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c4a33939a7
linux/tools/objtool/check.c
Peter Zijlstra c4a33939a7 objtool: Implement noinstr validation 
Validate that any call out of .noinstr.text is in between
instr_begin() and instr_end() annotations.

This annotation is useful to ensure correct behaviour wrt tracing
sensitive code like entry/exit and idle code. When we run code in a
sensitive context we want a guarantee no unknown code is ran.

Since this validation relies on knowing the section of call
destination symbols, we must run it on vmlinux.o instead of on
individual object files.

Add two options:

 -d/--duplicate "duplicate validation for vmlinux"
 -l/--vmlinux "vmlinux.o validation"

Where the latter auto-detects when objname ends with "vmlinux.o" and
the former will force all validations, also those already done on
!vmlinux object files.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20200416115119.106268040@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2020-04-22 10:53:50 +02:00

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// SPDX-License-Identifier: GPL-2.0-or-later
/*
* Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
*/
#include <string.h>
#include <stdlib.h>
#include "builtin.h"
#include "check.h"
#include "elf.h"
#include "special.h"
#include "arch.h"
#include "warn.h"
#include <linux/hashtable.h>
#include <linux/kernel.h>
#define FAKE_JUMP_OFFSET -1
#define C_JUMP_TABLE_SECTION ".rodata..c_jump_table"
struct alternative {
struct list_head list;
struct instruction *insn;
bool skip_orig;
};
const char *objname;
struct cfi_init_state initial_func_cfi;
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 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(file, func, insn) \
for (insn = find_insn(file, func->sec, func->offset); \
insn; \
insn = next_insn_same_func(file, insn))
#define sym_for_each_insn(file, sym, insn) \
for (insn = find_insn(file, sym->sec, sym->offset); \
insn && &insn->list != &file->insn_list && \
insn->sec == sym->sec && \
insn->offset < sym->offset + sym->len; \
insn = list_next_entry(insn, list))
#define sym_for_each_insn_continue_reverse(file, sym, insn) \
for (insn = list_prev_entry(insn, list); \
&insn->list != &file->insn_list && \
insn->sec == sym->sec && insn->offset >= sym->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))
static bool is_static_jump(struct instruction *insn)
{
return insn->type == INSN_JUMP_CONDITIONAL ||
insn->type == INSN_JUMP_UNCONDITIONAL;
}
static bool is_sibling_call(struct instruction *insn)
{
/* An indirect jump is either a sibling call or a jump to a table. */
if (insn->type == INSN_JUMP_DYNAMIC)
return list_empty(&insn->alts);
if (!is_static_jump(insn))
return false;
/* add_jump_destinations() sets insn->call_dest for sibling calls. */
return !!insn->call_dest;
}
/*
* 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.
*/
static bool __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",
"__reiserfs_panic",
"lbug_with_loc",
"fortify_panic",
"usercopy_abort",
"machine_real_restart",
"rewind_stack_do_exit",
"kunit_try_catch_throw",
};
if (!func)
return false;
if (func->bind == STB_WEAK)
return false;
if (func->bind == STB_GLOBAL)
for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
if (!strcmp(func->name, global_noreturns[i]))
return true;
if (!func->len)
return false;
insn = find_insn(file, func->sec, func->offset);
if (!insn->func)
return false;
func_for_each_insn(file, func, insn) {
empty = false;
if (insn->type == INSN_RETURN)
return false;
}
if (empty)
return false;
/*
* 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 (is_sibling_call(insn)) {
struct instruction *dest = insn->jump_dest;
if (!dest)
/* sibling call to another file */
return false;
/* local sibling call */
if (recursion == 5) {
/*
* Infinite recursion: two functions have
* sibling calls to each other. This is a very
* rare case. It means they aren't dead ends.
*/
return false;
}
return __dead_end_function(file, dest->func, recursion+1);
}
}
return true;
}
static bool dead_end_function(struct objtool_file *file, struct symbol *func)
{
return __dead_end_function(file, func, 0);
}
static void init_cfi_state(struct cfi_state *cfi)
{
int i;
for (i = 0; i < CFI_NUM_REGS; i++) {
cfi->regs[i].base = CFI_UNDEFINED;
cfi->vals[i].base = CFI_UNDEFINED;
}
cfi->cfa.base = CFI_UNDEFINED;
cfi->drap_reg = CFI_UNDEFINED;
cfi->drap_offset = -1;
}
static void clear_insn_state(struct insn_state *state)
{
memset(state, 0, sizeof(*state));
init_cfi_state(&state->cfi);
}
/*
* 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;
unsigned long nr_insns = 0;
int ret;
for_each_sec(file, sec) {
if (!(sec->sh.sh_flags & SHF_EXECINSTR))
continue;
if (strcmp(sec->name, ".altinstr_replacement") &&
strcmp(sec->name, ".altinstr_aux") &&
strncmp(sec->name, ".discard.", 9))
sec->text = true;
if (!strcmp(sec->name, ".noinstr.text"))
sec->noinstr = true;
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);
INIT_LIST_HEAD(&insn->stack_ops);
init_cfi_state(&insn->cfi);
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_ops);
if (ret)
goto err;
hash_add(file->insn_hash, &insn->hash, insn->offset);
list_add_tail(&insn->list, &file->insn_list);
nr_insns++;
}
list_for_each_entry(func, &sec->symbol_list, list) {
if (func->type != STT_FUNC || func->alias != func)
continue;
if (!find_insn(file, sec, func->offset)) {
WARN("%s(): can't find starting instruction",
func->name);
return -1;
}
sym_for_each_insn(file, func, insn)
insn->func = func;
}
}
if (stats)
printf("nr_insns: %lu\n", nr_insns);
return 0;
err:
free(insn);
return ret;
}
/*
* Mark "ud2" instructions and manually annotated dead ends.
