smatch_constraints.c

   1 /*
   2  * Copyright (C) 2017 Oracle.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License
   6  * as published by the Free Software Foundation; either version 2
   7  * of the License, or (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
  16  */
  17
  18 /*
  19  * Basically I see constraints as a way of saying "x <= some_limit".  The
  20  * problem is that smatch_capped is not granullar enough.
  21  *
  22  * This is mostly for finding out of bounds errors.  So there are different
  23  * types of constraints.  Quite often we have "foo->xxx[i] = 42;" and we want
  24  * to verify that "i" is less than foo->size.
  25  *
  26  * My idea was that we could automatically figure out these constraints.  And we
  27  * could load them in the DB so that they are the same every time.  As in a
  28  * constraint could be "< (struct whatever)->size" and give that in ID that
  29  * would be constant until you completely wiped the DB.  So when you do a normal
  30  * DB rebuild then the first thing it will do is preserve all the constraints.
  31  * I guess the reason to do it this way is to save space...  I sometimes suspect
  32  * that worrying about saving space is premature optimization.
  33  *
  34  * The other thing that I want to do a little bit different here is how I merge
  35  * constraints.  If a constraint is true on both sides, then that's normal.  If
  36  * we merge constraint 23 and 67 then we get constraint 23|67.  If we merge 23
  37  * with &undefined then we get &undefined.  We can also have two constraints
  38  * that are both true so we could have (45&23)|12 which means either both 45 and
  39  * 23 are true or 12 is true.
  40  *
  41  */
  42
  43
  44 #include "smatch.h"
  45 #include "smatch_extra.h"
  46 #include "smatch_slist.h"
  47
  48 static int my_id;
  49
  50 ALLOCATOR(constraint, "constraints");
  51
  52 static void add_constraint(struct constraint_list **list, int op, int constraint)
  53 {
  54         struct constraint *tmp, *new;
  55
  56         FOR_EACH_PTR(*list, tmp) {
  57                 if (tmp->id < constraint)
  58                         continue;
  59                 if (tmp->id == constraint) {
  60                         if (tmp->op == SPECIAL_LTE)
  61                                 return;
  62                         if (op == '<')
  63                                 return;
  64
  65                         new = __alloc_constraint(0);
  66                         new->op = op;
  67                         new->id = constraint;
  68                         REPLACE_CURRENT_PTR(tmp, new);
  69                         return;
  70                 }
  71
  72                 new = __alloc_constraint(0);
  73                 new->op = op;
  74                 new->id = constraint;
  75                 INSERT_CURRENT(new, tmp);
  76                 return;
  77         } END_FOR_EACH_PTR(tmp);
  78
  79         new = __alloc_constraint(0);
  80         new->op = op;
  81         new->id = constraint;
  82         add_ptr_list(list, new);
  83 }
  84
  85 static struct constraint_list *merge_constraint_lists(struct constraint_list *one, struct constraint_list *two)
  86 {
  87         struct constraint_list *ret = NULL;
  88         struct constraint *tmp;
  89
  90         // FIXME: not || but &&
  91         FOR_EACH_PTR(one, tmp) {
  92                 add_constraint(&ret, tmp->op, tmp->id);
  93         } END_FOR_EACH_PTR(tmp);
  94
  95         FOR_EACH_PTR(two, tmp) {
  96                 add_constraint(&ret, tmp->op, tmp->id);
  97         } END_FOR_EACH_PTR(tmp);
  98
  99         return ret;
 100 }
 101
 102 static struct constraint_list *clone_constraint_list(struct constraint_list *list)
 103 {
 104         struct constraint_list *ret = NULL;
 105         struct constraint *tmp;
 106
 107         FOR_EACH_PTR(list, tmp) {
 108                 add_constraint(&ret, tmp->op, tmp->id);
 109         } END_FOR_EACH_PTR(tmp);
 110
 111         return ret;
 112 }
 113
