check.c 51.2 KB
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/*
 * Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 */

#include <string.h>
#include <stdlib.h>

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#include "builtin.h"
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#include "check.h"
#include "elf.h"
#include "special.h"
#include "arch.h"
#include "warn.h"

#include <linux/hashtable.h>
#include <linux/kernel.h>

struct alternative {
	struct list_head list;
	struct instruction *insn;
};

const char *objname;
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struct cfi_state initial_func_cfi;
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struct instruction *find_insn(struct objtool_file *file,
			      struct section *sec, unsigned long offset)
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{
	struct instruction *insn;

	hash_for_each_possible(file->insn_hash, insn, hash, offset)
		if (insn->sec == sec && insn->offset == offset)
			return insn;

	return NULL;
}

static struct instruction *next_insn_same_sec(struct objtool_file *file,
					      struct instruction *insn)
{
	struct instruction *next = list_next_entry(insn, list);

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	if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
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		return NULL;

	return next;
}

#define func_for_each_insn(file, func, insn)				\
	for (insn = find_insn(file, func->sec, func->offset);		\
	     insn && &insn->list != &file->insn_list &&			\
		insn->sec == func->sec &&				\
		insn->offset < func->offset + func->len;		\
	     insn = list_next_entry(insn, list))

#define func_for_each_insn_continue_reverse(file, func, insn)		\
	for (insn = list_prev_entry(insn, list);			\
	     &insn->list != &file->insn_list &&				\
		insn->sec == func->sec && insn->offset >= func->offset;	\
	     insn = list_prev_entry(insn, list))

#define sec_for_each_insn_from(file, insn)				\
	for (; insn; insn = next_insn_same_sec(file, insn))

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#define sec_for_each_insn_continue(file, insn)				\
	for (insn = next_insn_same_sec(file, insn); insn;		\
	     insn = next_insn_same_sec(file, insn))
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/*
 * Check if the function has been manually whitelisted with the
 * STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted
 * due to its use of a context switching instruction.
 */
static bool ignore_func(struct objtool_file *file, struct symbol *func)
{
	struct rela *rela;

	/* check for STACK_FRAME_NON_STANDARD */
	if (file->whitelist && file->whitelist->rela)
		list_for_each_entry(rela, &file->whitelist->rela->rela_list, list) {
			if (rela->sym->type == STT_SECTION &&
			    rela->sym->sec == func->sec &&
			    rela->addend == func->offset)
				return true;
			if (rela->sym->type == STT_FUNC && rela->sym == func)
				return true;
		}

	return false;
}

/*
 * This checks to see if the given function is a "noreturn" function.
 *
 * For global functions which are outside the scope of this object file, we
 * have to keep a manual list of them.
 *
 * For local functions, we have to detect them manually by simply looking for
 * the lack of a return instruction.
 *
 * Returns:
 *  -1: error
 *   0: no dead end
 *   1: dead end
 */
static int __dead_end_function(struct objtool_file *file, struct symbol *func,
			       int recursion)
{
	int i;
	struct instruction *insn;
	bool empty = true;

	/*
	 * Unfortunately these have to be hard coded because the noreturn
	 * attribute isn't provided in ELF data.
	 */
	static const char * const global_noreturns[] = {
		"__stack_chk_fail",
		"panic",
		"do_exit",
		"do_task_dead",
		"__module_put_and_exit",
		"complete_and_exit",
		"kvm_spurious_fault",
		"__reiserfs_panic",
		"lbug_with_loc",
		"fortify_panic",
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		"usercopy_abort",
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	};

	if (func->bind == STB_WEAK)
		return 0;

	if (func->bind == STB_GLOBAL)
		for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
			if (!strcmp(func->name, global_noreturns[i]))
				return 1;

	if (!func->sec)
		return 0;

	func_for_each_insn(file, func, insn) {
		empty = false;

		if (insn->type == INSN_RETURN)
			return 0;
	}

	if (empty)
		return 0;

	/*
	 * A function can have a sibling call instead of a return.  In that
	 * case, the function's dead-end status depends on whether the target
	 * of the sibling call returns.
	 */
	func_for_each_insn(file, func, insn) {
		if (insn->sec != func->sec ||
		    insn->offset >= func->offset + func->len)
			break;

		if (insn->type == INSN_JUMP_UNCONDITIONAL) {
			struct instruction *dest = insn->jump_dest;
			struct symbol *dest_func;

			if (!dest)
				/* sibling call to another file */
				return 0;

			if (dest->sec != func->sec ||
			    dest->offset < func->offset ||
			    dest->offset >= func->offset + func->len) {
				/* local sibling call */
				dest_func = find_symbol_by_offset(dest->sec,
								  dest->offset);
				if (!dest_func)
					continue;

				if (recursion == 5) {
					WARN_FUNC("infinite recursion (objtool bug!)",
						  dest->sec, dest->offset);
					return -1;
				}

				return __dead_end_function(file, dest_func,
							   recursion + 1);
			}
		}

		if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
			/* sibling call */
			return 0;
	}

	return 1;
}

static int dead_end_function(struct objtool_file *file, struct symbol *func)
{
	return __dead_end_function(file, func, 0);
}

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static void clear_insn_state(struct insn_state *state)
{
	int i;

	memset(state, 0, sizeof(*state));
	state->cfa.base = CFI_UNDEFINED;
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	for (i = 0; i < CFI_NUM_REGS; i++) {
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		state->regs[i].base = CFI_UNDEFINED;
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		state->vals[i].base = CFI_UNDEFINED;
	}
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	state->drap_reg = CFI_UNDEFINED;
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	state->drap_offset = -1;
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}

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/*
 * Call the arch-specific instruction decoder for all the instructions and add
 * them to the global instruction list.
 */
static int decode_instructions(struct objtool_file *file)
{
	struct section *sec;
	struct symbol *func;
	unsigned long offset;
	struct instruction *insn;
	int ret;

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	for_each_sec(file, sec) {
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		if (!(sec->sh.sh_flags & SHF_EXECINSTR))
			continue;

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		if (strcmp(sec->name, ".altinstr_replacement") &&
		    strcmp(sec->name, ".altinstr_aux") &&
		    strncmp(sec->name, ".discard.", 9))
			sec->text = true;

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		for (offset = 0; offset < sec->len; offset += insn->len) {
			insn = malloc(sizeof(*insn));
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			if (!insn) {
				WARN("malloc failed");
				return -1;
			}
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			memset(insn, 0, sizeof(*insn));
			INIT_LIST_HEAD(&insn->alts);
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			clear_insn_state(&insn->state);

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			insn->sec = sec;
			insn->offset = offset;

			ret = arch_decode_instruction(file->elf, sec, offset,
						      sec->len - offset,
						      &insn->len, &insn->type,
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						      &insn->immediate,
						      &insn->stack_op);
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			if (ret)
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				goto err;
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			if (!insn->type || insn->type > INSN_LAST) {
				WARN_FUNC("invalid instruction type %d",
					  insn->sec, insn->offset, insn->type);
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				ret = -1;
				goto err;
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			}

			hash_add(file->insn_hash, &insn->hash, insn->offset);
			list_add_tail(&insn->list, &file->insn_list);
		}

		list_for_each_entry(func, &sec->symbol_list, list) {
			if (func->type != STT_FUNC)
				continue;

			if (!find_insn(file, sec, func->offset)) {
				WARN("%s(): can't find starting instruction",
				     func->name);
				return -1;
			}

			func_for_each_insn(file, func, insn)
				if (!insn->func)
					insn->func = func;
		}
	}

	return 0;
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err:
	free(insn);
	return ret;
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}