*/
static int add_dead_ends(struct objtool_file *file)
{
struct section *sec;
struct rela *rela;
struct instruction *insn;
bool found;
/*
* 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.
*/
sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
if (!sec)
goto reachable;
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;
}
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;
}
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;
struct rela *rela;
sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
if (!sec)
return;
list_for_each_entry(rela, &sec->rela_list, list) {
switch (rela->sym->type) {
case STT_FUNC:
func = rela->sym;
break;
case STT_SECTION:
func = find_func_by_offset(rela->sym->sec, rela->addend);
if (!func)
continue;
break;
default:
WARN("unexpected relocation symbol type in %s: %d", sec->name, rela->sym->type);
continue;
}
func_for_each_insn(file, func, insn)
insn->ignore = true;
}
}
/*
* This is a whitelist of functions that is allowed to be called with AC set.
* The list is meant to be minimal and only contains compiler instrumentation
* ABI and a few functions used to implement *_{to,from}_user() functions.
*
* These functions must not directly change AC, but may PUSHF/POPF.
*/
static const char *uaccess_safe_builtin[] = {
/* KASAN */
"kasan_report",
"check_memory_region",
/* KASAN out-of-line */
"__asan_loadN_noabort",
"__asan_load1_noabort",
"__asan_load2_noabort",
"__asan_load4_noabort",
"__asan_load8_noabort",
"__asan_load16_noabort",
"__asan_storeN_noabort",
"__asan_store1_noabort",
"__asan_store2_noabort",
"__asan_store4_noabort",
"__asan_store8_noabort",
"__asan_store16_noabort",
/* KASAN in-line */
"__asan_report_load_n_noabort",
"__asan_report_load1_noabort",
"__asan_report_load2_noabort",
"__asan_report_load4_noabort",
"__asan_report_load8_noabort",
"__asan_report_load16_noabort",
"__asan_report_store_n_noabort",
"__asan_report_store1_noabort",
"__asan_report_store2_noabort",
"__asan_report_store4_noabort",
"__asan_report_store8_noabort",
"__asan_report_store16_noabort",
/* KCOV */
"write_comp_data",
"__sanitizer_cov_trace_pc",
"__sanitizer_cov_trace_const_cmp1",
"__sanitizer_cov_trace_const_cmp2",
"__sanitizer_cov_trace_const_cmp4",
"__sanitizer_cov_trace_const_cmp8",
"__sanitizer_cov_trace_cmp1",
"__sanitizer_cov_trace_cmp2",
"__sanitizer_cov_trace_cmp4",
"__sanitizer_cov_trace_cmp8",
"__sanitizer_cov_trace_switch",
/* UBSAN */
"ubsan_type_mismatch_common",
"__ubsan_handle_type_mismatch",
"__ubsan_handle_type_mismatch_v1",
"__ubsan_handle_shift_out_of_bounds",
/* misc */
"csum_partial_copy_generic",
"__memcpy_mcsafe",
"mcsafe_handle_tail",
"ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
NULL
};
static void add_uaccess_safe(struct objtool_file *file)
{
struct symbol *func;
const char **name;
if (!uaccess)
return;
for (name = uaccess_safe_builtin; *name; name++) {
func = find_symbol_by_name(file->elf, *name);
if (!func)
continue;
func->uaccess_safe = true;
}
}
/*
* 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_ignore_alternatives(struct objtool_file *file)
{
struct section *sec;
struct rela *rela;
struct instruction *insn;
sec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
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.ignore_alts entry");
return -1;
}
insn->ignore_alts = true;
}
return 0;
}
/*
* 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 (!is_static_jump(insn))
continue;
if (insn->ignore || insn->offset == FAKE_JUMP_OFFSET)
continue;
rela = find_rela_by_dest_range(file->elf, insn->sec,
insn->offset, insn->len);
if (!rela) {
dest_sec = insn->sec;
dest_off = arch_jump_destination(insn);
} else if (rela->sym->type == STT_SECTION) {
dest_sec = rela->sym->sec;
dest_off = arch_dest_rela_offset(rela->addend);
} else if (rela->sym->sec->idx) {
dest_sec = rela->sym->sec;
dest_off = rela->sym->sym.st_value +
arch_dest_rela_offset(rela->addend);
} else if (strstr(rela->sym->name, "_indirect_thunk_")) {
/*
* Retpoline jumps are really dynamic jumps in
* disguise, so convert them accordingly.
*/
if (insn->type == INSN_JUMP_UNCONDITIONAL)
insn->type = INSN_JUMP_DYNAMIC;
else
insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;
insn->retpoline_safe = true;
continue;
} else {
/* external sibling call */
insn->call_dest = rela->sym;
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;
}
/*
* Cross-function jump.
*/
if (insn->func && insn->jump_dest->func &&
insn->func != insn->jump_dest->func) {
/*
* For GCC 8+, create parent/child links for any cold
* subfunctions. This is _mostly_ redundant with a
* similar initialization in read_symbols().
*
* If a function has aliases, we want the *first* such
* function in the symbol table to be the subfunction's
* parent. In that case we overwrite the
* initialization done in read_symbols().