 114 static struct smatch_state *alloc_constraint_state(struct constraint_list *list)
 115 {
 116         struct smatch_state *state;
 117         struct constraint *con;
 118         static char buf[256];
 119         int cnt = 0;
 120
 121         FOR_EACH_PTR(list, con) {
 122                 if (cnt != 0)
 123                         cnt += snprintf(buf + cnt, sizeof(buf) - cnt, ", ");
 124                 cnt += snprintf(buf + cnt, sizeof(buf) - cnt, "%s%d",
 125                                 show_special(con->op), con->id);
 126         } END_FOR_EACH_PTR(con);
 127
 128         state = __alloc_smatch_state(0);
 129         state->name = alloc_string(buf);
 130         state->data = list;
 131         return state;
 132 }
 133
 134 static struct smatch_state *merge_func(struct smatch_state *s1, struct smatch_state *s2)
 135 {
 136         struct constraint_list *list;
 137
 138         // FIXME:  use the dead code below instead
 139         if (strcmp(s1->name, s2->name) == 0)
 140                 return s1;
 141         return &merged;
 142
 143         list = merge_constraint_lists(s1->data, s2->data);
 144         return alloc_constraint_state(list);
 145 }
 146
 147 static int negate_gt(int op)
 148 {
 149         switch (op) {
 150         case '>':
 151         case SPECIAL_UNSIGNED_GT:
 152         case SPECIAL_GTE:
 153         case SPECIAL_UNSIGNED_GTE:
 154                 return negate_comparison(op);
 155         }
 156         return op;
 157 }
 158
 159 static char *get_toplevel_name(struct expression *expr)
 160 {
 161         struct symbol *sym;
 162         char buf[256];
 163
 164         expr = strip_expr(expr);
 165         if (expr->type != EXPR_SYMBOL || !expr->symbol || !expr->symbol->ident)
 166                 return NULL;
 167
 168         sym = expr->symbol;
 169         if (!(sym->ctype.modifiers & MOD_TOPLEVEL))
 170                 return NULL;
 171
 172         if (sym->ctype.modifiers & MOD_STATIC)
 173                 snprintf(buf, sizeof(buf), "%s %s", get_base_file(), sym->ident->name);
 174         else
 175                 snprintf(buf, sizeof(buf), "extern %s", sym->ident->name);
 176
 177         return alloc_string(buf);
 178 }
 179
 180 char *get_constraint_str(struct expression *expr)
 181 {
 182         char *name;
 183
 184         name = get_toplevel_name(expr);
 185         if (name)
 186                 return name;
 187         return get_member_name(expr);
 188 }
 189
 190 static int save_int_callback(void *_p, int argc, char **argv, char **azColName)
 191 {
 192         int *p = _p;
 193
 194         *p = atoi(argv[0]);
 195         return 0;
 196 }
 197
 198 static int constraint_str_to_id(const char *str)
 199 {
 200         int id = -1;
 201
 202         run_sql(save_int_callback, &id,
 203                 "select id from constraints where str = '%s'", str);
 204
 205         return id;
 206 }
 207
 208 static int save_constraint_str(void *_str, int argc, char **argv, char **azColName)
 209 {
 210         char **str = _str;
 211
 212         *str = alloc_string(argv[0]);
 213         return 0;
 214 }
 215
 216 static char *constraint_id_to_str(int id)
 217 {
 218         char *str = NULL;
 219
 220         run_sql(save_constraint_str, &str,
 221                 "select str from constraints where id = '%d'", id);
 222
 223         return str;
 224 }
 225
 226 static int save_op_callback(void *_p, int argc, char **argv, char **azColName)
 227 {
 228         int *p = _p;
 229
 230         if (argv[0][0] == '<' && argv[0][1] == '=')
 231                 *p = SPECIAL_LTE;
 232         else
 233                 *p = '<';
 234         return 0;
 235 }
 236
 237 static int save_str_callback(void *_p, int argc, char **argv, char **azColName)
 238 {
 239         char *p = _p;
 240
 241         if (!p) {
 242                 p = alloc_string(argv[0]);
 243         } else {
 244                 char buf[256];
 245
 246                 snprintf(buf, sizeof(buf), "%s, %s", p, argv[0]);
 247                 p = alloc_string(buf);
 248         }
 249         return 0;
 250 }
 251
