/* * Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com> * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation; either version 2 * of the License, or (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, see <http://www.gnu.org/licenses/>. */ /* * objtool check: * * This command analyzes every .o file and ensures the validity of its stack * trace metadata. It enforces a set of rules on asm code and C inline * assembly code so that stack traces can be reliable. * * For more information, see tools/objtool/Documentation/stack-validation.txt. */ #include <string.h> #include <stdlib.h> #include <subcmd/parse-options.h> #include "builtin.h" #include "elf.h" #include "special.h" #include "arch.h" #include "warn.h" #include <linux/hashtable.h> #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0])) #define STATE_FP_SAVED 0x1 #define STATE_FP_SETUP 0x2 #define STATE_FENTRY 0x4 struct instruction { struct list_head list; struct hlist_node hash; struct section *sec; unsigned long offset; unsigned int len, state; unsigned char type; unsigned long immediate; bool alt_group, visited; struct symbol *call_dest; struct instruction *jump_dest; struct list_head alts; struct symbol *func; }; struct alternative { struct list_head list; struct instruction *insn; }; struct objtool_file { struct elf *elf; struct list_head insn_list; DECLARE_HASHTABLE(insn_hash, 16); struct section *rodata, *whitelist; bool ignore_unreachables, c_file; }; const char *objname; static bool nofp; static struct instruction *find_insn(struct objtool_file *file, struct section *sec, unsigned long offset) { struct instruction *insn; hash_for_each_possible(file->insn_hash, insn, hash, offset) if (insn->sec == sec && insn->offset == offset) return insn; return NULL; } static struct instruction *next_insn_same_sec(struct objtool_file *file, struct instruction *insn) { struct instruction *next = list_next_entry(insn, list); if (&next->list == &file->insn_list || next->sec != insn->sec) return NULL; return next; } static bool gcov_enabled(struct objtool_file *file) { struct section *sec; struct symbol *sym; list_for_each_entry(sec, &file->elf->sections, list) list_for_each_entry(sym, &sec->symbol_list, list) if (!strncmp(sym->name, "__gcov_.", 8)) return true; return false; } #define for_each_insn(file, insn) \ list_for_each_entry(insn, &file->insn_list, list) #define func_for_each_insn(file, func, insn) \ for (insn = find_insn(file, func->sec, func->offset); \ insn && &insn->list != &file->insn_list && \ insn->sec == func->sec && \ insn->offset < func->offset + func->len; \ insn = list_next_entry(insn, list)) #define func_for_each_insn_continue_reverse(file, func, insn) \ for (insn = list_prev_entry(insn, list); \ &insn->list != &file->insn_list && \ insn->sec == func->sec && insn->offset >= func->offset; \ insn = list_prev_entry(insn, list)) #define sec_for_each_insn_from(file, insn) \ for (; insn; insn = next_insn_same_sec(file, insn)) /* * Check if the function has been manually whitelisted with the * STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted * due to its use of a context switching instruction. */ static bool ignore_func(struct objtool_file *file, struct symbol *func) { struct rela *rela; struct instruction *insn; /* check for STACK_FRAME_NON_STANDARD */ if (file->whitelist && file->whitelist->rela) list_for_each_entry(rela, &file->whitelist->rela->rela_list, list) { if (rela->sym->type == STT_SECTION && rela->sym->sec == func->sec && rela->addend == func->offset) return true; if (rela->sym->type == STT_FUNC && rela->sym == func) return true; } /* check if it has a context switching instruction */ func_for_each_insn(file, func, insn) if (insn->type == INSN_CONTEXT_SWITCH) return true; return false; } /* * This checks to see if the given function is a "noreturn" function. * * For global functions which are outside the scope of this object file, we * have to keep a manual list