check.c 52.3 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;
}

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static struct instruction *next_insn_same_func(struct objtool_file *file,
					       struct instruction *insn)
{
	struct instruction *next = list_next_entry(insn, list);
	struct symbol *func = insn->func;

	if (!func)
		return NULL;

	if (&next->list != &file->insn_list && next->func == func)
		return next;

	/* Check if we're already in the subfunction: */
	if (func == func->cfunc)
		return NULL;

	/* Move to the subfunction: */
	return find_insn(file, func->cfunc->sec, func->cfunc->offset);
}

#define func_for_each_insn_all(file, func, insn)			\
	for (insn = find_insn(file, func->sec, func->offset);		\
	     insn;							\
	     insn = next_insn_same_func(file, insn))

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#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;

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	if (!func->len)
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		return 0;

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	insn = find_insn(file, func->sec, func->offset);
	if (!insn->func)
		return 0;

	func_for_each_insn_all(file, func, insn) {
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		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.
	 */
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	func_for_each_insn_all(file, func, insn) {
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		if (insn->type == INSN_JUMP_UNCONDITIONAL) {
			struct instruction *dest = insn->jump_dest;

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

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			if (dest->func && dest->func->pfunc != insn->func->pfunc) {
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				/* local sibling call */
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				if (recursion == 5) {
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					/*
					 * Infinite recursion: two functions
					 * have sibling calls to each other.
					 * This is a very rare case.  It means
					 * they aren't dead ends.
					 */
					return 0;
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				}

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				return __dead_end_function(file, dest->func,
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							   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;

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			func_for_each_insn_all(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;
	}

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	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;
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	}

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

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		*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;

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		insn->ignore = orig_insn->ignore_alts;

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		if (insn->type != INSN_JUMP_CONDITIONAL &&
		    insn->type != INSN_JUMP_UNCONDITIONAL)
			continue;

		if (!insn->immediate)
			continue;

		dest_off = insn->offset + insn->len + insn->immediate;
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		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;
			}
690
			insn->jump_dest = fake_jump;
691
		}
692 693 694 695 696 697 698 699 700 701 702 703 704 705

		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;
	}

706 707
	if (fake_jump)
		list_add(&fake_jump->list, &last_new_insn->list);
708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788

	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;
		}

789 790 791 792 793 794 795
		alt = malloc(sizeof(*alt));
		if (!alt) {
			WARN("malloc failed");
			ret = -1;
			goto out;
		}

796 797 798 799 800 801 802 803 804 805 806
		alt->insn = new_insn;
		list_add_tail(&alt->list, &orig_insn->alts);

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

out:
	return ret;
}

807 808
static int add_switch_table(struct objtool_file *file, struct instruction *insn,
			    struct rela *table, struct rela *next_table)
809 810 811 812
{
	struct rela *rela = table;
	struct instruction *alt_insn;
	struct alternative *alt;
813 814
	struct symbol *pfunc = insn->func->pfunc;
	unsigned int prev_offset = 0;
815 816 817 818 819

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

820 821 822 823 824 825 826 827 828
		/* Make sure the switch table entries are consecutive: */
		if (prev_offset && rela->offset != prev_offset + 8)
			break;

		/* Detect function pointers from contiguous objects: */
		if (rela->sym->sec == pfunc->sec &&
		    rela->addend == pfunc->offset)
			break;

829 830
		alt_insn = find_insn(file, rela->sym->sec, rela->addend);
		if (!alt_insn)
831 832
			break;

833
		/* Make sure the jmp dest is in the function or subfunction: */
834
		if (alt_insn->func->pfunc != pfunc)
835
			break;
836 837 838 839 840 841 842 843 844

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

		alt->insn = alt_insn;
		list_add_tail(&alt->list, &insn->alts);
845 846 847 848 849 850 851
		prev_offset = rela->offset;
	}

	if (!prev_offset) {
		WARN_FUNC("can't find switch jump table",
			  insn->sec, insn->offset);
		return -1;
852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890
	}

	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.
 *
891 892 893 894
 *    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.
 *
895 896
 *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
 *    ensure the same register is used in the mov and jump instructions.
897 898
 *
 *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
899 900 901 902 903 904 905
 */
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;
906
	unsigned long table_offset;
907

908
	/* case 1 & 2 */
909
	text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
910 911 912
	if (text_rela && text_rela->sym == file->rodata->sym &&
	    !find_symbol_containing(file->rodata, text_rela->addend)) {

