cregit-Linux how code gets into the kernel

Release 4.14 tools/objtool/check.c

Directory: tools/objtool
/*
 * Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 */

#include <string.h>
#include <stdlib.h>

#include "check.h"
#include "elf.h"
#include "special.h"
#include "arch.h"
#include "warn.h"

#include <linux/hashtable.h>
#include <linux/kernel.h>


struct alternative {
	
struct list_head list;
	
struct instruction *insn;
};


const char *objname;

static bool no_fp;

struct cfi_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; }

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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; }

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#define func_for_each_insn(file, func, insn) \ for (insn = find_insn(file, func->sec, func->offset); \ insn && &insn->list != &file->insn_list && \ insn->sec == func->sec && \ insn->offset < func->offset + func->len; \ insn = list_next_entry(insn, list)) #define func_for_each_insn_continue_reverse(file, func, insn) \ for (insn = list_prev_entry(insn, list); \ &insn->list != &file->insn_list && \ insn->sec == func->sec && insn->offset >= func->offset; \ insn = list_prev_entry(insn, list)) #define sec_for_each_insn_from(file, insn) \ for (; insn; insn = next_insn_same_sec(file, insn)) #define sec_for_each_insn_continue(file, insn) \ for (insn = next_insn_same_sec(file, insn); insn; \ insn = next_insn_same_sec(file, insn)) /* * Check if the function has been manually whitelisted with the * STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted * due to its use of a context switching instruction. */
static bool ignore_func(struct objtool_file *file, struct symbol *func) { struct rela *rela; /* 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; } return false; }

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/* * This checks to see if the given function is a "noreturn" function. * * For global functions which are outside the scope of this object file, we * have to keep a manual list of them. * * For local functions, we have to detect them manually by simply looking for * the lack of a return instruction. * * Returns: * -1: error * 0: no dead end * 1: dead end */
static int __dead_end_function(struct objtool_file *file, struct symbol *func, int recursion) { int i; struct instruction *insn; bool empty = true; /* * Unfortunately these have to be hard coded because the noreturn * attribute isn't provided in ELF data. */ static const char * const global_noreturns[] = { "__stack_chk_fail", "panic", "do_exit", "do_task_dead", "__module_put_and_exit", "complete_and_exit", "kvm_spurious_fault", "__reiserfs_panic", "lbug_with_loc", "fortify_panic", }; if (func->bind == STB_WEAK) return 0; if (func->bind == STB_GLOBAL) for (i = 0; i < ARRAY_SIZE(global_noreturns); i++) if (!strcmp(func->name, global_noreturns[i])) return 1; if (!func->sec) return 0; func_for_each_insn(file, func, insn) { empty = false; if (insn->type == INSN_RETURN) return 0; } if (empty) return 0; /* * A function can have a sibling call instead of a return. In that * case, the function's dead-end status depends on whether the target * of the sibling call returns. */ func_for_each_insn(file, func, insn) { if (insn->sec != func->sec || insn->offset >= func->offset + func->len) break; if (insn->type == INSN_JUMP_UNCONDITIONAL) { struct instruction *dest = insn->jump_dest; struct symbol *dest_func; if (!dest) /* sibling call to another file */ return 0; if (dest->sec != func->sec || dest->offset < func->offset || dest->offset >= func->offset + func->len) { /* local sibling call */ dest_func = find_symbol_by_offset(dest->sec, dest->offset); if (!dest_func) continue; if (recursion == 5) { WARN_FUNC("infinite recursion (objtool bug!)", dest->sec, dest->offset); return -1; } return __dead_end_function(file, dest_func, recursion + 1); } } if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts)) /* sibling call */ return 0; } return 1; }

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static int dead_end_function(struct objtool_file *file, struct symbol *func) { return __dead_end_function(file, func, 0); }

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static void clear_insn_state(struct insn_state *state) { int i; memset(state, 0, sizeof(*state)); state->cfa.base = CFI_UNDEFINED; for (i = 0; i < CFI_NUM_REGS; i++) { state->regs[i].base = CFI_UNDEFINED; state->vals[i].base = CFI_UNDEFINED; } state->drap_reg = CFI_UNDEFINED; state->drap_offset = -1; }

