scripts/gcc-plugins/latent_entropy_plugin.c

   1 /*
   2  * Copyright 2012-2016 by the PaX Team <pageexec@freemail.hu>
   3  * Copyright 2016 by Emese Revfy <re.emese@gmail.com>
   4  * Licensed under the GPL v2
   5  *
   6  * Note: the choice of the license means that the compilation process is
   7  *       NOT 'eligible' as defined by gcc's library exception to the GPL v3,
   8  *       but for the kernel it doesn't matter since it doesn't link against
   9  *       any of the gcc libraries
  10  *
  11  * This gcc plugin helps generate a little bit of entropy from program state,
  12  * used throughout the uptime of the kernel. Here is an instrumentation example:
  13  *
  14  * before:
  15  * void __latent_entropy test(int argc, char *argv[])
  16  * {
  17  *      if (argc <= 1)
  18  *              printf("%s: no command arguments :(\n", *argv);
  19  *      else
  20  *              printf("%s: %d command arguments!\n", *argv, args - 1);
  21  * }
  22  *
  23  * after:
  24  * void __latent_entropy test(int argc, char *argv[])
  25  * {
  26  *      // latent_entropy_execute() 1.
  27  *      unsigned long local_entropy;
  28  *      // init_local_entropy() 1.
  29  *      void *local_entropy_frameaddr;
  30  *      // init_local_entropy() 3.
  31  *      unsigned long tmp_latent_entropy;
  32  *
  33  *      // init_local_entropy() 2.
  34  *      local_entropy_frameaddr = __builtin_frame_address(0);
  35  *      local_entropy = (unsigned long) local_entropy_frameaddr;
  36  *
  37  *      // init_local_entropy() 4.
  38  *      tmp_latent_entropy = latent_entropy;
  39  *      // init_local_entropy() 5.
  40  *      local_entropy ^= tmp_latent_entropy;
  41  *
  42  *      // latent_entropy_execute() 3.
  43  *      if (argc <= 1) {
  44  *              // perturb_local_entropy()
  45  *              local_entropy += 4623067384293424948;
  46  *              printf("%s: no command arguments :(\n", *argv);
  47  *              // perturb_local_entropy()
  48  *      } else {
  49  *              local_entropy ^= 3896280633962944730;
  50  *              printf("%s: %d command arguments!\n", *argv, args - 1);
  51  *      }
  52  *
  53  *      // latent_entropy_execute() 4.
  54  *      tmp_latent_entropy = rol(tmp_latent_entropy, local_entropy);
  55  *      latent_entropy = tmp_latent_entropy;
  56  * }
  57  *
  58  * TODO:
  59  * - add ipa pass to identify not explicitly marked candidate functions
  60  * - mix in more program state (function arguments/return values,
  61  *   loop variables, etc)
  62  * - more instrumentation control via attribute parameters
  63  *
  64  * BUGS:
  65  * - none known
  66  *
  67  * Options:
  68  * -fplugin-arg-latent_entropy_plugin-disable
  69  *
  70  * Attribute: __attribute__((latent_entropy))
  71  *  The latent_entropy gcc attribute can be only on functions and variables.
  72  *  If it is on a function then the plugin will instrument it. If the attribute
  73  *  is on a variable then the plugin will initialize it with a random value.
  74  *  The variable must be an integer, an integer array type or a structure
  75  *  with integer fields.
  76  */
  77
  78 #include "gcc-common.h"
  79
  80 __visible int plugin_is_GPL_compatible;
  81
  82 static GTY(()) tree latent_entropy_decl;
  83
  84 static struct plugin_info latent_entropy_plugin_info = {
  85         .version        = "201606141920vanilla",
  86         .help           = "disable\tturn off latent entropy instrumentation\n",
  87 };
  88
  89 static unsigned HOST_WIDE_INT seed;
  90 /*
  91  * get_random_seed() (this is a GCC function) generates the seed.
  92  * This is a simple random generator without any cryptographic security because
  93  * the entropy doesn't come from here.
