/* * Copyright (C) 2015 Josh Poimboeuf * * 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 . */ /* * 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 #include #include "builtin.h" #include "elf.h" #include "special.h" #include "arch.h" #include "warn.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 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 alternative { struct list_head list; struct instruction *insn; }; struct objtool_file { struct elf *elf; struct list_head insns; }; const char *objname; static bool nofp; static struct instruction *find_instruction(struct objtool_file *file, struct section *sec, unsigned long offset) { struct instruction *insn; list_for_each_entry(insn, &file->insns, list) if (insn->sec == sec && insn->offset == offset) return insn; return NULL; } /* * 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 section *macro_sec; struct rela *rela; struct instruction *insn; /* check for STACK_FRAME_NON_STANDARD */ macro_sec = find_section_by_name(file->elf, "__func_stack_frame_non_standard"); if (macro_sec && macro_sec->rela) list_for_each_entry(rela, ¯o_sec->rela->relas, list) if (rela->sym->sec == func->sec && rela->addend == func->offset) return true; /* check if it has a context switching instruction */ insn = find_instruction(file, func->sec, func->offset); if (!insn) return false; list_for_each_entry_from(insn, &file->insns, list) { if (insn->sec != func->sec || insn->offset >= func->offset + func->len) break; 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, *func_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_insn = find_instruction(file, func->sec, func->offset); if (!func_insn) return 0; insn = func_insn; list_for_each_entry_from(insn, &file->insns, list) { if (insn->sec != func->sec || insn->offset >= func->offset + func->len) break; 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. */ insn = func_insn; list_for_each_entry_from(insn, &file->insns, list) { 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) /* 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 insns list. */ static int decode_instructions(struct objtool_file *file) { struct section *sec; unsigned long offset; struct instruction *insn; int ret; INIT_LIST_HEAD(&file->insns); 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; } list_add_tail(&insn->list, &file->insns); } } return 0; } /* * Warnings shouldn't be reported for ignored functions. */ static void get_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->symbols, list) { if (func->type != STT_FUNC) continue; if (!ignore_func(file, func)) continue; insn = find_instruction(file, sec, func->offset); if (!insn) continue; list_for_each_entry_from(insn, &file->insns, list) { if (insn->sec != func->sec || insn->offset >= func->offset + func->len) break; insn->visited = true; } } } } /* * Find the destination instructions for all jumps. */ static int get_jump_destinations(struct objtool_file *file) { struct instruction *insn; struct rela *rela; struct section *dest_sec; unsigned long dest_off; list_for_each_entry(insn, &file->insns, list) { 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_instruction(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 get_call_destinations(struct objtool_file *file) { struct instruction *insn; unsigned long dest_off; struct rela *rela; list_for_each_entry(insn, &file->insns, list) { 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; list_for_each_entry_from(insn, &file->insns, list) { if (insn->sec != special_alt->orig_sec || 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 (list_is_last(&last_orig_insn->list, &file->insns) || list_next_entry(last_orig_insn, list)->sec != special_alt->orig_sec) { 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; list_for_each_entry_from(insn, &file->insns, list) { if (insn->sec != special_alt->new_sec || 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 get_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_instruction(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_instruction(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; } /* * 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 get_switch_alts(struct objtool_file *file) { struct instruction *insn, *alt_insn; struct rela *rodata_rela, *rela; struct section *rodata; struct symbol *func; struct alternative *alt; list_for_each_entry(insn, &file->insns, list) { if (insn->type != INSN_JUMP_DYNAMIC) continue; rodata_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len); if (!rodata_rela || strcmp(rodata_rela->sym->name, ".rodata")) continue; rodata = find_section_by_name(file->elf, ".rodata"); if (!rodata || !rodata->rela) continue; /* common case: jmpq *[addr](,%rax,8) */ rela = find_rela_by_dest(rodata, rodata_rela->addend); /* rare case: jmpq *[addr](%rip) */ if (!rela) rela = find_rela_by_dest(rodata, rodata_rela->addend + 4); if (!rela) continue; func = find_containing_func(insn->sec, insn->offset); if (!func) { WARN_FUNC("can't find containing func", insn->sec, insn->offset); return -1; } list_for_each_entry_from(rela, &rodata->rela->relas, list) { if (rela->sym->sec != insn->sec || rela->addend <= func->offset || rela->addend >= func->offset + func->len) break; alt_insn = find_instruction(file, insn->sec, rela->addend); if (!alt_insn) { WARN("%s: can't find instruction at %s+0x%x", 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 decode_sections(struct objtool_file *file) { int ret; ret = decode_instructions(file); if (ret) return ret; get_ignores(file); ret = get_jump_destinations(file); if (ret) return ret; ret = get_call_destinations(file); if (ret) return ret; ret = get_special_section_alts(file); if (ret) return ret; ret = get_switch_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); } /* * 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; unsigned char state; int ret, warnings = 0; 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); warnings++; } while (1) { if (insn->visited) { if (insn->state != state) { WARN_FUNC("frame pointer state mismatch", sec, insn->offset); warnings++; } return warnings; } /* * Catch a rare case where a noreturn function falls through to * the next function. */ if (is_fentry_call(insn) && (state & STATE_FENTRY)) return warnings; insn->visited = true; insn->state = state; list_for_each_entry(alt, &insn->alts, list) { ret = validate_branch(file, alt->insn, state); warnings += ret; } switch (insn->type) { case INSN_FP_SAVE: if (!nofp) { if (state & STATE_FP_SAVED) { WARN_FUNC("duplicate frame pointer save", sec, insn->offset); warnings++; } 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); warnings++; } 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); warnings++; } return warnings; case INSN_CALL: if (is_fentry_call(insn)) { state |= STATE_FENTRY; break; } ret = dead_end_function(file, insn->call_dest); if (ret == 1) return warnings; if (ret == -1) warnings++; /* fallthrough */ case INSN_CALL_DYNAMIC: if (!nofp && !has_valid_stack_frame(insn)) { WARN_FUNC("call without frame pointer save/setup", sec, insn->offset); warnings++; } break; case INSN_JUMP_CONDITIONAL: case INSN_JUMP_UNCONDITIONAL: if (insn->jump_dest) { ret = validate_branch(file, insn->jump_dest, state); warnings += ret; } else if (has_modified_stack_frame(insn)) { WARN_FUNC("sibling call from callable instruction with changed frame pointer", sec, insn->offset); warnings++; } /* else it's a sibling call */ if (insn->type == INSN_JUMP_UNCONDITIONAL) return warnings; 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); warnings++; } return warnings; case INSN_BUG: return warnings; default: break; } insn = list_next_entry(insn, list); if (&insn->list == &file->insns || insn->sec != sec) { WARN("%s: unexpected end of section", sec->name); warnings++; return warnings; } } return warnings; } 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->symbols, 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 instruction *insn, unsigned long func_end) { 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_end) 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; unsigned long func_end; int ret, warnings = 0; list_for_each_entry(sec, &file->elf->sections, list) { list_for_each_entry(func, &sec->symbols, list) { if (func->type != STT_FUNC) continue; insn = find_instruction(file, sec, func->offset); if (!insn) { WARN("%s(): can't find starting instruction", func->name); warnings++; continue; } ret = validate_branch(file, insn, 0); warnings += ret; } } list_for_each_entry(sec, &file->elf->sections, list) { list_for_each_entry(func, &sec->symbols, list) { if (func->type != STT_FUNC) continue; insn = find_instruction(file, sec, func->offset); if (!insn) continue; func_end = func->offset + func->len; list_for_each_entry_from(insn, &file->insns, list) { if (insn->sec != func->sec || insn->offset >= func_end) break; if (insn->visited) continue; if (!ignore_unreachable_insn(insn, func_end)) { WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset); warnings++; } insn->visited = true; } } } return warnings; } static int validate_uncallable_instructions(struct objtool_file *file) { struct instruction *insn; int warnings = 0; list_for_each_entry(insn, &file->insns, list) { 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->insns, list) { list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) { list_del(&alt->list); free(alt); } list_del(&insn->list); free(insn); } elf_close(file->elf); } const char * const check_usage[] = { "objtool check [] 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.insns); 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; }