diff options
Diffstat (limited to 'tools/objtool/builtin-check.c')
| -rw-r--r-- | tools/objtool/builtin-check.c | 1206 |
1 files changed, 1206 insertions, 0 deletions
diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c new file mode 100644 index 000000000..e8a1e69eb --- /dev/null +++ b/tools/objtool/builtin-check.c @@ -0,0 +1,1206 @@ +/* + * Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com> + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * as published by the Free Software Foundation; either version 2 + * of the License, or (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, see <http://www.gnu.org/licenses/>. + */ + +/* + * objtool check: + * + * This command analyzes every .o file and ensures the validity of its stack + * trace metadata. It enforces a set of rules on asm code and C inline + * assembly code so that stack traces can be reliable. + * + * For more information, see tools/objtool/Documentation/stack-validation.txt. + */ + +#include <string.h> +#include <subcmd/parse-options.h> + +#include "builtin.h" +#include "elf.h" +#include "special.h" +#include "arch.h" +#include "warn.h" + +#include <linux/hashtable.h> + +#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0])) + +#define STATE_FP_SAVED 0x1 +#define STATE_FP_SETUP 0x2 +#define STATE_FENTRY 0x4 + +struct instruction { + struct list_head list; + struct hlist_node hash; + struct section *sec; + unsigned long offset; + unsigned int len, state; + unsigned char type; + unsigned long immediate; + bool alt_group, visited; + struct symbol *call_dest; + struct instruction *jump_dest; + struct list_head alts; + struct symbol *func; +}; + +struct alternative { + struct list_head list; + struct instruction *insn; +}; + +struct objtool_file { + struct elf *elf; + struct list_head insn_list; + DECLARE_HASHTABLE(insn_hash, 16); + struct section *rodata, *whitelist; + bool ignore_unreachables, c_file; +}; + +const char *objname; +static bool nofp; + +static struct instruction *find_insn(struct objtool_file *file, + struct section *sec, unsigned long offset) +{ + struct instruction *insn; + + hash_for_each_possible(file->insn_hash, insn, hash, offset) + if (insn->sec == sec && insn->offset == offset) + return insn; + + return NULL; +} + +static struct instruction *next_insn_same_sec(struct objtool_file *file, + struct instruction *insn) +{ + struct instruction *next = list_next_entry(insn, list); + + if (&next->list == &file->insn_list || next->sec != insn->sec) + return NULL; + + return next; +} + +#define for_each_insn(file, insn) \ + list_for_each_entry(insn, &file->insn_list, list) + +#define func_for_each_insn(file, func, insn) \ + for (insn = find_insn(file, func->sec, func->offset); \ + insn && &insn->list != &file->insn_list && \ + insn->sec == func->sec && \ + insn->offset < func->offset + func->len; \ + insn = list_next_entry(insn, list)) + +#define sec_for_each_insn_from(file, insn) \ + for (; insn; insn = next_insn_same_sec(file, insn)) + + +/* + * Check if the function has been manually whitelisted with the + * STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted + * due to its use of a context switching instruction. + */ +static bool ignore_func(struct objtool_file *file, struct symbol *func) +{ + struct rela *rela; + struct instruction *insn; + + /* check for STACK_FRAME_NON_STANDARD */ + if (file->whitelist && file->whitelist->rela) + list_for_each_entry(rela, &file->whitelist->rela->rela_list, list) + if (rela->sym->sec == func->sec && + rela->addend == func->offset) + return true; + + /* check if it has a context switching instruction */ + func_for_each_insn(file, func, insn) + if (insn->type == INSN_CONTEXT_SWITCH) + return true; + + return false; +} + +/* + * This checks to see if the given function is a "noreturn" function. + * + * For global functions which are outside the scope of this object file, we + * have to keep a manual list of them. + * + * For local functions, we have to