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/* * Call the arch-specific instruction decoder for all the instructions and add * them to the global instruction list. */
static int decode_instructions(struct objtool_file *file) { struct section *sec; struct symbol *func; unsigned long offset; struct instruction *insn; int ret; for_each_sec(file, sec) { if (!(sec->sh.sh_flags & SHF_EXECINSTR)) continue; if (strcmp(sec->name, ".altinstr_replacement") && strcmp(sec->name, ".altinstr_aux") && strncmp(sec->name, ".discard.", 9)) sec->text = 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); clear_insn_state(&insn->state); insn->sec = sec; insn->offset = offset; ret = arch_decode_instruction(file->elf, sec, offset, sec->len - offset, &insn->len, &insn->type, &insn->immediate, &insn->stack_op); if (ret) goto err; if (!insn->type || insn->type > INSN_LAST) { WARN_FUNC("invalid instruction type %d", insn->sec, insn->offset, insn->type); ret = -1; goto err; } 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; err: free(insn); return ret; }

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Josh Poimboeuf35894.96%375.00%
Kamalesh Babulal195.04%125.00%
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/* * 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; }

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/* * Warnings shouldn't be reported for ignored functions. */
static void add_ignores(struct objtool_file *file) { struct instruction *insn; struct section *sec; struct symbol *func; for_each_sec(file, sec) { list_for_each_entry(func, &sec->symbol_list, list) { if (func->type != STT_FUNC) continue; if (!ignore_func(file, func)) continue; func_for_each_insn(file, func, insn) insn->ignore = true; } } }

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/* * Find the destination instructions for all jumps. */
static int add_jump_destinations(struct objtool_file *file) { struct instruction *insn; struct rela *rela; struct section *dest_sec; unsigned long dest_off; for_each_insn(file, insn) { if (insn->type != INSN_JUMP_CONDITIONAL && insn->type != INSN_JUMP_UNCONDITIONAL) continue; if (insn->ignore) continue; rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len); if (!rela) { dest_sec = insn->sec; dest_off = insn->offset + insn->len + insn->immediate; } else if (rela->sym->type == STT_SECTION) { dest_sec = rela->sym->sec; dest_off = rela->addend + 4; } else if (rela->sym->sec->idx) { dest_sec = rela->sym->sec; dest_off = rela->sym->sym.st_value + rela->addend + 4; } else { /* sibling call */ insn->jump_dest = 0; continue; } insn->jump_dest = find_insn(file, dest_sec, dest_off); if (!insn->jump_dest) { /* * This is a special case where an alt instruction * jumps past the end of the section. These are * handled later in handle_group_alt(). */ if (!strcmp(insn->sec->name, ".altinstr_replacement")) continue; WARN_FUNC("can't find jump dest instruction at %s+0x%lx", insn->sec, insn->offset, dest_sec->name, dest_off); return -1; } } return 0; }

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/* * 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; }

