1312 lines
31 KiB
C
1312 lines
31 KiB
C
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/*
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* Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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/*
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* objtool check:
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*
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* This command analyzes every .o file and ensures the validity of its stack
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* trace metadata. It enforces a set of rules on asm code and C inline
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* assembly code so that stack traces can be reliable.
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*
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* For more information, see tools/objtool/Documentation/stack-validation.txt.
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*/
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#include <string.h>
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#include <stdlib.h>
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#include <subcmd/parse-options.h>
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#include "builtin.h"
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#include "elf.h"
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#include "special.h"
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#include "arch.h"
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#include "warn.h"
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#include <linux/hashtable.h>
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#include <linux/kernel.h>
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#define STATE_FP_SAVED 0x1
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#define STATE_FP_SETUP 0x2
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#define STATE_FENTRY 0x4
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struct instruction {
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struct list_head list;
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struct hlist_node hash;
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struct section *sec;
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unsigned long offset;
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unsigned int len, state;
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unsigned char type;
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unsigned long immediate;
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bool alt_group, visited, dead_end;
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struct symbol *call_dest;
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struct instruction *jump_dest;
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struct list_head alts;
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struct symbol *func;
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};
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struct alternative {
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struct list_head list;
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struct instruction *insn;
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};
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struct objtool_file {
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struct elf *elf;
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struct list_head insn_list;
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DECLARE_HASHTABLE(insn_hash, 16);
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struct section *rodata, *whitelist;
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bool ignore_unreachables, c_file;
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};
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const char *objname;
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static bool nofp;
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static struct instruction *find_insn(struct objtool_file *file,
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struct section *sec, unsigned long offset)
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{
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struct instruction *insn;
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hash_for_each_possible(file->insn_hash, insn, hash, offset)
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if (insn->sec == sec && insn->offset == offset)
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return insn;
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return NULL;
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}
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static struct instruction *next_insn_same_sec(struct objtool_file *file,
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struct instruction *insn)
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{
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struct instruction *next = list_next_entry(insn, list);
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if (&next->list == &file->insn_list || next->sec != insn->sec)
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return NULL;
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return next;
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}
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static bool gcov_enabled(struct objtool_file *file)
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{
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struct section *sec;
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struct symbol *sym;
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list_for_each_entry(sec, &file->elf->sections, list)
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list_for_each_entry(sym, &sec->symbol_list, list)
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if (!strncmp(sym->name, "__gcov_.", 8))
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return true;
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return false;
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}
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#define for_each_insn(file, insn) \
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list_for_each_entry(insn, &file->insn_list, list)
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#define func_for_each_insn(file, func, insn) \
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for (insn = find_insn(file, func->sec, func->offset); \
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insn && &insn->list != &file->insn_list && \
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insn->sec == func->sec && \
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insn->offset < func->offset + func->len; \
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insn = list_next_entry(insn, list))
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#define func_for_each_insn_continue_reverse(file, func, insn) \
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for (insn = list_prev_entry(insn, list); \
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&insn->list != &file->insn_list && \
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insn->sec == func->sec && insn->offset >= func->offset; \
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insn = list_prev_entry(insn, list))
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#define sec_for_each_insn_from(file, insn) \
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for (; insn; insn = next_insn_same_sec(file, insn))
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/*
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* Check if the function has been manually whitelisted with the
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* STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted
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* due to its use of a context switching instruction.
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*/
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static bool ignore_func(struct objtool_file *file, struct symbol *func)
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{
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struct rela *rela;
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struct instruction *insn;
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/* check for STACK_FRAME_NON_STANDARD */
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if (file->whitelist && file->whitelist->rela)
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list_for_each_entry(rela, &file->whitelist->rela->rela_list, list) {
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if (rela->sym->type == STT_SECTION &&
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rela->sym->sec == func->sec &&
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rela->addend == func->offset)
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return true;
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if (rela->sym->type == STT_FUNC && rela->sym == func)
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return true;
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}
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/* check if it has a context switching instruction */
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func_for_each_insn(file, func, insn)
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if (insn->type == INSN_CONTEXT_SWITCH)
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return true;
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return false;
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}
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/*
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* This checks to see if the given function is a "noreturn" function.
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*
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* For global functions which are outside the scope of this object file, we
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* have to keep a manual list of them.
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*
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* For local functions, we have to detect them manually by simply looking for
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* the lack of a return instruction.
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*
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* Returns:
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* -1: error
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* 0: no dead end
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* 1: dead end
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*/
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static int __dead_end_function(struct objtool_file *file, struct symbol *func,
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int recursion)
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{
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int i;
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struct instruction *insn;
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bool empty = true;
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/*
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* Unfortunately these have to be hard coded because the noreturn
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* attribute isn't provided in ELF data.
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*/
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static const char * const global_noreturns[] = {
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"__stack_chk_fail",
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"panic",
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"do_exit",
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"do_task_dead",
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"__module_put_and_exit",
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"complete_and_exit",
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"kvm_spurious_fault",
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"__reiserfs_panic",
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"lbug_with_loc",
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"fortify_panic",
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};
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if (func->bind == STB_WEAK)
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return 0;
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if (func->bind == STB_GLOBAL)
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for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
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if (!strcmp(func->name, global_noreturns[i]))
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return 1;
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if (!func->sec)
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return 0;
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func_for_each_insn(file, func, insn) {
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empty = false;
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if (insn->type == INSN_RETURN)
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return 0;
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}
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if (empty)
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return 0;
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/*
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* A function can have a sibling call instead of a return. In that
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* case, the function's dead-end status depends on whether the target
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* of the sibling call returns.