detect them manually by simply looking for + * the lack of a return instruction. + * + * Returns: + * -1: error + * 0: no dead end + * 1: dead end + */ +static int __dead_end_function(struct objtool_file *file, struct symbol *func, + int recursion) +{ + int i; + struct instruction *insn; + bool empty = true; + + /* + * Unfortunately these have to be hard coded because the noreturn + * attribute isn't provided in ELF data. + */ + static const char * const global_noreturns[] = { + "__stack_chk_fail", + "panic", + "do_exit", + "__module_put_and_exit", + "complete_and_exit", + "kvm_spurious_fault", + "__reiserfs_panic", + "lbug_with_loc" + }; + + if (func->bind == STB_WEAK) + return 0; + + if (func->bind == STB_GLOBAL) + for (i = 0; i < ARRAY_SIZE(global_noreturns); i++) + if (!strcmp(func->name, global_noreturns[i])) + return 1; + + if (!func->sec) + return 0; + + func_for_each_insn(file, func, insn) { + empty = false; + + if (insn->type == INSN_RETURN) + return 0; + } + + if (empty) + return 0; + + /* + * A function can have a sibling call instead of a return. In that + * case, the function's dead-end status depends on whether the target + * of the sibling call returns. + */ + func_for_each_insn(file, func, insn) { + if (insn->sec != func->sec || + insn->offset >= func->offset + func->len) + break; + + if (insn->type == INSN_JUMP_UNCONDITIONAL) { + struct instruction *dest = insn->jump_dest; + struct symbol *dest_func; + + if (!dest) + /* sibling call to another file */ + return 0; + + if (dest->sec != func->sec || + dest->offset < func->offset || + dest->offset >= func->offset + func->len) { + /* local sibling call */ + dest_func = find_symbol_by_offset(dest->sec, + dest->offset); + if (!dest_func) + continue; + + if (recursion == 5) { + WARN_FUNC("infinite recursion (objtool bug!)", + dest->sec, dest->offset); + return -1; + } + + return __dead_end_function(file, dest_func, + recursion + 1); + } + } + + if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts)) + /* sibling call */ + return 0; + } + + return 1; +} + +static int dead_end_function(struct objtool_file *file, struct symbol *func) +{ + return __dead_end_function(file, func, 0); +} + +/* + * Call the arch-specific instruction decoder for all the instructions and add + * them to the global instruction list. + */ +static int decode_instructions(struct objtool_file *file) +{ + struct section *sec; + struct symbol *func; + unsigned long offset; + struct instruction *insn; + int ret; + + list_for_each_entry(sec, &file->elf->sections, list) { + + if (!(sec->sh.sh_flags & SHF_EXECINSTR)) + continue; + + for (offset = 0; offset < sec->len; offset += insn->len) { + insn = malloc(sizeof(*insn)); + memset(insn, 0, sizeof(*insn)); + + INIT_LIST_HEAD(&insn->alts); + insn->sec = sec; + insn->offset = offset; + + ret = arch_decode_instruction(file->elf, sec, offset, + sec->len - offset, + &insn->len, &insn->type, + &insn->immediate); + if (ret) + return ret; + + if (!insn->type || insn->type > INSN_LAST) { + WARN_FUNC("invalid instruction type %d", + insn->sec, insn->offset, insn->type); + return -1; + } + + hash_add(file->insn_hash, &insn->hash, insn->offset); + list_add_tail(&insn->list, &file->insn_list); + } + + list_for_each_entry(func, &sec->symbol_list, list) { + if (func->type != STT_FUNC) + continue; + + if (!find_insn(file, sec, func->offset)) { + WARN("%s(): can't find starting instruction", + func->name); + return -1; + } + + func_for_each_insn(file, func, insn) + if (!insn->func) + insn->func = func; + } + } + + return 0; +} + +/* + * Warnings shouldn't be reported for ignored functions. + */ +static void add_ignores(struct objtool_file *file) +{ + struct instruction *insn; + struct section *sec; + struct symbol *func; + + list_for_each_entry(sec, &file->elf->sections, list) { + list_for_each_entry(func, &sec->symbol_list, list) { + if (func->type != STT_FUNC) + continue; + + if (!ignore_func(file, func)) + continue; + + func_for_each_insn(file, func, insn) + insn->visited = true; + } + } +} + +/* + * Find the destination instructions for all jumps. + */ +static int add_jump_destinations(struct objtool_file *file) +{ + struct instruction *insn; + struct rela *rela; + struct section *dest_sec; + unsigned long dest_off; + + for_each_insn(file, insn) { + if (insn->type != INSN_JUMP_CONDITIONAL && + insn->type != INSN_JUMP_UNCONDITIONAL) + continue; + + /* skip ignores */ + if (insn->visited) + continue; + + rela = find_rela_by_dest_range(insn->sec, insn->offset, + insn->len); + if (!rela) { + dest_sec = insn->sec; + dest_off = insn->offset + insn->len + insn->immediate; + } else if (rela->sym->type == STT_SECTION) { + dest_sec = rela->sym->sec; + dest_off = rela->addend + 4; + } else if (rela->sym->sec->idx) { + dest_sec = rela->sym->sec; + dest_off = rela->sym->sym.st_value + rela->addend + 4; + } else { + /* sibling call */ + insn->jump_dest = 0; + continue; + } + + insn->jump_dest = find_insn(file, dest_sec, dest_off); + if (!insn->jump_dest) { + + /* + * This is a special case where an alt instruction + * jumps past the end of the section. These are + * handled later in handle_group_alt(). + */ + if (!strcmp(insn->sec->name, ".altinstr_replacement")) + continue; + + WARN_FUNC("can't find jump dest instruction at %s+0x%lx", + insn->sec, insn->offset, dest_sec->name, + dest_off); + return -1; + } + } + + return 0; +} + +/* + * Find the destination instructions for all calls. + */ +static int add_call_destinations(struct objtool_file *file) +{ + struct instruction *insn; + unsigned long dest_off; + struct rela *rela; + + for_each_insn(file, insn) { + if (insn->type != INSN_CALL) + continue; + + rela = find_rela_by_dest_range(insn->sec, insn->offset, + insn->len); + if (!rela) { + dest_off = insn->offset + insn->len + insn->immediate; + insn->call_dest = find_symbol_by_offset(insn->sec, + dest_off); + if (!insn->call_dest) { + WARN_FUNC("can't find call dest symbol at offset 0x%lx", + insn->sec, insn->offset, dest_off); + return -1; + } + } else if (rela->sym->type == STT_SECTION) { + insn->call_dest = find_symbol_by_offset(rela->sym->sec, + rela->addend+4); + if (!insn->call_dest || + insn->call_dest->type != STT_FUNC) { + WARN_FUNC("can't find call dest symbol at %s+0x%x", + insn->sec, insn->offset, + rela->sym->sec->name, + rela->addend + 4); + return -1; + } + } else + insn->call_dest = rela->sym; + } + + return 0; +} + +/* + * The .alternatives section requires some extra special care, over and above + * what other special sections require: + * + * 1. Because alternatives are patched in-place, we need to insert a fake jump + * instruction at the end so that validate_branch() skips all the original + * replaced instructions when validating the new instruction path. + * + * 2. An added wrinkle is that the new instruction length might be zero. In + * that case the old instructions are replaced with noops. We simulate that + * by creating a fake jump as the only new instruction. + * + * 3. In some cases, the alternative section includes an instruction which + * conditionally jumps to the _end_ of the entry. We have to modify these + * jumps' destinations to point back to .text rather than the end of the + * entry in .altinstr_replacement. + * + * 4. It has been requested that we don't validate the !POPCNT feature path + * which is a "very very small percentage of machines". + */ +static int handle_group_alt(struct objtool_file *file, + struct special_alt *special_alt, + struct instruction *orig_insn, + struct instruction **new_insn) +{ + struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump; + unsigned long dest_off; + + last_orig_insn = NULL; + insn = orig_insn; + sec_for_each_insn_from(file, insn) { + if (insn->offset >= special_alt->orig_off + special_alt->orig_len) + break; + + if (special_alt->skip_orig) + insn->type = INSN_NOP; + + insn->alt_group = true; + last_orig_insn = insn; + } + + if (!next_insn_same_sec(file, last_orig_insn)) { + WARN("%s: don't know how to handle alternatives at end of section", + special_alt->orig_sec->name); + return -1; + } + + fake_jump = malloc(sizeof(*fake_jump)); + if (!fake_jump) { + WARN("malloc failed"); + return -1; + } + memset(fake_jump, 0, sizeof(*fake_jump)); + INIT_LIST_HEAD(&fake_jump->alts); + fake_jump->sec = special_alt->new_sec; + fake_jump->offset = -1; + fake_jump->type = INSN_JUMP_UNCONDITIONAL; + fake_jump->jump_dest = list_next_entry(last_orig_insn, list); + + if (!special_alt->new_len) { + *new_insn = fake_jump; + return 0; + } + + last_new_insn = NULL; + insn = *new_insn; + sec_for_each_insn_from(file, insn) { + if (insn->offset >= special_alt->new_off + special_alt->new_len) + break; + + last_new_insn = insn; + + if (insn->type != INSN_JUMP_CONDITIONAL && + insn->type != INSN_JUMP_UNCONDITIONAL) + continue; + + if (!insn->immediate) + continue; + + dest_off = insn->offset + insn->len + insn->immediate; + if (dest_off == special_alt->new_off + special_alt->new_len) + insn->jump_dest = fake_jump; + + if (!insn->jump_dest) { + WARN_FUNC("can't find alternative jump destination", + insn->sec, insn->offset); + return -1; + } + } + + if (!last_new_insn) { + WARN_FUNC("can't find last new alternative instruction", + special_alt->new_sec, special_alt->new_off); + return -1; + } + + list_add(&fake_jump->list, &last_new_insn->list); + + return 0; +} + +/* + * A jump table entry can either convert a nop to a jump or a jump to a nop. + * If the original instruction is a jump, make the alt entry an effective nop + * by just skipping the original instruction. + */ +static int handle_jump_alt(struct objtool_file *file, + struct special_alt *special_alt, + struct instruction *orig_insn, + struct instruction **new_insn) +{ + if (orig_insn->type == INSN_NOP) + return 0; + + if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) { + WARN_FUNC("unsupported instruction at jump label", + orig_insn->sec, orig_insn->offset); + return -1; + } + + *new_insn = list_next_entry(orig_insn, list); + return 0; +} + +/* + * Read all the special sections which have alternate instructions which can be + * patched in or redirected to at runtime. Each instruction having alternate + * instruction(s) has them added to its insn->alts list, which will be + * traversed in validate_branch(). + */ +static int add_special_section_alts(struct objtool_file *file) +{ + struct list_head special_alts; + struct instruction *orig_insn, *new_insn; + struct special_alt *special_alt, *tmp; + struct alternative *alt; + int ret; + + ret = special_get_alts(file->elf, &special_alts); + if (ret) + return ret; + + list_for_each_entry_safe(special_alt, tmp, &special_alts, list) { + alt = malloc(sizeof(*alt)); + if (!alt) { + WARN("malloc failed"); + ret = -1; + goto out; + } + + orig_insn = find_insn(file, special_alt->orig_sec, + special_alt->orig_off); + if (!orig_insn) { + WARN_FUNC("special: can't find orig instruction", + special_alt->orig_sec, special_alt->orig_off); + ret = -1; + goto out; + } + + new_insn = NULL; + if (!special_alt->group || special_alt->new_len) { + new_insn = find_insn(file, special_alt->new_sec, + special_alt->new_off); + if (!new_insn) { + WARN_FUNC("special: can't find new instruction", + special_alt->new_sec, + special_alt->new_off); + ret = -1; + goto out; + } + } + + if (special_alt->group) { + ret = handle_group_alt(file, special_alt, orig_insn, + &new_insn); + if (ret) + goto out; + } else if (special_alt->jump_or_nop) { + ret = handle_jump_alt(file, special_alt, orig_insn, + &new_insn); + if (ret) + goto out; + } + + alt->insn = new_insn; + list_add_tail(&alt->list, &orig_insn->alts); + + list_del(&special_alt->list); + free(special_alt); + } + +out: + return ret; +} + +static int add_switch_table(struct objtool_file *file, struct symbol *func, + struct instruction *insn, struct rela *table, + struct rela *next_table) +{ + struct rela *rela = table; + struct