1 /* 2 * Copyright 2011-2017 by the PaX Team <pageexec@freemail.hu> 3 * Modified by Alexander Popov <alex.popov@linux.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 is needed for tracking the lowest border of the kernel stack. 12 * It instruments the kernel code inserting stackleak_track_stack() calls: 13 * - after alloca(); 14 * - for the functions with a stack frame size greater than or equal 15 * to the "track-min-size" plugin parameter. 16 * 17 * This plugin is ported from grsecurity/PaX. For more information see: 18 * https://grsecurity.net/ 19 * https://pax.grsecurity.net/ 20 * 21 * Debugging: 22 * - use fprintf() to stderr, debug_generic_expr(), debug_gimple_stmt(), 23 * print_rtl_single() and debug_rtx(); 24 * - add "-fdump-tree-all -fdump-rtl-all" to the plugin CFLAGS in 25 * Makefile.gcc-plugins to see the verbose dumps of the gcc passes; 26 * - use gcc -E to understand the preprocessing shenanigans; 27 * - use gcc with enabled CFG/GIMPLE/SSA verification (--enable-checking). 28 */ 29 30 #include "gcc-common.h" 31 32 __visible int plugin_is_GPL_compatible; 33 34 static int track_frame_size = -1; 35 static bool build_for_x86 = false; 36 static const char track_function[] = "stackleak_track_stack"; 37 static bool disable = false; 38 static bool verbose = false; 39 40 /* 41 * Mark these global variables (roots) for gcc garbage collector since 42 * they point to the garbage-collected memory. 43 */ 44 static GTY(()) tree track_function_decl; 45 46 static struct plugin_info stackleak_plugin_info = { 47 .version = "201707101337", 48 .help = "track-min-size=nn\ttrack stack for functions with a stack frame size >= nn bytes\n" 49 "arch=target_arch\tspecify target build arch\n" 50 "disable\t\tdo not activate the plugin\n" 51 "verbose\t\tprint info about the instrumentation\n" 52 }; 53 54 static void add_stack_tracking_gcall(gimple_stmt_iterator *gsi, bool after) 55 { 56 gimple stmt; 57 gcall *gimple_call; 58 cgraph_node_ptr node; 59 basic_block bb; 60 61 /* Insert calling stackleak_track_stack() */ 62 stmt = gimple_build_call(track_function_decl, 0); 63 gimple_call = as_a_gcall(stmt); 64 if (after) 65 gsi_insert_after(gsi, gimple_call, GSI_CONTINUE_LINKING); 66 else 67 gsi_insert_before(gsi, gimple_call, GSI_SAME_STMT); 68 69 /* Update the cgraph */ 70 bb = gimple_bb(gimple_call); 71 node = cgraph_get_create_node(track_function_decl); 72 gcc_assert(node); 73 cgraph_create_edge(cgraph_get_node(current_function_decl), node, 74 gimple_call, bb->count, 75 compute_call_stmt_bb_frequency(current_function_decl, bb)); 76 } 77 78 static bool is_alloca(gimple stmt) 79 { 80 if (gimple_call_builtin_p(stmt, BUILT_IN_ALLOCA)) 81 return true; 82 83 #if BUILDING_GCC_VERSION >= 4007 84 if (gimple_call_builtin_p(stmt, BUILT_IN_ALLOCA_WITH_ALIGN)) 85 return true; 86 #endif 87 88 return false; 89 } 90 91 static tree get_current_stack_pointer_decl(void) 92 { 93 varpool_node_ptr node; 94 95 FOR_EACH_VARIABLE(node) { 96 tree var = NODE_DECL(node); 97 tree name = DECL_NAME(var); 98 99 if (DECL_NAME_LENGTH(var) != sizeof("current_stack_pointer") - 1) 100 continue; 101 102 if (strcmp(IDENTIFIER_POINTER(name), "current_stack_pointer")) 103 continue; 104 105 return var; 106 } 107 108 if (verbose) { 109 fprintf(stderr, "stackleak: missing current_stack_pointer in %s()\n", 110 DECL_NAME_POINTER(current_function_decl)); 111 } 112 return NULL_TREE; 113 } 114 