  94  */
  95 static unsigned HOST_WIDE_INT get_random_const(void)
  96 {
  97         unsigned int i;
  98         unsigned HOST_WIDE_INT ret = 0;
  99
 100         for (i = 0; i < 8 * sizeof(ret); i++) {
 101                 ret = (ret << 1) | (seed & 1);
 102                 seed >>= 1;
 103                 if (ret & 1)
 104                         seed ^= 0xD800000000000000ULL;
 105         }
 106
 107         return ret;
 108 }
 109
 110 static tree tree_get_random_const(tree type)
 111 {
 112         unsigned long long mask;
 113
 114         mask = 1ULL << (TREE_INT_CST_LOW(TYPE_SIZE(type)) - 1);
 115         mask = 2 * (mask - 1) + 1;
 116
 117         if (TYPE_UNSIGNED(type))
 118                 return build_int_cstu(type, mask & get_random_const());
 119         return build_int_cst(type, mask & get_random_const());
 120 }
 121
 122 static tree handle_latent_entropy_attribute(tree *node, tree name,
 123                                                 tree args __unused,
 124                                                 int flags __unused,
 125                                                 bool *no_add_attrs)
 126 {
 127         tree type;
 128 #if BUILDING_GCC_VERSION <= 4007
 129         VEC(constructor_elt, gc) *vals;
 130 #else
 131         vec<constructor_elt, va_gc> *vals;
 132 #endif
 133
 134         switch (TREE_CODE(*node)) {
 135         default:
 136                 *no_add_attrs = true;
 137                 error("%qE attribute only applies to functions and variables",
 138                         name);
 139                 break;
 140
 141         case VAR_DECL:
 142                 if (DECL_INITIAL(*node)) {
 143                         *no_add_attrs = true;
 144                         error("variable %qD with %qE attribute must not be initialized",
 145                                 *node, name);
 146                         break;
 147                 }
 148
 149                 if (!TREE_STATIC(*node)) {
 150                         *no_add_attrs = true;
 151                         error("variable %qD with %qE attribute must not be local",
 152                                 *node, name);
 153                         break;
 154                 }
 155
 156                 type = TREE_TYPE(*node);
 157                 switch (TREE_CODE(type)) {
 158                 default:
 159                         *no_add_attrs = true;
 160                         error("variable %qD with %qE attribute must be an integer or a fixed length integer array type or a fixed sized structure with integer fields",
 161                                 *node, name);
 162                         break;
 163
 164                 case RECORD_TYPE: {
 165                         tree fld, lst = TYPE_FIELDS(type);
 166                         unsigned int nelt = 0;
 167
 168                         for (fld = lst; fld; nelt++, fld = TREE_CHAIN(fld)) {
 169                                 tree fieldtype;
 170
 171                                 fieldtype = TREE_TYPE(fld);
 172                                 if (TREE_CODE(fieldtype) == INTEGER_TYPE)
 173                                         continue;
 174
 175                                 *no_add_attrs = true;
 176                                 error("structure variable %qD with %qE attribute has a non-integer field %qE",
 177                                         *node, name, fld);
 178                                 break;
 179                         }
 180
 181                         if (fld)
 182                                 break;
 183
 184 #if BUILDING_GCC_VERSION <= 4007
 185                         vals = VEC_alloc(constructor_elt, gc, nelt);
 186 #else
 187                         vec_alloc(vals, nelt);
 188 #endif
 189
 190                         for (fld = lst; fld; fld = TREE_CHAIN(fld)) {
 191                                 tree random_const, fld_t = TREE_TYPE(fld);
 192
 193                                 random_const = tree_get_random_const(fld_t);
 194                                 CONSTRUCTOR_APPEND_ELT(vals, fld, random_const);
 195                         }
 196
 197                         /* Initialize the fields with random constants */
 198                         DECL_INITIAL(*node) = build_constructor(type, vals);
 199                         break;
 200                 }
 201
