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         vec<constructor_elt, va_gc> *vals;
 129
 130         switch (TREE_CODE(*node)) {
 131         default:
 132                 *no_add_attrs = true;
 133                 error("%qE attribute only applies to functions and variables",
 134                         name);
 135                 break;
 136
 137         case VAR_DECL:
 138                 if (DECL_INITIAL(*node)) {
 139                         *no_add_attrs = true;
 140                         error("variable %qD with %qE attribute must not be initialized",
 141                                 *node, name);
 142                         break;
 143                 }
 144
 145                 if (!TREE_STATIC(*node)) {
 146                         *no_add_attrs = true;
 147                         error("variable %qD with %qE attribute must not be local",
 148                                 *node, name);
 149                         break;
 150                 }
 151
 152                 type = TREE_TYPE(*node);
 153                 switch (TREE_CODE(type)) {
 154                 default:
 155                         *no_add_attrs = true;
 156                         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",
 157                                 *node, name);
 158                         break;
 159
 160                 case RECORD_TYPE: {
 161                         tree fld, lst = TYPE_FIELDS(type);
 162                         unsigned int nelt = 0;
 163
 164                         for (fld = lst; fld; nelt++, fld = TREE_CHAIN(fld)) {
 165                                 tree fieldtype;
 166
 167                                 fieldtype = TREE_TYPE(fld);
 168                                 if (TREE_CODE(fieldtype) == INTEGER_TYPE)
 169                                         continue;
 170
 171                                 *no_add_attrs = true;
 172                                 error("structure variable %qD with %qE attribute has a non-integer field %qE",
 173                                         *node, name, fld);
 174                                 break;
 175                         }
 176
 177                         if (fld)
 178                                 break;
 179
 180                         vec_alloc(vals, nelt);
 181
 182                         for (fld = lst; fld; fld = TREE_CHAIN(fld)) {
 183                                 tree random_const, fld_t = TREE_TYPE(fld);
 184
 185                                 random_const = tree_get_random_const(fld_t);
 186                                 CONSTRUCTOR_APPEND_ELT(vals, fld, random_const);
 187                         }
 188
 189                         /* Initialize the fields with random constants */
 190                         DECL_INITIAL(*node) = build_constructor(type, vals);
 191                         break;
 192                 }
 193
 194                 /* Initialize the variable with a random constant */
 195                 case INTEGER_TYPE:
 196                         DECL_INITIAL(*node) = tree_get_random_const(type);
 197                         break;
 198
 199                 case ARRAY_TYPE: {
 200                         tree elt_type, array_size, elt_size;
 201                         unsigned int i, nelt;
 202                         HOST_WIDE_INT array_size_int, elt_size_int;
 203
 204                         elt_type = TREE_TYPE(type);
 205                         elt_size = TYPE_SIZE_UNIT(TREE_TYPE(type));
 206                         array_size = TYPE_SIZE_UNIT(type);
 207
 208                         if (TREE_CODE(elt_type) != INTEGER_TYPE || !array_size
 209                                 || TREE_CODE(array_size) != INTEGER_CST) {
 210                                 *no_add_attrs = true;
 211                                 error("array variable %qD with %qE attribute must be a fixed length integer array type",
 212                                         *node, name);
 213                                 break;
 214                         }
 215
 216                         array_size_int = TREE_INT_CST_LOW(array_size);
 217                         elt_size_int = TREE_INT_CST_LOW(elt_size);
 218                         nelt = array_size_int / elt_size_int;
 219
 220                         vec_alloc(vals, nelt);
 221
 222                         for (i = 0; i < nelt; i++) {
 223                                 tree cst = size_int(i);
 224                                 tree rand_cst = tree_get_random_const(elt_type);
 225
 226                                 CONSTRUCTOR_APPEND_ELT(vals, cst, rand_cst);
 227                         }
 228
 229                         /*
 230                          * Initialize the elements of the array with random
 231                          * constants
 232                          */
 233                         DECL_INITIAL(*node) = build_constructor(type, vals);
 234                         break;
 235                 }
 236                 }
 237                 break;
 238
 239         case FUNCTION_DECL:
 240                 break;
 241         }
 242
 243         return NULL_TREE;
 244 }
 245
 246 static struct attribute_spec latent_entropy_attr = { };
 247
 248 static void register_attributes(void *event_data __unused, void *data __unused)
 249 {
 250         latent_entropy_attr.name                = "latent_entropy";
 251         latent_entropy_attr.decl_required       = true;
 252         latent_entropy_attr.handler             = handle_latent_entropy_attribute;
 253
 254         register_attribute(&latent_entropy_attr);
 255 }
 256
 257 static bool latent_entropy_gate(void)
 258 {
 259         tree list;
 260
 261         /* don't bother with noreturn functions for now */
 262         if (TREE_THIS_VOLATILE(current_function_decl))
 263                 return false;
 264
 265         /* gcc-4.5 doesn't discover some trivial noreturn functions */
 266         if (EDGE_COUNT(EXIT_BLOCK_PTR_FOR_FN(cfun)->preds) == 0)
 267                 return false;
 268
 269         list = DECL_ATTRIBUTES(current_function_decl);
 270         return lookup_attribute("latent_entropy", list) != NULL_TREE;
 271 }
 272
 273 static tree create_var(tree type, const char *name)
 274 {
 275         tree var;
 276
 277         var = create_tmp_var(type, name);
 278         add_referenced_var(var);
 279         mark_sym_for_renaming(var);
 280         return var;
 281 }
 282
 283 /*
 284  * Set up the next operation and its constant operand to use in the latent
 285  * entropy PRNG. When RHS is specified, the request is for perturbing the
 286  * local latent entropy variable, otherwise it is for perturbing the global
 287  * latent entropy variable where the two operands are already given by the
 288  * local and global latent entropy variables themselves.