*
* However this code can't completely replace the
* read_symbols() code because this doesn't detect the
* case where the parent function's only reference to a
* subfunction is through a jump table.
*/
if (!strstr(insn->func->name, ".cold.") &&
strstr(insn->jump_dest->func->name, ".cold.")) {
insn->func->cfunc = insn->jump_dest->func;
insn->jump_dest->func->pfunc = insn->func;
} else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
insn->jump_dest->offset == insn->jump_dest->func->offset) {
/* internal sibling call */
insn->call_dest = insn->jump_dest->func;
}
}
}
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(file->elf, insn->sec,
insn->offset, insn->len);
if (!rela) {
dest_off = arch_jump_destination(insn);
insn->call_dest = find_func_by_offset(insn->sec, dest_off);
if (!insn->call_dest)
insn->call_dest = find_symbol_by_offset(insn->sec, dest_off);
if (insn->ignore)
continue;
if (!insn->call_dest) {
WARN_FUNC("unsupported intra-function call",
insn->sec, insn->offset);
if (retpoline)
WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
return -1;
}
if (insn->func && insn->call_dest->type != STT_FUNC) {
WARN_FUNC("unsupported call to non-function",
insn->sec, insn->offset);
return -1;
}
} else if (rela->sym->type == STT_SECTION) {
dest_off = arch_dest_rela_offset(rela->addend);
insn->call_dest = find_func_by_offset(rela->sym->sec,
dest_off);
if (!insn->call_dest) {
WARN_FUNC("can't find call dest symbol at %s+0x%lx",
insn->sec, insn->offset,
rela->sym->sec->name,
dest_off);
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.
*/
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 = NULL;
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;
insn->alt_group = true;
last_orig_insn = insn;
}
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);
INIT_LIST_HEAD(&fake_jump->stack_ops);
init_cfi_state(&fake_jump->cfi);
fake_jump->sec = special_alt->new_sec;
fake_jump->offset = FAKE_JUMP_OFFSET;
fake_jump->type = INSN_JUMP_UNCONDITIONAL;
fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
fake_jump->func = orig_insn->func;
}
if (!special_alt->new_len) {
if (!fake_jump) {
WARN("%s: empty alternative at end of section",
special_alt->orig_sec->name);
return -1;
}
*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;
insn->ignore = orig_insn->ignore_alts;
insn->func = orig_insn->func;
/*
* Since alternative replacement code is copy/pasted by the
* kernel after applying relocations, generally such code can't
* have relative-address relocation references to outside the
* .altinstr_replacement section, unless the arch's
* alternatives code can adjust the relative offsets
* accordingly.
*
* The x86 alternatives code adjusts the offsets only when it
* encounters a branch instruction at the very beginning of the
* replacement group.
*/
if ((insn->offset != special_alt->new_off ||
(insn->type != INSN_CALL && !is_static_jump(insn))) &&
find_rela_by_dest_range(file->elf, insn->sec, insn->offset, insn->len)) {
WARN_FUNC("unsupported relocation in alternatives section",
insn->sec, insn->offset);
return -1;
}
if (!is_static_jump(insn))
continue;
if (!insn->immediate)
continue;
dest_off = arch_jump_destination(insn);
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;
}
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;
}
if (fake_jump)
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) {
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) {
if (!special_alt->orig_len) {
WARN_FUNC("empty alternative entry",
orig_insn->sec, orig_insn->offset);
continue;
}
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 = malloc(sizeof(*alt));
if (!alt) {
WARN("malloc failed");
ret = -1;
goto out;
}
alt->insn = new_insn;
alt->skip_orig = special_alt->skip_orig;
orig_insn->ignore_alts |= special_alt->skip_alt;
list_add_tail(&alt->list, &orig_insn->alts);
list_del(&special_alt->list);
free(special_alt);
}
out:
return ret;
}
static int add_jump_table(struct objtool_file *file, struct instruction *insn,
struct rela *table)
{
struct rela *rela = table;
struct instruction *dest_insn;
struct alternative *alt;
struct symbol *pfunc = insn->func->pfunc;
unsigned int prev_offset = 0;
/*
* Each @rela is a switch table relocation which points to the target
* instruction.
*/
list_for_each_entry_from(rela, &table->sec->rela_list, list) {
/* Check for the end of the table: */
if (rela != table && rela->jump_table_start)
break;
/* Make sure the 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;
dest_insn = find_insn(file, rela->sym->sec, rela->addend);
if (!dest_insn)
break;
/* Make sure the destination is in the same function: */
if (!dest_insn->func || dest_insn->func->pfunc != pfunc)
break;
alt = malloc(sizeof(*alt));
if (!alt) {
WARN("malloc failed");
return -1;
}
alt->insn = dest_insn;
list_add_tail(&alt->list, &insn->alts);
prev_offset = rela->offset;
}
if (!prev_offset) {
WARN_FUNC("can't find switch jump table",
insn->sec, insn->offset);
return -1;
}
return 0;
}
/*
* find_jump_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.
*
* 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.
*
* TODO: Once we have DWARF CFI and smarter instruction decoding logic,
* ensure the same register is used in the mov and jump instructions.
*
* NOTE: RETPOLINE made it harder still to decode dynamic jumps.
