfi
.cfa
.offset
||
1359 state
->stack_size
!= initial_func_cfi
.cfa
.offset
||
1363 for (i
= 0; i
< CFI_NUM_REGS
; i
++)
1364 if (state
->regs
[i
].base
!= initial_func_cfi
.regs
[i
].base
||
1365 state
->regs
[i
].offset
!= initial_func_cfi
.regs
[i
].offset
)
1371 static bool has_valid_stack_frame(struct insn_state
*state
)
1373 if (state
->cfa
.base
== CFI_BP
&& state
->regs
[CFI_BP
].base
== CFI_CFA
&&
1374 state
->regs
[CFI_BP
].offset
== -16)
1377 if (state
->drap
&& state
->regs
[CFI_BP
].base
== CFI_BP
)
1383 static int update_insn_state_regs(struct instruction
*insn
, struct insn_state
*state
)
1385 struct cfi_reg
*cfa
= &state
->cfa
;
1386 struct stack_op
*op
= &insn
->stack_op
;
1388 if (cfa
->base
!= CFI_SP
)
1392 if (op
->dest
.type
== OP_DEST_PUSH
|| op
->dest
.type
== OP_DEST_PUSHF
)
1396 if (op
->src
.type
== OP_SRC_POP
|| op
->src
.type
== OP_SRC_POPF
)
1399 /* add immediate to sp */
1400 if (op
->dest
.type
== OP_DEST_REG
&& op
->src
.type
== OP_SRC_ADD
&&
1401 op
->dest
.reg
== CFI_SP
&& op
->src
.reg
== CFI_SP
)
1402 cfa
->offset
-= op
->src
.offset
;
1407 static void save_reg(struct insn_state
*state
, unsigned char reg
, int base
,
1410 if (arch_callee_saved_reg(reg
) &&
1411 state
->regs
[reg
].base
== CFI_UNDEFINED
) {
1412 state
->regs
[reg
].base
= base
;
1413 state
->regs
[reg
].offset
= offset
;
1417 static void restore_reg(struct insn_state
*state
, unsigned char reg
)
1419 state
->regs
[reg
].base
= CFI_UNDEFINED
;
1420 state
->regs
[reg
].offset
= 0;
1424 * A note about DRAP stack alignment:
1426 * GCC has the concept of a DRAP register, which is used to help keep track of
1427 * the stack pointer when aligning the stack. r10 or r13 is used as the DRAP
1428 * register. The typical DRAP pattern is:
1430 * 4c 8d 54 24 08 lea 0x8(%rsp),%r10
1431 * 48 83 e4 c0 and $0xffffffffffffffc0,%rsp
1432 * 41 ff 72 f8 pushq -0x8(%r10)
1434 * 48 89 e5 mov %rsp,%rbp
1441 * 49 8d 62 f8 lea -0x8(%r10),%rsp
1444 * There are some variations in the epilogues, like:
1452 * 49 8d 62 f8 lea -0x8(%r10),%rsp
1457 * 4c 8b 55 e8 mov -0x18(%rbp),%r10
1458 * 48 8b 5d e0 mov -0x20(%rbp),%rbx
1459 * 4c 8b 65 f0 mov -0x10(%rbp),%r12
1460 * 4c 8b 6d f8 mov -0x8(%rbp),%r13
1462 * 49 8d 62 f8 lea -0x8(%r10),%rsp
1465 * Sometimes r13 is used as the DRAP register, in which case it's saved and
1466 * restored beforehand:
1469 * 4c 8d 6c 24 10 lea 0x10(%rsp),%r13
1470 * 48 83 e4 f0 and $0xfffffffffffffff0,%rsp
1472 * 49 8d 65 f0 lea -0x10(%r13),%rsp
1476 static int update_insn_state(struct instruction
*insn
, struct insn_state
*state
)
1478 struct stack_op
*op
= &insn
->stack_op
;
1479 struct cfi_reg
*cfa
= &state
->cfa
;
1480 struct cfi_reg
*regs
= state
->regs
;
1482 /* stack operations don't make sense with an undefined CFA */
1483 if (cfa
->base
== CFI_UNDEFINED
) {
1485 WARN_FUNC("undefined stack state", insn
->sec
, insn
->offset
);
1491 if (state
->type
== ORC_TYPE_REGS
|| state
->type
== ORC_TYPE_REGS_IRET
)
1492 return update_insn_state_regs(insn
, state
);
1494 switch (op
->dest
.type
) {
1497 switch (op
->src
.type
) {