913 914 915 916 917 918
		table_offset = text_rela->addend;
		if (text_rela->type == R_X86_64_PC32) {
			/* case 2 */
			table_offset += 4;
			file->ignore_unreachables = true;
		}
919

920
		rodata_rela = find_rela_by_dest(file->rodata, table_offset);
921 922
		if (!rodata_rela)
			return NULL;
923

924 925 926 927
		return rodata_rela;
	}

	/* case 3 */
928 929 930 931 932 933 934 935 936 937 938 939 940
	/*
	 * 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)) {

941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956
		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;

957 958 959 960
		table_offset = text_rela->addend;
		if (text_rela->type == R_X86_64_PC32)
			table_offset += 4;

961 962 963 964
		/*
		 * Make sure the .rodata address isn't associated with a
		 * symbol.  gcc jump tables are anonymous data.
		 */
965
		if (find_symbol_containing(file->rodata, table_offset))
966 967
			continue;

968 969 970 971
		/* mov [rodata addr], %reg */
		rodata_rela = find_rela_by_dest(file->rodata, table_offset);
		if (rodata_rela)
			return rodata_rela;
972 973 974 975 976
	}

	return NULL;
}

977

978 979 980
static int add_func_switch_tables(struct objtool_file *file,
				  struct symbol *func)
{
981
	struct instruction *insn, *last = NULL, *prev_jump = NULL;
982 983 984
	struct rela *rela, *prev_rela = NULL;
	int ret;

985
	func_for_each_insn_all(file, func, insn) {
986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002
		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;
		}

1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015
		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) {
1016
			ret = add_switch_table(file, prev_jump, prev_rela, rela);
1017 1018 1019 1020 1021 1022 1023 1024 1025
			if (ret)
				return ret;
		}

		prev_jump = insn;
		prev_rela = rela;
	}

	if (prev_jump) {
1026
		ret = add_switch_table(file, prev_jump, prev_rela, NULL);
1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047
		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;

1048
	for_each_sec(file, sec) {
1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061
		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;
}

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 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
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;
}

1155 1156
static int read_retpoline_hints(struct objtool_file *file)
{
J
Josh Poimboeuf 已提交
1157
	struct section *sec;
1158 1159 1160
	struct instruction *insn;
	struct rela *rela;

J
Josh Poimboeuf 已提交
1161
	sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1162 1163 1164
	if (!sec)
		return 0;

J
Josh Poimboeuf 已提交
1165 1166 1167
	list_for_each_entry(rela, &sec->rela_list, list) {
		if (rela->sym->type != STT_SECTION) {
			WARN("unexpected relocation symbol type in %s", sec->name);
1168 1169 1170 1171 1172
			return -1;
		}

		insn = find_insn(file, rela->sym->sec, rela->addend);
		if (!insn) {
J
Josh Poimboeuf 已提交
1173
			WARN("bad .discard.retpoline_safe entry");
1174 1175 1176 1177 1178
			return -1;
		}

		if (insn->type != INSN_JUMP_DYNAMIC &&
		    insn->type != INSN_CALL_DYNAMIC) {
J
Josh Poimboeuf 已提交
1179
			WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1180 1181 1182 1183 1184 1185 1186 1187 1188 1189
				  insn->sec, insn->offset);
			return -1;
		}

		insn->retpoline_safe = true;
	}

	return 0;
}

1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203
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);

1204 1205 1206 1207
	ret = add_nospec_ignores(file);
	if (ret)
		return ret;

1208 1209 1210 1211
	ret = add_jump_destinations(file);
	if (ret)
		return ret;

1212
	ret = add_special_section_alts(file);
1213 1214 1215
	if (ret)
		return ret;

1216
	ret = add_call_destinations(file);
1217 1218 1219 1220 1221 1222 1223
	if (ret)
		return ret;

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

1224 1225 1226 1227
	ret = read_unwind_hints(file);
	if (ret)
		return ret;

1228 1229 1230 1231
	ret = read_retpoline_hints(file);
	if (ret)
		return ret;

1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244
	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;
}

1245
static bool has_modified_stack_frame(struct insn_state *state)
1246
{
1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272
	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;
1273 1274
}

1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298
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;
}

1299 1300
static void save_reg(struct insn_state *state, unsigned char reg, int base,
		     int offset)
1301
{
1302
	if (arch_callee_saved_reg(reg) &&
1303 1304 1305 1306
	    state->regs[reg].base == CFI_UNDEFINED) {
		state->regs[reg].base = base;
		state->regs[reg].offset = offset;
	}
1307 1308
}