 289  *
 290  * The operation is one of add/xor/rol when instrumenting the local entropy
 291  * variable and one of add/xor when perturbing the global entropy variable.
 292  * Rotation is not used for the latter case because it would transmit less
 293  * entropy to the global variable than the other two operations.
 294  */
 295 static enum tree_code get_op(tree *rhs)
 296 {
 297         static enum tree_code op;
 298         unsigned HOST_WIDE_INT random_const;
 299
 300         random_const = get_random_const();
 301
 302         switch (op) {
 303         case BIT_XOR_EXPR:
 304                 op = PLUS_EXPR;
 305                 break;
 306
 307         case PLUS_EXPR:
 308                 if (rhs) {
 309                         op = LROTATE_EXPR;
 310                         /*
 311                          * This code limits the value of random_const to
 312                          * the size of a long for the rotation
 313                          */
 314                         random_const %= TYPE_PRECISION(long_unsigned_type_node);
 315                         break;
 316                 }
 317
 318         case LROTATE_EXPR:
 319         default:
 320                 op = BIT_XOR_EXPR;
 321                 break;
 322         }
 323         if (rhs)
 324                 *rhs = build_int_cstu(long_unsigned_type_node, random_const);
 325         return op;
 326 }
 327
 328 static gimple create_assign(enum tree_code code, tree lhs, tree op1,
 329                                 tree op2)
 330 {
 331         return gimple_build_assign_with_ops(code, lhs, op1, op2);
 332 }
 333
 334 static void perturb_local_entropy(basic_block bb, tree local_entropy)
 335 {
 336         gimple_stmt_iterator gsi;
 337         gimple assign;
 338         tree rhs;
 339         enum tree_code op;
 340
 341         op = get_op(&rhs);
 342         assign = create_assign(op, local_entropy, local_entropy, rhs);
 343         gsi = gsi_after_labels(bb);
 344         gsi_insert_before(&gsi, assign, GSI_NEW_STMT);
 345         update_stmt(assign);
 346 }
 347
 348 static void __perturb_latent_entropy(gimple_stmt_iterator *gsi,
 349                                         tree local_entropy)
 350 {
 351         gimple assign;
 352         tree temp;
 353         enum tree_code op;
 354
 355         /* 1. create temporary copy of latent_entropy */
 356         temp = create_var(long_unsigned_type_node, "temp_latent_entropy");
 357
 358         /* 2. read... */
 359         add_referenced_var(latent_entropy_decl);
 360         mark_sym_for_renaming(latent_entropy_decl);
 361         assign = gimple_build_assign(temp, latent_entropy_decl);
 362         gsi_insert_before(gsi, assign, GSI_NEW_STMT);
 363         update_stmt(assign);
 364
 365         /* 3. ...modify... */
 366         op = get_op(NULL);
 367         assign = create_assign(op, temp, temp, local_entropy);
 368         gsi_insert_after(gsi, assign, GSI_NEW_STMT);
 369         update_stmt(assign);
 370
 371         /* 4. ...write latent_entropy */
 372         assign = gimple_build_assign(latent_entropy_decl, temp);
 373         gsi_insert_after(gsi, assign, GSI_NEW_STMT);
 374         update_stmt(assign);
 375 }
 376
 377 static bool handle_tail_calls(basic_block bb, tree local_entropy)
 378 {
 379         gimple_stmt_iterator gsi;
 380
 381         for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) {
 382                 gcall *call;
 383                 gimple stmt = gsi_stmt(gsi);
 384
 385                 if (!is_gimple_call(stmt))
 386                         continue;
 387
 388                 call = as_a_gcall(stmt);
 389                 if (!gimple_call_tail_p(call))
 390                         continue;
 391
 392                 __perturb_latent_entropy(&gsi, local_entropy);
 393                 return true;
 394         }
 395
 396         return false;
 397 }
 398
 399 static void perturb_latent_entropy(tree local_entropy)
 400 {
 401         edge_iterator ei;
 402         edge e, last_bb_e;
 403         basic_block last_bb;
 404
 405         gcc_assert(single_pred_p(EXIT_BLOCK_PTR_FOR_FN(cfun)));
 406         last_bb_e = single_pred_edge(EXIT_BLOCK_PTR_FOR_FN(cfun));
 407
 408         FOR_EACH_EDGE(e, ei, last_bb_e->src->preds) {