1500 if (op
->src
.reg
== CFI_SP
&& op
->dest
.reg
== CFI_BP
&&
1501 cfa
->base
== CFI_SP
&&
1502 regs
[CFI_BP
].base
== CFI_CFA
&&
1503 regs
[CFI_BP
].offset
== -cfa
->offset
) {
1505 /* mov %rsp, %rbp */
1506 cfa
->base
= op
->dest
.reg
;
1507 state
->bp_scratch
= false;
1510 else if (op
->src
.reg
== CFI_SP
&&
1511 op
->dest
.reg
== CFI_BP
&& state
->drap
) {
1513 /* drap: mov %rsp, %rbp */
1514 regs
[CFI_BP
].base
= CFI_BP
;
1515 regs
[CFI_BP
].offset
= -state
->stack_size
;
1516 state
->bp_scratch
= false;
1519 else if (op
->src
.reg
== CFI_SP
&& cfa
->base
== CFI_SP
) {
1524 * This is needed for the rare case where GCC
1531 state
->vals
[op
->dest
.reg
].base
= CFI_CFA
;
1532 state
->vals
[op
->dest
.reg
].offset
= -state
->stack_size
;
1535 else if (op
->src
.reg
== CFI_BP
&& op
->dest
.reg
== CFI_SP
&&
1536 cfa
->base
== CFI_BP
) {
1541 * Restore the original stack pointer (Clang).
1543 state
->stack_size
= -state
->regs
[CFI_BP
].offset
;
1546 else if (op
->dest
.reg
== cfa
->base
) {
1548 /* mov %reg, %rsp */
1549 if (cfa
->base
== CFI_SP
&&
1550 state
->vals
[op
->src
.reg
].base
== CFI_CFA
) {
1553 * This is needed for the rare case
1554 * where GCC does something dumb like:
1556 * lea 0x8(%rsp), %rcx
1560 cfa
->offset
= -state
->vals
[op
->src
.reg
].offset
;
1561 state
->stack_size
= cfa
->offset
;
1564 cfa
->base
= CFI_UNDEFINED
;
1572 if (op
->dest
.reg
== CFI_SP
&& op
->src
.reg
== CFI_SP
) {
1575 state
->stack_size
-= op
->src
.offset
;
1576 if (cfa
->base
== CFI_SP
)
1577 cfa
->offset
-= op
->src
.offset
;
1581 if (op
->dest
.reg
== CFI_SP
&& op
->src
.reg
== CFI_BP
) {
1583 /* lea disp(%rbp), %rsp */
1584 state
->stack_size
= -(op
->src
.offset
+ regs
[CFI_BP
].offset
);
1588 if (op
->src
.reg
== CFI_SP
&& cfa
->base
== CFI_SP
) {
1590 /* drap: lea disp(%rsp), %drap */
1591 state
->drap_reg
= op
->dest
.reg
;
1594 * lea disp(%rsp), %reg
1596 * This is needed for the rare case where GCC
1597 * does something dumb like:
1599 * lea 0x8(%rsp), %rcx
1603 state
->vals
[op
->dest
.reg
].base
= CFI_CFA
;
1604 state
->vals
[op
->dest
.reg
].offset
= \
1605 -state
->stack_size
+ op
->src
.offset
;
1610 if (state
->drap
&& op
->dest
.reg
== CFI_SP
&&
1611 op
->src
.reg
== state
->drap_reg
) {
1613 /* drap: lea disp(%drap), %rsp */
1615 cfa
->offset
= state
->stack_size
= -op
->src
.offset
;
1616 state
->drap_reg
= CFI_UNDEFINED
;
1617 state
->drap
= false;
1621 if (op
->dest
.reg
== state
->cfa
.base
) {
1622 WARN_FUNC("unsupported stack register modification",
1623 insn
->sec
, insn
->offset
);
1630 if (op
->dest
.reg
!= CFI_SP
||
1631 (state
->drap_reg
!= CFI_UNDEFINED
&& cfa
->base
!= CFI_SP
) ||
1632 (state
->drap_reg
== CFI_UNDEFINED
&& cfa
->base
!= CFI_BP
)) {
1633 WARN_FUNC("unsupported stack pointer realignment",
1634 insn
->sec
, insn
->offset
);
1638 if (state
->drap_reg
!= CFI_UNDEFINED
) {
1639 /* drap: and imm, %rsp */
1640 cfa
->base
= state
->drap_reg
;
1641 cfa
->offset
= state
->stack_size
= 0;
1646 * Older versions of GCC (4.8ish) realign the stack
1647 * without DRAP, with a frame pointer.