*/
static struct rela *find_jump_table(struct objtool_file *file,
struct symbol *func,
struct instruction *insn)
{
struct rela *text_rela, *table_rela;
struct instruction *dest_insn, *orig_insn = insn;
struct section *table_sec;
unsigned long table_offset;
/*
* 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 != &file->insn_list && insn->func && insn->func->pfunc == func;
insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
if (insn != orig_insn && 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(file->elf, insn->sec,
insn->offset, insn->len);
if (!text_rela || text_rela->sym->type != STT_SECTION ||
!text_rela->sym->sec->rodata)
continue;
table_offset = text_rela->addend;
table_sec = text_rela->sym->sec;
if (text_rela->type == R_X86_64_PC32)
table_offset += 4;
/*
* Make sure the .rodata address isn't associated with a
* symbol. GCC jump tables are anonymous data.
*
* Also support C jump tables which are in the same format as
* switch jump tables. For objtool to recognize them, they
* need to be placed in the C_JUMP_TABLE_SECTION section. They
* have symbols associated with them.
*/
if (find_symbol_containing(table_sec, table_offset) &&
strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
continue;
/*
* Each table entry has a rela associated with it. The rela
* should reference text in the same function as the original
* instruction.
*/
table_rela = find_rela_by_dest(file->elf, table_sec, table_offset);
if (!table_rela)
continue;
dest_insn = find_insn(file, table_rela->sym->sec, table_rela->addend);
if (!dest_insn || !dest_insn->func || dest_insn->func->pfunc != func)
continue;
/*
* Use of RIP-relative switch jumps is quite rare, and
* indicates a rare GCC quirk/bug which can leave dead code
* behind.
*/
if (text_rela->type == R_X86_64_PC32)
file->ignore_unreachables = true;
return table_rela;
}
return NULL;
}
/*
* First pass: Mark the head of each jump table so that in the next pass,
* we know when a given jump table ends and the next one starts.
*/
static void mark_func_jump_tables(struct objtool_file *file,
struct symbol *func)
{
struct instruction *insn, *last = NULL;
struct rela *rela;
func_for_each_insn(file, func, insn) {
if (!last)
last = insn;
/*
* Store back-pointers for unconditional forward jumps such
* that find_jump_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;
}
if (insn->type != INSN_JUMP_DYNAMIC)
continue;
rela = find_jump_table(file, func, insn);
if (rela) {
rela->jump_table_start = true;
insn->jump_table = rela;
}
}
}
static int add_func_jump_tables(struct objtool_file *file,
struct symbol *func)
{
struct instruction *insn;
int ret;
func_for_each_insn(file, func, insn) {
if (!insn->jump_table)
continue;
ret = add_jump_table(file, insn, insn->jump_table);
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_jump_table_alts(struct objtool_file *file)
{
struct section *sec;
struct symbol *func;
int ret;
if (!file->rodata)
return 0;
for_each_sec(file, sec) {
list_for_each_entry(func, &sec->symbol_list, list) {
if (func->type != STT_FUNC)
continue;
mark_func_jump_tables(file, func);
ret = add_func_jump_tables(file, func);
if (ret)
return ret;
}
}
return 0;
}
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(file->elf, 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->cfi.cfa;
if (hint->type == UNWIND_HINT_TYPE_RET_OFFSET) {
insn->ret_offset = hint->sp_offset;
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->cfi.type = hint->type;
insn->cfi.end = hint->end;
}
return 0;
}
static int read_retpoline_hints(struct objtool_file *file)
{
struct section *sec;
struct instruction *insn;
struct rela *rela;
sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
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.retpoline_safe entry");
return -1;
}
if (insn->type != INSN_JUMP_DYNAMIC &&
insn->type != INSN_CALL_DYNAMIC) {
WARN_FUNC("retpoline_safe hint not an indirect jump/call",
insn->sec, insn->offset);
return -1;
}
insn->retpoline_safe = true;
}
return 0;
}
static int read_instr_hints(struct objtool_file *file)
{
struct section *sec;
struct instruction *insn;
struct rela *rela;
sec = find_section_by_name(file->elf, ".rela.discard.instr_end");
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.instr_end entry");
return -1;
}
insn->instr--;
}
sec = find_section_by_name(file->elf, ".rela.discard.instr_begin");
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.instr_begin entry");
return -1;
}
insn->instr++;
}
return 0;
}
static void mark_rodata(struct objtool_file *file)
{
struct section *sec;
bool found = false;
/*
* Search for the following rodata sections, each of which can
* potentially contain jump tables:
*
* - .rodata: can contain GCC switch tables
* - .rodata.<func>: same, if -fdata-sections is being used
* - .rodata..c_jump_table: contains C annotated jump tables
*
* .rodata.str1.* sections are ignored; they don't contain jump tables.
