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 == '<')
  61                                 return;
  62                         if (op == SPECIAL_LTE)
  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_func_constraint(struct expression *expr)
 160 {
 161         char buf[256];
 162         char *name;
 163
 164         if (is_fake_call(expr))
 165                 return NULL;
 166         name = expr_to_str(expr->fn);
 167         if (!name)
 168                 return NULL;
 169         snprintf(buf, sizeof(buf), "%s()", name);
 170         free_string(name);
 171         return alloc_string(buf);
 172 }
 173
 174 static char *get_toplevel_name(struct expression *expr)
 175 {
 176         struct symbol *sym;
 177         char buf[256];
 178
 179         expr = strip_expr(expr);
 180         if (expr->type != EXPR_SYMBOL || !expr->symbol || !expr->symbol->ident)
 181                 return NULL;
 182
 183         sym = expr->symbol;
 184         if (!(sym->ctype.modifiers & MOD_TOPLEVEL))
 185                 return NULL;
 186
 187         if (sym->ctype.modifiers & MOD_STATIC)
 188                 snprintf(buf, sizeof(buf), "%s %s", get_base_file(), sym->ident->name);
 189         else
 190                 snprintf(buf, sizeof(buf), "extern %s", sym->ident->name);
 191
 192         return alloc_string(buf);
 193 }
 194
 195 char *get_constraint_str(struct expression *expr)
 196 {
 197         char *name;
 198
 199         expr = strip_expr(expr);
 200         if (!expr)
 201                 return NULL;
 202         if (expr->type == EXPR_CALL)
 203                 return get_func_constraint(expr);
 204         if (expr->type == EXPR_BINOP)
 205                 return expr_to_str(expr);
 206         name = get_toplevel_name(expr);
 207         if (name)
 208                 return name;
 209         return get_member_name(expr);
 210 }
 211
 212 static int save_int_callback(void *_p, int argc, char **argv, char **azColName)
 213 {
 214         int *p = _p;
 215
 216         *p = atoi(argv[0]);
 217         return 0;
 218 }
 219
 220 static int constraint_str_to_id(const char *str)
 221 {
 222         int id = -1;
 223
 224         run_sql(save_int_callback, &id,
 225                 "select id from constraints where str = '%q'", str);
 226
 227         return id;
 228 }
 229
 230 static int save_constraint_str(void *_str, int argc, char **argv, char **azColName)
 231 {
 232         char **str = _str;
 233
 234         *str = alloc_string(argv[0]);
 235         return 0;
 236 }
 237
 238 static char *constraint_id_to_str(int id)
 239 {
 240         char *str = NULL;
 241
 242         run_sql(save_constraint_str, &str,
 243                 "select str from constraints where id = '%d'", id);
 244
 245         return str;
 246 }
 247
 248 static int save_op_callback(void *_p, int argc, char **argv, char **azColName)
 249 {
 250         int *p = _p;
 251
 252         if (argv[0][0] == '<' && argv[0][1] == '=')
 253                 *p = SPECIAL_LTE;
 254         else
 255                 *p = '<';
 256         return 0;
 257 }
 258
 259 static int save_str_callback(void *_p, int argc, char **argv, char **azColName)
 260 {
 261         char **p = _p;
 262
 263         if (!*p) {
 264                 *p = alloc_string(argv[0]);
 265         } else {
 266                 char buf[256];
 267
 268                 snprintf(buf, sizeof(buf), "%s, %s", *p, argv[0]);
 269                 *p = alloc_string(buf);
 270         }
 271         return 0;
 272 }
 273
 274 char *get_required_constraint(const char *data_str)
 275 {
 276         char *required = NULL;
 277
 278         run_sql(save_str_callback, &required,
 279                 "select bound from constraints_required where data = '%q'", data_str);
 280
 281         return required;
 282 }
 283
 284 static int get_required_op(char *data_str, char *con_str)
 285 {
 286         int op = 0;
 287
 288         run_sql(save_op_callback, &op,
 289                 "select op from constraints_required where data = '%q' and bound = '%q'", data_str, con_str);
 290
 291         return op;
 292 }
 293
 294 char *unmet_constraint(struct expression *data, struct expression *offset)