1654 if (!state
->drap
&& op
->dest
.type
== OP_DEST_REG
&&
1655 op
->dest
.reg
== cfa
->base
) {
1661 if (state
->drap
&& cfa
->base
== CFI_BP_INDIRECT
&&
1662 op
->dest
.type
== OP_DEST_REG
&&
1663 op
->dest
.reg
== state
->drap_reg
&&
1664 state
->drap_offset
== -state
->stack_size
) {
1666 /* drap: pop %drap */
1667 cfa
->base
= state
->drap_reg
;
1669 state
->drap_offset
= -1;
1671 } else if (regs
[op
->dest
.reg
].offset
== -state
->stack_size
) {
1674 restore_reg(state
, op
->dest
.reg
);
1677 state
->stack_size
-= 8;
1678 if (cfa
->base
== CFI_SP
)
1683 case OP_SRC_REG_INDIRECT
:
1684 if (state
->drap
&& op
->src
.reg
== CFI_BP
&&
1685 op
->src
.offset
== state
->drap_offset
) {
1687 /* drap: mov disp(%rbp), %drap */
1688 cfa
->base
= state
->drap_reg
;
1690 state
->drap_offset
= -1;
1693 if (state
->drap
&& op
->src
.reg
== CFI_BP
&&
1694 op
->src
.offset
== regs
[op
->dest
.reg
].offset
) {
1696 /* drap: mov disp(%rbp), %reg */
1697 restore_reg(state
, op
->dest
.reg
);
1699 } else if (op
->src
.reg
== cfa
->base
&&
1700 op
->src
.offset
== regs
[op
->dest
.reg
].offset
+ cfa
->offset
) {
1702 /* mov disp(%rbp), %reg */
1703 /* mov disp(%rsp), %reg */
1704 restore_reg(state
, op
->dest
.reg
);
1710 WARN_FUNC("unknown stack-related instruction",
1711 insn
->sec
, insn
->offset
);
1719 state
->stack_size
+= 8;
1720 if (cfa
->base
== CFI_SP
)
1723 if (op
->src
.type
!= OP_SRC_REG
)
1727 if (op
->src
.reg
== cfa
->base
&& op
->src
.reg
== state
->drap_reg
) {
1729 /* drap: push %drap */
1730 cfa
->base
= CFI_BP_INDIRECT
;
1731 cfa
->offset
= -state
->stack_size
;
1733 /* save drap so we know when to restore it */
1734 state
->drap_offset
= -state
->stack_size
;
1736 } else if (op
->src
.reg
== CFI_BP
&& cfa
->base
== state
->drap_reg
) {
1738 /* drap: push %rbp */
1739 state
->stack_size
= 0;
1741 } else if (regs
[op
->src
.reg
].base
== CFI_UNDEFINED
) {
1743 /* drap: push %reg */
1744 save_reg(state
, op
->src
.reg
, CFI_BP
, -state
->stack_size
);
1750 save_reg(state
, op
->src
.reg
, CFI_CFA
, -state
->stack_size
);
1753 /* detect when asm code uses rbp as a scratch register */
1754 if (!no_fp
&& insn
->func
&& op
->src
.reg
== CFI_BP
&&
1755 cfa
->base
!= CFI_BP
)
1756 state
->bp_scratch
= true;
1759 case OP_DEST_REG_INDIRECT
:
1762 if (op
->src
.reg
== cfa
->base
&& op
->src
.reg
== state
->drap_reg
) {
1764 /* drap: mov %drap, disp(%rbp) */
1765 cfa
->base
= CFI_BP_INDIRECT
;
1766 cfa
->offset
= op
->dest
.offset
;
1768 /* save drap offset so we know when to restore it */
1769 state
->drap_offset
= op
->dest
.offset
;
1772 else if (regs
[op
->src
.reg
].base
== CFI_UNDEFINED
) {
1774 /* drap: mov reg, disp(%rbp) */
1775 save_reg(state
, op
->src
.reg
, CFI_BP
, op
->dest
.offset
);
1778 } else if (op
->dest
.reg
== cfa
->base
) {
1780 /* mov reg, disp(%rbp) */
1781 /* mov reg, disp(%rsp) */
1782 save_reg(state
, op
->src
.reg
, CFI_CFA
,
1783 op
->dest
.offset
- state
->cfa
.offset
);
1789 if ((!state
->drap
&& cfa
->base
!= CFI_BP
) ||
1790 (state
->drap
&& cfa
->base
!= state
->drap_reg
)) {
1791 WARN_FUNC("leave instruction with modified stack frame",