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Josh Poimboeuf213100.00%1100.00%
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/* * The .alternatives section requires some extra special care, over and above * what other special sections require: * * 1. Because alternatives are patched in-place, we need to insert a fake jump * instruction at the end so that validate_branch() skips all the original * replaced instructions when validating the new instruction path. * * 2. An added wrinkle is that the new instruction length might be zero. In * that case the old instructions are replaced with noops. We simulate that * by creating a fake jump as the only new instruction. * * 3. In some cases, the alternative section includes an instruction which * conditionally jumps to the _end_ of the entry. We have to modify these * jumps' destinations to point back to .text rather than the end of the * entry in .altinstr_replacement. * * 4. It has been requested that we don't validate the !POPCNT feature path * which is a "very very small percentage of machines". */
static int handle_group_alt(struct objtool_file *file, struct special_alt *special_alt, struct instruction *orig_insn, struct instruction **new_insn) { struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump; unsigned long dest_off; last_orig_insn = NULL; insn = orig_insn; sec_for_each_insn_from(file, insn) { if (insn->offset >= special_alt->orig_off + special_alt->orig_len) break; if (special_alt->skip_orig) insn->type = INSN_NOP; insn->alt_group = true; last_orig_insn = insn; } if (!next_insn_same_sec(file, last_orig_insn)) { WARN("%s: don't know how to handle alternatives at end of section", special_alt->orig_sec->name); return -1; } fake_jump = malloc(sizeof(*fake_jump)); if (!fake_jump) { WARN("malloc failed"); return -1; } memset(fake_jump, 0, sizeof(*fake_jump)); INIT_LIST_HEAD(&fake_jump->alts); clear_insn_state(&fake_jump->state); fake_jump->sec = special_alt->new_sec; fake_jump->offset = -1; fake_jump->type = INSN_JUMP_UNCONDITIONAL; fake_jump->jump_dest = list_next_entry(last_orig_insn, list); fake_jump->ignore = true; if (!special_alt->new_len) { *new_insn = fake_jump; return 0; } last_new_insn = NULL; insn = *new_insn; sec_for_each_insn_from(file, insn) { if (insn->offset >= special_alt->new_off + special_alt->new_len) break; last_new_insn = insn; if (insn->type != INSN_JUMP_CONDITIONAL && insn->type != INSN_JUMP_UNCONDITIONAL) continue; if (!insn->immediate) continue; dest_off = insn->offset + insn->len + insn->immediate; if (dest_off == special_alt->new_off + special_alt->new_len) insn->jump_dest = fake_jump; if (!insn->jump_dest) { WARN_FUNC("can't find alternative jump destination", insn->sec, insn->offset); return -1; } } if (!last_new_insn) { WARN_FUNC("can't find last new alternative instruction", special_alt->new_sec, special_alt->new_off); return -1; } list_add(&fake_jump->list, &last_new_insn->list); return 0; }

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Josh Poimboeuf393100.00%2100.00%
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/* * 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; }

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Josh Poimboeuf78100.00%1100.00%
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/* * 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; }

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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; }

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Josh Poimboeuf196100.00%1100.00%
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/* * find_switch_table() - Given a dynamic jump, find the switch jump table in * .rodata associated with it. * * There are 3 basic patterns: * * 1. jmpq *[rodata addr](,%reg,8) * * This is the most common case by far. It jumps to an address in a simple * jump table which is stored in .rodata. * * 2. jmpq *[rodata addr](%rip) * * This is caused by a rare GCC quirk, currently only seen in three driver * functions in the kernel, only with certain obscure non-distro configs. * * As part of an optimization, GCC makes a copy of an existing switch jump * table, modifies it, and then hard-codes the jump (albeit with an indirect * jump) to use a single entry in the table. The rest of the jump table and * some of its jump targets remain as dead code. * * In such a case we can just crudely ignore all unreachable instruction * warnings for the entire object file. Ideally we would just ignore them * for the function, but that would require redesigning the code quite a * bit. And honestly that's just not worth doing: unreachable instruction * warnings are of questionable value anyway, and this is such a rare issue. * * 3. mov [rodata addr],%reg1 * ... some instructions ... * jmpq *(%reg1,%reg2,8) * * This is a fairly uncommon pattern which is new for GCC 6. As of this * writing, there are 11 occurrences of it in the allmodconfig kernel. * * TODO: Once we have DWARF CFI and smarter instruction decoding logic, * ensure the same register is used in the mov and jump instructions. */
static struct rela *find_switch_table(struct objtool_file *file, struct symbol *func, struct instruction *insn) { struct rela *text_rela, *rodata_rela; struct instruction *orig_insn = insn; text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len); if (text_rela && text_rela->sym == file->rodata->sym) { /* case 1 */ rodata_rela = find_rela_by_dest(file->rodata, text_rela->addend); if (rodata_rela) return rodata_rela; /* case 2 */ rodata_rela = find_rela_by_dest(file->rodata, text_rela->addend + 4); if (!rodata_rela) return NULL; file->ignore_unreachables = true; return rodata_rela; } /* case 3 */ func_for_each_insn_continue_reverse(file, func, insn) { if (insn->type == INSN_JUMP_DYNAMIC) break; /* allow small jumps within the range */ if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest && (insn->jump_dest->offset <= insn->offset || insn->jump_dest->offset > orig_insn->offset)) break; /* look for a relocation which references .rodata */ text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len); if (!text_rela || text_rela->sym != file->rodata->sym) continue; /* * Make sure the .rodata address isn't associated with a * symbol. gcc jump tables are anonymous data. */ if (find_symbol_containing(file->rodata, text_rela->addend)) continue; return find_rela_by_dest(file->rodata, text_rela->addend); } return NULL; }