/*
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 * Mark "ud2" instructions and manually annotated dead ends.
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 */
static int add_dead_ends(struct objtool_file *file)
{
	struct section *sec;
	struct rela *rela;
	struct instruction *insn;
	bool found;

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	/*
	 * By default, "ud2" is a dead end unless otherwise annotated, because
	 * GCC 7 inserts it for certain divide-by-zero cases.
	 */
	for_each_insn(file, insn)
		if (insn->type == INSN_BUG)
			insn->dead_end = true;

	/*
	 * Check for manually annotated dead ends.
	 */
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	sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
	if (!sec)
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		goto reachable;
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	list_for_each_entry(rela, &sec->rela_list, list) {
		if (rela->sym->type != STT_SECTION) {
			WARN("unexpected relocation symbol type in %s", sec->name);
			return -1;
		}
		insn = find_insn(file, rela->sym->sec, rela->addend);
		if (insn)
			insn = list_prev_entry(insn, list);
		else if (rela->addend == rela->sym->sec->len) {
			found = false;
			list_for_each_entry_reverse(insn, &file->insn_list, list) {
				if (insn->sec == rela->sym->sec) {
					found = true;
					break;
				}
			}

			if (!found) {
				WARN("can't find unreachable insn at %s+0x%x",
				     rela->sym->sec->name, rela->addend);
				return -1;
			}
		} else {
			WARN("can't find unreachable insn at %s+0x%x",
			     rela->sym->sec->name, rela->addend);
			return -1;
		}

		insn->dead_end = true;
	}

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reachable:
	/*
	 * These manually annotated reachable checks are needed for GCC 4.4,
	 * where the Linux unreachable() macro isn't supported.  In that case
	 * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
	 * not a dead end.
	 */
	sec = find_section_by_name(file->elf, ".rela.discard.reachable");
	if (!sec)
		return 0;

	list_for_each_entry(rela, &sec->rela_list, list) {
		if (rela->sym->type != STT_SECTION) {
			WARN("unexpected relocation symbol type in %s", sec->name);
			return -1;
		}
		insn = find_insn(file, rela->sym->sec, rela->addend);
		if (insn)
			insn = list_prev_entry(insn, list);
		else if (rela->addend == rela->sym->sec->len) {
			found = false;
			list_for_each_entry_reverse(insn, &file->insn_list, list) {
				if (insn->sec == rela->sym->sec) {
					found = true;
					break;
				}
			}

			if (!found) {
				WARN("can't find reachable insn at %s+0x%x",
				     rela->sym->sec->name, rela->addend);
				return -1;
			}
		} else {
			WARN("can't find reachable insn at %s+0x%x",
			     rela->sym->sec->name, rela->addend);
			return -1;
		}

		insn->dead_end = false;
	}

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	return 0;
}

/*
 * Warnings shouldn't be reported for ignored functions.
 */
static void add_ignores(struct objtool_file *file)
{
	struct instruction *insn;
	struct section *sec;
	struct symbol *func;

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	for_each_sec(file, sec) {
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		list_for_each_entry(func, &sec->symbol_list, list) {
			if (func->type != STT_FUNC)
				continue;

			if (!ignore_func(file, func))
				continue;

			func_for_each_insn(file, func, insn)
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				insn->ignore = true;
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		}
	}
}

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/*
 * FIXME: For now, just ignore any alternatives which add retpolines.  This is
 * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
 * But it at least allows objtool to understand the control flow *around* the
 * retpoline.
 */
static int add_nospec_ignores(struct objtool_file *file)
{
	struct section *sec;
	struct rela *rela;
	struct instruction *insn;

	sec = find_section_by_name(file->elf, ".rela.discard.nospec");
	if (!sec)
		return 0;

	list_for_each_entry(rela, &sec->rela_list, list) {
		if (rela->sym->type != STT_SECTION) {
			WARN("unexpected relocation symbol type in %s", sec->name);
			return -1;
		}

		insn = find_insn(file, rela->sym->sec, rela->addend);
		if (!insn) {
			WARN("bad .discard.nospec entry");
			return -1;
		}

		insn->ignore_alts = true;
	}

	return 0;
}

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/*
 * Find the destination instructions for all jumps.
 */
static int add_jump_destinations(struct objtool_file *file)
{
	struct instruction *insn;
	struct rela *rela;
	struct section *dest_sec;
	unsigned long dest_off;

	for_each_insn(file, insn) {
		if (insn->type != INSN_JUMP_CONDITIONAL &&
		    insn->type != INSN_JUMP_UNCONDITIONAL)
			continue;

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		if (insn->ignore)
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			continue;

		rela = find_rela_by_dest_range(insn->sec, insn->offset,
					       insn->len);
		if (!rela) {
			dest_sec = insn->sec;
			dest_off = insn->offset + insn->len + insn->immediate;
		} else if (rela->sym->type == STT_SECTION) {
			dest_sec = rela->sym->sec;
			dest_off = rela->addend + 4;
		} else if (rela->sym->sec->idx) {
			dest_sec = rela->sym->sec;
			dest_off = rela->sym->sym.st_value + rela->addend + 4;
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		} else if (strstr(rela->sym->name, "_indirect_thunk_")) {
			/*
			 * Retpoline jumps are really dynamic jumps in
			 * disguise, so convert them accordingly.
			 */
			insn->type = INSN_JUMP_DYNAMIC;
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			insn->retpoline_safe = true;
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			continue;
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		} else {
			/* sibling call */
			insn->jump_dest = 0;
			continue;
		}

		insn->jump_dest = find_insn(file, dest_sec, dest_off);
		if (!insn->jump_dest) {

			/*
			 * This is a special case where an alt instruction
			 * jumps past the end of the section.  These are
			 * handled later in handle_group_alt().
			 */
			if (!strcmp(insn->sec->name, ".altinstr_replacement"))
				continue;

			WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
				  insn->sec, insn->offset, dest_sec->name,
				  dest_off);
			return -1;
		}
	}

	return 0;
}

/*
 * Find the destination instructions for all calls.
 */
static int add_call_destinations(struct objtool_file *file)
{
	struct instruction *insn;
	unsigned long dest_off;
	struct rela *rela;

	for_each_insn(file, insn) {
		if (insn->type != INSN_CALL)
			continue;

		rela = find_rela_by_dest_range(insn->sec, insn->offset,
					       insn->len);
		if (!rela) {
			dest_off = insn->offset + insn->len + insn->immediate;
			insn->call_dest = find_symbol_by_offset(insn->sec,
								dest_off);
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			if (!insn->call_dest && !insn->ignore) {
				WARN_FUNC("unsupported intra-function call",
					  insn->sec, insn->offset);
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				if (retpoline)
					WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
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				return -1;
			}
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		} else if (rela->sym->type == STT_SECTION) {
			insn->call_dest = find_symbol_by_offset(rela->sym->sec,
								rela->addend+4);
			if (!insn->call_dest ||
			    insn->call_dest->type != STT_FUNC) {
				WARN_FUNC("can't find call dest symbol at %s+0x%x",
					  insn->sec, insn->offset,
					  rela->sym->sec->name,
					  rela->addend + 4);
				return -1;
			}
		} else
			insn->call_dest = rela->sym;
	}

	return 0;
}

/*
 * The .alternatives section requires some extra special care, over and above
 * what other special sections require:
 *
 * 1. Because alternatives are patched in-place, we need to insert a fake jump
 *    instruction at the end so that validate_branch() skips all the original
 *    replaced instructions when validating the new instruction path.
 *
 * 2. An added wrinkle is that the new instruction length might be zero.  In
 *    that case the old instructions are replaced with noops.  We simulate that
 *    by creating a fake jump as the only new instruction.
 *
 * 3. In some cases, the alternative section includes an instruction which
 *    conditionally jumps to the _end_ of the entry.  We have to modify these
 *    jumps' destinations to point back to .text rather than the end of the
 *    entry in .altinstr_replacement.
 *
 * 4. It has been requested that we don't validate the !POPCNT feature path
 *    which is a "very very small percentage of machines".
 */
static int handle_group_alt(struct objtool_file *file,
			    struct special_alt *special_alt,
			    struct instruction *orig_insn,
			    struct instruction **new_insn)
{
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	struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
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	unsigned long dest_off;

	last_orig_insn = NULL;
	insn = orig_insn;
	sec_for_each_insn_from(file, insn) {
		if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
			break;

		if (special_alt->skip_orig)
			insn->type = INSN_NOP;

		insn->alt_group = true;
		last_orig_insn = insn;
	}

616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
	if (next_insn_same_sec(file, last_orig_insn)) {
		fake_jump = malloc(sizeof(*fake_jump));
		if (!fake_jump) {
			WARN("malloc failed");
			return -1;
		}
		memset(fake_jump, 0, sizeof(*fake_jump));
		INIT_LIST_HEAD(&fake_jump->alts);
		clear_insn_state(&fake_jump->state);

		fake_jump->sec = special_alt->new_sec;
		fake_jump->offset = -1;
		fake_jump->type = INSN_JUMP_UNCONDITIONAL;
		fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
		fake_jump->ignore = true;
631
632
633
	}

	if (!special_alt->new_len) {
634
635
636
637
638
639
		if (!fake_jump) {
			WARN("%s: empty alternative at end of section",
			     special_alt->orig_sec->name);
			return -1;
		}

640
641
642
643
644
645
646
647
648
649
650
651
		*new_insn = fake_jump;
		return 0;
	}

	last_new_insn = NULL;
	insn = *new_insn;
	sec_for_each_insn_from(file, insn) {
		if (insn->offset >= special_alt->new_off + special_alt->new_len)
			break;

		last_new_insn = insn;

652
653
		insn->ignore = orig_insn->ignore_alts;

654
655
656
657
658
659
660
661
		if (insn->type != INSN_JUMP_CONDITIONAL &&
		    insn->type != INSN_JUMP_UNCONDITIONAL)
			continue;

		if (!insn->immediate)
			continue;

		dest_off = insn->offset + insn->len + insn->immediate;
662
663
664
665
666
667
		if (dest_off == special_alt->new_off + special_alt->new_len) {
			if (!fake_jump) {
				WARN("%s: alternative jump to end of section",
				     special_alt->orig_sec->name);
				return -1;
			}
668
			insn->jump_dest = fake_jump;
669
		}
670
671
672
673
674
675
676
677
678
679
680
681
682
683

		if (!insn->jump_dest) {
			WARN_FUNC("can't find alternative jump destination",
				  insn->sec, insn->offset);
			return -1;
		}
	}

	if (!last_new_insn) {
		WARN_FUNC("can't find last new alternative instruction",
			  special_alt->new_sec, special_alt->new_off);
		return -1;
	}

684
685
	if (fake_jump)
		list_add(&fake_jump->list, &last_new_insn->list);
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
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751
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753
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760
761
762
763
764
765
766

	return 0;
}

/*
 * A jump table entry can either convert a nop to a jump or a jump to a nop.
 * If the original instruction is a jump, make the alt entry an effective nop
 * by just skipping the original instruction.
 */
static int handle_jump_alt(struct objtool_file *file,
			   struct special_alt *special_alt,
			   struct instruction *orig_insn,
			   struct instruction **new_insn)
{
	if (orig_insn->type == INSN_NOP)
		return 0;

	if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
		WARN_FUNC("unsupported instruction at jump label",
			  orig_insn->sec, orig_insn->offset);
		return -1;
	}

	*new_insn = list_next_entry(orig_insn, list);
	return 0;
}

/*
 * Read all the special sections which have alternate instructions which can be
 * patched in or redirected to at runtime.  Each instruction having alternate
 * instruction(s) has them added to its insn->alts list, which will be
 * traversed in validate_branch().
 */
static int add_special_section_alts(struct objtool_file *file)
{
	struct list_head special_alts;
	struct instruction *orig_insn, *new_insn;
	struct special_alt *special_alt, *tmp;
	struct alternative *alt;
	int ret;

	ret = special_get_alts(file->elf, &special_alts);
	if (ret)
		return ret;

	list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {

		orig_insn = find_insn(file, special_alt->orig_sec,
				      special_alt->orig_off);
		if (!orig_insn) {
			WARN_FUNC("special: can't find orig instruction",
				  special_alt->orig_sec, special_alt->orig_off);
			ret = -1;
			goto out;
		}

		new_insn = NULL;
		if (!special_alt->group || special_alt->new_len) {
			new_insn = find_insn(file, special_alt->new_sec,
					     special_alt->new_off);
			if (!new_insn) {
				WARN_FUNC("special: can't find new instruction",
					  special_alt->new_sec,
					  special_alt->new_off);
				ret = -1;
				goto out;
			}
		}

		if (special_alt->group) {
			ret = handle_group_alt(file, special_alt, orig_insn,
					       &new_insn);
			if (ret)
				goto out;
		} else if (special_alt->jump_or_nop) {
			ret = handle_jump_alt(file, special_alt, orig_insn,
					      &new_insn);
			if (ret)
				goto out;
		}

767
768
769
770
771
772
773
		alt = malloc(sizeof(*alt));
		if (!alt) {
			WARN("malloc failed");
			ret = -1;
			goto out;
		}