*/
for_each_sec(file, sec) {
if (!strncmp(sec->name, ".rodata", 7) &&
!strstr(sec->name, ".str1.")) {
sec->rodata = true;
found = true;
}
}
file->rodata = found;
}
static int decode_sections(struct objtool_file *file)
{
int ret;
mark_rodata(file);
ret = decode_instructions(file);
if (ret)
return ret;
ret = add_dead_ends(file);
if (ret)
return ret;
add_ignores(file);
add_uaccess_safe(file);
ret = add_ignore_alternatives(file);
if (ret)
return ret;
ret = add_jump_destinations(file);
if (ret)
return ret;
ret = add_special_section_alts(file);
if (ret)
return ret;
ret = add_call_destinations(file);
if (ret)
return ret;
ret = add_jump_table_alts(file);
if (ret)
return ret;
ret = read_unwind_hints(file);
if (ret)
return ret;
ret = read_retpoline_hints(file);
if (ret)
return ret;
ret = read_instr_hints(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, struct insn_state *state)
{
u8 ret_offset = insn->ret_offset;
struct cfi_state *cfi = &state->cfi;
int i;
if (cfi->cfa.base != initial_func_cfi.cfa.base || cfi->drap)
return true;
if (cfi->cfa.offset != initial_func_cfi.cfa.offset + ret_offset)
return true;
if (cfi->stack_size != initial_func_cfi.cfa.offset + ret_offset)
return true;
for (i = 0; i < CFI_NUM_REGS; i++) {
if (cfi->regs[i].base != initial_func_cfi.regs[i].base ||
cfi->regs[i].offset != initial_func_cfi.regs[i].offset)
return true;
}
return false;
}
static bool has_valid_stack_frame(struct insn_state *state)
{
struct cfi_state *cfi = &state->cfi;
if (cfi->cfa.base == CFI_BP && cfi->regs[CFI_BP].base == CFI_CFA &&
cfi->regs[CFI_BP].offset == -16)
return true;
if (cfi->drap && cfi->regs[CFI_BP].base == CFI_BP)
return true;
return false;
}
static int update_cfi_state_regs(struct instruction *insn,
struct cfi_state *cfi,
struct stack_op *op)
{
struct cfi_reg *cfa = &cfi->cfa;
if (cfa->base != CFI_SP)
return 0;
/* push */
if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
cfa->offset += 8;
/* pop */
if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
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;
}
static void save_reg(struct cfi_state *cfi, unsigned char reg, int base, int offset)
{
if (arch_callee_saved_reg(reg) &&
cfi->regs[reg].base == CFI_UNDEFINED) {
cfi->regs[reg].base = base;
cfi->regs[reg].offset = offset;
}
}
static void restore_reg(struct cfi_state *cfi, unsigned char reg)
{
cfi->regs[reg].base = initial_func_cfi.regs[reg].base;
cfi->regs[reg].offset = initial_func_cfi.regs[reg].offset;
}
/*
* 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_cfi_state(struct instruction *insn, struct cfi_state *cfi,
struct stack_op *op)
{
struct cfi_reg *cfa = &cfi->cfa;
struct cfi_reg *regs = cfi->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;
}
if (cfi->type == ORC_TYPE_REGS || cfi->type == ORC_TYPE_REGS_IRET)
return update_cfi_state_regs(insn, cfi, op);
switch (op->dest.type) {
case OP_DEST_REG:
switch (op->src.type) {
case OP_SRC_REG:
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;
cfi->bp_scratch = false;
}
else if (op->src.reg == CFI_SP &&
op->dest.reg == CFI_BP && cfi->drap) {
/* drap: mov %rsp, %rbp */
regs[CFI_BP].base = CFI_BP;
regs[CFI_BP].offset = -cfi->stack_size;
cfi->bp_scratch = false;
}
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
*/
cfi->vals[op->dest.reg].base = CFI_CFA;
cfi->vals[op->dest.reg].offset = -cfi->stack_size;
}
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).
*/
cfi->stack_size = -cfi->regs[CFI_BP].offset;
}
else if (op->dest.reg == cfa->base) {
/* mov %reg, %rsp */
if (cfa->base == CFI_SP &&
cfi->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 = -cfi->vals[op->src.reg].offset;
cfi->stack_size = cfa->offset;
} else {
cfa->base = CFI_UNDEFINED;
cfa->offset = 0;
}
}
break;
case OP_SRC_ADD:
if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
/* add imm, %rsp */
cfi->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 */
cfi->stack_size = -(op->src.offset + regs[CFI_BP].offset);
break;
}
if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
/* drap: lea disp(%rsp), %drap */
cfi->drap_reg = op->dest.reg;
/*
* lea disp(%rsp), %reg
*
* This is needed for the rare case where GCC
* does something dumb like:
*
* lea 0x8(%rsp), %rcx
* ...
* mov %rcx, %rsp
*/
cfi->vals[op->dest.reg].base = CFI_CFA;
cfi->vals[op->dest.reg].offset = \
-cfi->stack_size + op->src.offset;
break;
}
if (cfi->drap && op->dest.reg == CFI_SP &&
op->src.reg == cfi->drap_reg) {
/* drap: lea disp(%drap), %rsp */
cfa->base = CFI_SP;
cfa->offset = cfi->stack_size = -op->src.offset;
cfi->drap_reg = CFI_UNDEFINED;
cfi->drap = false;
break;
}
if (op->dest.reg == cfi->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 ||
(cfi->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
(cfi->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
WARN_FUNC("unsupported stack pointer realignment",
insn->sec, insn->offset);
return -1;
}
if (cfi->drap_reg != CFI_UNDEFINED) {
/* drap: and imm, %rsp */
cfa->base = cfi->drap_reg;
cfa->offset = cfi->stack_size = 0;
cfi->drap = true;
}
/*
* Older versions of GCC (4.8ish) realign the stack
* without DRAP, with a frame pointer.
