kernel_optimize_test/tools/objtool/builtin-check.c
Josh Poimboeuf d1091c7fa3 objtool: Improve detection of BUG() and other dead ends
The BUG() macro's use of __builtin_unreachable() via the unreachable()
macro tells gcc that the instruction is a dead end, and that it's safe
to assume the current code path will not execute past the previous
instruction.

On x86, the BUG() macro is implemented with the 'ud2' instruction.  When
objtool's branch analysis sees that instruction, it knows the current
code path has come to a dead end.

Peter Zijlstra has been working on a patch to change the WARN macros to
use 'ud2'.  That patch will break objtool's assumption that 'ud2' is
always a dead end.

Generally it's best for objtool to avoid making those kinds of
assumptions anyway.  The more ignorant it is of kernel code internals,
the better.

So create a more generic way for objtool to detect dead ends by adding
an annotation to the unreachable() macro.  The annotation stores a
pointer to the end of the unreachable code path in an '__unreachable'
section.  Objtool can read that section to find the dead ends.

Tested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/41a6d33971462ebd944a1c60ad4bf5be86c17b77.1487712920.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-02-24 09:10:52 +01:00

1303 lines
31 KiB
C

/*
* Copyright (C) 2015 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/>.
*/
/*
* objtool check:
*
* This command analyzes every .o file and ensures the validity of its stack
* trace metadata. It enforces a set of rules on asm code and C inline
* assembly code so that stack traces can be reliable.
*
* For more information, see tools/objtool/Documentation/stack-validation.txt.
*/
#include <string.h>
#include <stdlib.h>
#include <subcmd/parse-options.h>
#include "builtin.h"
#include "elf.h"
#include "special.h"
#include "arch.h"
#include "warn.h"
#include <linux/hashtable.h>
#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
#define STATE_FP_SAVED 0x1
#define STATE_FP_SETUP 0x2
#define STATE_FENTRY 0x4
struct instruction {
struct list_head list;
struct hlist_node hash;
struct section *sec;
unsigned long offset;
unsigned int len, state;
unsigned char type;
unsigned long immediate;
bool alt_group, visited, dead_end;
struct symbol *call_dest;
struct instruction *jump_dest;
struct list_head alts;
struct symbol *func;
};
struct alternative {
struct list_head list;
struct instruction *insn;
};
struct objtool_file {
struct elf *elf;
struct list_head insn_list;
DECLARE_HASHTABLE(insn_hash, 16);
struct section *rodata, *whitelist;
bool ignore_unreachables, c_file;
};
const char *objname;
static bool nofp;
static struct instruction *find_insn(struct objtool_file *file,
struct section *sec, unsigned long offset)
{
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);
if (&next->list == &file->insn_list || next->sec != insn->sec)
return NULL;
return next;
}
static bool gcov_enabled(struct objtool_file *file)
{
struct section *sec;
struct symbol *sym;
list_for_each_entry(sec, &file->elf->sections, list)
list_for_each_entry(sym, &sec->symbol_list, list)
if (!strncmp(sym->name, "__gcov_.", 8))
return true;
return false;
}
#define for_each_insn(file, insn) \
list_for_each_entry(insn, &file->insn_list, list)
#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))
/*
* 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;
struct instruction *insn;
/* 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;
}
/* check if it has a context switching instruction */
func_for_each_insn(file, func, insn)
if (insn->type == INSN_CONTEXT_SWITCH)
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"
};
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);
}
/*
* 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;
list_for_each_entry(sec, &file->elf->sections, list) {
if (!(sec->sh.sh_flags & SHF_EXECINSTR))
continue;
for (offset = 0; offset < sec->len; offset += insn->len) {
insn = malloc(sizeof(*insn));
memset(insn, 0, sizeof(*insn));
INIT_LIST_HEAD(&insn->alts);
insn->sec = sec;
insn->offset = offset;
ret = arch_decode_instruction(file->elf, sec, offset,
sec->len - offset,
&insn->len, &insn->type,
&insn->immediate);
if (ret)
return ret;
if (!insn->type || insn->type > INSN_LAST) {
WARN_FUNC("invalid instruction type %d",
insn->sec, insn->offset, insn->type);
return -1;
}
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;
}
/*
* Find all uses of the unreachable() macro, which are code path dead ends.
*/
static int add_dead_ends(struct objtool_file *file)
{
struct section *sec;
struct rela *rela;
struct instruction *insn;
bool found;
sec = find_section_by_name(file->elf, ".rela__unreachable");