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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; }

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Josh Poimboeuf143100.00%1100.00%
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/* * For some switch statements, gcc generates a jump table in the .rodata * section which contains a list of addresses within the function to jump to. * This finds these jump tables and adds them to the insn->alts lists. */
static int add_switch_table_alts(struct objtool_file *file) { struct section *sec; struct symbol *func; int ret; if (!file->rodata || !file->rodata->rela) return 0; for_each_sec(file, sec) { list_for_each_entry(func, &sec->symbol_list, list) { if (func->type != STT_FUNC) continue; ret = add_func_switch_tables(file, func); if (ret) return ret; } } return 0; }

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Josh Poimboeuf87100.00%2100.00%
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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(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->state.cfa; if (hint->type == UNWIND_HINT_TYPE_SAVE) { insn->save = true; continue; } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) { insn->restore = true; insn->hint = true; 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->state.type = hint->type; } return 0; }

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Josh Poimboeuf405100.00%2100.00%
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static int decode_sections(struct objtool_file *file) { int ret; ret = decode_instructions(file); if (ret) return ret; ret = add_dead_ends(file); if (ret) return ret; add_ignores(file); ret = add_jump_destinations(file); if (ret) return ret; ret = add_call_destinations(file); if (ret) return ret; ret = add_special_section_alts(file); if (ret) return ret; ret = add_switch_table_alts(file); if (ret) return ret; ret = read_unwind_hints(file); if (ret) return ret; return 0; }

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Josh Poimboeuf120100.00%1100.00%
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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; }

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Josh Poimboeuf45100.00%2100.00%
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static bool has_modified_stack_frame(struct insn_state *state) { int i; if (state->cfa.base != initial_func_cfi.cfa.base || state->cfa.offset != initial_func_cfi.cfa.offset || state->stack_size != initial_func_cfi.cfa.offset || state->drap) return true; for (i = 0; i < CFI_NUM_REGS; i++) if (state->regs[i].base != initial_func_cfi.regs[i].base || state->regs[i].offset != initial_func_cfi.regs[i].offset) return true; return false; }

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Josh Poimboeuf114100.00%2100.00%
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static bool has_valid_stack_frame(struct insn_state *state) { if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA && state->regs[CFI_BP].offset == -16) return true; if (state->drap && state->regs[CFI_BP].base == CFI_BP) return true; return false; }

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Josh Poimboeuf70100.00%2100.00%
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static int update_insn_state_regs(struct instruction *insn, struct insn_state *state) { struct cfi_reg *cfa = &state->cfa; struct stack_op *op = &insn->stack_op; if (cfa->base != CFI_SP) return 0; /* push */ if (op->dest.type == OP_DEST_PUSH) cfa->offset += 8; /* pop */ if (op->src.type == OP_SRC_POP) 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; }

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Josh Poimboeuf129100.00%1100.00%
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static void save_reg(struct insn_state *state, unsigned char reg, int base, int offset) { if (arch_callee_saved_reg(reg) && state->regs[reg].base == CFI_UNDEFINED) { state->regs[reg].base = base; state->regs[reg].offset = offset; } }

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Josh Poimboeuf63100.00%1100.00%
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static void restore_reg(struct insn_state *state, unsigned char reg) { state->regs[reg].base = CFI_UNDEFINED; state->regs[reg].offset = 0; }