 202                 /* Initialize the variable with a random constant */
 203                 case INTEGER_TYPE:
 204                         DECL_INITIAL(*node) = tree_get_random_const(type);
 205                         break;
 206
 207                 case ARRAY_TYPE: {
 208                         tree elt_type, array_size, elt_size;
 209                         unsigned int i, nelt;
 210                         HOST_WIDE_INT array_size_int, elt_size_int;
 211
 212                         elt_type = TREE_TYPE(type);
 213                         elt_size = TYPE_SIZE_UNIT(TREE_TYPE(type));
 214                         array_size = TYPE_SIZE_UNIT(type);
 215
 216                         if (TREE_CODE(elt_type) != INTEGER_TYPE || !array_size
 217                                 || TREE_CODE(array_size) != INTEGER_CST) {
 218                                 *no_add_attrs = true;
 219                                 error("array variable %qD with %qE attribute must be a fixed length integer array type",
 220                                         *node, name);
 221                                 break;
 222                         }
 223
 224                         array_size_int = TREE_INT_CST_LOW(array_size);
 225                         elt_size_int = TREE_INT_CST_LOW(elt_size);
 226                         nelt = array_size_int / elt_size_int;
 227
 228 #if BUILDING_GCC_VERSION <= 4007
 229                         vals = VEC_alloc(constructor_elt, gc, nelt);
 230 #else
 231                         vec_alloc(vals, nelt);
 232 #endif
 233
 234                         for (i = 0; i < nelt; i++) {
 235                                 tree cst = size_int(i);
 236                                 tree rand_cst = tree_get_random_const(elt_type);
 237
 238                                 CONSTRUCTOR_APPEND_ELT(vals, cst, rand_cst);
 239                         }
 240
 241                         /*
 242                          * Initialize the elements of the array with random
 243                          * constants
 244                          */
 245                         DECL_INITIAL(*node) = build_constructor(type, vals);
 246                         break;
 247                 }
 248                 }
 249                 break;
 250
 251         case FUNCTION_DECL:
 252                 break;
 253         }
 254
 255         return NULL_TREE;
 256 }
 257
 258 static struct attribute_spec latent_entropy_attr = { };
 259
 260 static void register_attributes(void *event_data __unused, void *data __unused)
 261 {
 262         latent_entropy_attr.name                = "latent_entropy";
 263         latent_entropy_attr.decl_required       = true;
 264         latent_entropy_attr.handler             = handle_latent_entropy_attribute;
 265
 266         register_attribute(&latent_entropy_attr);
 267 }
 268
 269 static bool latent_entropy_gate(void)
 270 {
 271         tree list;
 272
 273         /* don't bother with noreturn functions for now */
 274         if (TREE_THIS_VOLATILE(current_function_decl))
 275                 return false;
 276
 277         /* gcc-4.5 doesn't discover some trivial noreturn functions */
 278         if (EDGE_COUNT(EXIT_BLOCK_PTR_FOR_FN(cfun)->preds) == 0)
 279                 return false;
 280
 281         list = DECL_ATTRIBUTES(current_function_decl);
 282         return lookup_attribute("latent_entropy", list) != NULL_TREE;
 283 }
 284
 285 static tree create_var(tree type, const char *name)
 286 {
 287         tree var;
 288
 289         var = create_tmp_var(type, name);
 290         add_referenced_var(var);
 291         mark_sym_for_renaming(var);
 292         return var;
 293 }
 294
 295 /*
 296  * Set up the next operation and its constant operand to use in the latent
 297  * entropy PRNG. When RHS is specified, the request is for perturbing the
 298  * local latent entropy variable, otherwise it is for perturbing the global
 299  * latent entropy variable where the two operands are already given by the
 300  * local and global latent entropy variables themselves.
 301  *
 302  * The operation is one of add/xor/rol when instrumenting the local entropy
 303  * variable and one of add/xor when perturbing the global entropy variable.
 304  * Rotation is not used for the latter case because it would transmit less
 305  * entropy to the global variable than the other two operations.