 252 char *get_required_constraint(const char *data_str)
 253 {
 254         char *required = NULL;
 255
 256         run_sql(save_str_callback, &required,
 257                 "select bound from constraints_required where data = '%s'", data_str);
 258
 259         return required;
 260 }
 261
 262 static int get_required_op(char *data_str, char *con_str)
 263 {
 264         int op = 0;
 265
 266         run_sql(save_op_callback, &op,
 267                 "select op from constraints_required where data = '%s' and bound = '%s'", data_str, con_str);
 268
 269         return op;
 270 }
 271
 272 char *unmet_constraint(struct expression *data, struct expression *offset)
 273 {
 274         struct smatch_state *state;
 275         struct constraint_list *list;
 276         struct constraint *con;
 277         char *data_str;
 278         char *required;
 279         int req_op;
 280         int found = 0;
 281
 282         state = get_state_expr(my_id, offset);
 283         if (!state)
 284                 return NULL;
 285         list = state->data;
 286
 287         data_str = get_constraint_str(data);
 288         if (!data_str)
 289                 return NULL;
 290
 291         required = get_required_constraint(data_str);
 292         if (!required)
 293                 return NULL;
 294
 295         FOR_EACH_PTR(list, con) {
 296                 char *con_str;
 297
 298                 con_str = constraint_id_to_str(con->id);
 299                 if (!con_str) {
 300                         sm_msg("constraint %d not found", con->id);
 301                         continue;
 302                 }
 303
 304                 req_op = get_required_op(data_str, con_str);
 305                 free_string(con_str);
 306                 if (!req_op)
 307                         continue;
 308                 if (con->op == '<' || con->op == req_op) {
 309                         found = 1;
 310                         goto free_data;
 311                 }
 312         } END_FOR_EACH_PTR(con);
 313
 314 free_data:
 315         if (found) {
 316                 free_string(required);
 317                 required = NULL;
 318         }
 319         free_string(data_str);
 320         return required;
 321 }
 322
 323 struct string_list *saved_constraints;
 324 static void save_new_constraint(const char *con)
 325 {
 326         if (local_debug)
 327                 sm_msg("saving '%s'", con);
 328         if (list_has_string(saved_constraints, con))
 329                 return;
 330         insert_string(&saved_constraints, con);
 331         sql_save_constraint(con);
 332 }
 333
 334 static void match_condition(struct expression *expr)
 335 {
 336         struct expression *left, *right;
 337         struct constraint_list *constraints;
 338         struct smatch_state *state;
 339         char *constraint;
 340         int constraint_id;
 341         int op;
 342
 343         if (expr->type != EXPR_COMPARE)
 344                 return;
 345
 346         if (expr->op == SPECIAL_EQUAL ||
 347             expr->op == SPECIAL_NOTEQUAL)
 348                 return;
 349
 350         left = expr->left;
 351         right = expr->right;
 352
 353         constraint = get_constraint_str(right);
 354         if (!constraint)
 355                 return;
 356         constraint_id = constraint_str_to_id(constraint);
 357         if (constraint_id < 0)
 358                 save_new_constraint(constraint);
 359         free_string(constraint);
 360         if (constraint_id < 0)
 361                 return;
 362
 363         constraints = get_constraints(left);
 364         constraints = clone_constraint_list(constraints);
 365         op = negate_gt(expr->op);
 366         add_constraint(&constraints, op, constraint_id);
 367         state = alloc_constraint_state(constraints);
 368
 369         if (op == expr->op)
 370                 set_true_false_states_expr(my_id, left, state, NULL);
 371         else
 372                 set_true_false_states_expr(my_id, left, NULL, state);
 373 }
 374
 375 struct constraint_list *get_constraints(struct expression *expr)