774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
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795
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802
803
804
805
806
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811
812
813
814
815
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817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
		alt->insn = new_insn;
		list_add_tail(&alt->list, &orig_insn->alts);

		list_del(&special_alt->list);
		free(special_alt);
	}

out:
	return ret;
}

static int add_switch_table(struct objtool_file *file, struct symbol *func,
			    struct instruction *insn, struct rela *table,
			    struct rela *next_table)
{
	struct rela *rela = table;
	struct instruction *alt_insn;
	struct alternative *alt;

	list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
		if (rela == next_table)
			break;

		if (rela->sym->sec != insn->sec ||
		    rela->addend <= func->offset ||
		    rela->addend >= func->offset + func->len)
			break;

		alt_insn = find_insn(file, insn->sec, rela->addend);
		if (!alt_insn) {
			WARN("%s: can't find instruction at %s+0x%x",
			     file->rodata->rela->name, insn->sec->name,
			     rela->addend);
			return -1;
		}

		alt = malloc(sizeof(*alt));
		if (!alt) {
			WARN("malloc failed");
			return -1;
		}

		alt->insn = alt_insn;
		list_add_tail(&alt->list, &insn->alts);
	}

	return 0;
}

/*
 * find_switch_table() - Given a dynamic jump, find the switch jump table in
 * .rodata associated with it.
 *
 * There are 3 basic patterns:
 *
 * 1. jmpq *[rodata addr](,%reg,8)
 *
 *    This is the most common case by far.  It jumps to an address in a simple
 *    jump table which is stored in .rodata.
 *
 * 2. jmpq *[rodata addr](%rip)
 *
 *    This is caused by a rare GCC quirk, currently only seen in three driver
 *    functions in the kernel, only with certain obscure non-distro configs.
 *
 *    As part of an optimization, GCC makes a copy of an existing switch jump
 *    table, modifies it, and then hard-codes the jump (albeit with an indirect
 *    jump) to use a single entry in the table.  The rest of the jump table and
 *    some of its jump targets remain as dead code.
 *
 *    In such a case we can just crudely ignore all unreachable instruction
 *    warnings for the entire object file.  Ideally we would just ignore them
 *    for the function, but that would require redesigning the code quite a
 *    bit.  And honestly that's just not worth doing: unreachable instruction
 *    warnings are of questionable value anyway, and this is such a rare issue.
 *
 * 3. mov [rodata addr],%reg1
 *    ... some instructions ...
 *    jmpq *(%reg1,%reg2,8)
 *
 *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
 *    writing, there are 11 occurrences of it in the allmodconfig kernel.
 *
857
858
859
860
 *    As of GCC 7 there are quite a few more of these and the 'in between' code
 *    is significant. Esp. with KASAN enabled some of the code between the mov
 *    and jmpq uses .rodata itself, which can confuse things.
 *
861
862
 *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
 *    ensure the same register is used in the mov and jump instructions.
863
864
 *
 *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
 */
static struct rela *find_switch_table(struct objtool_file *file,
				      struct symbol *func,
				      struct instruction *insn)
{
	struct rela *text_rela, *rodata_rela;
	struct instruction *orig_insn = insn;

	text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
	if (text_rela && text_rela->sym == file->rodata->sym) {
		/* case 1 */
		rodata_rela = find_rela_by_dest(file->rodata,
						text_rela->addend);
		if (rodata_rela)
			return rodata_rela;

		/* case 2 */
		rodata_rela = find_rela_by_dest(file->rodata,
						text_rela->addend + 4);
		if (!rodata_rela)
			return NULL;
886

887
888
889
890
891
		file->ignore_unreachables = true;
		return rodata_rela;
	}

	/* case 3 */
892
893
894
895
896
897
898
899
900
901
902
903
904
	/*
	 * Backward search using the @first_jump_src links, these help avoid
	 * much of the 'in between' code. Which avoids us getting confused by
	 * it.
	 */
	for (insn = list_prev_entry(insn, list);

	     &insn->list != &file->insn_list &&
	     insn->sec == func->sec &&
	     insn->offset >= func->offset;

	     insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {

905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
		if (insn->type == INSN_JUMP_DYNAMIC)
			break;

		/* allow small jumps within the range */
		if (insn->type == INSN_JUMP_UNCONDITIONAL &&
		    insn->jump_dest &&
		    (insn->jump_dest->offset <= insn->offset ||
		     insn->jump_dest->offset > orig_insn->offset))
		    break;

		/* look for a relocation which references .rodata */
		text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
						    insn->len);
		if (!text_rela || text_rela->sym != file->rodata->sym)
			continue;

		/*
		 * Make sure the .rodata address isn't associated with a
		 * symbol.  gcc jump tables are anonymous data.
		 */
		if (find_symbol_containing(file->rodata, text_rela->addend))
			continue;

		return find_rela_by_dest(file->rodata, text_rela->addend);
	}

	return NULL;
}

934

935
936
937
static int add_func_switch_tables(struct objtool_file *file,
				  struct symbol *func)
{
938
	struct instruction *insn, *last = NULL, *prev_jump = NULL;
939
940
941
942
	struct rela *rela, *prev_rela = NULL;
	int ret;

	func_for_each_insn(file, func, insn) {
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
		if (!last)
			last = insn;

		/*
		 * Store back-pointers for unconditional forward jumps such
		 * that find_switch_table() can back-track using those and
		 * avoid some potentially confusing code.
		 */
		if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
		    insn->offset > last->offset &&
		    insn->jump_dest->offset > insn->offset &&
		    !insn->jump_dest->first_jump_src) {

			insn->jump_dest->first_jump_src = insn;
			last = insn->jump_dest;
		}

960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
		if (insn->type != INSN_JUMP_DYNAMIC)
			continue;

		rela = find_switch_table(file, func, insn);
		if (!rela)
			continue;

		/*
		 * We found a switch table, but we don't know yet how big it
		 * is.  Don't add it until we reach the end of the function or
		 * the beginning of another switch table in the same function.
		 */
		if (prev_jump) {
			ret = add_switch_table(file, func, prev_jump, prev_rela,
					       rela);
			if (ret)
				return ret;
		}

		prev_jump = insn;
		prev_rela = rela;
	}

	if (prev_jump) {
		ret = add_switch_table(file, func, prev_jump, prev_rela, NULL);
		if (ret)
			return ret;
	}

	return 0;
}

/*
 * For some switch statements, gcc generates a jump table in the .rodata
 * section which contains a list of addresses within the function to jump to.
 * This finds these jump tables and adds them to the insn->alts lists.
 */
static int add_switch_table_alts(struct objtool_file *file)
{
	struct section *sec;
	struct symbol *func;
	int ret;

	if (!file->rodata || !file->rodata->rela)
		return 0;

1006
	for_each_sec(file, sec) {
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
		list_for_each_entry(func, &sec->symbol_list, list) {
			if (func->type != STT_FUNC)
				continue;

			ret = add_func_switch_tables(file, func);
			if (ret)
				return ret;
		}
	}

	return 0;
}

1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
static int read_unwind_hints(struct objtool_file *file)
{
	struct section *sec, *relasec;
	struct rela *rela;
	struct unwind_hint *hint;
	struct instruction *insn;
	struct cfi_reg *cfa;
	int i;

	sec = find_section_by_name(file->elf, ".discard.unwind_hints");
	if (!sec)
		return 0;

	relasec = sec->rela;
	if (!relasec) {
		WARN("missing .rela.discard.unwind_hints section");
		return -1;
	}

	if (sec->len % sizeof(struct unwind_hint)) {
		WARN("struct unwind_hint size mismatch");
		return -1;
	}

	file->hints = true;

	for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
		hint = (struct unwind_hint *)sec->data->d_buf + i;

		rela = find_rela_by_dest(sec, i * sizeof(*hint));
		if (!rela) {
			WARN("can't find rela for unwind_hints[%d]", i);
			return -1;
		}

		insn = find_insn(file, rela->sym->sec, rela->addend);
		if (!insn) {
			WARN("can't find insn for unwind_hints[%d]", i);
			return -1;
		}

		cfa = &insn->state.cfa;

		if (hint->type == UNWIND_HINT_TYPE_SAVE) {
			insn->save = true;
			continue;