of them. * * For local functions, we have to detect them manually by simply looking for * the lack of a return instruction. * * Returns: * -1: error * 0: no dead end * 1: dead end */ static int __dead_end_function(struct objtool_file *file, struct symbol *func, int recursion) { int i; struct instruction *insn; bool empty = true; /* * Unfortunately these have to be hard coded because the noreturn * attribute isn't provided in ELF data. */ static const char * const global_noreturns[] = { "__stack_chk_fail", "panic", "do_exit", "do_task_dead", "__module_put_and_exit", "complete_and_exit", "kvm_spurious_fault", "__reiserfs_panic", "lbug_with_loc" }; if (func->bind == STB_WEAK) return 0; if (func->bind == STB_GLOBAL) for (i = 0; i < ARRAY_SIZE(global_noreturns); i++) if (!strcmp(func->name, global_noreturns[i])) return 1; if (!func->sec) return 0; func_for_each_insn(file, func, insn) { empty = false; if (insn->type == INSN_RETURN) return 0; } if (empty) return 0; /* * A function can have a sibling call instead of a return. In that * case, the function's dead-end status depends on whether the target * of the sibling call returns. */ func_for_each_insn(file, func, insn) { if (insn->sec != func->sec || insn->offset >= func->offset + func->len) break; if (insn->type == INSN_JUMP_UNCONDITIONAL) { struct instruction *dest = insn->jump_dest; struct symbol *dest_func; if (!dest) /* sibling call to another file */ return 0; if (dest->sec != func->sec || dest->offset < func->offset || dest->offset >= func->offset + func->len) { /* local sibling call */ dest_func = find_symbol_by_offset(dest->sec, dest->offset); if (!dest_func) continue; if (recursion == 5) { WARN_FUNC("infinite recursion (objtool bug!)", dest->sec, dest->offset); return -1; } return __dead_end_function(file, dest_func, recursion + 1); } } if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts)) /* sibling call */ return 0; } return 1; } static int dead_end_function(struct objtool_file *file, struct symbol *func) { return __dead_end_function(file, func, 0); } /* * Call the arch-specific instruction decoder for all the instructions and add * them to the global instruction list. */ static int decode_instructions(struct objtool_file *file) { struct section *sec; struct symbol *func; unsigned long offset; struct instruction *insn; int ret; list_for_each_entry(sec, &file->elf->sections, list) { if (!(sec->sh.sh_flags & SHF_EXECINSTR)) continue; for (offset = 0; offset < sec->len; offset += insn->len) { insn = malloc(sizeof(*insn)); memset(insn, 0, sizeof(*insn)); INIT_LIST_HEAD(&insn->alts); insn->sec = sec; insn->offset = offset; ret = arch_decode_instruction(file->elf, sec, offset, sec->len - offset, &insn->len, &insn->type, &insn->immediate); if (ret) return ret; if (!insn->type || insn->type > INSN_LAST) { WARN_FUNC("invalid instruction type %d", insn->sec, insn->offset, insn->type); return -1; } hash_add(file->insn_hash, &insn->hash, insn->offset); list_add_tail(&insn->list, &file->insn_list); } list_for_each_entry(func, &sec->symbol_list, list) { if (func->type != STT_FUNC) continue; if (!find_insn(file, sec, func->offset)) { WARN("%s(): can't find starting instruction", func->name); return -1; } func_for_each_insn(file, func, insn) if (!insn->func) insn->func = func; } } return 0; } /* * Warnings shouldn't be reported for ignored functions. */ static void add_ignores(struct objtool_file *file) { struct instruction *insn; struct section *sec; struct symbol *func; list_for_each_entry(sec, &file->elf->sections, list) { list_for_each_entry(func, &sec->symbol_list, list) { if (func->type != STT_FUNC) continue; if (!ignore_func(file, func)) continue; func_for_each_insn(file, func, insn) insn->visited = true; } } } /* * Find the destination instructions for all jumps. */ static int add_jump_destinations(struct objtool_file *file) { struct instruction *insn; struct rela *rela; struct section *dest_sec; unsigned