*/
break;
case OP_SRC_POP:
case OP_SRC_POPF:
if (!cfi->drap && op->dest.reg == cfa->base) {
/* pop %rbp */
cfa->base = CFI_SP;
}
if (cfi->drap && cfa->base == CFI_BP_INDIRECT &&
op->dest.reg == cfi->drap_reg &&
cfi->drap_offset == -cfi->stack_size) {
/* drap: pop %drap */
cfa->base = cfi->drap_reg;
cfa->offset = 0;
cfi->drap_offset = -1;
} else if (regs[op->dest.reg].offset == -cfi->stack_size) {
/* pop %reg */
restore_reg(cfi, op->dest.reg);
}
cfi->stack_size -= 8;
if (cfa->base == CFI_SP)
cfa->offset -= 8;
break;
case OP_SRC_REG_INDIRECT:
if (cfi->drap && op->src.reg == CFI_BP &&
op->src.offset == cfi->drap_offset) {
/* drap: mov disp(%rbp), %drap */
cfa->base = cfi->drap_reg;
cfa->offset = 0;
cfi->drap_offset = -1;
}
if (cfi->drap && op->src.reg == CFI_BP &&
op->src.offset == regs[op->dest.reg].offset) {
/* drap: mov disp(%rbp), %reg */
restore_reg(cfi, 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(cfi, op->dest.reg);
}
break;
default:
WARN_FUNC("unknown stack-related instruction",
insn->sec, insn->offset);
return -1;
}
break;
case OP_DEST_PUSH:
case OP_DEST_PUSHF:
cfi->stack_size += 8;
if (cfa->base == CFI_SP)
cfa->offset += 8;
if (op->src.type != OP_SRC_REG)
break;
if (cfi->drap) {
if (op->src.reg == cfa->base && op->src.reg == cfi->drap_reg) {
/* drap: push %drap */
cfa->base = CFI_BP_INDIRECT;
cfa->offset = -cfi->stack_size;
/* save drap so we know when to restore it */
cfi->drap_offset = -cfi->stack_size;
} else if (op->src.reg == CFI_BP && cfa->base == cfi->drap_reg) {
/* drap: push %rbp */
cfi->stack_size = 0;
} else if (regs[op->src.reg].base == CFI_UNDEFINED) {
/* drap: push %reg */
save_reg(cfi, op->src.reg, CFI_BP, -cfi->stack_size);
}
} else {
/* push %reg */
save_reg(cfi, op->src.reg, CFI_CFA, -cfi->stack_size);
}
/* detect when asm code uses rbp as a scratch register */
if (!no_fp && insn->func && op->src.reg == CFI_BP &&
cfa->base != CFI_BP)
cfi->bp_scratch = true;
break;
case OP_DEST_REG_INDIRECT:
if (cfi->drap) {
if (op->src.reg == cfa->base && op->src.reg == cfi->drap_reg) {
/* drap: mov %drap, disp(%rbp) */
cfa->base = CFI_BP_INDIRECT;
cfa->offset = op->dest.offset;
/* save drap offset so we know when to restore it */
cfi->drap_offset = op->dest.offset;
}
else if (regs[op->src.reg].base == CFI_UNDEFINED) {
/* drap: mov reg, disp(%rbp) */
save_reg(cfi, 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(cfi, op->src.reg, CFI_CFA,
op->dest.offset - cfi->cfa.offset);
}
break;
case OP_DEST_LEAVE:
if ((!cfi->drap && cfa->base != CFI_BP) ||
(cfi->drap && cfa->base != cfi->drap_reg)) {
WARN_FUNC("leave instruction with modified stack frame",
insn->sec, insn->offset);
return -1;
}
/* leave (mov %rbp, %rsp; pop %rbp) */
cfi->stack_size = -cfi->regs[CFI_BP].offset - 8;
restore_reg(cfi, CFI_BP);
if (!cfi->drap) {
cfa->base = CFI_SP;
cfa->offset -= 8;
}
break;
case OP_DEST_MEM:
if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
WARN_FUNC("unknown stack-related memory operation",
insn->sec, insn->offset);
return -1;
}
/* pop mem */
cfi->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 int handle_insn_ops(struct instruction *insn, struct insn_state *state)
{
struct stack_op *op;
list_for_each_entry(op, &insn->stack_ops, list) {
int res;
res = update_cfi_state(insn, &state->cfi, op);
if (res)
return res;
if (op->dest.type == OP_DEST_PUSHF) {
if (!state->uaccess_stack) {
state->uaccess_stack = 1;
} else if (state->uaccess_stack >> 31) {
WARN_FUNC("PUSHF stack exhausted",
insn->sec, insn->offset);
return 1;
}
state->uaccess_stack <<= 1;
state->uaccess_stack |= state->uaccess;
}
if (op->src.type == OP_SRC_POPF) {
if (state->uaccess_stack) {
state->uaccess = state->uaccess_stack & 1;
state->uaccess_stack >>= 1;
if (state->uaccess_stack == 1)
state->uaccess_stack = 0;
}
}
}
return 0;
}
static bool insn_cfi_match(struct instruction *insn, struct cfi_state *cfi2)
{
struct cfi_state *cfi1 = &insn->cfi;
int i;
if (memcmp(&cfi1->cfa, &cfi2->cfa, sizeof(cfi1->cfa))) {
WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
insn->sec, insn->offset,
cfi1->cfa.base, cfi1->cfa.offset,
cfi2->cfa.base, cfi2->cfa.offset);
} else if (memcmp(&cfi1->regs, &cfi2->regs, sizeof(cfi1->regs))) {
for (i = 0; i < CFI_NUM_REGS; i++) {
if (!memcmp(&cfi1->regs[i], &cfi2->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, cfi1->regs[i].base, cfi1->regs[i].offset,
i, cfi2->regs[i].base, cfi2->regs[i].offset);
break;
}
} else if (cfi1->type != cfi2->type) {
WARN_FUNC("stack state mismatch: type1=%d type2=%d",
insn->sec, insn->offset, cfi1->type, cfi2->type);
} else if (cfi1->drap != cfi2->drap ||
(cfi1->drap && cfi1->drap_reg != cfi2->drap_reg) ||
