linux/tools/objtool/check.c

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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>
#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;
static bool nofp;
struct cfi_state initial_func_cfi;
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 || &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;
for_each_sec(file, sec)
list_for_each_entry(sym, &sec->symbol_list, list)
if (!strncmp(sym->name, "__gcov_.", 8))
return true;
return false;
}
#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))
#define sec_for_each_insn_continue(file, insn) \
for (insn = next_insn_same_sec(file, insn); 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;
objtool: Silence warnings for functions which use IRET Previously, objtool ignored functions which have the IRET instruction in them. That's because it assumed that such functions know what they're doing with respect to frame pointers. With the new "objtool 2.0" changes, it stopped ignoring such functions, and started complaining about them: arch/x86/kernel/alternative.o: warning: objtool: do_sync_core()+0x1b: unsupported instruction in callable function arch/x86/kernel/alternative.o: warning: objtool: text_poke()+0x1a8: unsupported instruction in callable function arch/x86/kernel/ftrace.o: warning: objtool: do_sync_core()+0x16: unsupported instruction in callable function arch/x86/kernel/cpu/mcheck/mce.o: warning: objtool: machine_check_poll()+0x166: unsupported instruction in callable function arch/x86/kernel/cpu/mcheck/mce.o: warning: objtool: do_machine_check()+0x147: unsupported instruction in callable function Silence those warnings for now. They can be re-enabled later, once we have unwind hints which will allow the code to annotate the IRET usages. Reported-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Jiri Slaby <jslaby@suse.cz> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: live-patching@vger.kernel.org Fixes: baa41469a7b9 ("objtool: Implement stack validation 2.0") Link: http://lkml.kernel.org/r/20170630140934.mmwtpockvpupahro@treble Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-06-30 16:09:34 +02:00
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;
}
objtool: Silence warnings for functions which use IRET Previously, objtool ignored functions which have the IRET instruction in them. That's because it assumed that such functions know what they're doing with respect to frame pointers. With the new "objtool 2.0" changes, it stopped ignoring such functions, and started complaining about them: arch/x86/kernel/alternative.o: warning: objtool: do_sync_core()+0x1b: unsupported instruction in callable function arch/x86/kernel/alternative.o: warning: objtool: text_poke()+0x1a8: unsupported instruction in callable function arch/x86/kernel/ftrace.o: warning: objtool: do_sync_core()+0x16: unsupported instruction in callable function arch/x86/kernel/cpu/mcheck/mce.o: warning: objtool: machine_check_poll()+0x166: unsupported instruction in callable function arch/x86/kernel/cpu/mcheck/mce.o: warning: objtool: do_machine_check()+0x147: unsupported instruction in callable function Silence those warnings for now. They can be re-enabled later, once we have unwind hints which will allow the code to annotate the IRET usages. Reported-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Jiri Slaby <jslaby@suse.cz> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: live-patching@vger.kernel.org Fixes: baa41469a7b9 ("objtool: Implement stack validation 2.0") Link: http://lkml.kernel.org/r/20170630140934.mmwtpockvpupahro@treble Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-06-30 16:09:34 +02:00
/* 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",
"fortify_panic",
};
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);
}
static void clear_insn_state(struct insn_state *state)
{
int i;
memset(state, 0, sizeof(*state));
state->cfa.base = CFI_UNDEFINED;
for (i = 0; i < CFI_NUM_REGS; i++)
state->regs[i].base = CFI_UNDEFINED;
state->drap_reg = CFI_UNDEFINED;
}
/*
* 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;
for_each_sec(file, sec) {
if (!(sec->sh.sh_flags & SHF_EXECINSTR))
continue;
for (offset = 0; offset < sec->len; offset += insn->len) {
insn = malloc(sizeof(*insn));
if (!insn) {
WARN("malloc failed");
return -1;
}
memset(insn, 0, sizeof(*insn));
INIT_LIST_HEAD(&insn->alts);
clear_insn_state(&insn->state);
insn->sec = sec;
insn->offset = offset;
ret = arch_decode_instruction(file->elf, sec, offset,
sec->len - offset,
&insn->len, &insn->type,
&insn->immediate,
&insn->stack_op);
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.discard.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 %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;
}
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;
for_each_sec(file, sec) {
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->ignore = 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;
if (insn->ignore)
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);
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;
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;
/* look for a relocation which references .rodata */
text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
insn->len);
if (!text_rela || text_rela->sym != file->rodata->sym)
continue;
/*
* Make sure the .rodata address isn't associated with a
* symbol. gcc jump tables are anonymous data.