1309
static void restore_reg(struct insn_state *state, unsigned char reg)
1310
{
1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382
	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;
	}

1383 1384 1385
	if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
		return update_insn_state_regs(insn, state);

1386 1387 1388 1389 1390 1391
	switch (op->dest.type) {

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

		case OP_SRC_REG:
1392 1393 1394 1395 1396 1397 1398 1399 1400
			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;
			}
1401

1402 1403
			else if (op->src.reg == CFI_SP &&
				 op->dest.reg == CFI_BP && state->drap) {
1404

1405 1406 1407 1408 1409
				/* drap: mov %rsp, %rbp */
				regs[CFI_BP].base = CFI_BP;
				regs[CFI_BP].offset = -state->stack_size;
				state->bp_scratch = false;
			}
1410

1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424
			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;
1425 1426
			}

J
Josh Poimboeuf 已提交
1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437
			else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
				 cfa->base == CFI_BP) {

				/*
				 * mov %rbp, %rsp
				 *
				 * Restore the original stack pointer (Clang).
				 */
				state->stack_size = -state->regs[CFI_BP].offset;
			}

1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458
			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;
				}
1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479
			}

			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;
			}

1480
			if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1481 1482 1483

				/* drap: lea disp(%rsp), %drap */
				state->drap_reg = op->dest.reg;
1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498

				/*
				 * 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;

1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551
				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;
			}

1552 1553 1554 1555
			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) {
1556

1557 1558 1559 1560
				/* drap: pop %drap */
				cfa->base = state->drap_reg;
				cfa->offset = 0;
				state->drap_offset = -1;
1561

1562
			} else if (regs[op->dest.reg].offset == -state->stack_size) {
1563

1564
				/* pop %reg */
1565 1566 1567 1568 1569 1570 1571 1572 1573 1574
				restore_reg(state, op->dest.reg);
			}

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

			break;

		case OP_SRC_REG_INDIRECT:
1575 1576 1577 1578 1579 1580 1581 1582 1583
			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;
			}

1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622
			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;

1623 1624
				/* save drap so we know when to restore it */
				state->drap_offset = -state->stack_size;
1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643

			} 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 */
1644
		if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657
		    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;

1658 1659
				/* save drap offset so we know when to restore it */
				state->drap_offset = op->dest.offset;
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 1705 1706 1707 1708 1709 1710 1711 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744
			}

			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;
		}

1745 1746 1747 1748
	} else if (state1->type != state2->type) {
		WARN_FUNC("stack state mismatch: type1=%d type2=%d",
			  insn->sec, insn->offset, state1->type, state2->type);

1749
	} else if (state1->drap != state2->drap ||
1750 1751 1752
		 (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)",
1753
			  insn->sec, insn->offset,
1754 1755
			  state1->drap, state1->drap_reg, state1->drap_offset,
			  state2->drap, state2->drap_reg, state2->drap_offset);
1756 1757 1758 1759 1760

	} else
		return true;

	return false;
1761 1762 1763 1764 1765 1766 1767 1768
}

/*
 * 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.
 */
1769 1770
static int validate_branch(struct objtool_file *file, struct instruction *first,
			   struct insn_state state)
1771 1772
{
	struct alternative *alt;
1773
	struct instruction *insn, *next_insn;
1774 1775 1776 1777 1778 1779 1780 1781 1782 1783
	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);
1784
		return 1;
1785 1786 1787
	}

	while (1) {
1788 1789
		next_insn = next_insn_same_sec(file, insn);

1790
		if (file->c_file && func && insn->func && func != insn->func->pfunc) {
1791 1792 1793
			WARN("%s() falls through to next function %s()",
			     func->name, insn->func->name);
			return 1;
1794 1795
		}

1796
		func = insn->func ? insn->func->pfunc : NULL;
1797

1798 1799 1800
		if (func && insn->ignore) {
			WARN_FUNC("BUG: why am I validating an ignored function?",
				  sec, insn->offset);
1801
			return 1;
1802 1803
		}

1804
		if (insn->visited) {
1805
			if (!insn->hint && !insn_state_match(insn, &state))
1806 1807 1808 1809 1810
				return 1;

			return 0;
		}

1811 1812 1813 1814 1815 1816
		if (insn->hint) {
			if (insn->restore) {
				struct instruction *save_insn, *i;

				i = insn;
				save_insn = NULL;
1817
				func_for_each_insn_continue_reverse(file, insn->func, i) {
1818 1819 1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839 1840 1841 1842 1843 1844 1845 1846 1847 1848 1849 1850 1851 1852
					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;
1853