instruction *alt_insn; + struct alternative *alt; + + list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) { + if (rela == next_table) + break; + + if (rela->sym->sec != insn->sec || + rela->addend <= func->offset || + rela->addend >= func->offset + func->len) + break; + + alt_insn = find_insn(file, insn->sec, rela->addend); + if (!alt_insn) { + WARN("%s: can't find instruction at %s+0x%x", + file->rodata->rela->name, insn->sec->name, + rela->addend); + return -1; + } + + alt = malloc(sizeof(*alt)); + if (!alt) { + WARN("malloc failed"); + return -1; + } + + alt->insn = alt_insn; + list_add_tail(&alt->list, &insn->alts); + } + + return 0; +} + +static int add_func_switch_tables(struct objtool_file *file, + struct symbol *func) +{ + struct instruction *insn, *prev_jump; + struct rela *text_rela, *rodata_rela, *prev_rela; + int ret; + + prev_jump = NULL; + + func_for_each_insn(file, func, insn) { + if (insn->type != INSN_JUMP_DYNAMIC) + continue; + + text_rela = find_rela_by_dest_range(insn->sec, insn->offset, + insn->len); + if (!text_rela || text_rela->sym != file->rodata->sym) + continue; + + /* common case: jmpq *[addr](,%rax,8) */ + rodata_rela = find_rela_by_dest(file->rodata, + text_rela->addend); + + /* + * rare case: jmpq *[addr](%rip) + * + * This check is for 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. + * + * kbuild reports: + * - https://lkml.kernel.org/r/201603231906.LWcVUpxm%25fengguang.wu@intel.com + * - https://lkml.kernel.org/r/201603271114.K9i45biy%25fengguang.wu@intel.com + * - https://lkml.kernel.org/r/201603291058.zuJ6ben1%25fengguang.wu@intel.com + * + * gcc bug: + * - https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70604 + */ + if (!rodata_rela) { + rodata_rela = find_rela_by_dest(file->rodata, + text_rela->addend + 4); + if (rodata_rela) + file->ignore_unreachables = true; + } + + if (!rodata_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, + rodata_rela); + if (ret) + return ret; + } + + prev_jump = insn; + prev_rela = rodata_rela; + } + + if (prev_jump) { + ret = add_switch_table(file, func, prev_jump, prev_rela, NULL); + if (ret) + return ret; + } + + return 0; +} + +/* + * For some switch statements, gcc generates a jump table in the .rodata + * section which contains a list of addresses within the function to jump to. + * This finds these jump tables and adds them to the insn->alts lists. + */ +static int add_switch_table_alts(struct objtool_file *file) +{ + struct section *sec; + struct symbol *func; + int ret; + + if (!file->rodata || !file->rodata->rela) + return 0; + + list_for_each_entry(sec, &file->elf->sections, list) { + list_for_each_entry(func, &sec->symbol_list, list) { + if (func->type != STT_FUNC) + continue; + + ret = add_func_switch_tables(file, func); + if (ret) + return ret; + } + } + + return 0; +} + +static int decode_sections(struct objtool_file *file) +{ + int ret; + + ret = decode_instructions(file); + if (ret) + return ret; + + add_ignores(file); + + ret = add_jump_destinations(file); + if (ret) + return ret; + + ret = add_call_destinations(file); + if (ret) + return ret; + + ret = add_special_section_alts(file); + if (ret) + return ret; + + ret = add_switch_table_alts(file); + if (ret) + return ret; + + return 0; +} + +static bool is_fentry_call(struct instruction *insn) +{ + if (insn->type == INSN_CALL && + insn->call_dest->type == STT_NOTYPE && + !strcmp(insn->call_dest->name, "__fentry__")) + return true; + + return false; +} + +static bool has_modified_stack_frame(struct instruction *insn) +{ + return (insn->state & STATE_FP_SAVED) || + (insn->state & STATE_FP_SETUP); +} + +static bool has_valid_stack_frame(struct instruction *insn) +{ + return (insn->state & STATE_FP_SAVED) && + (insn->state & STATE_FP_SETUP); +} + +static unsigned int frame_state(unsigned long state) +{ + return (state & (STATE_FP_SAVED | STATE_FP_SETUP)); +} + +/* + * Follow the branch starting at the given instruction, and