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*/
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func_for_each_insn(file, func, insn) {
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if (insn->sec != func->sec ||
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insn->offset >= func->offset + func->len)
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break;
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if (insn->type == INSN_JUMP_UNCONDITIONAL) {
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struct instruction *dest = insn->jump_dest;
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struct symbol *dest_func;
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if (!dest)
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/* sibling call to another file */
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return 0;
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if (dest->sec != func->sec ||
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dest->offset < func->offset ||
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dest->offset >= func->offset + func->len) {
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/* local sibling call */
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dest_func = find_symbol_by_offset(dest->sec,
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dest->offset);
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if (!dest_func)
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continue;
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if (recursion == 5) {
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WARN_FUNC("infinite recursion (objtool bug!)",
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dest->sec, dest->offset);
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return -1;
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}
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return __dead_end_function(file, dest_func,
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recursion + 1);
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}
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}
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if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
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/* sibling call */
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return 0;
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}
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return 1;
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}
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static int dead_end_function(struct objtool_file *file, struct symbol *func)
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{
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return __dead_end_function(file, func, 0);
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}
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/*
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* Call the arch-specific instruction decoder for all the instructions and add
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* them to the global instruction list.
|
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*/
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static int decode_instructions(struct objtool_file *file)
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{
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struct section *sec;
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struct symbol *func;
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unsigned long offset;
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||
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struct instruction *insn;
|
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int ret;
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list_for_each_entry(sec, &file->elf->sections, list) {
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if (!(sec->sh.sh_flags & SHF_EXECINSTR))
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continue;
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||
|
|
||
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for (offset = 0; offset < sec->len; offset += insn->len) {
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insn = malloc(sizeof(*insn));
|
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memset(insn, 0, sizeof(*insn));
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||
|
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||
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INIT_LIST_HEAD(&insn->alts);
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insn->sec = sec;
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insn->offset = offset;
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||
|
|
||
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ret = arch_decode_instruction(file->elf, sec, offset,
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sec->len - offset,
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&insn->len, &insn->type,
|
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&insn->immediate);
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if (ret)
|
||
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return ret;
|
||
|
|
||
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if (!insn->type || insn->type > INSN_LAST) {
|
||
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WARN_FUNC("invalid instruction type %d",
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insn->sec, insn->offset, insn->type);
|
||
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return -1;
|
||
|
}
|
||
|
|
||
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hash_add(file->insn_hash, &insn->hash, insn->offset);
|
||
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list_add_tail(&insn->list, &file->insn_list);
|
||
|
}
|
||
|
|
||
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list_for_each_entry(func, &sec->symbol_list, list) {
|
||
|
if (func->type != STT_FUNC)
|
||
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continue;
|
||
|
|
||
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if (!find_insn(file, sec, func->offset)) {
|
||
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WARN("%s(): can't find starting instruction",
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||
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func->name);
|
||
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return -1;
|
||
|
}
|
||
|
|
||
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func_for_each_insn(file, func, insn)
|
||
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if (!insn->func)
|
||
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insn->func = func;
|
||
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}
|
||
|
}
|
||
|
|
||
|
return 0;
|
||
|
}
|
||
|
|
||
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/*
|
||
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* Find all uses of the unreachable() macro, which are code path dead ends.
|
||
|
*/
|
||
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static int add_dead_ends(struct objtool_file *file)
|
||
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{
|
||
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struct section *sec;
|
||
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struct rela *rela;
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||
|
struct instruction *insn;
|
||
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bool found;
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||
|
|
||
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sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
|
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|
if (!sec)
|
||
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return 0;
|
||
|
|
||
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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);
|
||
|
}
|
||
|
|
||
|
const char * const check_usage[] = {
|
||
|
"objtool check [<options>] file.o",
|
||
|
NULL,
|
||
|
};
|
||
|
|
||
|
int cmd_check(int argc, const char **argv)
|
||
|
{
|
||
|
struct objtool_file file;
|
||
|
int ret, warnings = 0;
|
||
|
|
||
|
const struct option options[] = {
|
||
|
OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"),
|
||
|
OPT_END(),
|
||
|
};
|
||
|
|
||
|
argc = parse_options(argc, argv, options, check_usage, 0);
|
||
|
|
||
|
if (argc != 1)
|
||
|
usage_with_options(check_usage, options);
|
||
|
|
||
|
objname = argv[0];
|
||
|
|
||
|
file.elf = elf_open(objname);
|
||
|
if (!file.elf) {
|
||
|
fprintf(stderr, "error reading elf file %s\n", objname);
|
||
|
return 1;
|
||
|
}
|
||
|
|
||
|
INIT_LIST_HEAD(&file.insn_list);
|
||
|
hash_init(file.insn_hash);
|
||
|
file.whitelist = find_section_by_name(file.elf, ".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;
|
||
|
}
|