 306  */
 307 static enum tree_code get_op(tree *rhs)
 308 {
 309         static enum tree_code op;
 310         unsigned HOST_WIDE_INT random_const;
 311
 312         random_const = get_random_const();
 313
 314         switch (op) {
 315         case BIT_XOR_EXPR:
 316                 op = PLUS_EXPR;
 317                 break;
 318
 319         case PLUS_EXPR:
 320                 if (rhs) {
 321                         op = LROTATE_EXPR;
 322                         /*
 323                          * This code limits the value of random_const to
 324                          * the size of a long for the rotation
 325                          */
 326                         random_const %= TYPE_PRECISION(long_unsigned_type_node);
 327                         break;
 328                 }
 329
 330         case LROTATE_EXPR:
 331         default:
 332                 op = BIT_XOR_EXPR;
 333                 break;
 334         }
 335         if (rhs)
 336                 *rhs = build_int_cstu(long_unsigned_type_node, random_const);
 337         return op;
 338 }
 339
 340 static gimple create_assign(enum tree_code code, tree lhs, tree op1,
 341                                 tree op2)
 342 {
 343         return gimple_build_assign_with_ops(code, lhs, op1, op2);
 344 }
 345
 346 static void perturb_local_entropy(basic_block bb, tree local_entropy)
 347 {
 348         gimple_stmt_iterator gsi;
 349         gimple assign;
 350         tree rhs;
 351         enum tree_code op;
 352
 353         op = get_op(&rhs);
 354         assign = create_assign(op, local_entropy, local_entropy, rhs);
 355         gsi = gsi_after_labels(bb);
 356         gsi_insert_before(&gsi, assign, GSI_NEW_STMT);
 357         update_stmt(assign);
 358 }
 359
 360 static void __perturb_latent_entropy(gimple_stmt_iterator *gsi,
 361                                         tree local_entropy)
 362 {
 363         gimple assign;
 364         tree temp;
 365         enum tree_code op;
 366
 367         /* 1. create temporary copy of latent_entropy */
 368         temp = create_var(long_unsigned_type_node, "temp_latent_entropy");
 369
 370         /* 2. read... */
 371         add_referenced_var(latent_entropy_decl);
 372         mark_sym_for_renaming(latent_entropy_decl);
 373         assign = gimple_build_assign(temp, latent_entropy_decl);
 374         gsi_insert_before(gsi, assign, GSI_NEW_STMT);
 375         update_stmt(assign);
 376
 377         /* 3. ...modify... */
 378         op = get_op(NULL);
 379         assign = create_assign(op, temp, temp, local_entropy);
 380         gsi_insert_after(gsi, assign, GSI_NEW_STMT);
 381         update_stmt(assign);
 382
 383         /* 4. ...write latent_entropy */
 384         assign = gimple_build_assign(latent_entropy_decl, temp);
 385         gsi_insert_after(gsi, assign, GSI_NEW_STMT);
 386         update_stmt(assign);
 387 }
 388
 389 static bool handle_tail_calls(basic_block bb, tree local_entropy)
 390 {
 391         gimple_stmt_iterator gsi;
 392
 393         for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) {
 394                 gcall *call;
 395                 gimple stmt = gsi_stmt(gsi);
 396
 397                 if (!is_gimple_call(stmt))
 398                         continue;
 399
 400                 call = as_a_gcall(stmt);
 401                 if (!gimple_call_tail_p(call))
 402                         continue;
 403
 404                 __perturb_latent_entropy(&gsi, local_entropy);
 405                 return true;
 406         }
 407
 408         return false;
 409 }
 410
 411 static void perturb_latent_entropy(tree local_entropy)
 412 {
 413         edge_iterator ei;
 414         edge e, last_bb_e;
 415         basic_block last_bb;
 416
 417         gcc_assert(single_pred_p(EXIT_BLOCK_PTR_FOR_FN(cfun)));
 418         last_bb_e = single_pred_edge(EXIT_BLOCK_PTR_FOR_FN(cfun));
 419
 420         FOR_EACH_EDGE(e, ei, last_bb_e->src->preds) {
 421                 if (ENTRY_BLOCK_PTR_FOR_FN(cfun) == e->src)
 422                         continue;
 423                 if (EXIT_BLOCK_PTR_FOR_FN(cfun) == e->src)
 424                         continue;
 425
 426                 handle_tail_calls(e->src, local_entropy);