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Josh Poimboeuf37100.00%1100.00%
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/* * A note about DRAP stack alignment: * * GCC has the concept of a DRAP register, which is used to help keep track of * the stack pointer when aligning the stack. r10 or r13 is used as the DRAP * register. The typical DRAP pattern is: * * 4c 8d 54 24 08 lea 0x8(%rsp),%r10 * 48 83 e4 c0 and $0xffffffffffffffc0,%rsp * 41 ff 72 f8 pushq -0x8(%r10) * 55 push %rbp * 48 89 e5 mov %rsp,%rbp * (more pushes) * 41 52 push %r10 * ... * 41 5a pop %r10 * (more pops) * 5d pop %rbp * 49 8d 62 f8 lea -0x8(%r10),%rsp * c3 retq * * There are some variations in the epilogues, like: * * 5b pop %rbx * 41 5a pop %r10 * 41 5c pop %r12 * 41 5d pop %r13 * 41 5e pop %r14 * c9 leaveq * 49 8d 62 f8 lea -0x8(%r10),%rsp * c3 retq * * and: * * 4c 8b 55 e8 mov -0x18(%rbp),%r10 * 48 8b 5d e0 mov -0x20(%rbp),%rbx * 4c 8b 65 f0 mov -0x10(%rbp),%r12 * 4c 8b 6d f8 mov -0x8(%rbp),%r13 * c9 leaveq * 49 8d 62 f8 lea -0x8(%r10),%rsp * c3 retq * * Sometimes r13 is used as the DRAP register, in which case it's saved and * restored beforehand: * * 41 55 push %r13 * 4c 8d 6c 24 10 lea 0x10(%rsp),%r13 * 48 83 e4 f0 and $0xfffffffffffffff0,%rsp * ... * 49 8d 65 f0 lea -0x10(%r13),%rsp * 41 5d pop %r13 * c3 retq */
static int update_insn_state(struct instruction *insn, struct insn_state *state) { struct stack_op *op = &insn->stack_op; struct cfi_reg *cfa = &state->cfa; struct cfi_reg *regs = state->regs; /* stack operations don't make sense with an undefined CFA */ if (cfa->base == CFI_UNDEFINED) { if (insn->func) { WARN_FUNC("undefined stack state", insn->sec, insn->offset); return -1; } return 0; } if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET) return update_insn_state_regs(insn, state); 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; state->bp_scratch = false; } else if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP && state->drap) { /* drap: mov %rsp, %rbp */ regs[CFI_BP].base = CFI_BP; regs[CFI_BP].offset = -state->stack_size; state->bp_scratch = false; } else if (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 */ state->vals[op->dest.reg].base = CFI_CFA; state->vals[op->dest.reg].offset = -state->stack_size; } else if (op->dest.reg == cfa->base) { /* mov %reg, %rsp */ if (cfa->base == CFI_SP && state->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 = -state->vals[op->src.reg].offset; state->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 */ state->stack_size -= op->src.offset; if (cfa->base == CFI_SP) cfa->offset -= op->src.offset; break; } if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) { /* lea disp(%rbp), %rsp */ state->stack_size = -(op->src.offset + regs[CFI_BP].offset); break; } if (op->src.reg == CFI_SP && cfa->base == CFI_SP) { /* drap: lea disp(%rsp), %drap */ state->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 */ state->vals[op->dest.reg].base = CFI_CFA; state->vals[op->dest.reg].offset = \ -state->stack_size + op->src.offset; break; } if (state->drap && op->dest.reg == CFI_SP && op->src.reg == state->drap_reg) { /* drap: lea disp(%drap), %rsp */ cfa->base = CFI_SP; cfa->offset = state->stack_size = -op->src.offset; state->drap_reg = CFI_UNDEFINED; state->drap = false; break; } if (op->dest.reg == state->cfa.base) { WARN_FUNC("unsupported stack register modification", insn->sec, insn->offset); return -1; } break; case OP_SRC_AND: if (op->dest.reg != CFI_SP || (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) || (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) { WARN_FUNC("unsupported stack pointer realignment", insn->sec, insn->offset); return -1; } if (state->drap_reg != CFI_UNDEFINED) { /* drap: and imm, %rsp */ cfa->base = state->drap_reg; cfa->offset = state->stack_size = 0; state->drap = true; } /* * Older versions of GCC (4.8ish) realign the stack * without DRAP, with a frame pointer. */ break; case OP_SRC_POP: if (!state->drap && op->dest.type == OP_DEST_REG && op->dest.reg == cfa->base) { /* pop %rbp */ cfa->base = CFI_SP; } if (state->drap && cfa->base == CFI_BP_INDIRECT && op->dest.type == OP_DEST_REG && op->dest.reg == state->drap_reg && state->drap_offset == -state->stack_size) { /* drap: pop %drap */ cfa->base = state->drap_reg; cfa->offset = 0; state->drap_offset = -1; } else if (regs[op->dest.reg].offset == -state->stack_size) { /* pop %reg */ restore_reg(state, op->dest.reg); } state->stack_size -= 8; if (cfa->base == CFI_SP) cfa->offset -= 8; break; case OP_SRC_REG_INDIRECT: if (state->drap && op->src.reg == CFI_BP && op->src.offset == state->drap_offset) { /* drap: mov disp(%rbp), %drap */ cfa->base = state->drap_reg; cfa->offset = 0; state->drap_offset = -1; } if (state->drap && op->src.reg == CFI_BP && op->src.offset == regs[op->dest.reg].offset) { /* drap: mov disp(%rbp), %reg */ restore_reg(state, op->dest.reg); } else if (op->src.reg == cfa->base && op->src.offset == regs[op->dest.reg].offset + cfa->offset) { /* mov disp(%rbp), %reg */ /* mov disp(%rsp), %reg */ restore_reg(state, op->dest.reg); } break; default: WARN_FUNC("unknown stack-related instruction", insn->sec, insn->offset); return -1; } break; case OP_DEST_PUSH: state->stack_size += 8; if (cfa->base == CFI_SP) cfa->offset += 8; if (op->src.type != OP_SRC_REG) break; if (state->drap) { if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) { /* drap: push %drap */ cfa->base = CFI_BP_INDIRECT; cfa->offset = -state->stack_size; /* save drap so we know when to restore it */ state->drap_offset = -state->stack_size; } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) { /* drap: push %rbp */ state->stack_size = 0; } else if (regs[op->src.reg].base == CFI_UNDEFINED) { /* drap: push %reg */ save_reg(state, op->src.reg, CFI_BP, -state->stack_size); } } else { /* push %reg */ save_reg(state, op->src.reg, CFI_CFA, -state->stack_size); } /* detect when asm code uses rbp as a scratch register */ if (!no_fp && insn->func && op->src.reg == CFI_BP && cfa->base != CFI_BP) state->bp_scratch = true; break; case OP_DEST_REG_INDIRECT: if (state->drap) { if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) { /* drap: mov %drap, disp(%rbp) */ cfa->base = CFI_BP_INDIRECT; cfa->offset = op->dest.offset; /* save drap offset so we know when to restore it */ state->drap_offset = op->dest.offset; } else if (regs[op->src.reg].base == CFI_UNDEFINED) { /* drap: mov reg, disp(%rbp) */ save_reg(state, op->src.reg, CFI_BP, op->dest.offset); } } else if (op->dest.reg == cfa->base) { /* mov reg, disp(%rbp) */ /* mov reg, disp(%rsp) */ save_reg(state, op->src.reg, CFI_CFA, op->dest.offset - state->cfa.offset); } break; case OP_DEST_LEAVE: if ((!state->drap && cfa->base != CFI_BP) || (state->drap && cfa->base != state->drap_reg)) { WARN_FUNC("leave instruction with modified stack frame", insn->sec, insn->offset); return -1; } /* leave (mov %rbp, %rsp; pop %rbp) */ state->stack_size = -state->regs[CFI_BP].offset - 8; restore_reg(state, CFI_BP); if (!state->drap) { cfa->base = CFI_SP; cfa->offset -= 8; } break; case OP_DEST_MEM: if (op->src.type != OP_SRC_POP) { WARN_FUNC("unknown stack-related memory operation", insn->sec, insn->offset); return -1; } /* pop mem */ state->stack_size -= 8; if (cfa->base == CFI_SP) cfa->offset -= 8; break; default: WARN_FUNC("unknown stack-related instruction", insn->sec, insn->offset); return -1; } return 0; }