 295 {
 296         struct smatch_state *state;
 297         struct constraint_list *list;
 298         struct constraint *con;
 299         char *data_str;
 300         char *required;
 301         int req_op;
 302
 303         data_str = get_constraint_str(data);
 304         if (!data_str)
 305                 return NULL;
 306
 307         required = get_required_constraint(data_str);
 308         if (!required)
 309                 goto free_data;
 310
 311         state = get_state_expr(my_id, offset);
 312         if (!state)
 313                 goto free_data;
 314         list = state->data;
 315
 316         /* check the list of bounds on our index against the list that work */
 317         FOR_EACH_PTR(list, con) {
 318                 char *con_str;
 319
 320                 con_str = constraint_id_to_str(con->id);
 321                 if (!con_str) {
 322                         sm_msg("constraint %d not found", con->id);
 323                         continue;
 324                 }
 325
 326                 req_op = get_required_op(data_str, con_str);
 327                 free_string(con_str);
 328                 if (!req_op)
 329                         continue;
 330                 if (con->op == '<' || con->op == req_op) {
 331                         free_string(required);
 332                         required = NULL;
 333                         goto free_data;
 334                 }
 335         } END_FOR_EACH_PTR(con);
 336
 337 free_data:
 338         free_string(data_str);
 339         return required;
 340 }
 341
 342 struct string_list *saved_constraints;
 343 static void save_new_constraint(const char *con)
 344 {
 345         if (!insert_string(&saved_constraints, con))
 346                 return;
 347         sql_save_constraint(con);
 348 }
 349
 350 static void handle_comparison(struct expression *left, int op, struct expression *right)
 351 {
 352         struct constraint_list *constraints;
 353         struct smatch_state *state;
 354         char *constraint;
 355         int constraint_id;
 356         int orig_op = op;
 357         sval_t sval;
 358
 359         /* known values are handled in smatch extra */
 360         if (get_value(left, &sval) || get_value(right, &sval))
 361                 return;
 362
 363         constraint = get_constraint_str(right);
 364         if (!constraint)
 365                 return;
 366         constraint_id = constraint_str_to_id(constraint);
 367         if (constraint_id < 0)
 368                 save_new_constraint(constraint);
 369         free_string(constraint);
 370         if (constraint_id < 0)
 371                 return;
 372
 373         constraints = get_constraints(left);
 374         constraints = clone_constraint_list(constraints);
 375         op = negate_gt(orig_op);
 376         add_constraint(&constraints, remove_unsigned_from_comparison(op), constraint_id);
 377         state = alloc_constraint_state(constraints);
 378
 379         if (op == orig_op)
 380                 set_true_false_states_expr(my_id, left, state, NULL);
 381         else
 382                 set_true_false_states_expr(my_id, left, NULL, state);
 383 }
 384
 385 static void match_condition(struct expression *expr)
 386 {
 387         if (expr->type != EXPR_COMPARE)
 388                 return;
 389
 390         if (expr->op == SPECIAL_EQUAL ||
 391             expr->op == SPECIAL_NOTEQUAL)
 392                 return;
 393
 394         handle_comparison(expr->left, expr->op, expr->right);
 395         handle_comparison(expr->right, flip_comparison(expr->op), expr->left);
 396 }
 397
 398 struct constraint_list *get_constraints(struct expression *expr)
 399 {
 400         struct smatch_state *state;
 401
 402         state = get_state_expr(my_id, expr);
 403         if (!state)
 404                 return NULL;
 405         return state->data;
 406 }
 407
 408 static void match_caller_info(struct expression *expr)
 409 {
 410         struct expression *tmp;
 411         struct smatch_state *state;
 412         int i;
 413
 414         i = -1;
 415         FOR_EACH_PTR(expr->args, tmp) {
 416                 i++;