recursively follow + * any other branches (jumps). Meanwhile, track the frame pointer state at + * each instruction and validate all the rules described in + * tools/objtool/Documentation/stack-validation.txt. + */ +static int validate_branch(struct objtool_file *file, + struct instruction *first, unsigned char first_state) +{ + struct alternative *alt; + struct instruction *insn; + struct section *sec; + struct symbol *func = NULL; + unsigned char state; + int ret; + + insn = first; + sec = insn->sec; + state = first_state; + + if (insn->alt_group && list_empty(&insn->alts)) { + WARN_FUNC("don't know how to handle branch to middle of alternative instruction group", + sec, insn->offset); + return 1; + } + + while (1) { + if (file->c_file && insn->func) { + if (func && func != insn->func) { + WARN("%s() falls through to next function %s()", + func->name, insn->func->name); + return 1; + } + + func = insn->func; + } + + if (insn->visited) { + if (frame_state(insn->state) != frame_state(state)) { + WARN_FUNC("frame pointer state mismatch", + sec, insn->offset); + return 1; + } + + return 0; + } + + insn->visited = true; + insn->state = state; + + list_for_each_entry(alt, &insn->alts, list) { + ret = validate_branch(file, alt->insn, state); + if (ret) + return 1; + } + + switch (insn->type) { + + case INSN_FP_SAVE: + if (!nofp) { + if (state & STATE_FP_SAVED) { + WARN_FUNC("duplicate frame pointer save", + sec, insn->offset); + return 1; + } + state |= STATE_FP_SAVED; + } + break; + + case INSN_FP_SETUP: + if (!nofp) { + if (state & STATE_FP_SETUP) { + WARN_FUNC("duplicate frame pointer setup", + sec, insn->offset); + return 1; + } + state |= STATE_FP_SETUP; + } + break; + + case INSN_FP_RESTORE: + if (!nofp) { + if (has_valid_stack_frame(insn)) + state &= ~STATE_FP_SETUP; + + state &= ~STATE_FP_SAVED; + } + break; + + case INSN_RETURN: + if (!nofp && has_modified_stack_frame(insn)) { + WARN_FUNC("return without frame pointer restore", + sec, insn->offset); + return 1; + } + return 0; + + case INSN_CALL: + if (is_fentry_call(insn)) { + state |= STATE_FENTRY; + break; + } + + ret = dead_end_function(file, insn->call_dest); + if (ret == 1) + return 0; + if (ret == -1) + return 1; + + /* fallthrough */ + case INSN_CALL_DYNAMIC: + if (!nofp && !has_valid_stack_frame(insn)) { + WARN_FUNC("call without frame pointer save/setup", + sec, insn->offset); + return 1; + } + break; + + case INSN_JUMP_CONDITIONAL: + case INSN_JUMP_UNCONDITIONAL: + if (insn->jump_dest) { + ret = validate_branch(file, insn->jump_dest, + state); + if (ret) + return 1; + } else if (has_modified_stack_frame(insn)) { + WARN_FUNC("sibling call from callable instruction with changed frame pointer", + sec, insn->offset); + return 1; + } /* else it's a sibling call */ + + if (insn->type == INSN_JUMP_UNCONDITIONAL) + return 0; + + break; + + case INSN_JUMP_DYNAMIC: + if (list_empty(&insn->alts) && + has_modified_stack_frame(insn)) { + WARN_FUNC("sibling call from callable instruction with changed frame pointer", + sec, insn->offset); + return 1; + } + + return 0; + + case INSN_BUG: + return 0; + + default: + break; + } + + insn = next_insn_same_sec(file, insn); + if (!insn) { + WARN("%s: unexpected end of section", sec->name); + return 1; + } + } + + return 0; +} + +static bool is_gcov_insn(struct instruction *insn) +{ + struct rela *rela; + struct section *sec; + struct symbol *sym; + unsigned long offset; + + rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len); + if (!rela) + return false; + + if (rela->sym->type != STT_SECTION) + return false; + + sec = rela->sym->sec; + offset = rela->addend + insn->offset + insn->len - rela->offset; + + list_for_each_entry(sym, &sec->symbol_list, list) { + if (sym->type != STT_OBJECT) + continue; + + if (offset >= sym->offset && offset < sym->offset + sym->len) + return (!memcmp(sym->name, "__gcov0.", 8)); + } + + return false; +} + +static bool is_kasan_insn(struct instruction *insn) +{ + return (insn->type == INSN_CALL && + !strcmp(insn->call_dest->name, "__asan_handle_no_return")); +} + +static bool is_ubsan_insn(struct instruction *insn) +{ + return (insn->type == INSN_CALL && + !strcmp(insn->call_dest->name, + "__ubsan_handle_builtin_unreachable")); +} + +static bool ignore_unreachable_insn(struct symbol *func, + struct instruction *insn) +{ + int i; + + if (insn->type == INSN_NOP) + return true; + + if (is_gcov_insn(insn)) + return true; + + /* + * Check if this (or a subsequent) instruction is related to + * CONFIG_UBSAN or CONFIG_KASAN. + * + * End the search at 5 instructions to avoid going into the weeds. + */ + for (i = 0; i < 5; i++) { + + if (is_kasan_insn(insn) || is_ubsan_insn(insn)) + return true; + + if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest) { + insn = insn->jump_dest; + continue; + } + + if (insn->offset + insn->len >= func->offset + func->len) + break; + insn = list_next_entry(insn, list); + } + + return false; +} + +static int validate_functions(struct objtool_file *file) +{ + struct section *sec; + struct symbol *func; + struct instruction *insn; + int ret, warnings = 0; + + list_for_each_entry(sec, &file->elf->sections, list) { + list_for_each_entry(func, &sec->symbol_list, list) { + if (func->type != STT_FUNC) + continue; + + insn = find_insn(file, sec, func->offset); + if (!insn) + continue; + + ret = validate_branch(file, insn, 0); + warnings += ret; + } + } + + list_for_each_entry(sec, &file->elf->sections, list) { + list_for_each_entry(func, &sec->symbol_list, list) { + if (func->type != STT_FUNC) + continue; + + func_for_each_insn(file, func, insn) { + if (insn->visited) + continue; + + insn->visited = true; + + if (file->ignore_unreachables || warnings || + ignore_unreachable_insn(func, insn)) + continue; + + WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset); + warnings++; + } + } + } + + return warnings; +} + +static int validate_uncallable_instructions(struct objtool_file *file) +{ + struct instruction *insn; + int warnings = 0; + + for_each_insn(file, insn) { + if (!insn->visited && insn->type == INSN_RETURN) { + WARN_FUNC("return instruction outside of a callable function", + insn->sec, insn->offset); + warnings++; + } + } + + return warnings; +} + +static void cleanup(struct objtool_file *file) +{ + struct instruction *insn, *tmpinsn; + struct alternative *alt, *tmpalt; + + list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) { + list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) { + list_del(&alt->list); + free(alt); + } + list_del(&insn->list); + hash_del(&insn->hash); + free(insn); + } + elf_close(file->elf); +} + +const char * const check_usage[] = { + "objtool check [<options>] file.o", + NULL, +}; + +int cmd_check(int argc, const char **argv) +{ + struct objtool_file file; + int ret, warnings = 0; + + const struct option options[] = { + OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"), + OPT_END(), + }; + + argc = parse_options(argc, argv, options, check_usage, 0); + + if (argc != 1) + usage_with_options(check_usage, options); + + objname = argv[0]; + + file.elf = elf_open(objname); + if (!file.elf) { + fprintf(stderr, "error reading elf file %s\n", objname); + return 1; + } + + INIT_LIST_HEAD(&file.insn_list); + hash_init(file.insn_hash); + file.whitelist = find_section_by_name(file.elf, "__func_stack_frame_non_standard"); + file.rodata = find_section_by_name(file.elf, ".rodata"); + file.ignore_unreachables = false; + file.c_file = find_section_by_name(file.elf, ".comment"); + + ret = decode_sections(&file); + if (ret < 0) + goto out; + warnings += ret; + + ret = validate_functions(&file); + if (ret < 0) + goto out; + warnings += ret; + + ret = validate_uncallable_instructions(&file); + if (ret < 0) + goto out; + warnings += ret; + +out: + cleanup(&file); + + /* ignore warnings for now until we get all the code cleaned up */ + if (ret || warnings) + return 0; + return 0; +} |