long dest_off; for_each_insn(file, insn) { if (insn->type != INSN_JUMP_CONDITIONAL && insn->type != INSN_JUMP_UNCONDITIONAL) continue; /* skip ignores */ if (insn->visited) continue; rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len); if (!rela) { dest_sec = insn->sec; dest_off = insn->offset + insn->len + insn->immediate; } else if (rela->sym->type == STT_SECTION) { dest_sec = rela->sym->sec; dest_off = rela->addend + 4; } else if (rela->sym->sec->idx) { dest_sec = rela->sym->sec; dest_off = rela->sym->sym.st_value + rela->addend + 4; } else { /* sibling call */ insn->jump_dest = 0; continue; } insn->jump_dest = find_insn(file, dest_sec, dest_off); if (!insn->jump_dest) { /* * This is a special case where an alt instruction * jumps past the end of the section. These are * handled later in handle_group_alt(). */ if (!strcmp(insn->sec->name, ".altinstr_replacement")) continue; WARN_FUNC("can't find jump dest instruction at %s+0x%lx", insn->sec, insn->offset, dest_sec->name, dest_off); return -1; } } return 0; } /* * Find the destination instructions for all calls. */ static int add_call_destinations(struct objtool_file *file) { struct instruction *insn; unsigned long dest_off; struct rela *rela; for_each_insn(file, insn) { if (insn->type != INSN_CALL) continue; rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len); if (!rela) { dest_off = insn->offset + insn->len + insn->immediate; insn->call_dest = find_symbol_by_offset(insn->sec, dest_off); if (!insn->call_dest) { WARN_FUNC("can't find call dest symbol at offset 0x%lx", insn->sec, insn->offset, dest_off); return -1; } } else if (rela->sym->type == STT_SECTION) { insn->call_dest = find_symbol_by_offset(rela->sym->sec, rela->addend+4); if (!insn->call_dest || insn->call_dest->type != STT_FUNC) { WARN_FUNC("can't find call dest symbol at %s+0x%x", insn->sec, insn->offset, rela->sym->sec->name, rela->addend + 4); return -1; } } else insn->call_dest = rela->sym; } return 0; } /* * The .alternatives section requires some extra special care, over and above * what other special sections require: * * 1. Because alternatives are patched in-place, we need to insert a fake jump * instruction at the end so that validate_branch() skips all the original * replaced instructions when validating the new instruction path. * * 2. An added wrinkle is that the new instruction length might be zero. In * that case the old instructions are replaced with noops. We simulate that * by creating a fake jump as the only new instruction. * * 3. In some cases, the alternative section includes an instruction which * conditionally jumps to the _end_ of the entry. We have to modify these * jumps' destinations to point back to .text rather than the end of the * entry in .altinstr_replacement. * * 4. It has been requested that we don't validate the !POPCNT feature path * which is a "very very small percentage of machines". */ static int handle_group_alt(struct objtool_file *file, struct special_alt *special_alt, struct instruction *orig_insn, struct instruction **new_insn) { struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump; unsigned long dest_off; last_orig_insn = NULL; insn = orig_insn; sec_for_each_insn_from(file, insn) { if (insn->offset >= special_alt->orig_off + special_alt->orig_len) break; if (special_alt->skip_orig) insn->type = INSN_NOP; insn->alt_group = true; last_orig_insn = insn; } if (!next_insn_same_sec(file, last_orig_insn)) { WARN("%s: don't know how to handle alternatives at end of section", special_alt->orig_sec->name); return -1; } fake_jump = malloc(sizeof(*fake_jump)); if (!fake_jump) { WARN("malloc failed"); return -1; } memset(fake_jump, 0, sizeof(*fake_jump)); INIT_LIST_HEAD(&fake_jump->alts); fake_jump->sec = special_alt->new_sec; fake_jump->offset = -1; fake_jump->type = INSN_JUMP_UNCONDITIONAL; fake_jump->jump_dest = list_next_entry(last_orig_insn, list); if (!special_alt->new_len) { *new_insn = fake_jump; return 0; } last_new_insn = NULL; insn = *new_insn; sec_for_each_insn_from(file, insn) { if (insn->offset >= special_alt->new_off + special_alt->new_len) break; last_new_insn = insn; if (insn->type != INSN_JUMP_CONDITIONAL && insn->type != INSN_JUMP_UNCONDITIONAL) continue; if (!insn->immediate) continue; dest_off = insn->offset + insn->len + insn->immediate; if (dest_off == special_alt->new_off + special_alt->new_len) insn->jump_dest = fake_jump; if (!insn->jump_dest) { WARN_FUNC("can't find alternative jump destination", insn->sec, insn->offset); return -1; } } if (!last_new_insn) { WARN_FUNC("can't find last new alternative instruction", special_alt->new_sec, special_alt->new_off); return -1; } list_add(&fake_jump->list, &last_new_insn->list); return 0; } /* * A jump table entry can either convert a nop to a jump or a jump to a nop. * If the original instruction is a jump, make the alt entry an effective nop * by just skipping the original instruction. */ static int handle_jump_alt(struct objtool_file *file, struct special_alt *special_alt, struct instruction *orig_insn, struct instruction **new_insn) { if (orig_insn->type == INSN_NOP) return 0; if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) { WARN_FUNC("unsupported instruction at jump label", orig_insn->sec, orig_insn->offset); return -1; } *new_insn = list_next_entry(orig_insn, list); return 0; } /* * Read all the special sections which have alternate instructions which can be * patched in or redirected to at runtime. Each instruction having alternate * instruction(s) has them added to its insn->alts list, which will be * traversed in validate_branch(). */ static int add_special_section_alts(struct objtool_file *file) { struct list_head special_alts; struct instruction *orig_insn, *new_insn; struct special_alt *special_alt, *tmp; struct alternative *alt; int ret; ret = special_get_alts(file->elf, &special_alts); if (ret) return ret; list_for_each_entry_safe(special_alt, tmp, &special_alts, list) { alt = malloc(sizeof(*alt)); if (!alt) { WARN("malloc failed"); ret = -1; goto out; } orig_insn = find_insn(file, special_alt->orig_sec, special_alt->orig_off); if (!orig_insn) { WARN_FUNC("special: can't find orig instruction", special_alt->orig_sec, special_alt->orig_off); ret = -1; goto out; } new_insn = NULL; if (!special_alt->group || special_alt->new_len) { new_insn = find_insn(file, special_alt->new_sec, special_alt->new_off); if (!new_insn) { WARN_FUNC("special: can't find new instruction", special_alt->new_sec, special_alt->new_off); ret = -1; goto out; } } if (special_alt->group) { ret = handle_group_alt(file, special_alt, orig_insn, &new_insn); if (ret) goto out; } else if (special_alt->jump_or_nop) { ret = handle_jump_alt(file, special_alt, orig_insn, &new_insn); if (ret) goto out; } alt->insn = new_insn; list_add_tail(&alt->list, &orig_insn->alts); list_del(&special_alt->list); free(special_alt); } out: return ret; } static int add_switch_table(struct objtool_file *file, struct symbol *func, struct instruction *insn, struct rela *table, struct rela *next_table) { struct rela *rela = table; struct instruction *alt_insn; struct alternative *alt; list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) { if (rela == next_table) break; if (rela->sym->sec != insn->sec || rela->addend <= func->offset || rela->addend >= func->offset + func->len) break; alt_insn = find_insn(file, insn->sec, rela->addend); if (!alt_insn) { WARN("%s: can't find instruction at %s+0x%x", file->rodata->rela->name, insn->sec->name, rela->addend); return -1; } alt = malloc(sizeof(*alt)); if (!alt) { WARN("malloc failed"); return -1; } alt->insn = alt_insn; list_add_tail(&alt->list, &insn->alts); } return 0; } /* * find_switch_table() - Given a dynamic jump, find the switch jump table in * .rodata associated with it. * * There are 3 basic patterns: * * 1. jmpq *[rodata addr](,%reg,8) * * This is the