1792 insn
->sec
, insn
->offset
);
1796 /* leave (mov %rbp, %rsp; pop %rbp) */
1798 state
->stack_size
= -state
->regs
[CFI_BP
].offset
- 8;
1799 restore_reg(state
, CFI_BP
);
1809 if (op
->src
.type
!= OP_SRC_POP
&& op
->src
.type
!= OP_SRC_POPF
) {
1810 WARN_FUNC("unknown stack-related memory operation",
1811 insn
->sec
, insn
->offset
);
1816 state
->stack_size
-= 8;
1817 if (cfa
->base
== CFI_SP
)
1823 WARN_FUNC("unknown stack-related instruction",
1824 insn
->sec
, insn
->offset
);
1831 static bool insn_state_match(struct instruction
*insn
, struct insn_state
*state
)
1833 struct insn_state
*state1
= &insn
->state
, *state2
= state
;
1836 if (memcmp(&state1
->cfa
, &state2
->cfa
, sizeof(state1
->cfa
))) {
1837 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1838 insn
->sec
, insn
->offset
,
1839 state1
->cfa
.base
, state1
->cfa
.offset
,
1840 state2
->cfa
.base
, state2
->cfa
.offset
);
1842 } else if (memcmp(&state1
->regs
, &state2
->regs
, sizeof(state1
->regs
))) {
1843 for (i
= 0; i
< CFI_NUM_REGS
; i
++) {
1844 if (!memcmp(&state1
->regs
[i
], &state2
->regs
[i
],
1845 sizeof(struct cfi_reg
)))
1848 WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1849 insn
->sec
, insn
->offset
,
1850 i
, state1
->regs
[i
].base
, state1
->regs
[i
].offset
,
1851 i
, state2
->regs
[i
].base
, state2
->regs
[i
].offset
);
1855 } else if (state1
->type
!= state2
->type
) {
1856 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1857 insn
->sec
, insn
->offset
, state1
->type
, state2
->type
);
1859 } else if (state1
->drap
!= state2
->drap
||
1860 (state1
->drap
&& state1
->drap_reg
!= state2
->drap_reg
) ||
1861 (state1
->drap
&& state1
->drap_offset
!= state2
->drap_offset
)) {
1862 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1863 insn
->sec
, insn
->offset
,
1864 state1
->drap
, state1
->drap_reg
, state1
->drap_offset
,
1865 state2
->drap
, state2
->drap_reg
, state2
->drap_offset
);
1873 static inline bool func_uaccess_safe(struct symbol
*func
)
1876 return func
->alias
->uaccess_safe
;
1881 static inline const char *insn_dest_name(struct instruction
*insn
)
1883 if (insn
->call_dest
)
1884 return insn
->call_dest
->name
;
1889 static int validate_call(struct instruction
*insn
, struct insn_state
*state
)
1891 if (state
->uaccess
&& !func_uaccess_safe(insn
->call_dest
)) {
1892 WARN_FUNC("call to %s() with UACCESS enabled",
1893 insn
->sec
, insn
->offset
, insn_dest_name(insn
));
1898 WARN_FUNC("call to %s() with DF set",
1899 insn
->sec
, insn
->offset
, insn_dest_name(insn
));
1906 static int validate_sibling_call(struct instruction
*insn
, struct insn_state
*state
)
1908 if (has_modified_stack_frame(state
)) {
1909 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1910 insn
->sec
, insn
->offset
);
1914 return validate_call(insn
, state
);
1918 * Follow the branch starting at the given instruction, and recursively follow
1919 * any other branches (jumps). Meanwhile, track the frame pointer state at
1920 * each instruction and validate all the rules described in
1921 * tools/objtool/Documentation/stack-validation.txt.