 417                 state = get_state_expr(my_id, tmp);
 418                 if (!state || state == &merged || state == &undefined)
 419                         continue;
 420                 sql_insert_caller_info(expr, CONSTRAINT, i, "$", state->name);
 421         } END_FOR_EACH_PTR(tmp);
 422 }
 423
 424 static void struct_member_callback(struct expression *call, int param, char *printed_name, struct sm_state *sm)
 425 {
 426         if (sm->state == &merged || sm->state == &undefined)
 427                 return;
 428         sql_insert_caller_info(call, CONSTRAINT, param, printed_name, sm->state->name);
 429 }
 430
 431 static struct smatch_state *constraint_str_to_state(char *value)
 432 {
 433         struct constraint_list *list = NULL;
 434         char *p = value;
 435         int op;
 436         long long id;
 437
 438         while (true) {
 439                 op = '<';
 440                 if (*p != '<')
 441                         return &undefined;
 442                 p++;
 443                 if (*p == '=') {
 444                         op = SPECIAL_LTE;
 445                         p++;
 446                 }
 447                 id = strtoll(p, &p, 10);
 448                 add_constraint(&list, op, id);
 449                 if (*p != ',')
 450                         break;
 451                 p++;
 452                 if (*p != ' ')
 453                         return &undefined;
 454         }
 455
 456         return alloc_constraint_state(list);
 457 }
 458
 459 static void set_param_constrained(const char *name, struct symbol *sym, char *key, char *value)
 460 {
 461         char fullname[256];
 462
 463         if (strcmp(key, "*$") == 0)
 464                 snprintf(fullname, sizeof(fullname), "*%s", name);
 465         else if (strncmp(key, "$", 1) == 0)
 466                 snprintf(fullname, 256, "%s%s", name, key + 1);
 467         else
 468                 return;
 469
 470         set_state(my_id, name, sym, constraint_str_to_state(value));
 471 }
 472
 473 static void print_return_implies_constrained(int return_id, char *return_ranges, struct expression *expr)
 474 {
 475         struct smatch_state *orig;
 476         struct sm_state *sm;
 477         const char *param_name;
 478         int param;
 479
 480         FOR_EACH_MY_SM(my_id, __get_cur_stree(), sm) {
 481                 if (sm->state == &merged || sm->state == &undefined)
 482                         continue;
 483
 484                 param = get_param_num_from_sym(sm->sym);
 485                 if (param < 0)
 486                         continue;
 487
 488                 orig = get_state_stree(get_start_states(), my_id, sm->name, sm->sym);
 489                 if (orig && strcmp(sm->state->name, orig->name) == 0)
 490                         continue;
 491
 492                 param_name = get_param_name(sm);
 493                 if (!param_name)
 494                         continue;
 495
 496                 sql_insert_return_states(return_id, return_ranges, CONSTRAINT,
 497                                          param, param_name, sm->state->name);
 498         } END_FOR_EACH_SM(sm);
 499 }
 500
 501 static void db_returns_constrained(struct expression *expr, int param, char *key, char *value)
 502 {
 503         char *name;
 504         struct symbol *sym;
 505
 506         name = return_state_to_var_sym(expr, param, key, &sym);
 507         if (!name || !sym)
 508                 goto free;
 509
 510         set_state(my_id, name, sym, constraint_str_to_state(value));
 511 free:
 512         free_string(name);
 513 }
 514
 515 void register_constraints(int id)
 516 {
 517         my_id = id;
 518
 519         set_dynamic_states(my_id);
 520         add_merge_hook(my_id, &merge_func);
 521         add_hook(&match_condition, CONDITION_HOOK);
 522
 523         add_hook(&match_caller_info, FUNCTION_CALL_HOOK);
 524         add_member_info_callback(my_id, struct_member_callback);
 525         select_caller_info_hook(&set_param_constrained, CONSTRAINT);
 526
 527         add_split_return_callback(print_return_implies_constrained);
 528         select_return_states_hook(CONSTRAINT, &db_returns_constrained);
 529 }