		} else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
			insn->restore = true;
			insn->hint = true;
			continue;
		}

		insn->hint = true;

		switch (hint->sp_reg) {
		case ORC_REG_UNDEFINED:
			cfa->base = CFI_UNDEFINED;
			break;
		case ORC_REG_SP:
			cfa->base = CFI_SP;
			break;
		case ORC_REG_BP:
			cfa->base = CFI_BP;
			break;
		case ORC_REG_SP_INDIRECT:
			cfa->base = CFI_SP_INDIRECT;
			break;
		case ORC_REG_R10:
			cfa->base = CFI_R10;
			break;
		case ORC_REG_R13:
			cfa->base = CFI_R13;
			break;
		case ORC_REG_DI:
			cfa->base = CFI_DI;
			break;
		case ORC_REG_DX:
			cfa->base = CFI_DX;
			break;
		default:
			WARN_FUNC("unsupported unwind_hint sp base reg %d",
				  insn->sec, insn->offset, hint->sp_reg);
			return -1;
		}

		cfa->offset = hint->sp_offset;
		insn->state.type = hint->type;
	}

	return 0;
}

1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
static int read_retpoline_hints(struct objtool_file *file)
{
	struct section *sec, *relasec;
	struct instruction *insn;
	struct rela *rela;
	int i;

	sec = find_section_by_name(file->elf, ".discard.retpoline_safe");
	if (!sec)
		return 0;

	relasec = sec->rela;
	if (!relasec) {
		WARN("missing .rela.discard.retpoline_safe section");
		return -1;
	}

	if (sec->len % sizeof(unsigned long)) {
		WARN("retpoline_safe size mismatch: %d %ld", sec->len, sizeof(unsigned long));
		return -1;
	}

	for (i = 0; i < sec->len / sizeof(unsigned long); i++) {
		rela = find_rela_by_dest(sec, i * sizeof(unsigned long));
		if (!rela) {
			WARN("can't find rela for retpoline_safe[%d]", i);
			return -1;
		}

		insn = find_insn(file, rela->sym->sec, rela->addend);
		if (!insn) {
			WARN("can't find insn for retpoline_safe[%d]", i);
			return -1;
		}

		if (insn->type != INSN_JUMP_DYNAMIC &&
		    insn->type != INSN_CALL_DYNAMIC) {
			WARN_FUNC("retpoline_safe hint not a indirect jump/call",
				  insn->sec, insn->offset);
			return -1;
		}

		insn->retpoline_safe = true;
	}

	return 0;
}

1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
static int decode_sections(struct objtool_file *file)
{
	int ret;

	ret = decode_instructions(file);
	if (ret)
		return ret;

	ret = add_dead_ends(file);
	if (ret)
		return ret;

	add_ignores(file);

1175
1176
1177
1178
	ret = add_nospec_ignores(file);
	if (ret)
		return ret;

1179
1180
1181
1182
	ret = add_jump_destinations(file);
	if (ret)
		return ret;

1183
	ret = add_special_section_alts(file);
1184
1185
1186
	if (ret)
		return ret;

1187
	ret = add_call_destinations(file);
1188
1189
1190
1191
1192
1193
1194
	if (ret)
		return ret;

	ret = add_switch_table_alts(file);
	if (ret)
		return ret;

1195
1196
1197
1198
	ret = read_unwind_hints(file);
	if (ret)
		return ret;

1199
1200
1201
1202
	ret = read_retpoline_hints(file);
	if (ret)
		return ret;

1203
1204
1205
1206
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1210
1211
1212
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1214
1215
	return 0;
}

static bool is_fentry_call(struct instruction *insn)
{
	if (insn->type == INSN_CALL &&
	    insn->call_dest->type == STT_NOTYPE &&
	    !strcmp(insn->call_dest->name, "__fentry__"))
		return true;

	return false;
}

1216
static bool has_modified_stack_frame(struct insn_state *state)
1217
{
1218
1219
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1221
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1225
1226
1227
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1231
1232
1233
1234
1235
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1243
	int i;

	if (state->cfa.base != initial_func_cfi.cfa.base ||
	    state->cfa.offset != initial_func_cfi.cfa.offset ||
	    state->stack_size != initial_func_cfi.cfa.offset ||
	    state->drap)
		return true;

	for (i = 0; i < CFI_NUM_REGS; i++)
		if (state->regs[i].base != initial_func_cfi.regs[i].base ||
		    state->regs[i].offset != initial_func_cfi.regs[i].offset)
			return true;

	return false;
}

static bool has_valid_stack_frame(struct insn_state *state)
{
	if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
	    state->regs[CFI_BP].offset == -16)
		return true;

	if (state->drap && state->regs[CFI_BP].base == CFI_BP)
		return true;

	return false;
1244
1245
}

1246
1247
1248
1249
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1253
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1269
static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
{
	struct cfi_reg *cfa = &state->cfa;
	struct stack_op *op = &insn->stack_op;

	if (cfa->base != CFI_SP)
		return 0;

	/* push */
	if (op->dest.type == OP_DEST_PUSH)
		cfa->offset += 8;

	/* pop */
	if (op->src.type == OP_SRC_POP)
		cfa->offset -= 8;

	/* add immediate to sp */
	if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
	    op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
		cfa->offset -= op->src.offset;

	return 0;
}

1270
1271
static void save_reg(struct insn_state *state, unsigned char reg, int base,
		     int offset)
1272
{
1273
	if (arch_callee_saved_reg(reg) &&
1274
1275
1276
1277
	    state->regs[reg].base == CFI_UNDEFINED) {
		state->regs[reg].base = base;
		state->regs[reg].offset = offset;
	}
1278
1279
}

1280
static void restore_reg(struct insn_state *state, unsigned char reg)
1281
{
1282
1283
1284
1285
1286
1287
1288
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1290
1291
1292
1293
1294
1295
1296
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1312
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1322
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1328
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1331
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1334
1335
1336
1337
1338
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1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
	state->regs[reg].base = CFI_UNDEFINED;
	state->regs[reg].offset = 0;
}