1923 static int validate_branch(struct objtool_file
*file
, struct instruction
*first
,
1924 struct insn_state state
)
1926 struct alternative
*alt
;
1927 struct instruction
*insn
, *next_insn
;
1928 struct section
*sec
;
1929 struct symbol
*func
= NULL
;
1935 if (insn
->alt_group
&& list_empty(&insn
->alts
)) {
1936 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
1942 next_insn
= next_insn_same_sec(file
, insn
);
1944 if (file
->c_file
&& func
&& insn
->func
&& func
!= insn
->func
->pfunc
) {
1945 WARN("%s() falls through to next function %s()",
1946 func
->name
, insn
->func
->name
);
1951 func
= insn
->func
->pfunc
;
1953 if (func
&& insn
->ignore
) {
1954 WARN_FUNC("BUG: why am I validating an ignored function?",
1959 if (insn
->visited
) {
1960 if (!insn
->hint
&& !insn_state_match(insn
, &state
))
1963 /* If we were here with AC=0, but now have AC=1, go again */
1964 if (insn
->state
.uaccess
|| !state
.uaccess
)
1969 if (insn
->restore
) {
1970 struct instruction
*save_insn
, *i
;
1974 func_for_each_insn_continue_reverse(file
, insn
->func
, i
) {
1982 WARN_FUNC("no corresponding CFI save for CFI restore",
1987 if (!save_insn
->visited
) {
1989 * Oops, no state to copy yet.
1990 * Hopefully we can reach this
1991 * instruction from another branch
1992 * after the save insn has been
1998 WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
2003 insn
->state
= save_insn
->state
;
2006 state
= insn
->state
;
2009 insn
->state
= state
;
2011 insn
->visited
= true;
2013 if (!insn
->ignore_alts
) {
2014 bool skip_orig
= false;
2016 list_for_each_entry(alt
, &insn
->alts
, list
) {
2020 ret
= validate_branch(file
, alt
->insn
, state
);
2023 BT_FUNC("(alt)", insn
);
2032 switch (insn
->type
) {
2035 if (state
.uaccess
&& !func_uaccess_safe(func
)) {
2036 WARN_FUNC("return with UACCESS enabled", sec
, insn
->offset
);
2040 if (!state
.uaccess
&& func_uaccess_safe(func
)) {
2041 WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function", sec
, insn
->offset
);
2046 WARN_FUNC("return with DF set", sec
, insn
->offset
);
2050 if (func
&& has_modified_stack_frame(&state
)) {
2051 WARN_FUNC("return with modified stack frame",
2056 if (state
.bp_scratch
) {
2057 WARN("%s uses BP as a scratch register",
2065 case INSN_CALL_DYNAMIC
:
2066 ret
= validate_call(insn
, &state
);
2070 if (insn
->type
== INSN_CALL
) {
2071 if (is_fentry_call(insn
))
2074 ret
= dead_end_function(file
, insn
->call_dest
);
2081 if (!no_fp
&& func
&& !has_valid_stack_frame(&state
)) {
2082 WARN_FUNC("call without frame pointer save/setup",
2088 case INSN_JUMP_CONDITIONAL
:
2089 case INSN_JUMP_UNCONDITIONAL
:
2090 if (func
&& !insn
->jump_dest
) {
2091 ret
= validate_sibling_call(insn
, &state
);
2095 } else if (insn
->jump_dest
&&
2096 (!func
|| !insn
->jump_dest
->func
||
2097 insn
->jump_dest
->func
->pfunc
== func
)) {
2098 ret
= validate_branch(file
, insn
->jump_dest
,
2102 BT_FUNC("(branch)", insn
);
2107 if (insn
->type
== INSN_JUMP_UNCONDITIONAL
)
2112 case INSN_JUMP_DYNAMIC
:
2113 if (func
&& list_empty(&insn
->alts
)) {
2114 ret
= validate_sibling_call(insn
, &state
);
2121 case INSN_CONTEXT_SWITCH