 427         }
 428
 429         last_bb = single_pred(EXIT_BLOCK_PTR_FOR_FN(cfun));
 430         if (!handle_tail_calls(last_bb, local_entropy)) {
 431                 gimple_stmt_iterator gsi = gsi_last_bb(last_bb);
 432
 433                 __perturb_latent_entropy(&gsi, local_entropy);
 434         }
 435 }
 436
 437 static void init_local_entropy(basic_block bb, tree local_entropy)
 438 {
 439         gimple assign, call;
 440         tree frame_addr, rand_const, tmp, fndecl, udi_frame_addr;
 441         enum tree_code op;
 442         unsigned HOST_WIDE_INT rand_cst;
 443         gimple_stmt_iterator gsi = gsi_after_labels(bb);
 444
 445         /* 1. create local_entropy_frameaddr */
 446         frame_addr = create_var(ptr_type_node, "local_entropy_frameaddr");
 447
 448         /* 2. local_entropy_frameaddr = __builtin_frame_address() */
 449         fndecl = builtin_decl_implicit(BUILT_IN_FRAME_ADDRESS);
 450         call = gimple_build_call(fndecl, 1, integer_zero_node);
 451         gimple_call_set_lhs(call, frame_addr);
 452         gsi_insert_before(&gsi, call, GSI_NEW_STMT);
 453         update_stmt(call);
 454
 455         udi_frame_addr = fold_convert(long_unsigned_type_node, frame_addr);
 456         assign = gimple_build_assign(local_entropy, udi_frame_addr);
 457         gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
 458         update_stmt(assign);
 459
 460         /* 3. create temporary copy of latent_entropy */
 461         tmp = create_var(long_unsigned_type_node, "temp_latent_entropy");
 462
 463         /* 4. read the global entropy variable into local entropy */
 464         add_referenced_var(latent_entropy_decl);
 465         mark_sym_for_renaming(latent_entropy_decl);
 466         assign = gimple_build_assign(tmp, latent_entropy_decl);
 467         gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
 468         update_stmt(assign);
 469
 470         /* 5. mix local_entropy_frameaddr into local entropy */
 471         assign = create_assign(BIT_XOR_EXPR, local_entropy, local_entropy, tmp);
 472         gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
 473         update_stmt(assign);
 474
 475         rand_cst = get_random_const();
 476         rand_const = build_int_cstu(long_unsigned_type_node, rand_cst);
 477         op = get_op(NULL);
 478         assign = create_assign(op, local_entropy, local_entropy, rand_const);
 479         gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
 480         update_stmt(assign);
 481 }
 482
 483 static bool create_latent_entropy_decl(void)
 484 {
 485         varpool_node_ptr node;
 486
 487         if (latent_entropy_decl != NULL_TREE)
 488                 return true;
 489
 490         FOR_EACH_VARIABLE(node) {
 491                 tree name, var = NODE_DECL(node);
 492
 493                 if (DECL_NAME_LENGTH(var) < sizeof("latent_entropy") - 1)
 494                         continue;
 495
 496                 name = DECL_NAME(var);
 497                 if (strcmp(IDENTIFIER_POINTER(name), "latent_entropy"))
 498                         continue;
 499
 500                 latent_entropy_decl = var;
 501                 break;
 502         }
 503
 504         return latent_entropy_decl != NULL_TREE;
 505 }
 506
 507 static unsigned int latent_entropy_execute(void)
 508 {
 509         basic_block bb;
 510         tree local_entropy;
 511
 512         if (!create_latent_entropy_decl())
 513                 return 0;
 514
 515         /* prepare for step 2 below */
 516         gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
 517         bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
 518         if (!single_pred_p(bb)) {
 519                 split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
 520                 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
 521                 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
 522         }
 523
 524         /* 1. create the local entropy variable */
 525         local_entropy = create_var(long_unsigned_type_node, "local_entropy");
 526
 527         /* 2. initialize the local entropy variable */