 409                 if (ENTRY_BLOCK_PTR_FOR_FN(cfun) == e->src)
 410                         continue;
 411                 if (EXIT_BLOCK_PTR_FOR_FN(cfun) == e->src)
 412                         continue;
 413
 414                 handle_tail_calls(e->src, local_entropy);
 415         }
 416
 417         last_bb = single_pred(EXIT_BLOCK_PTR_FOR_FN(cfun));
 418         if (!handle_tail_calls(last_bb, local_entropy)) {
 419                 gimple_stmt_iterator gsi = gsi_last_bb(last_bb);
 420
 421                 __perturb_latent_entropy(&gsi, local_entropy);
 422         }
 423 }
 424
 425 static void init_local_entropy(basic_block bb, tree local_entropy)
 426 {
 427         gimple assign, call;
 428         tree frame_addr, rand_const, tmp, fndecl, udi_frame_addr;
 429         enum tree_code op;
 430         unsigned HOST_WIDE_INT rand_cst;
 431         gimple_stmt_iterator gsi = gsi_after_labels(bb);
 432
 433         /* 1. create local_entropy_frameaddr */
 434         frame_addr = create_var(ptr_type_node, "local_entropy_frameaddr");
 435
 436         /* 2. local_entropy_frameaddr = __builtin_frame_address() */
 437         fndecl = builtin_decl_implicit(BUILT_IN_FRAME_ADDRESS);
 438         call = gimple_build_call(fndecl, 1, integer_zero_node);
 439         gimple_call_set_lhs(call, frame_addr);
 440         gsi_insert_before(&gsi, call, GSI_NEW_STMT);
 441         update_stmt(call);
 442
 443         udi_frame_addr = fold_convert(long_unsigned_type_node, frame_addr);
 444         assign = gimple_build_assign(local_entropy, udi_frame_addr);
 445         gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
 446         update_stmt(assign);
 447
 448         /* 3. create temporary copy of latent_entropy */
 449         tmp = create_var(long_unsigned_type_node, "temp_latent_entropy");
 450
 451         /* 4. read the global entropy variable into local entropy */
 452         add_referenced_var(latent_entropy_decl);
 453         mark_sym_for_renaming(latent_entropy_decl);
 454         assign = gimple_build_assign(tmp, latent_entropy_decl);
 455         gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
 456         update_stmt(assign);
 457
 458         /* 5. mix local_entropy_frameaddr into local entropy */
 459         assign = create_assign(BIT_XOR_EXPR, local_entropy, local_entropy, tmp);
 460         gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
 461         update_stmt(assign);
 462
 463         rand_cst = get_random_const();
 464         rand_const = build_int_cstu(long_unsigned_type_node, rand_cst);
 465         op = get_op(NULL);
 466         assign = create_assign(op, local_entropy, local_entropy, rand_const);
 467         gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
 468         update_stmt(assign);
 469 }
 470
 471 static bool create_latent_entropy_decl(void)
 472 {
 473         varpool_node_ptr node;
 474
 475         if (latent_entropy_decl != NULL_TREE)
 476                 return true;
 477
 478         FOR_EACH_VARIABLE(node) {
 479                 tree name, var = NODE_DECL(node);
 480
 481                 if (DECL_NAME_LENGTH(var) < sizeof("latent_entropy") - 1)
 482                         continue;
 483
 484                 name = DECL_NAME(var);
 485                 if (strcmp(IDENTIFIER_POINTER(name), "latent_entropy"))
 486                         continue;
 487
 488                 latent_entropy_decl = var;
 489                 break;
 490         }
 491
 492         return latent_entropy_decl != NULL_TREE;
 493 }
 494
 495 static unsigned int latent_entropy_execute(void)
 496 {
 497         basic_block bb;
 498         tree local_entropy;
 499
 500         if (!create_latent_entropy_decl())
 501                 return 0;
 502
 503         /* prepare for step 2 below */
 504         gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
 505         bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
 506         if (!single_pred_p(bb)) {
 507                 split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
 508                 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
 509                 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
 510         }
 511
 512         /* 1. create the local entropy variable */
 513         local_entropy = create_var(long_unsigned_type_node, "local_entropy");