1854 1855
		insn->visited = true;

1856 1857 1858 1859 1860 1861
		if (!insn->ignore_alts) {
			list_for_each_entry(alt, &insn->alts, list) {
				ret = validate_branch(file, alt->insn, state);
				if (ret)
					return 1;
			}
1862 1863 1864 1865 1866
		}

		switch (insn->type) {

		case INSN_RETURN:
1867 1868
			if (func && has_modified_stack_frame(&state)) {
				WARN_FUNC("return with modified stack frame",
1869 1870 1871
					  sec, insn->offset);
				return 1;
			}
1872 1873 1874 1875 1876 1877 1878

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

1879 1880 1881
			return 0;

		case INSN_CALL:
1882
			if (is_fentry_call(insn))
1883 1884 1885 1886 1887 1888 1889 1890 1891 1892
				break;

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

			/* fallthrough */
		case INSN_CALL_DYNAMIC:
1893
			if (!no_fp && func && !has_valid_stack_frame(&state)) {
1894 1895 1896 1897 1898 1899 1900 1901
				WARN_FUNC("call without frame pointer save/setup",
					  sec, insn->offset);
				return 1;
			}
			break;

		case INSN_JUMP_CONDITIONAL:
		case INSN_JUMP_UNCONDITIONAL:
1902 1903
			if (insn->jump_dest &&
			    (!func || !insn->jump_dest->func ||
1904
			     insn->jump_dest->func->pfunc == func)) {
1905 1906 1907 1908
				ret = validate_branch(file, insn->jump_dest,
						      state);
				if (ret)
					return 1;
1909

1910 1911
			} else if (func && has_modified_stack_frame(&state)) {
				WARN_FUNC("sibling call from callable instruction with modified stack frame",
1912 1913
					  sec, insn->offset);
				return 1;
1914
			}
1915 1916 1917 1918 1919 1920 1921

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

			break;

		case INSN_JUMP_DYNAMIC:
1922 1923 1924
			if (func && list_empty(&insn->alts) &&
			    has_modified_stack_frame(&state)) {
				WARN_FUNC("sibling call from callable instruction with modified stack frame",
1925 1926 1927 1928 1929 1930
					  sec, insn->offset);
				return 1;
			}

			return 0;

1931 1932 1933 1934 1935 1936 1937 1938
		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;

1939 1940
		case INSN_STACK:
			if (update_insn_state(insn, &state))
1941
				return 1;
1942 1943 1944

			break;

1945 1946 1947 1948 1949 1950 1951
		default:
			break;
		}

		if (insn->dead_end)
			return 0;

1952 1953 1954
		if (!next_insn) {
			if (state.cfa.base == CFI_UNDEFINED)
				return 0;
1955 1956 1957
			WARN("%s: unexpected end of section", sec->name);
			return 1;
		}
1958 1959

		insn = next_insn;
1960 1961 1962 1963 1964
	}

	return 0;
}

1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985
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;
}

1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
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;

1999 2000 2001 2002 2003 2004 2005 2006 2007
		/*
		 * .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;

2008 2009 2010 2011 2012 2013 2014 2015 2016 2017
		WARN_FUNC("indirect %s found in RETPOLINE build",
			  insn->sec, insn->offset,
			  insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");

		warnings++;
	}

	return warnings;
}

2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030
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"));
}

2031
static bool ignore_unreachable_insn(struct instruction *insn)
2032 2033 2034
{
	int i;

2035 2036 2037 2038 2039 2040
	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.
2041 2042 2043
	 *
	 * Also ignore alternative replacement instructions.  This can happen
	 * when a whitelisted function uses one of the ALTERNATIVE macros.
2044
	 */
2045 2046 2047
	if (!strcmp(insn->sec->name, ".fixup") ||
	    !strcmp(insn->sec->name, ".altinstr_replacement") ||
	    !strcmp(insn->sec->name, ".altinstr_aux"))
2048 2049 2050 2051 2052 2053 2054 2055
		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.
	 */
2056 2057
	if (!insn->func)
		return false;
2058 2059 2060 2061 2062
	for (i = 0; i < 5; i++) {

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

2063 2064 2065 2066 2067 2068 2069 2070
		if (insn->type == INSN_JUMP_UNCONDITIONAL) {
			if (insn->jump_dest &&
			    insn->jump_dest->func == insn->func) {
				insn = insn->jump_dest;
				continue;
			}

			break;
2071 2072
		}

2073
		if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2074
			break;
2075