/*
 * A note about DRAP stack alignment:
 *
 * GCC has the concept of a DRAP register, which is used to help keep track of
 * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
 * register.  The typical DRAP pattern is:
 *
 *   4c 8d 54 24 08		lea    0x8(%rsp),%r10
 *   48 83 e4 c0		and    $0xffffffffffffffc0,%rsp
 *   41 ff 72 f8		pushq  -0x8(%r10)
 *   55				push   %rbp
 *   48 89 e5			mov    %rsp,%rbp
 *				(more pushes)
 *   41 52			push   %r10
 *				...
 *   41 5a			pop    %r10
 *				(more pops)
 *   5d				pop    %rbp
 *   49 8d 62 f8		lea    -0x8(%r10),%rsp
 *   c3				retq
 *
 * There are some variations in the epilogues, like:
 *
 *   5b				pop    %rbx
 *   41 5a			pop    %r10
 *   41 5c			pop    %r12
 *   41 5d			pop    %r13
 *   41 5e			pop    %r14
 *   c9				leaveq
 *   49 8d 62 f8		lea    -0x8(%r10),%rsp
 *   c3				retq
 *
 * and:
 *
 *   4c 8b 55 e8		mov    -0x18(%rbp),%r10
 *   48 8b 5d e0		mov    -0x20(%rbp),%rbx
 *   4c 8b 65 f0		mov    -0x10(%rbp),%r12
 *   4c 8b 6d f8		mov    -0x8(%rbp),%r13
 *   c9				leaveq
 *   49 8d 62 f8		lea    -0x8(%r10),%rsp
 *   c3				retq
 *
 * Sometimes r13 is used as the DRAP register, in which case it's saved and
 * restored beforehand:
 *
 *   41 55			push   %r13
 *   4c 8d 6c 24 10		lea    0x10(%rsp),%r13
 *   48 83 e4 f0		and    $0xfffffffffffffff0,%rsp
 *				...
 *   49 8d 65 f0		lea    -0x10(%r13),%rsp
 *   41 5d			pop    %r13
 *   c3				retq
 */
static int update_insn_state(struct instruction *insn, struct insn_state *state)
{
	struct stack_op *op = &insn->stack_op;
	struct cfi_reg *cfa = &state->cfa;
	struct cfi_reg *regs = state->regs;

	/* stack operations don't make sense with an undefined CFA */
	if (cfa->base == CFI_UNDEFINED) {
		if (insn->func) {
			WARN_FUNC("undefined stack state", insn->sec, insn->offset);
			return -1;
		}
		return 0;
	}

1354
1355
1356
	if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
		return update_insn_state_regs(insn, state);

1357
1358
1359
1360
1361
1362
	switch (op->dest.type) {

	case OP_DEST_REG:
		switch (op->src.type) {

		case OP_SRC_REG:
1363
1364
1365
1366
1367
1368
1369
1370
1371
			if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
			    cfa->base == CFI_SP &&
			    regs[CFI_BP].base == CFI_CFA &&
			    regs[CFI_BP].offset == -cfa->offset) {

				/* mov %rsp, %rbp */
				cfa->base = op->dest.reg;
				state->bp_scratch = false;
			}
1372

1373
1374
			else if (op->src.reg == CFI_SP &&
				 op->dest.reg == CFI_BP && state->drap) {
1375

1376
1377
1378
1379
1380
				/* drap: mov %rsp, %rbp */
				regs[CFI_BP].base = CFI_BP;
				regs[CFI_BP].offset = -state->stack_size;
				state->bp_scratch = false;
			}
1381

1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
			else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {

				/*
				 * mov %rsp, %reg
				 *
				 * This is needed for the rare case where GCC
				 * does:
				 *
				 *   mov    %rsp, %rax
				 *   ...
				 *   mov    %rax, %rsp
				 */
				state->vals[op->dest.reg].base = CFI_CFA;
				state->vals[op->dest.reg].offset = -state->stack_size;
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
			}

			else if (op->dest.reg == cfa->base) {

				/* mov %reg, %rsp */
				if (cfa->base == CFI_SP &&
				    state->vals[op->src.reg].base == CFI_CFA) {

					/*
					 * This is needed for the rare case
					 * where GCC does something dumb like:
					 *
					 *   lea    0x8(%rsp), %rcx
					 *   ...
					 *   mov    %rcx, %rsp
					 */
					cfa->offset = -state->vals[op->src.reg].offset;
					state->stack_size = cfa->offset;

				} else {
					cfa->base = CFI_UNDEFINED;
					cfa->offset = 0;
				}
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
			}

			break;

		case OP_SRC_ADD:
			if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {

				/* add imm, %rsp */
				state->stack_size -= op->src.offset;
				if (cfa->base == CFI_SP)
					cfa->offset -= op->src.offset;
				break;
			}

			if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {

				/* lea disp(%rbp), %rsp */
				state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
				break;
			}

1440
			if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1441
1442
1443

				/* drap: lea disp(%rsp), %drap */
				state->drap_reg = op->dest.reg;
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458

				/*
				 * lea disp(%rsp), %reg
				 *
				 * This is needed for the rare case where GCC
				 * does something dumb like:
				 *
				 *   lea    0x8(%rsp), %rcx
				 *   ...
				 *   mov    %rcx, %rsp
				 */
				state->vals[op->dest.reg].base = CFI_CFA;
				state->vals[op->dest.reg].offset = \
					-state->stack_size + op->src.offset;

1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
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1478
1479
1480
1481
1482
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1485
1486
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1488
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1490
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1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
				break;
			}

			if (state->drap && op->dest.reg == CFI_SP &&
			    op->src.reg == state->drap_reg) {

				 /* drap: lea disp(%drap), %rsp */
				cfa->base = CFI_SP;
				cfa->offset = state->stack_size = -op->src.offset;
				state->drap_reg = CFI_UNDEFINED;
				state->drap = false;
				break;
			}

			if (op->dest.reg == state->cfa.base) {
				WARN_FUNC("unsupported stack register modification",
					  insn->sec, insn->offset);
				return -1;
			}

			break;

		case OP_SRC_AND:
			if (op->dest.reg != CFI_SP ||
			    (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
			    (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
				WARN_FUNC("unsupported stack pointer realignment",
					  insn->sec, insn->offset);
				return -1;
			}

			if (state->drap_reg != CFI_UNDEFINED) {
				/* drap: and imm, %rsp */
				cfa->base = state->drap_reg;
				cfa->offset = state->stack_size = 0;
				state->drap = true;
			}

			/*
			 * Older versions of GCC (4.8ish) realign the stack
			 * without DRAP, with a frame pointer.
			 */

			break;

		case OP_SRC_POP:
			if (!state->drap && op->dest.type == OP_DEST_REG &&
			    op->dest.reg == cfa->base) {

				/* pop %rbp */
				cfa->base = CFI_SP;
			}

1512
1513
1514
1515
			if (state->drap && cfa->base == CFI_BP_INDIRECT &&
			    op->dest.type == OP_DEST_REG &&
			    op->dest.reg == state->drap_reg &&
			    state->drap_offset == -state->stack_size) {
1516

1517
1518
1519
1520
				/* drap: pop %drap */
				cfa->base = state->drap_reg;
				cfa->offset = 0;
				state->drap_offset = -1;
1521

1522
			} else if (regs[op->dest.reg].offset == -state->stack_size) {
1523

1524
				/* pop %reg */
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
				restore_reg(state, op->dest.reg);
			}

			state->stack_size -= 8;
			if (cfa->base == CFI_SP)
				cfa->offset -= 8;

			break;

		case OP_SRC_REG_INDIRECT:
1535
1536
1537
1538
1539
1540
1541
1542
1543
			if (state->drap && op->src.reg == CFI_BP &&
			    op->src.offset == state->drap_offset) {