 376 {
 377         struct smatch_state *state;
 378
 379         state = get_state_expr(my_id, expr);
 380         if (!state)
 381                 return NULL;
 382         return state->data;
 383 }
 384
 385 static void match_caller_info(struct expression *expr)
 386 {
 387         struct expression *tmp;
 388         struct smatch_state *state;
 389         int i;
 390
 391         i = -1;
 392         FOR_EACH_PTR(expr->args, tmp) {
 393                 i++;
 394                 state = get_state_expr(my_id, tmp);
 395                 if (!state || state == &merged || state == &undefined)
 396                         continue;
 397                 sql_insert_caller_info(expr, CONSTRAINT, i, "$", state->name);
 398         } END_FOR_EACH_PTR(tmp);
 399 }
 400
 401 static void struct_member_callback(struct expression *call, int param, char *printed_name, struct sm_state *sm)
 402 {
 403         if (sm->state == &merged || sm->state == &undefined)
 404                 return;
 405         sql_insert_caller_info(call, CONSTRAINT, param, printed_name, sm->state->name);
 406 }
 407
 408 static void print_return_implies_constrained(int return_id, char *return_ranges, struct expression *expr)
 409 {
 410         struct smatch_state *orig;
 411         struct sm_state *sm;
 412         const char *param_name;
 413         int param;
 414
 415         FOR_EACH_MY_SM(my_id, __get_cur_stree(), sm) {
 416                 if (sm->state == &merged || sm->state == &undefined)
 417                         continue;
 418
 419                 param = get_param_num_from_sym(sm->sym);
 420                 if (param < 0)
 421                         continue;
 422
 423                 orig = get_state_stree(get_start_states(), my_id, sm->name, sm->sym);
 424                 if (orig && strcmp(sm->state->name, orig->name) == 0)
 425                         continue;
 426
 427                 param_name = get_param_name(sm);
 428                 if (!param_name)
 429                         continue;
 430
 431                 sql_insert_return_states(return_id, return_ranges, CONSTRAINT,
 432                                          param, param_name, sm->state->name);
 433         } END_FOR_EACH_SM(sm);
 434 }
 435
 436 static struct smatch_state *constraint_str_to_state(char *value)
 437 {
 438         struct constraint_list *list = NULL;
 439         char *p = value;
 440         int op;
 441         long long id;
 442
 443         while (true) {
 444                 op = '<';
 445                 if (*p != '<')
 446                         return &undefined;
 447                 p++;
 448                 if (*p == '=') {
 449                         op = SPECIAL_LTE;
 450                         p++;
 451                 }
 452                 id = strtoll(p, &p, 10);
 453                 add_constraint(&list, op, id);
 454                 if (*p != ',')
 455                         break;
 456                 p++;
 457                 if (*p != ' ')
 458                         return &undefined;
 459         }
 460
 461         return alloc_constraint_state(list);
 462 }
 463
 464 static void db_returns_constrained(struct expression *expr, int param, char *key, char *value)
 465 {
 466         char *name;
 467         struct symbol *sym;
 468
 469         name = return_state_to_var_sym(expr, param, key, &sym);
 470         if (!name || !sym)
 471                 goto free;
 472
 473         set_state(my_id, name, sym, constraint_str_to_state(value));
 474 free:
 475         free_string(name);
 476 }
 477
 478 void register_constraints(int id)
 479 {
 480         my_id = id;
 481
 482         add_merge_hook(my_id, &merge_func);
 483         add_hook(&match_condition, CONDITION_HOOK);
 484
 485         add_hook(&match_caller_info, FUNCTION_CALL_HOOK);
 486         add_member_info_callback(my_id, struct_member_callback);
 487
 488         add_split_return_callback(print_return_implies_constrained);
 489         select_return_states_hook(CONSTRAINT, &db_returns_constrained);
 490 }