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Josh Poimboeuf1589100.00%7100.00%
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static bool insn_state_match(struct instruction *insn, struct insn_state *state) { struct insn_state *state1 = &insn->state, *state2 = state; int i; if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) { WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d", insn->sec, insn->offset, state1->cfa.base, state1->cfa.offset, state2->cfa.base, state2->cfa.offset); } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) { for (i = 0; i < CFI_NUM_REGS; i++) { if (!memcmp(&state1->regs[i], &state2->regs[i], sizeof(struct cfi_reg))) continue; WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d", insn->sec, insn->offset, i, state1->regs[i].base, state1->regs[i].offset, i, state2->regs[i].base, state2->regs[i].offset); break; } } else if (state1->type != state2->type) { WARN_FUNC("stack state mismatch: type1=%d type2=%d", insn->sec, insn->offset, state1->type, state2->type); } else if (state1->drap != state2->drap || (state1->drap && state1->drap_reg != state2->drap_reg) || (state1->drap && state1->drap_offset != state2->drap_offset)) { WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)", insn->sec, insn->offset, state1->drap, state1->drap_reg, state1->drap_offset, state2->drap, state2->drap_reg, state2->drap_offset); } else return true; return false; }

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Josh Poimboeuf337100.00%4100.00%
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/* * Follow the branch starting at the given instruction, and recursively follow * any other branches (jumps). Meanwhile, track the frame pointer state at * each instruction and validate all the rules described in * tools/objtool/Documentation/stack-validation.txt. */
static int validate_branch(struct objtool_file *file, struct instruction *first, struct insn_state state) { struct alternative *alt; struct instruction *insn, *next_insn; struct section *sec; struct symbol *func = NULL; int ret; insn = first; sec = insn->sec; if (insn->alt_group && list_empty(&insn->alts)) { WARN_FUNC("don't know how to handle branch to middle of alternative instruction group", sec, insn->offset); return 1; } while (1) { next_insn = next_insn_same_sec(file, insn); if (file->c_file && func && insn->func && func != insn->func) { WARN("%s() falls through to next function %s()", func->name, insn->func->name); return 1; } if (insn->func) func = insn->func; if (func && insn->ignore) { WARN_FUNC("BUG: why am I validating an ignored function?", sec, insn->offset); return 1; } if (insn->visited) { if (!insn->hint && !insn_state_match(insn, &state)) return 1; return 0; } if (insn->hint) { if (insn->restore) { struct instruction *save_insn, *i; i = insn; save_insn = NULL; func_for_each_insn_continue_reverse(file, func, i) { if (i->save) { save_insn = i; break; } } if (!save_insn) { WARN_FUNC("no corresponding CFI save for CFI restore", sec, insn->offset); return 1; } if (!save_insn->visited) { /* * Oops, no state to copy yet. * Hopefully we can reach this * instruction from another branch * after the save insn has been * visited. */ if (insn == first) return 0; WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo", sec, insn->offset); return 1; } insn->state = save_insn->state; } state = insn->state; } else insn->state = state; insn->visited = true; list_for_each_entry(alt, &insn->alts, list) { ret = validate_branch(file, alt->insn, state); if (ret) return 1; } switch (insn->type) { case INSN_RETURN: if (func && has_modified_stack_frame(&state)) { WARN_FUNC("return with modified stack frame", sec, insn->offset); return 1; } if (state.bp_scratch) { WARN("%s uses BP as a scratch register", insn->func->name); return 1; } return 0; case INSN_CALL: if (is_fentry_call(insn)) break; ret = dead_end_function(file, insn->call_dest); if (ret == 1) return 0; if (ret == -1) return 1; /* fallthrough */ case INSN_CALL_DYNAMIC: if (!no_fp && func && !has_valid_stack_frame(&state)) { WARN_FUNC("call without frame pointer save/setup", sec, insn->offset); return 1; } break; case INSN_JUMP_CONDITIONAL: case INSN_JUMP_UNCONDITIONAL: if (insn->jump_dest && (!func || !insn->jump_dest->func || func == insn->jump_dest->func)) { ret = validate_branch(file, insn->jump_dest, state); if (ret) return 1; } else if (func && has_modified_stack_frame(&state)) { WARN_FUNC("sibling call from callable instruction with modified stack frame", sec, insn->offset); return 1; } if (insn->type == INSN_JUMP_UNCONDITIONAL) return 0; break; case INSN_JUMP_DYNAMIC: if (func && list_empty(&insn->alts) && has_modified_stack_frame(&state)) { WARN_FUNC("sibling call from callable instruction with modified stack frame", sec, insn->offset); return 1; } return 0; case INSN_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 (update_insn_state(insn, &state)) return 1; break; default: break; } if (insn->dead_end) return 0; insn = next_insn; if (!insn) { WARN("%s: unexpected end of section", sec->name); return 1; } } return 0; }