:
2122 if (func
&& (!next_insn
|| !next_insn
->hint
)) {
2123 WARN_FUNC("unsupported instruction in callable function",
2130 if (update_insn_state(insn
, &state
))
2133 if (insn
->stack_op
.dest
.type
== OP_DEST_PUSHF
) {
2134 if (!state
.uaccess_stack
) {
2135 state
.uaccess_stack
= 1;
2136 } else if (state
.uaccess_stack
>> 31) {
2137 WARN_FUNC("PUSHF stack exhausted", sec
, insn
->offset
);
2140 state
.uaccess_stack
<<= 1;
2141 state
.uaccess_stack
|= state
.uaccess
;
2144 if (insn
->stack_op
.src
.type
== OP_SRC_POPF
) {
2145 if (state
.uaccess_stack
) {
2146 state
.uaccess
= state
.uaccess_stack
& 1;
2147 state
.uaccess_stack
>>= 1;
2148 if (state
.uaccess_stack
== 1)
2149 state
.uaccess_stack
= 0;
2156 if (state
.uaccess
) {
2157 WARN_FUNC("recursive UACCESS enable", sec
, insn
->offset
);
2161 state
.uaccess
= true;
2165 if (!state
.uaccess
&& insn
->func
) {
2166 WARN_FUNC("redundant UACCESS disable", sec
, insn
->offset
);
2170 if (func_uaccess_safe(func
) && !state
.uaccess_stack
) {
2171 WARN_FUNC("UACCESS-safe disables UACCESS", sec
, insn
->offset
);
2175 state
.uaccess
= false;
2180 WARN_FUNC("recursive STD", sec
, insn
->offset
);
2186 if (!state
.df
&& insn
->func
)
2187 WARN_FUNC("redundant CLD", sec
, insn
->offset
);
2200 if (state
.cfa
.base
== CFI_UNDEFINED
)
2202 WARN("%s: unexpected end of section", sec
->name
);
2212 static int validate_unwind_hints(struct objtool_file
*file
)
2214 struct instruction
*insn
;
2215 int ret
, warnings
= 0;
2216 struct insn_state state
;
2221 clear_insn_state(&state
);
2223 for_each_insn(file
, insn
) {
2224 if (insn
->hint
&& !insn
->visited
) {
2225 ret
= validate_branch(file
, insn
, state
);
2226 if (ret
&& backtrace
)
2227 BT_FUNC("<=== (hint)", insn
);
2235 static int validate_retpoline(struct objtool_file
*file
)
2237 struct instruction
*insn
;
2240 for_each_insn(file
, insn
) {
2241 if (insn
->type
!= INSN_JUMP_DYNAMIC
&&
2242 insn
->type
!= INSN_CALL_DYNAMIC
)
2245 if (insn
->retpoline_safe
)
2249 * .init.text code is ran before userspace and thus doesn't
2250 * strictly need retpolines, except for modules which are
2251 * loaded late, they very much do need retpoline in their
2254 if (!strcmp(insn
->sec
->name
, ".init.text") && !module
)
2257 WARN_FUNC("indirect %s found in RETPOLINE build",
2258 insn
->sec
, insn
->offset
,
2259 insn
->type
== INSN_JUMP_DYNAMIC
? "jump" : "call");
2267 static bool is_kasan_insn(struct instruction
*insn
)
2269 return (insn
->type
== INSN_CALL
&&
2270 !strcmp(insn
->call_dest
->name
, "__asan_handle_no_return"));
2273 static bool is_ubsan_insn(struct instruction
*insn
)
2275 return (insn
->type
== INSN_CALL
&&
2276 !strcmp(insn
->call_dest
->name
,
2277 "__ubsan_handle_builtin_unreachable"));
2280 static bool ignore_unreachable_insn(struct instruction
*insn
)
2284 if (insn
->ignore
|| insn
->type
== INSN_NOP
)
2288 * Ignore any unused exceptions. This can happen when a whitelisted
2289 * function has an exception table entry.
2291 * Also ignore alternative replacement instructions. This can happen
2292 * when a whitelisted function uses one of the ALTERNATIVE macros.
