objtool-y += arch/$(SRCARCH)/
objtool-y += builtin-check.o
+objtool-y += check.o
objtool-y += elf.o
objtool-y += special.o
objtool-y += objtool.o
/*
- * Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com>
+ * 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
* 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>
-#include <linux/kernel.h>
-
-#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, dead_end;
- 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",
- "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;
-}
-
-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;
-}
-
-/*
- * Find all uses of the unreachable() macro, which are code path dead ends.
- */
-static int add_dead_ends(struct objtool_file *file)
-{
- struct section *sec;
- struct rela *rela;
- struct instruction *insn;
- bool found;
-
- sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
- 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 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;
- }
-
- 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;
- }
+#include "check.h"
- 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;
- }
- }
+bool nofp;
- 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;
-
- /* 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;
-}
-
-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;
-
- 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;
-
- 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;
-
- default:
- break;
- }
-
- if (insn->dead_end)
- return 0;
-
- 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[] = {
+static const char * const check_usage[] = {
"objtool check [<options>] file.o",
NULL,
};
+const struct option check_options[] = {
+ OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"),
+ OPT_END(),
+};
+
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(),
- };
+ const char *objname;
- argc = parse_options(argc, argv, options, check_usage, 0);
+ argc = parse_options(argc, argv, check_options, check_usage, 0);
if (argc != 1)
- usage_with_options(check_usage, options);
+ usage_with_options(check_usage, check_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, ".discard.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;
+ return check(objname, nofp);
}
--- /dev/null
+/*
+ * 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>
+
+#define STATE_FP_SAVED 0x1
+#define STATE_FP_SETUP 0x2
+#define STATE_FENTRY 0x4
+
+struct alternative {
+ struct list_head list;
+ struct instruction *insn;
+};
+
+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",
+ "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;
+}
+
+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;
+}
+
+/*
+ * Find all uses of the unreachable() macro, which are code path dead ends.
+ */
+static int add_dead_ends(struct objtool_file *file)
+{
+ struct section *sec;
+ struct rela *rela;
+ struct instruction *insn;
+ bool found;
+
+ sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
+ 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 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;
+ }
+
+ 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;
+
+ /* 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;
+}
+
+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;
+
+ 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;
+
+ 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;
+
+ default:
+ break;
+ }
+
+ if (insn->dead_end)
+ return 0;
+
+ 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);
+}
+
+int check(const char *_objname, bool _nofp)
+{
+ struct objtool_file file;
+ int ret, warnings = 0;
+
+ objname = _objname;
+ nofp = _nofp;
+
+ 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, ".discard.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;
+}
--- /dev/null
+/*
+ * Copyright (C) 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/>.
+ */
+
+#ifndef _CHECK_H
+#define _CHECK_H
+
+#include <stdbool.h>
+#include "elf.h"
+#include "arch.h"
+#include <linux/hashtable.h>
+
+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, dead_end;
+ struct symbol *call_dest;
+ struct instruction *jump_dest;
+ struct list_head alts;
+ struct symbol *func;
+};
+
+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;
+};
+
+int check(const char *objname, bool nofp);
+
+#endif /* _CHECK_H */
projects / kernel.git / commitdiff