(cfi1->drap && cfi1->drap_offset != cfi2->drap_offset)) {
WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
insn->sec, insn->offset,
cfi1->drap, cfi1->drap_reg, cfi1->drap_offset,
cfi2->drap, cfi2->drap_reg, cfi2->drap_offset);
} else
return true;
return false;
}
static inline bool func_uaccess_safe(struct symbol *func)
{
if (func)
return func->uaccess_safe;
return false;
}
static inline const char *call_dest_name(struct instruction *insn)
{
if (insn->call_dest)
return insn->call_dest->name;
return "{dynamic}";
}
static int validate_call(struct instruction *insn, struct insn_state *state)
{
if (state->noinstr && state->instr <= 0 &&
(!insn->call_dest || insn->call_dest->sec != insn->sec)) {
WARN_FUNC("call to %s() leaves .noinstr.text section",
insn->sec, insn->offset, call_dest_name(insn));
return 1;
}
if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
WARN_FUNC("call to %s() with UACCESS enabled",
insn->sec, insn->offset, call_dest_name(insn));
return 1;
}
if (state->df) {
WARN_FUNC("call to %s() with DF set",
insn->sec, insn->offset, call_dest_name(insn));
return 1;
}
return 0;
}
static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
{
if (has_modified_stack_frame(insn, state)) {
WARN_FUNC("sibling call from callable instruction with modified stack frame",
insn->sec, insn->offset);
return 1;
}
return validate_call(insn, state);
}
static int validate_return(struct symbol *func, struct instruction *insn, struct insn_state *state)
{
if (state->noinstr && state->instr > 0) {
WARN_FUNC("return with instrumentation enabled",
insn->sec, insn->offset);
return 1;
}
if (state->uaccess && !func_uaccess_safe(func)) {
WARN_FUNC("return with UACCESS enabled",
insn->sec, insn->offset);
return 1;
}
if (!state->uaccess && func_uaccess_safe(func)) {
WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function",
insn->sec, insn->offset);
return 1;
}
if (state->df) {
WARN_FUNC("return with DF set",
insn->sec, insn->offset);
return 1;
}
if (func && has_modified_stack_frame(insn, state)) {
WARN_FUNC("return with modified stack frame",
insn->sec, insn->offset);
return 1;
}
if (state->cfi.bp_scratch) {
WARN_FUNC("BP used as a scratch register",
insn->sec, insn->offset);
return 1;
}
return 0;
}
/*
* 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 symbol *func,
struct instruction *insn, struct insn_state state)
{
struct alternative *alt;
struct instruction *next_insn;
struct section *sec;
u8 visited;
int ret;
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) {
next_insn = next_insn_same_sec(file, insn);
if (file->c_file && func && insn->func && func != insn->func->pfunc) {
WARN("%s() falls through to next function %s()",
func->name, insn->func->name);
return 1;
}
if (func && insn->ignore) {
WARN_FUNC("BUG: why am I validating an ignored function?",
sec, insn->offset);
return 1;
}
visited = 1 << state.uaccess;
if (insn->visited) {
if (!insn->hint && !insn_cfi_match(insn, &state.cfi))
return 1;
if (insn->visited & visited)
return 0;
}
if (state.noinstr)
state.instr += insn->instr;
if (insn->hint)
state.cfi = insn->cfi;
else
insn->cfi = state.cfi;
insn->visited |= visited;
if (!insn->ignore_alts) {
bool skip_orig = false;
list_for_each_entry(alt, &insn->alts, list) {
if (alt->skip_orig)
skip_orig = true;
ret = validate_branch(file, func, alt->insn, state);
if (ret) {
if (backtrace)
BT_FUNC("(alt)", insn);
return ret;
}
}
if (skip_orig)
return 0;
}
switch (insn->type) {
case INSN_RETURN:
return validate_return(func, insn, &state);
case INSN_CALL:
case INSN_CALL_DYNAMIC:
ret = validate_call(insn, &state);
if (ret)
return ret;
if (!no_fp && func && !is_fentry_call(insn) &&
!has_valid_stack_frame(&state)) {
WARN_FUNC("call without frame pointer save/setup",
sec, insn->offset);
return 1;
}
if (dead_end_function(file, insn->call_dest))
return 0;
break;
case INSN_JUMP_CONDITIONAL:
case INSN_JUMP_UNCONDITIONAL:
if (func && is_sibling_call(insn)) {
ret = validate_sibling_call(insn, &state);
if (ret)
return ret;
} else if (insn->jump_dest) {
ret = validate_branch(file, func,
insn->jump_dest, state);
if (ret) {
if (backtrace)
BT_FUNC("(branch)", insn);
return ret;
}
}
if (insn->type == INSN_JUMP_UNCONDITIONAL)
return 0;
break;
case INSN_JUMP_DYNAMIC:
case INSN_JUMP_DYNAMIC_CONDITIONAL:
if (func && is_sibling_call(insn)) {
ret = validate_sibling_call(insn, &state);
if (ret)
return ret;
}
if (insn->type == INSN_JUMP_DYNAMIC)
return 0;
break;
case INSN_EXCEPTION_RETURN:
if (handle_insn_ops(insn, &state))
return 1;
/*
* This handles x86's sync_core() case, where we use an
* IRET to self. All 'normal' IRET instructions are in
* STT_NOTYPE entry symbols.
