cregit-Linux how code gets into the kernel

Release 4.7 tools/objtool/builtin-check.c

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

/*
 * objtool check:
 *
 * This command analyzes every .o file and ensures the validity of its stack
 * trace metadata.  It enforces a set of rules on asm code and C inline
 * assembly code so that stack traces can be reliable.
 *
 * For more information, see tools/objtool/Documentation/stack-validation.txt.
 */

#include <string.h>
#include <subcmd/parse-options.h>

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

#include <linux/hashtable.h>


#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))


#define STATE_FP_SAVED		0x1

#define STATE_FP_SETUP		0x2

#define STATE_FENTRY		0x4


struct instruction {
	
struct list_head list;
	
struct hlist_node hash;
	
struct section *sec;
	
unsigned long offset;
	

unsigned int len, state;
	
unsigned char type;
	
unsigned long immediate;
	

bool alt_group, visited;
	
struct symbol *call_dest;
	
struct instruction *jump_dest;
	
struct list_head alts;
	
struct symbol *func;
};


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


struct objtool_file {
	
struct elf *elf;
	
struct list_head insn_list;
	DECLARE_HASHTABLE(insn_hash, 16);
	

struct section *rodata, *whitelist;
	

bool ignore_unreachables, c_file;
};


const char *objname;

static bool nofp;


static struct instruction *find_insn(struct objtool_file *file, struct section *sec, unsigned long offset) { struct instruction *insn; hash_for_each_possible(file->insn_hash, insn, hash, offset) if (insn->sec == sec && insn->offset == offset) return insn; return NULL; }

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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->list == &file->insn_list || next->sec != insn->sec) return NULL; return next; }

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

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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", "__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; }

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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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/* * 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; }

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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; 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; } } }

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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; /* 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; }

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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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/* * 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; }

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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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/* * 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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static int add_func_switch_tables(struct objtool_file *file, struct symbol *func) { struct instruction *insn, *prev_jump; struct rela *text_rela, *rodata_rela, *prev_rela; int ret; prev_jump = NULL; func_for_each_insn(file, func, insn) { if (insn->type != INSN_JUMP_DYNAMIC) continue; text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len); if (!text_rela || text_rela->sym != file->rodata->sym) continue; /* common case: jmpq *[addr](,%rax,8) */ rodata_rela = find_rela_by_dest(file->rodata, text_rela->addend); /* * rare case: jmpq *[addr](%rip) * * This check is for a rare gcc quirk, currently only seen in * three driver functions in the kernel, only with certain * obscure non-distro configs. * * As part of an optimization, gcc makes a copy of an existing * switch jump table, modifies it, and then hard-codes the jump * (albeit with an indirect jump) to use a single entry in the * table. The rest of the jump table and some of its jump * targets remain as dead code. * * In such a case we can just crudely ignore all unreachable * instruction warnings for the entire object file. Ideally we * would just ignore them for the function, but that would * require redesigning the code quite a bit. And honestly * that's just not worth doing: unreachable instruction * warnings are of questionable value anyway, and this is such * a rare issue. * * kbuild reports: * - https://lkml.kernel.org/r/201603231906.LWcVUpxm%25fengguang.wu@intel.com * - https://lkml.kernel.org/r/201603271114.K9i45biy%25fengguang.wu@intel.com * - https://lkml.kernel.org/r/201603291058.zuJ6ben1%25fengguang.wu@intel.com * * gcc bug: * - https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70604 */ if (!rodata_rela) { rodata_rela = find_rela_by_dest(file->rodata, text_rela->addend + 4); if (rodata_rela) file->ignore_unreachables = true; } if (!rodata_rela) continue; /* * We found a switch table, but we don't know yet how big it * is. Don't add it until we reach the end of the function or * the beginning of another switch table in the same function. */ if (prev_jump) { ret = add_switch_table(file, func, prev_jump, prev_rela, rodata_rela); if (ret) return ret; }