 514
 515         /* 2. initialize the local entropy variable */
 516         init_local_entropy(bb, local_entropy);
 517
 518         bb = bb->next_bb;
 519
 520         /*
 521          * 3. instrument each BB with an operation on the
 522          *    local entropy variable
 523          */
 524         while (bb != EXIT_BLOCK_PTR_FOR_FN(cfun)) {
 525                 perturb_local_entropy(bb, local_entropy);
 526                 bb = bb->next_bb;
 527         }
 528
 529         /* 4. mix local entropy into the global entropy variable */
 530         perturb_latent_entropy(local_entropy);
 531         return 0;
 532 }
 533
 534 static void latent_entropy_start_unit(void *gcc_data __unused,
 535                                         void *user_data __unused)
 536 {
 537         tree type, id;
 538         int quals;
 539
 540         seed = get_random_seed(false);
 541
 542         if (in_lto_p)
 543                 return;
 544
 545         /* extern volatile unsigned long latent_entropy */
 546         quals = TYPE_QUALS(long_unsigned_type_node) | TYPE_QUAL_VOLATILE;
 547         type = build_qualified_type(long_unsigned_type_node, quals);
 548         id = get_identifier("latent_entropy");
 549         latent_entropy_decl = build_decl(UNKNOWN_LOCATION, VAR_DECL, id, type);
 550
 551         TREE_STATIC(latent_entropy_decl) = 1;
 552         TREE_PUBLIC(latent_entropy_decl) = 1;
 553         TREE_USED(latent_entropy_decl) = 1;
 554         DECL_PRESERVE_P(latent_entropy_decl) = 1;
 555         TREE_THIS_VOLATILE(latent_entropy_decl) = 1;
 556         DECL_EXTERNAL(latent_entropy_decl) = 1;
 557         DECL_ARTIFICIAL(latent_entropy_decl) = 1;
 558         lang_hooks.decls.pushdecl(latent_entropy_decl);
 559 }
 560
 561 #define PASS_NAME latent_entropy
 562 #define PROPERTIES_REQUIRED PROP_gimple_leh | PROP_cfg
 563 #define TODO_FLAGS_FINISH TODO_verify_ssa | TODO_verify_stmts | TODO_dump_func \
 564         | TODO_update_ssa
 565 #include "gcc-generate-gimple-pass.h"
 566
 567 __visible int plugin_init(struct plugin_name_args *plugin_info,
 568                           struct plugin_gcc_version *version)
 569 {
 570         bool enabled = true;
 571         const char * const plugin_name = plugin_info->base_name;
 572         const int argc = plugin_info->argc;
 573         const struct plugin_argument * const argv = plugin_info->argv;
 574         int i;
 575
 576         static const struct ggc_root_tab gt_ggc_r_gt_latent_entropy[] = {
 577                 {
 578                         .base = &latent_entropy_decl,
 579                         .nelt = 1,
 580                         .stride = sizeof(latent_entropy_decl),
 581                         .cb = &gt_ggc_mx_tree_node,
 582                         .pchw = &gt_pch_nx_tree_node
 583                 },
 584                 LAST_GGC_ROOT_TAB
 585         };
 586
 587         PASS_INFO(latent_entropy, "optimized", 1, PASS_POS_INSERT_BEFORE);
 588
 589         if (!plugin_default_version_check(version, &gcc_version)) {
 590                 error(G_("incompatible gcc/plugin versions"));
 591                 return 1;
 592         }
 593
 594         for (i = 0; i < argc; ++i) {
 595                 if (!(strcmp(argv[i].key, "disable"))) {
 596                         enabled = false;
 597                         continue;
 598                 }
 599                 error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key);
 600         }
 601
 602         register_callback(plugin_name, PLUGIN_INFO, NULL,
 603                                 &latent_entropy_plugin_info);
 604         if (enabled) {
 605                 register_callback(plugin_name, PLUGIN_START_UNIT,
 606                                         &latent_entropy_start_unit, NULL);
 607                 register_callback(plugin_name, PLUGIN_REGISTER_GGC_ROOTS,
 608                                   NULL, (void *)&gt_ggc_r_gt_latent_entropy);
 609                 register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL,
 610                                         &latent_entropy_pass_info);
 611         }
 612         register_callback(plugin_name, PLUGIN_ATTRIBUTES, register_attributes,
 613                                 NULL);
 614
 615         return 0;
 616 }