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 .rela__unreachable");
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;
}
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;
list_for_each_entry(sec, &file->elf->sections, list) {
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)
insn->visited = true;
}
}
}
/*
* 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;
/* skip ignores */
if (insn->visited)
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;
} 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);
if (!insn->call_dest) {
WARN_FUNC("can't find call dest symbol at offset 0x%lx",
insn->sec, insn->offset, dest_off);
return -1;
}
} 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)
{
struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump;
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;
}
if (!next_insn_same_sec(file, last_orig_insn)) {
WARN("%s: don't know how to handle alternatives at end of section",
special_alt->orig_sec->name);
return -1;
}
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);
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);
if (!special_alt->new_len) {
*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;
if (insn->type != INSN_JUMP_CONDITIONAL &&
insn->type != INSN_JUMP_UNCONDITIONAL)
continue;
if (!insn->immediate)
continue;
dest_off = insn->offset + insn->len + insn->immediate;
if (dest_off == special_alt->new_off + special_alt->new_len)
insn->jump_dest = fake_jump;
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;
}
list_add(&fake_jump->list, &last_new_insn->list);
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) {
alt = malloc(sizeof(*alt));
if (!alt) {
WARN("malloc failed");
ret = -1;
goto out;
}
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;
}
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.
*
* TODO: Once we have DWARF CFI and smarter instruction decoding logic,
* ensure the same register is used in the mov and jump instructions.
*/
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;
file->ignore_unreachables = true;
return rodata_rela;
}
/* case 3 */
func_for_each_insn_continue_reverse(file, func, insn) {
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;
text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
insn->len);
if (text_rela && text_rela->sym == file->rodata->sym)
return find_rela_by_dest(file->rodata,
text_rela->addend);
}
return NULL;
}
static int add_func_switch_tables(struct objtool_file *file,
struct symbol *func)
{
struct instruction *insn, *prev_jump = NULL;
struct rela *rela, *prev_rela = NULL;
int ret;
func_for_each_insn(file, func, insn) {
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;
list_for_each_entry(sec, &file->elf->sections, list) {
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;
}
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);
ret = add_jump_destinations(file);
if (ret)
return ret;
ret = add_call_destinations(file);
if (ret)
return ret;
ret = add_special_section_alts(file);
if (ret)
return ret;
ret = add_switch_table_alts(file);
if (ret)
return ret;
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;
}
static bool has_modified_stack_frame(struct instruction *insn)
{
return (insn->state & STATE_FP_SAVED) ||
(insn->state & STATE_FP_SETUP);
}
static bool has_valid_stack_frame(struct instruction *insn)
{
return (insn->state & STATE_FP_SAVED) &&
(insn->state & STATE_FP_SETUP);
}
static unsigned int frame_state(unsigned long state)
{
return (state & (STATE_FP_SAVED | STATE_FP_SETUP));
}
/*
* 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.
*/
static int validate_branch(struct objtool_file *file,
struct instruction *first, unsigned char first_state)
{
struct alternative *alt;
struct instruction *insn;
struct section *sec;
struct symbol *func = NULL;
unsigned char state;
int ret;
insn = first;
sec = insn->sec;
state = first_state;
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);
return 1;
}
while (1) {
if (file->c_file && insn->func) {
if (func && func != insn->func) {
WARN("%s() falls through to next function %s()",
func->name, insn->func->name);
return 1;
}
func = insn->func;
}
if (insn->visited) {
if (frame_state(insn->state) != frame_state(state)) {
WARN_FUNC("frame pointer state mismatch",
sec, insn->offset);
return 1;
}
return 0;
}
insn->visited = true;
insn->state = state;
list_for_each_entry(alt, &insn->alts, list) {
ret = validate_branch(file, alt->insn, state);
if (ret)
return 1;
}
switch (insn->type) {
case INSN_FP_SAVE:
if (!nofp) {
if (state & STATE_FP_SAVED) {
WARN_FUNC("duplicate frame pointer save",
sec, insn->offset);
return 1;
}
state |= STATE_FP_SAVED;
}
break;
case INSN_FP_SETUP:
if (!nofp) {