*/
if (find_symbol_containing(file->rodata, text_rela->addend))
continue;
return find_rela_by_dest(file->rodata, text_rela->addend);
}
return NULL;
}
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;
for_each_sec(file, sec) {
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 insn_state *state)
{
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;
}
static void save_reg(struct insn_state *state, unsigned char reg, int base,
int offset)
{
if ((arch_callee_saved_reg(reg) ||
(state->drap && reg == state->drap_reg)) &&
state->regs[reg].base == CFI_UNDEFINED) {
state->regs[reg].base = base;
state->regs[reg].offset = offset;
}
}
static void restore_reg(struct insn_state *state, unsigned char reg)
{
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;
}
switch (op->dest.type) {
case OP_DEST_REG:
switch (op->src.type) {
case OP_SRC_REG:
if (cfa->base == op->src.reg && cfa->base == CFI_SP &&
op->dest.reg == CFI_BP && regs[CFI_BP].base == CFI_CFA &&
regs[CFI_BP].offset == -cfa->offset) {
/* mov %rsp, %rbp */
cfa->base = op->dest.reg;
state->bp_scratch = false;
} else if (state->drap) {
/* drap: mov %rsp, %rbp */
regs[CFI_BP].base = CFI_BP;
regs[CFI_BP].offset = -state->stack_size;
state->bp_scratch = false;
} else if (!nofp) {
WARN_FUNC("unknown stack-related register move",
insn->sec, insn->offset);
return -1;
}
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;
}
if (op->dest.reg != CFI_BP && op->src.reg == CFI_SP &&
cfa->base == CFI_SP) {
/* drap: lea disp(%rsp), %drap */
state->drap_reg = op->dest.reg;
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;
}
if (regs[op->dest.reg].offset == -state->stack_size) {
if (state->drap && cfa->base == CFI_BP_INDIRECT &&
op->dest.type == OP_DEST_REG &&
op->dest.reg == state->drap_reg) {
/* drap: pop %drap */
cfa->base = state->drap_reg;
cfa->offset = 0;
}
restore_reg(state, op->dest.reg);
}
state->stack_size -= 8;
if (cfa->base == CFI_SP)
cfa->offset -= 8;
break;
case OP_SRC_REG_INDIRECT:
if (state->drap && op->src.reg == CFI_BP &&
op->src.offset == regs[op->dest.reg].offset) {
/* drap: mov disp(%rbp), %reg */
if (op->dest.reg == state->drap_reg) {
cfa->base = state->drap_reg;
cfa->offset = 0;
}
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;
/* save drap so we know when to undefine it */
save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
} 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 */
if (!nofp && insn->func && op->src.reg == CFI_BP &&
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;
/* save drap so we know when to undefine it */
save_reg(state, op->src.reg, CFI_CFA, op->dest.offset);
}
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;
}
} else if (state1->drap != state2->drap ||
(state1->drap && state1->drap_reg != state2->drap_reg)) {
WARN_FUNC("stack state mismatch: drap1=%d(%d) drap2=%d(%d)",
insn->sec, insn->offset,
state1->drap, state1->drap_reg,
state2->drap, state2->drap_reg);
} else
return true;
return false;
}
/*
* 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,
struct insn_state state)
{
struct alternative *alt;
struct instruction *insn;
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);
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 (func && insn->ignore) {
WARN_FUNC("BUG: why am I validating an ignored function?",
sec, insn->offset);
return -1;
}
if (insn->visited) {
if (!!insn_state_match(insn, &state))
return 1;
return 0;
}
insn->state = state;
insn->visited = true;
list_for_each_entry(alt, &insn->alts, list) {
ret = validate_branch(file, alt->insn, state);
if (ret)
return 1;
}
switch (insn->type) {
case INSN_RETURN:
if (func && has_modified_stack_frame(&state)) {
WARN_FUNC("return with modified stack frame",
sec, insn->offset);
return 1;
}
if (state.bp_scratch) {
WARN("%s uses BP as a scratch register",
insn->func->name);
return 1;
}
return 0;
case INSN_CALL:
if (is_fentry_call(insn))
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 && func && !has_valid_stack_frame(&state)) {
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 &&
(!func || !insn->jump_dest->func ||
func == insn->jump_dest->func)) {
ret = validate_branch(file, insn->jump_dest,
state);
if (ret)
return 1;
} else if (func && has_modified_stack_frame(&state)) {
WARN_FUNC("sibling call from callable instruction with modified stack frame",
sec, insn->offset);
return 1;
}
if (insn->type == INSN_JUMP_UNCONDITIONAL)
return 0;
break;
case INSN_JUMP_DYNAMIC:
if (func && list_empty(&insn->alts) &&
has_modified_stack_frame(&state)) {
WARN_FUNC("sibling call from callable instruction with modified stack frame",
sec, insn->offset);
return 1;
}
return 0;
case INSN_STACK:
if (update_insn_state(insn, &state))
return -1;
break;
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 instruction *insn)
{
int i;
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.
*/
if (!strcmp(insn->sec->name, ".fixup"))
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.
*/
if (!insn->func)
return false;
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 >= insn->func->offset + insn->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;
struct insn_state state;
int ret, warnings = 0;
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) {
list_for_each_entry(func, &sec->symbol_list, list) {
if (func->type != STT_FUNC)
continue;
insn = find_insn(file, sec, func->offset);
if (!insn || insn->ignore)
continue;
ret = validate_branch(file, insn, state);
warnings += ret;
}
}
return warnings;
}
static int validate_reachable_instructions(struct objtool_file *file)
{
struct instruction *insn;
if (file->ignore_unreachables)
return 0;
for_each_insn(file, insn) {
if (insn->visited || ignore_unreachable_insn(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. Do
* this here because this is an expensive function.
*/
if (gcov_enabled(file))
return 0;
WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
return 1;
}
return 0;
}
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);
}
int check(const char *_objname, bool _nofp)
{
struct objtool_file file;
int ret, warnings = 0;
objname = _objname;
nofp = _nofp;
file.elf = elf_open(objname);
if (!file.elf)
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.ignore_unreachables = false;
file.c_file = find_section_by_name(file.elf, ".comment");
arch_initial_func_cfi_state(&initial_func_cfi);
ret = decode_sections(&file);
if (ret < 0)
goto out;
warnings += ret;
if (list_empty(&file.insn_list))
goto out;
ret = validate_functions(&file);
if (ret < 0)
goto out;
warnings += ret;
if (!warnings) {
ret = validate_reachable_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;
}