most common case by far. It jumps to an address in a simple * jump table which is stored in .rodata. * * 2. jmpq *[rodata addr](%rip) * * This is caused by a rare GCC quirk, currently only seen in three driver * functions in the kernel, only with certain obscure non-distro configs. * * As part of an optimization, GCC makes a copy of an existing switch jump * table, modifies it, and then hard-codes the jump (albeit with an indirect * jump) to use a single entry in the table. The rest of the jump table and * some of its jump targets remain as dead code. * * In such a case we can just crudely ignore all unreachable instruction * warnings for the entire object file. Ideally we would just ignore them * for the function, but that would require redesigning the code quite a * bit. And honestly that's just not worth doing: unreachable instruction * warnings are of questionable value anyway, and this is such a rare issue. * * 3. mov [rodata addr],%reg1 * ... some instructions ... * jmpq *(%reg1,%reg2,8) * * This is a fairly uncommon pattern which is new for GCC 6. As of this * writing, there are 11 occurrences of it in the allmodconfig kernel. * * TODO: Once we have DWARF CFI and smarter instruction decoding logic, * ensure the same register is used in the mov and jump instructions. */ static struct rela *find_switch_table(struct objtool_file *file, struct symbol *func, struct instruction *insn) { struct rela *text_rela, *rodata_rela; struct instruction *orig_insn = insn; text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len); if (text_rela && text_rela->sym == file->rodata->sym) { /* case 1 */ rodata_rela = find_rela_by_dest(file->rodata, text_rela->addend); if (rodata_rela) return rodata_rela; /* case 2 */ rodata_rela = find_rela_by_dest(file->rodata, text_rela->addend + 4); if (!rodata_rela) return NULL; file->ignore_unreachables = true; return rodata_rela; } /* case 3 */ func_for_each_insn_continue_reverse(file, func, insn) { if (insn->type == INSN_JUMP_DYNAMIC) break; /* allow small jumps within the range */ if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest && (insn->jump_dest->offset <= insn->offset || insn->jump_dest->offset > orig_insn->offset)) break; text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len); if (text_rela && text_rela->sym == file->rodata->sym) return find_rela_by_dest(file->rodata, text_rela->addend); } return NULL; } static int add_func_switch_tables(struct objtool_file *file, struct symbol *func) { struct instruction *insn, *prev_jump = NULL; struct rela *rela, *prev_rela = NULL; int ret; func_for_each_insn(file, func, insn) { if (insn->type != INSN_JUMP_DYNAMIC) continue; rela = find_switch_table(file, func, insn); if (!rela) continue; /* * We found a switch table, but we don't know yet how big it * is. Don't add it until we reach the end of the function or * the beginning of another switch table in the same function. */ if (prev_jump) { ret = add_switch_table(file, func, prev_jump, prev_rela, rela); if (ret) return ret; } prev_jump = insn; prev_rela = rela; } if (prev_jump) { ret = add_switch_table(file, func, prev_jump, prev_rela, NULL); if (ret) return ret; } return 0; } /* * For some switch statements, gcc generates a jump table in the .rodata * section which contains a list of addresses within the function to jump to. * This finds these jump tables and adds them to the insn->alts lists. */ static int add_switch_table_alts(struct objtool_file *file) { struct section *sec; struct symbol *func; int ret; if (!file->rodata || !file->rodata->rela) return 0; list_for_each_entry(sec, &file->elf->sections, list) { list_for_each_entry(func, &sec->symbol_list, list) { if (func->type != STT_FUNC) continue; ret = add_func_switch_tables(file, func); if (ret) return ret; } } return 0; } static int decode_sections(struct objtool_file *file) { int ret; ret = decode_instructions(file); if (ret) return ret; 