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Josh Poimboeuf734100.00%6100.00%
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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, state); warnings += ret; } } return warnings; }

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Josh Poimboeuf82100.00%1100.00%
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static bool is_kasan_insn(struct instruction *insn) { return (insn->type == INSN_CALL && !strcmp(insn->call_dest->name, "__asan_handle_no_return")); }

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Josh Poimboeuf32100.00%1100.00%
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static bool is_ubsan_insn(struct instruction *insn) { return (insn->type == INSN_CALL && !strcmp(insn->call_dest->name, "__ubsan_handle_builtin_unreachable")); }

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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; /* * Check if this (or a subsequent) instruction is related to * CONFIG_UBSAN or CONFIG_KASAN. * * End the search at 5 instructions to avoid going into the weeds. */ if (!insn->func) return false; for (i = 0; i < 5; i++) { if (is_kasan_insn(insn) || is_ubsan_insn(insn)) return true; if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest) { insn = insn->jump_dest; continue; } if (insn->offset + insn->len >= insn->func->offset + insn->func->len) break; insn = list_next_entry(insn, list); } return false; }

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Josh Poimboeuf168100.00%3100.00%
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static int validate_functions(struct objtool_file *file) { struct section *sec; struct symbol *func; struct instruction *insn; struct insn_state state; int ret, warnings = 0; clear_insn_state(&state); state.cfa = initial_func_cfi.cfa; memcpy(&state.regs, &initial_func_cfi.regs, CFI_NUM_REGS * sizeof(struct cfi_reg)); state.stack_size = initial_func_cfi.cfa.offset; for_each_sec(file, sec) { list_for_each_entry(func, &sec->symbol_list, list) { if (func->type != STT_FUNC) continue; insn = find_insn(file, sec, func->offset); if (!insn || insn->ignore) continue; ret = validate_branch(file, insn, state); warnings += ret; } } return warnings; }

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Josh Poimboeuf150100.00%2100.00%
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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; }

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Josh Poimboeuf64100.00%2100.00%
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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); }

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Josh Poimboeuf92100.00%1100.00%
Total92100.00%1100.00%


int check(const char *_objname, bool _no_fp, bool no_unreachable, bool orc) { struct objtool_file file; int ret, warnings = 0; objname = _objname; no_fp = _no_fp; file.elf = elf_open(objname, orc ? O_RDWR : O_RDONLY); if (!file.elf) return 1; INIT_LIST_HEAD(&file.insn_list); hash_init(file.insn_hash); file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard"); file.rodata = find_section_by_name(file.elf, ".rodata"); file.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; 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: cleanup(&file); /* ignore warnings for now until we get all the code cleaned up */ if (ret || warnings) return 0; return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Josh Poimboeuf318100.00%5100.00%
Total318100.00%5100.00%


Overall Contributors

PersonTokensPropCommitsCommitProp
Josh Poimboeuf813199.77%1292.31%
Kamalesh Babulal190.23%17.69%
Total8150100.00%13100.00%
Directory: tools/objtool
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