*/
if (func)
break;
return 0;
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;
case INSN_STACK:
if (handle_insn_ops(insn, &state))
return 1;
break;
case INSN_STAC:
if (state.uaccess) {
WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
return 1;
}
state.uaccess = true;
break;
case INSN_CLAC:
if (!state.uaccess && func) {
WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
return 1;
}
if (func_uaccess_safe(func) && !state.uaccess_stack) {
WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
return 1;
}
state.uaccess = false;
break;
case INSN_STD:
if (state.df)
WARN_FUNC("recursive STD", sec, insn->offset);
state.df = true;
break;
case INSN_CLD:
if (!state.df && func)
WARN_FUNC("redundant CLD", sec, insn->offset);
state.df = false;
break;
default:
break;
}
if (insn->dead_end)
return 0;
if (!next_insn) {
if (state.cfi.cfa.base == CFI_UNDEFINED)
return 0;
WARN("%s: unexpected end of section", sec->name);
return 1;
}
insn = next_insn;
}
return 0;
}
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->func, insn, state);
if (ret && backtrace)
BT_FUNC("<=== (hint)", insn);
warnings += ret;
}
}
return warnings;
}
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;
/*
* .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;
WARN_FUNC("indirect %s found in RETPOLINE build",
insn->sec, insn->offset,
insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
warnings++;
}
return warnings;
}
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.
*
* Also ignore alternative replacement instructions. This can happen
* when a whitelisted function uses one of the ALTERNATIVE macros.
*/
if (!strcmp(insn->sec->name, ".fixup") ||
!strcmp(insn->sec->name, ".altinstr_replacement") ||
!strcmp(insn->sec->name, ".altinstr_aux"))
return true;
if (!insn->func)
return false;
/*
* CONFIG_UBSAN_TRAP inserts a UD2 when it sees
* __builtin_unreachable(). The BUG() macro has an unreachable() after
* the UD2, which causes GCC's undefined trap logic to emit another UD2
* (or occasionally a JMP to UD2).
*/
if (list_prev_entry(insn, list)->dead_end &&
(insn->type == INSN_BUG ||
(insn->type == INSN_JUMP_UNCONDITIONAL &&
insn->jump_dest && insn->jump_dest->type == INSN_BUG)))
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) {
if (insn->jump_dest &&
insn->jump_dest->func == insn->func) {
insn = insn->jump_dest;
continue;
}
break;
}
if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
break;
insn = list_next_entry(insn, list);
}
return false;
}
static int validate_section(struct objtool_file *file, struct section *sec)
{
struct symbol *func;
struct instruction *insn;
struct insn_state state;
int ret, warnings = 0;
/*
* We need the full vmlinux for noinstr validation, otherwise we can
* not correctly determine insn->call_dest->sec (external symbols do
* not have a section).
*/
if (vmlinux)
state.noinstr = sec->noinstr;
list_for_each_entry(func, &sec->symbol_list, list) {
if (func->type != STT_FUNC)
continue;
if (!func->len) {
WARN("%s() is missing an ELF size annotation",
func->name);
warnings++;
}
if (func->pfunc != func || func->alias != func)
continue;
insn = find_insn(file, sec, func->offset);
if (!insn || insn->ignore || insn->visited)
continue;
clear_insn_state(&state);
state.cfi.cfa = initial_func_cfi.cfa;
memcpy(&state.cfi.regs, &initial_func_cfi.regs,
CFI_NUM_REGS * sizeof(struct cfi_reg));
state.cfi.stack_size = initial_func_cfi.cfa.offset;
state.uaccess = func->uaccess_safe;
ret = validate_branch(file, func, insn, state);
if (ret && backtrace)
BT_FUNC("<=== (func)", insn);
warnings += ret;
}
return warnings;
}
static int validate_vmlinux_functions(struct objtool_file *file)
{
struct section *sec;
sec = find_section_by_name(file->elf, ".noinstr.text");
if (!sec)
return 0;
return validate_section(file, sec);
}
static int validate_functions(struct objtool_file *file)
{
struct section *sec;
int warnings = 0;
for_each_sec(file, sec)
warnings += validate_section(file, sec);
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;
WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
return 1;
}
return 0;
}
static struct objtool_file file;
int check(const char *_objname, bool orc)
{
int ret, warnings = 0;
objname = _objname;
file.elf = elf_read(objname, orc ? O_RDWR : O_RDONLY);
if (!file.elf)
return 1;
INIT_LIST_HEAD(&file.insn_list);
hash_init(file.insn_hash);
file.c_file = find_section_by_name(file.elf, ".comment");
file.ignore_unreachables = no_unreachable;
file.hints = false;
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;
if (vmlinux && !validate_dup) {
ret = validate_vmlinux_functions(&file);
if (ret < 0)
goto out;
warnings += ret;
goto out;
}
if (retpoline) {
ret = validate_retpoline(&file);
if (ret < 0)
return ret;
warnings += ret;
}
ret = validate_functions(&file);
if (ret < 0)
goto out;
warnings += ret;
ret = validate_unwind_hints(&file);
if (ret < 0)
goto out;
warnings += ret;
if (!warnings) {
ret = validate_reachable_instructions(&file);
if (ret < 0)
goto out;
warnings += ret;
}
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;
}
out:
if (ret < 0) {
/*
* Fatal error. The binary is corrupt or otherwise broken in
* some way, or objtool itself is broken. Fail the kernel
* build.
*/
return ret;
}
return 0;
}
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