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_kasan_insn(struct instruction *insn) { return (insn->type == INSN_CALL && !strcmp(insn->call_dest->name, "__asan_handle_no_return")); } static bool is_ubsan_insn(struct instruction *insn) { return (insn->type == INSN_CALL && !strcmp(insn->call_dest->name, "__ubsan_handle_builtin_unreachable")); } static bool ignore_unreachable_insn(struct symbol *func, struct instruction *insn) { int i; if (insn->type == INSN_NOP) return true; /* * Check if this (or a subsequent) instruction is related to * CONFIG_UBSAN or CONFIG_KASAN. * * End the search at 5 instructions to avoid going into the weeds. */ for (i = 0; i < 5; i++) { if (is_kasan_insn(insn) || is_ubsan_insn(insn)) return true; if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest) { insn = insn->jump_dest; continue; } if (insn->offset + insn->len >= func->offset + func->len) break; insn = list_next_entry(insn, list); } return false; } static int validate_functions(struct objtool_file *file) { struct section *sec; struct symbol *func; struct instruction *insn; int ret, warnings = 0; list_for_each_entry(sec, &file->elf->sections, list) { list_for_each_entry(func, &sec->symbol_list, list) { if (func->type != STT_FUNC) continue; insn = find_insn(file, sec, func->offset); if (!insn) continue; ret = validate_branch(file, insn, 0); warnings += ret; } } list_for_each_entry(sec, &file->elf->sections, list) { list_for_each_entry(func, &sec->symbol_list, list) { if (func->type != STT_FUNC) continue; func_for_each_insn(file, func, insn) { if (insn->visited) continue; insn->visited = true; if (file->ignore_unreachables || warnings || ignore_unreachable_insn(func, insn)) continue; /* * gcov produces a lot of unreachable * instructions. If we get an unreachable * warning and the file has gcov enabled, just * ignore it, and all other such warnings for * the file. */ if (!file->ignore_unreachables && gcov_enabled(file)) { file->ignore_unreachables = true; continue; } WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset); warnings++; } } } return warnings; } static int validate_uncallable_instructions(struct objtool_file *file) { struct instruction *insn; int warnings = 0; for_each_insn(file, insn) { if (!insn->visited && insn->type == INSN_RETURN) { WARN_FUNC("return instruction outside of a callable function", insn->sec, insn->offset); warnings++; } } return warnings; } static void cleanup(struct objtool_file *file) { struct instruction *insn, *tmpinsn; struct alternative *alt, *tmpalt; list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) { list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) { list_del(&alt->list); free(alt); } list_del(&insn->list); hash_del(&insn->hash); free(insn); } elf_close(file->elf); } const char * const check_usage[] = { "objtool check [<options>] file.o", NULL, }; int cmd_check(int argc, const char **argv) { struct objtool_file file; int ret, warnings = 0; const struct option options[] = { OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"), OPT_END(), }; argc = parse_options(argc, argv, options, check_usage, 0); if (argc != 1) usage_with_options(check_usage, options); objname = argv[0]; file.elf = elf_open(objname); if (!file.elf) { fprintf(stderr, "error reading elf file %s\n", objname); return 1; } INIT_LIST_HEAD(&file.insn_list); hash_init(file.insn_hash); file.whitelist = find_section_by_name(file.elf, "__func_stack_frame_non_standard"); file.rodata = find_section_by_name(file.elf, ".rodata"); file.ignore_unreachables = false; file.c_file = find_section_by_name(file.elf, ".comment"); ret = decode_sections(&file); if (ret < 0) goto out; warnings += ret; ret = validate_functions(&file); if (ret < 0) goto out; warnings += ret; ret = validate_uncallable_instructions(&file); if (ret < 0) goto out; warnings += ret; out: cleanup(&file); /* ignore warnings for now until we get all the code cleaned up */ if (ret || warnings) return 0; return 0; }