2076 2077 2078 2079 2080 2081 2082 2083 2084 2085 2086
		insn = list_next_entry(insn, list);
	}

	return false;
}

static int validate_functions(struct objtool_file *file)
{
	struct section *sec;
	struct symbol *func;
	struct instruction *insn;
2087
	struct insn_state state;
2088 2089
	int ret, warnings = 0;

2090 2091 2092 2093 2094 2095 2096 2097
	clear_insn_state(&state);

	state.cfa = initial_func_cfi.cfa;
	memcpy(&state.regs, &initial_func_cfi.regs,
	       CFI_NUM_REGS * sizeof(struct cfi_reg));
	state.stack_size = initial_func_cfi.cfa.offset;

	for_each_sec(file, sec) {
2098
		list_for_each_entry(func, &sec->symbol_list, list) {
2099
			if (func->type != STT_FUNC || func->pfunc != func)
2100 2101 2102
				continue;

			insn = find_insn(file, sec, func->offset);
2103
			if (!insn || insn->ignore)
2104 2105
				continue;

2106
			ret = validate_branch(file, insn, state);
2107 2108 2109 2110 2111 2112 2113
			warnings += ret;
		}
	}

	return warnings;
}

2114
static int validate_reachable_instructions(struct objtool_file *file)
2115 2116
{
	struct instruction *insn;
2117 2118 2119

	if (file->ignore_unreachables)
		return 0;
2120 2121

	for_each_insn(file, insn) {
2122 2123 2124 2125 2126
		if (insn->visited || ignore_unreachable_insn(insn))
			continue;

		WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
		return 1;
2127 2128
	}

2129
	return 0;
2130 2131 2132 2133 2134 2135 2136 2137 2138 2139 2140 2141 2142 2143 2144 2145 2146 2147 2148
}

static void cleanup(struct objtool_file *file)
{
	struct instruction *insn, *tmpinsn;
	struct alternative *alt, *tmpalt;

	list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
		list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
			list_del(&alt->list);
			free(alt);
		}
		list_del(&insn->list);
		hash_del(&insn->hash);
		free(insn);
	}
	elf_close(file->elf);
}

2149
int check(const char *_objname, bool orc)
2150 2151 2152 2153 2154 2155
{
	struct objtool_file file;
	int ret, warnings = 0;

	objname = _objname;

2156
	file.elf = elf_open(objname, orc ? O_RDWR : O_RDONLY);
2157
	if (!file.elf)
2158 2159 2160 2161 2162 2163 2164
		return 1;

	INIT_LIST_HEAD(&file.insn_list);
	hash_init(file.insn_hash);
	file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard");
	file.rodata = find_section_by_name(file.elf, ".rodata");
	file.c_file = find_section_by_name(file.elf, ".comment");
2165
	file.ignore_unreachables = no_unreachable;
2166
	file.hints = false;
2167

2168 2169
	arch_initial_func_cfi_state(&initial_func_cfi);

2170 2171 2172 2173 2174
	ret = decode_sections(&file);
	if (ret < 0)
		goto out;
	warnings += ret;

2175
	if (list_empty(&file.insn_list))
2176 2177
		goto out;

2178 2179 2180 2181 2182 2183 2184
	if (retpoline) {
		ret = validate_retpoline(&file);
		if (ret < 0)
			return ret;
		warnings += ret;
	}

2185
	ret = validate_functions(&file);
2186 2187 2188 2189
	if (ret < 0)
		goto out;
	warnings += ret;

2190 2191 2192 2193 2194
	ret = validate_unwind_hints(&file);
	if (ret < 0)
		goto out;
	warnings += ret;

2195 2196 2197 2198 2199 2200 2201
	if (!warnings) {
		ret = validate_reachable_instructions(&file);
		if (ret < 0)
			goto out;
		warnings += ret;
	}

2202 2203 2204 2205 2206 2207 2208 2209 2210 2211 2212 2213 2214 2215
	if (orc) {
		ret = create_orc(&file);
		if (ret < 0)
			goto out;

		ret = create_orc_sections(&file);
		if (ret < 0)
			goto out;

		ret = elf_write(file.elf);
		if (ret < 0)
			goto out;
	}

2216 2217 2218 2219 2220 2221 2222 2223
out:
	cleanup(&file);

	/* ignore warnings for now until we get all the code cleaned up */
	if (ret || warnings)
		return 0;
	return 0;
}