 528         init_local_entropy(bb, local_entropy);
 529
 530         bb = bb->next_bb;
 531
 532         /*
 533          * 3. instrument each BB with an operation on the
 534          *    local entropy variable
 535          */
 536         while (bb != EXIT_BLOCK_PTR_FOR_FN(cfun)) {
 537                 perturb_local_entropy(bb, local_entropy);
 538                 bb = bb->next_bb;
 539         };
 540
 541         /* 4. mix local entropy into the global entropy variable */
 542         perturb_latent_entropy(local_entropy);
 543         return 0;
 544 }
 545
 546 static void latent_entropy_start_unit(void *gcc_data __unused,
 547                                         void *user_data __unused)
 548 {
 549         tree type, id;
 550         int quals;
 551
 552         seed = get_random_seed(false);
 553
 554         if (in_lto_p)
 555                 return;
 556
 557         /* extern volatile unsigned long latent_entropy */
 558         quals = TYPE_QUALS(long_unsigned_type_node) | TYPE_QUAL_VOLATILE;
 559         type = build_qualified_type(long_unsigned_type_node, quals);
 560         id = get_identifier("latent_entropy");
 561         latent_entropy_decl = build_decl(UNKNOWN_LOCATION, VAR_DECL, id, type);
 562
 563         TREE_STATIC(latent_entropy_decl) = 1;
 564         TREE_PUBLIC(latent_entropy_decl) = 1;
 565         TREE_USED(latent_entropy_decl) = 1;
 566         DECL_PRESERVE_P(latent_entropy_decl) = 1;
 567         TREE_THIS_VOLATILE(latent_entropy_decl) = 1;
 568         DECL_EXTERNAL(latent_entropy_decl) = 1;
 569         DECL_ARTIFICIAL(latent_entropy_decl) = 1;
 570         lang_hooks.decls.pushdecl(latent_entropy_decl);
 571 }
 572
 573 #define PASS_NAME latent_entropy
 574 #define PROPERTIES_REQUIRED PROP_gimple_leh | PROP_cfg
 575 #define TODO_FLAGS_FINISH TODO_verify_ssa | TODO_verify_stmts | TODO_dump_func \
 576         | TODO_update_ssa
 577 #include "gcc-generate-gimple-pass.h"
 578
 579 __visible int plugin_init(struct plugin_name_args *plugin_info,
 580                           struct plugin_gcc_version *version)
 581 {
 582         bool enabled = true;
 583         const char * const plugin_name = plugin_info->base_name;
 584         const int argc = plugin_info->argc;
 585         const struct plugin_argument * const argv = plugin_info->argv;
 586         int i;
 587
 588         static const struct ggc_root_tab gt_ggc_r_gt_latent_entropy[] = {
 589                 {
 590                         .base = &latent_entropy_decl,
 591                         .nelt = 1,
 592                         .stride = sizeof(latent_entropy_decl),
 593                         .cb = &gt_ggc_mx_tree_node,
 594                         .pchw = &gt_pch_nx_tree_node
 595                 },
 596                 LAST_GGC_ROOT_TAB
 597         };
 598
 599         PASS_INFO(latent_entropy, "optimized", 1, PASS_POS_INSERT_BEFORE);
 600
 601         if (!plugin_default_version_check(version, &gcc_version)) {
 602                 error(G_("incompatible gcc/plugin versions"));
 603                 return 1;
 604         }
 605
 606         for (i = 0; i < argc; ++i) {
 607                 if (!(strcmp(argv[i].key, "disable"))) {
 608                         enabled = false;
 609                         continue;
 610                 }
 611                 error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key);
 612         }
 613
 614         register_callback(plugin_name, PLUGIN_INFO, NULL,
 615                                 &latent_entropy_plugin_info);
 616         if (enabled) {
 617                 register_callback(plugin_name, PLUGIN_START_UNIT,
 618                                         &latent_entropy_start_unit, NULL);
 619                 register_callback(plugin_name, PLUGIN_REGISTER_GGC_ROOTS,
 620                                   NULL, (void *)&gt_ggc_r_gt_latent_entropy);
 621                 register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL,
 622                                         &latent_entropy_pass_info);
 623         }
 624         register_callback(plugin_name, PLUGIN_ATTRIBUTES, register_attributes,
 625                                 NULL);
 626
 627         return 0;
 628 }