2294 if (!strcmp(insn
->sec
->name
, ".fixup") ||
2295 !strcmp(insn
->sec
->name
, ".altinstr_replacement") ||
2296 !strcmp(insn
->sec
->name
, ".altinstr_aux"))
2300 * Check if this (or a subsequent) instruction is related to
2301 * CONFIG_UBSAN or CONFIG_KASAN.
2303 * End the search at 5 instructions to avoid going into the weeds.
2307 for (i
= 0; i
< 5; i
++) {
2309 if (is_kasan_insn(insn
) || is_ubsan_insn(insn
))
2312 if (insn
->type
== INSN_JUMP_UNCONDITIONAL
) {
2313 if (insn
->jump_dest
&&
2314 insn
->jump_dest
->func
== insn
->func
) {
2315 insn
= insn
->jump_dest
;
2322 if (insn
->offset
+ insn
->len
>= insn
->func
->offset
+ insn
->func
->len
)
2325 insn
= list_next_entry(insn
, list
);
2331 static int validate_functions(struct objtool_file
*file
)
2333 struct section
*sec
;
2334 struct symbol
*func
;
2335 struct instruction
*insn
;
2336 struct insn_state state
;
2337 int ret
, warnings
= 0;
2339 clear_insn_state(&state
);
2341 state
.cfa
= initial_func_cfi
.cfa
;
2342 memcpy(&state
.regs
, &initial_func_cfi
.regs
,
2343 CFI_NUM_REGS
* sizeof(struct cfi_reg
));
2344 state
.stack_size
= initial_func_cfi
.cfa
.offset
;
2346 for_each_sec(file
, sec
) {
2347 list_for_each_entry(func
, &sec
->symbol_list
, list
) {
2348 if (func
->type
!= STT_FUNC
|| func
->pfunc
!= func
)
2351 insn
= find_insn(file
, sec
, func
->offset
);
2352 if (!insn
|| insn
->ignore
)
2355 state
.uaccess
= func
->alias
->uaccess_safe
;
2357 ret
= validate_branch(file
, insn
, state
);
2358 if (ret
&& backtrace
)
2359 BT_FUNC("<=== (func)", insn
);
2367 static int validate_reachable_instructions(struct objtool_file
*file
)
2369 struct instruction
*insn
;
2371 if (file
->ignore_unreachables
)
2374 for_each_insn(file
, insn
) {
2375 if (insn
->visited
|| ignore_unreachable_insn(insn
))
2378 WARN_FUNC("unreachable instruction", insn
->sec
, insn
->offset
);
2385 static void cleanup(struct objtool_file
*file
)
2387 struct instruction
*insn
, *tmpinsn
;
2388 struct alternative
*alt
, *tmpalt
;
2390 list_for_each_entry_safe(insn
, tmpinsn
, &file
->insn_list
, list
) {
2391 list_for_each_entry_safe(alt
, tmpalt
, &insn
->alts
, list
) {
2392 list_del(&alt
->list
);
2395 list_del(&insn
->list
);
2396 hash_del(&insn
->hash
);
2399 elf_close(file
->elf
);
2402 static struct objtool_file file
;
2404 int check(const char *_objname
, bool orc
)
2406 int ret
, warnings
= 0;
2410 file
.elf
= elf_open(objname
, orc
? O_RDWR
: O_RDONLY
);
2414 INIT_LIST_HEAD(&file
.insn_list
);
2415 hash_init(file
.insn_hash
);
2416 file
.c_file
= find_section_by_name(file
.elf
, ".comment");
2417 file
.ignore_unreachables
= no_unreachable
;
2420 arch_initial_func_cfi_state(&initial_func_cfi
);
2422 ret
= decode_sections(&file
);
2427 if (list_empty(&file
.insn_list
))
2431 ret
= validate_retpoline(&file
);
2437 ret
= validate_functions(&file
);
2442 ret
= validate_unwind_hints(&file
);
2448 ret
= validate_reachable_instructions(&file
);
2455 ret
= create_orc(&file
);
2459 ret
= create_orc_sections(&file
);
2463 ret
= elf_write(file
.elf
);
2471 /* ignore warnings for now until we get all the code cleaned up */
2472 if (ret
|| warnings
)