if (state & STATE_FP_SETUP) {
WARN_FUNC("duplicate frame pointer setup",
sec, insn->offset);
return 1;
}
state |= STATE_FP_SETUP;
}
break;
case INSN_FP_RESTORE:
if (!nofp) {
if (has_valid_stack_frame(insn))
state &= ~STATE_FP_SETUP;
state &= ~STATE_FP_SAVED;
}
break;
case INSN_RETURN:
if (!nofp && has_modified_stack_frame(insn)) {
WARN_FUNC("return without frame pointer restore",
sec, insn->offset);
return 1;
}
return 0;
case INSN_CALL:
if (is_fentry_call(insn)) {
state |= STATE_FENTRY;
break;
}
ret = dead_end_function(file, insn->call_dest);
if (ret == 1)
return 0;
if (ret == -1)
return 1;
/* fallthrough */
case INSN_CALL_DYNAMIC:
if (!nofp && !has_valid_stack_frame(insn)) {
WARN_FUNC("call without frame pointer save/setup",
sec, insn->offset);
return 1;
}
break;
case INSN_JUMP_CONDITIONAL:
case INSN_JUMP_UNCONDITIONAL:
if (insn->jump_dest) {
ret = validate_branch(file, insn->jump_dest,
state);
if (ret)
return 1;
} else if (has_modified_stack_frame(insn)) {
WARN_FUNC("sibling call from callable instruction with changed frame pointer",
sec, insn->offset);
return 1;
} /* else it's a sibling call */
if (insn->type == INSN_JUMP_UNCONDITIONAL)
return 0;
break;
case INSN_JUMP_DYNAMIC:
if (list_empty(&insn->alts) &&
has_modified_stack_frame(insn)) {
WARN_FUNC("sibling call from callable instruction with changed frame pointer",
sec, insn->offset);
return 1;
}
return 0;
default:
break;
}
if (insn->dead_end)
return 0;
insn = next_insn_same_sec(file, insn);
if (!insn) {
WARN("%s: unexpected end of section", sec->name);
return 1;
}
}
return 0;
}
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"));
}
static bool ignore_unreachable_insn(struct symbol *func,
struct instruction *insn)
{
int i;
if (insn->type == INSN_NOP)
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.
*/
for (i = 0; i < 5; i++) {
if (is_kasan_insn(insn) || is_ubsan_insn(insn))
return true;
if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest) {
insn = insn->jump_dest;
continue;
}
if (insn->offset + insn->len >= func->offset + func->len)
break;
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;
int ret, warnings = 0;
list_for_each_entry(sec, &file->elf->sections, list) {
list_for_each_entry(func, &sec->symbol_list, list) {
if (func->type != STT_FUNC)
continue;
insn = find_insn(file, sec, func->offset);
if (!insn)
continue;
ret = validate_branch(file, insn, 0);
warnings += ret;
}
}
list_for_each_entry(sec, &file->elf->sections, list) {
list_for_each_entry(func, &sec->symbol_list, list) {
if (func->type != STT_FUNC)
continue;
func_for_each_insn(file, func, insn) {
if (insn->visited)
continue;
insn->visited = true;
if (file->ignore_unreachables || warnings ||
ignore_unreachable_insn(func, insn))
continue;
/*
* gcov produces a lot of unreachable
* instructions. If we get an unreachable
* warning and the file has gcov enabled, just
* ignore it, and all other such warnings for
* the file.
*/
if (!file->ignore_unreachables &&
gcov_enabled(file)) {
file->ignore_unreachables = true;
continue;
}
WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset);
warnings++;
}
}
}
return warnings;
}
static int validate_uncallable_instructions(struct objtool_file *file)
{
struct instruction *insn;
int warnings = 0;
for_each_insn(file, insn) {
if (!insn->visited && insn->type == INSN_RETURN) {
WARN_FUNC("return instruction outside of a callable function",
insn->sec, insn->offset);
warnings++;
}
}
return warnings;
}
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);
}
const char * const check_usage[] = {
"objtool check [<options>] file.o",
NULL,
};
int cmd_check(int argc, const char **argv)
{
struct objtool_file file;
int ret, warnings = 0;
const struct option options[] = {
OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"),
OPT_END(),
};
argc = parse_options(argc, argv, options, check_usage, 0);
if (argc != 1)
usage_with_options(check_usage, options);
objname = argv[0];
file.elf = elf_open(objname);
if (!file.elf) {
fprintf(stderr, "error reading elf file %s\n", objname);
return 1;
}
INIT_LIST_HEAD(&file.insn_list);
hash_init(file.insn_hash);
file.whitelist = find_section_by_name(file.elf, "__func_stack_frame_non_standard");
file.rodata = find_section_by_name(file.elf, ".rodata");
file.ignore_unreachables = false;
file.c_file = find_section_by_name(file.elf, ".comment");
ret = decode_sections(&file);
if (ret < 0)
goto out;
warnings += ret;
ret = validate_functions(&file);
if (ret < 0)
goto out;
warnings += ret;
ret = validate_uncallable_instructions(&file);
if (ret < 0)
goto out;
warnings += ret;
out:
cleanup(&file);
/* ignore warnings for now until we get all the code cleaned up */
if (ret || warnings)
return 0;
return 0;
}