				/* drap: mov disp(%rbp), %drap */
				cfa->base = state->drap_reg;
				cfa->offset = 0;
				state->drap_offset = -1;
			}

1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
			if (state->drap && op->src.reg == CFI_BP &&
			    op->src.offset == regs[op->dest.reg].offset) {

				/* drap: mov disp(%rbp), %reg */
				restore_reg(state, op->dest.reg);

			} else if (op->src.reg == cfa->base &&
			    op->src.offset == regs[op->dest.reg].offset + cfa->offset) {

				/* mov disp(%rbp), %reg */
				/* mov disp(%rsp), %reg */
				restore_reg(state, op->dest.reg);
			}

			break;

		default:
			WARN_FUNC("unknown stack-related instruction",
				  insn->sec, insn->offset);
			return -1;
		}

		break;

	case OP_DEST_PUSH:
		state->stack_size += 8;
		if (cfa->base == CFI_SP)
			cfa->offset += 8;

		if (op->src.type != OP_SRC_REG)
			break;

		if (state->drap) {
			if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {

				/* drap: push %drap */
				cfa->base = CFI_BP_INDIRECT;
				cfa->offset = -state->stack_size;

1583
1584
				/* save drap so we know when to restore it */
				state->drap_offset = -state->stack_size;
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603

			} else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {

				/* drap: push %rbp */
				state->stack_size = 0;

			} else if (regs[op->src.reg].base == CFI_UNDEFINED) {

				/* drap: push %reg */
				save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
			}

		} else {

			/* push %reg */
			save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
		}

		/* detect when asm code uses rbp as a scratch register */
1604
		if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
		    cfa->base != CFI_BP)
			state->bp_scratch = true;
		break;

	case OP_DEST_REG_INDIRECT:

		if (state->drap) {
			if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {

				/* drap: mov %drap, disp(%rbp) */
				cfa->base = CFI_BP_INDIRECT;
				cfa->offset = op->dest.offset;

1618
1619
				/* save drap offset so we know when to restore it */
				state->drap_offset = op->dest.offset;
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
			}

			else if (regs[op->src.reg].base == CFI_UNDEFINED) {

				/* drap: mov reg, disp(%rbp) */
				save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
			}

		} else if (op->dest.reg == cfa->base) {

			/* mov reg, disp(%rbp) */
			/* mov reg, disp(%rsp) */
			save_reg(state, op->src.reg, CFI_CFA,
				 op->dest.offset - state->cfa.offset);
		}

		break;

	case OP_DEST_LEAVE:
		if ((!state->drap && cfa->base != CFI_BP) ||
		    (state->drap && cfa->base != state->drap_reg)) {
			WARN_FUNC("leave instruction with modified stack frame",
				  insn->sec, insn->offset);
			return -1;
		}

		/* leave (mov %rbp, %rsp; pop %rbp) */

		state->stack_size = -state->regs[CFI_BP].offset - 8;
		restore_reg(state, CFI_BP);

		if (!state->drap) {
			cfa->base = CFI_SP;
			cfa->offset -= 8;
		}

		break;

	case OP_DEST_MEM:
		if (op->src.type != OP_SRC_POP) {
			WARN_FUNC("unknown stack-related memory operation",
				  insn->sec, insn->offset);
			return -1;
		}

		/* pop mem */
		state->stack_size -= 8;
		if (cfa->base == CFI_SP)
			cfa->offset -= 8;

		break;

	default:
		WARN_FUNC("unknown stack-related instruction",
			  insn->sec, insn->offset);
		return -1;
	}

	return 0;
}

static bool insn_state_match(struct instruction *insn, struct insn_state *state)
{
	struct insn_state *state1 = &insn->state, *state2 = state;
	int i;

	if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
		WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
			  insn->sec, insn->offset,
			  state1->cfa.base, state1->cfa.offset,
			  state2->cfa.base, state2->cfa.offset);

	} else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
		for (i = 0; i < CFI_NUM_REGS; i++) {
			if (!memcmp(&state1->regs[i], &state2->regs[i],
				    sizeof(struct cfi_reg)))
				continue;

			WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
				  insn->sec, insn->offset,
				  i, state1->regs[i].base, state1->regs[i].offset,
				  i, state2->regs[i].base, state2->regs[i].offset);
			break;
		}

1705
1706
1707
1708
	} else if (state1->type != state2->type) {
		WARN_FUNC("stack state mismatch: type1=%d type2=%d",
			  insn->sec, insn->offset, state1->type, state2->type);

1709
	} else if (state1->drap != state2->drap ||
1710
1711
1712
		 (state1->drap && state1->drap_reg != state2->drap_reg) ||
		 (state1->drap && state1->drap_offset != state2->drap_offset)) {
		WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1713
			  insn->sec, insn->offset,
1714
1715
			  state1->drap, state1->drap_reg, state1->drap_offset,
			  state2->drap, state2->drap_reg, state2->drap_offset);
1716
1717
1718
1719
1720

	} else
		return true;

	return false;
1721
1722
1723
1724
1725
1726
1727
1728
}

/*
 * Follow the branch starting at the given instruction, and recursively follow
 * any other branches (jumps).  Meanwhile, track the frame pointer state at
 * each instruction and validate all the rules described in
 * tools/objtool/Documentation/stack-validation.txt.
 */
1729
1730
static int validate_branch(struct objtool_file *file, struct instruction *first,
			   struct insn_state state)
1731
1732
{
	struct alternative *alt;
1733
	struct instruction *insn, *next_insn;
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
	struct section *sec;
	struct symbol *func = NULL;
	int ret;

	insn = first;
	sec = insn->sec;

	if (insn->alt_group && list_empty(&insn->alts)) {
		WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
			  sec, insn->offset);
1744
		return 1;
1745
1746
1747
	}

	while (1) {
1748
1749
		next_insn = next_insn_same_sec(file, insn);

1750
1751
1752
1753
1754

		if (file->c_file && func && insn->func && func != insn->func) {
			WARN("%s() falls through to next function %s()",
			     func->name, insn->func->name);
			return 1;
1755
1756
		}

1757
1758
		if (insn->func)
			func = insn->func;
1759

1760
1761
1762
		if (func && insn->ignore) {
			WARN_FUNC("BUG: why am I validating an ignored function?",
				  sec, insn->offset);
1763
			return 1;
1764
1765
		}

1766
		if (insn->visited) {
1767
			if (!insn->hint && !insn_state_match(insn, &state))
1768
1769
1770
1771
1772
				return 1;

			return 0;
		}

1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
		if (insn->hint) {
			if (insn->restore) {
				struct instruction *save_insn, *i;

				i = insn;
				save_insn = NULL;
				func_for_each_insn_continue_reverse(file, func, i) {
					if (i->save) {
						save_insn = i;
						break;
					}
				}

				if (!save_insn) {
					WARN_FUNC("no corresponding CFI save for CFI restore",
						  sec, insn->offset);
					return 1;
				}

				if (!save_insn->visited) {
					/*
					 * Oops, no state to copy yet.
					 * Hopefully we can reach this
					 * instruction from another branch
					 * after the save insn has been
					 * visited.
					 */
					if (insn == first)
						return 0;

					WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
						  sec, insn->offset);
					return 1;
				}

				insn->state = save_insn->state;
			}

			state = insn->state;

		} else
			insn->state = state;
1815

1816
1817
		insn->visited = true;

1818
1819
1820
1821
1822
1823
		if (!insn->ignore_alts) {
			list_for_each_entry(alt, &insn->alts, list) {
				ret = validate_branch(file, alt->insn, state);
				if (ret)
					return 1;
			}
1824
1825
1826
1827
1828
		}

		switch (insn->type) {

		case INSN_RETURN:
1829
1830
			if (func && has_modified_stack_frame(&state)) {
				WARN_FUNC("return with modified stack frame",
1831
1832
1833
					  sec, insn->offset);
				return 1;
			}
1834
1835
1836
1837
1838
1839
1840

			if (state.bp_scratch) {
				WARN("%s uses BP as a scratch register",
				     insn->func->name);
				return 1;
			}

1841
1842
1843
			return 0;

		case INSN_CALL:
1844
			if (is_fentry_call(insn))
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
				break;

			ret = dead_end_function(file, insn->call_dest);
			if (ret == 1)
				return 0;
			if (ret == -1)
				return 1;

			/* fallthrough */
		case INSN_CALL_DYNAMIC:
1855
			if (!no_fp && func && !has_valid_stack_frame(&state)) {
1856
1857
1858
1859
1860
1861
1862
1863
				WARN_FUNC("call without frame pointer save/setup",
					  sec, insn->offset);
				return 1;
			}
			break;

		case INSN_JUMP_CONDITIONAL:
		case INSN_JUMP_UNCONDITIONAL:
1864
1865
1866
			if (insn->jump_dest &&
			    (!func || !insn->jump_dest->func ||
			     func == insn->jump_dest->func)) {
1867
1868
1869
1870
				ret = validate_branch(file, insn->jump_dest,
						      state);
				if (ret)
					return 1;
1871

1872
1873
			} else if (func && has_modified_stack_frame(&state)) {
				WARN_FUNC("sibling call from callable instruction with modified stack frame",
1874
1875
					  sec, insn->offset);
				return 1;
1876
			}
1877
1878
1879
1880
1881
1882
1883

			if (insn->type == INSN_JUMP_UNCONDITIONAL)
				return 0;

			break;

		case INSN_JUMP_DYNAMIC:
1884
1885
1886
			if (func && list_empty(&insn->alts) &&
			    has_modified_stack_frame(&state)) {
				WARN_FUNC("sibling call from callable instruction with modified stack frame",
1887
1888
1889
1890
1891
1892
					  sec, insn->offset);
				return 1;
			}

			return 0;

1893
1894
1895
1896
1897
1898
1899
1900
		case INSN_CONTEXT_SWITCH:
			if (func && (!next_insn || !next_insn->hint)) {
				WARN_FUNC("unsupported instruction in callable function",
					  sec, insn->offset);
				return 1;
			}
			return 0;

1901
1902
		case INSN_STACK:
			if (update_insn_state(insn, &state))
1903
				return 1;
1904
1905
1906

			break;

1907
1908
1909
1910
1911
1912
1913
		default:
			break;
		}

		if (insn->dead_end)
			return 0;

1914
1915
1916
		if (!next_insn) {
			if (state.cfa.base == CFI_UNDEFINED)
				return 0;
1917
1918
1919
			WARN("%s: unexpected end of section", sec->name);
			return 1;
		}
1920
1921

		insn = next_insn;
1922
1923
1924
1925
1926
	}

	return 0;
}

1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
static int validate_unwind_hints(struct objtool_file *file)
{
	struct instruction *insn;
	int ret, warnings = 0;
	struct insn_state state;

	if (!file->hints)
		return 0;

	clear_insn_state(&state);

	for_each_insn(file, insn) {
		if (insn->hint && !insn->visited) {
			ret = validate_branch(file, insn, state);
			warnings += ret;
		}
	}

	return warnings;
}

1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
static int validate_retpoline(struct objtool_file *file)
{
	struct instruction *insn;
	int warnings = 0;

	for_each_insn(file, insn) {
		if (insn->type != INSN_JUMP_DYNAMIC &&
		    insn->type != INSN_CALL_DYNAMIC)
			continue;

		if (insn->retpoline_safe)
			continue;

1961
1962
1963
1964
1965
1966
1967
1968
1969
		/*
		 * .init.text code is ran before userspace and thus doesn't
		 * strictly need retpolines, except for modules which are
		 * loaded late, they very much do need retpoline in their
		 * .init.text
		 */
		if (!strcmp(insn->sec->name, ".init.text") && !module)
			continue;

1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
		WARN_FUNC("indirect %s found in RETPOLINE build",
			  insn->sec, insn->offset,
			  insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");

		warnings++;
	}

	return warnings;
}

1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
static bool is_kasan_insn(struct instruction *insn)
{
	return (insn->type == INSN_CALL &&
		!strcmp(insn->call_dest->name, "__asan_handle_no_return"));
}

static bool is_ubsan_insn(struct instruction *insn)
{
	return (insn->type == INSN_CALL &&
		!strcmp(insn->call_dest->name,
			"__ubsan_handle_builtin_unreachable"));
}

1993
static bool ignore_unreachable_insn(struct instruction *insn)
1994
1995
1996
{
	int i;

1997
1998
1999
2000
2001
2002
	if (insn->ignore || insn->type == INSN_NOP)
		return true;

	/*
	 * Ignore any unused exceptions.  This can happen when a whitelisted
	 * function has an exception table entry.
2003
2004
2005
	 *
	 * Also ignore alternative replacement instructions.  This can happen
	 * when a whitelisted function uses one of the ALTERNATIVE macros.
2006
	 */
2007
2008
2009
	if (!strcmp(insn->sec->name, ".fixup") ||
	    !strcmp(insn->sec->name, ".altinstr_replacement") ||
	    !strcmp(insn->sec->name, ".altinstr_aux"))
2010
2011
2012
2013
2014
2015
2016
2017
		return true;

	/*
	 * Check if this (or a subsequent) instruction is related to
	 * CONFIG_UBSAN or CONFIG_KASAN.
	 *
	 * End the search at 5 instructions to avoid going into the weeds.
	 */
2018
2019
	if (!insn->func)
		return false;
2020
2021
2022
2023
2024
	for (i = 0; i < 5; i++) {

		if (is_kasan_insn(insn) || is_ubsan_insn(insn))
			return true;

2025
2026
2027
2028
2029
2030
2031
2032
		if (insn->type == INSN_JUMP_UNCONDITIONAL) {
			if (insn->jump_dest &&
			    insn->jump_dest->func == insn->func) {
				insn = insn->jump_dest;
				continue;
			}

			break;
2033
2034
		}

2035
		if (insn->offset + insn->len >= insn->func->offset + insn->func->len)