115 static void add_stack_tracking_gasm(gimple_stmt_iterator *gsi, bool after) 116 { 117 gasm *asm_call = NULL; 118 tree sp_decl, input; 119 vec<tree, va_gc> *inputs = NULL; 120 121 /* 'no_caller_saved_registers' is currently supported only for x86 */ 122 gcc_assert(build_for_x86); 123 124 /* 125 * Insert calling stackleak_track_stack() in asm: 126 * asm volatile("call stackleak_track_stack" 127 * :: "r" (current_stack_pointer)) 128 * Use ASM_CALL_CONSTRAINT trick from arch/x86/include/asm/asm.h. 129 * This constraint is taken into account during gcc shrink-wrapping 130 * optimization. It is needed to be sure that stackleak_track_stack() 131 * call is inserted after the prologue of the containing function, 132 * when the stack frame is prepared. 133 */ 134 sp_decl = get_current_stack_pointer_decl(); 135 if (sp_decl == NULL_TREE) { 136 add_stack_tracking_gcall(gsi, after); 137 return; 138 } 139 input = build_tree_list(NULL_TREE, build_const_char_string(2, "r")); 140 input = chainon(NULL_TREE, build_tree_list(input, sp_decl)); 141 vec_safe_push(inputs, input); 142 asm_call = gimple_build_asm_vec("call stackleak_track_stack", 143 inputs, NULL, NULL, NULL); 144 gimple_asm_set_volatile(asm_call, true); 145 if (after) 146 gsi_insert_after(gsi, asm_call, GSI_CONTINUE_LINKING); 147 else 148 gsi_insert_before(gsi, asm_call, GSI_SAME_STMT); 149 update_stmt(asm_call); 150 } 151 152 static void add_stack_tracking(gimple_stmt_iterator *gsi, bool after) 153 { 154 /* 155 * The 'no_caller_saved_registers' attribute is used for 156 * stackleak_track_stack(). If the compiler supports this attribute for 157 * the target arch, we can add calling stackleak_track_stack() in asm. 158 * That improves performance: we avoid useless operations with the 159 * caller-saved registers in the functions from which we will remove 160 * stackleak_track_stack() call during the stackleak_cleanup pass. 161 */ 162 if (lookup_attribute_spec(get_identifier("no_caller_saved_registers"))) 163 add_stack_tracking_gasm(gsi, after); 164 else 165 add_stack_tracking_gcall(gsi, after); 166 } 167 168 /* 169 * Work with the GIMPLE representation of the code. Insert the 170 * stackleak_track_stack() call after alloca() and into the beginning 171 * of the function if it is not instrumented. 172 */ 173 static unsigned int stackleak_instrument_execute(void) 174 { 175 basic_block bb, entry_bb; 176 bool prologue_instrumented = false, is_leaf = true; 177 gimple_stmt_iterator gsi = { 0 }; 178 179 /* 180 * ENTRY_BLOCK_PTR is a basic block which represents possible entry 181 * point of a function. This block does not contain any code and 182 * has a CFG edge to its successor. 183 */ 184 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 185 entry_bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); 186 187 /* 188 * Loop through the GIMPLE statements in each of cfun basic blocks. 189 * cfun is a global variable which represents the function that is 190 * currently processed. 191 */ 192 FOR_EACH_BB_FN(bb, cfun) { 193 for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) { 194 gimple stmt; 195 196 stmt = gsi_stmt(gsi); 197 198 /* Leaf function is a function which makes no calls */ 199 if (is_gimple_call(stmt)) 200 is_leaf = false; 201 202 if (!is_alloca(stmt)) 203 continue; 204 205 if (verbose) { 206 fprintf(stderr, "stackleak: be careful, alloca() in %s()\n", 207 DECL_NAME_POINTER(current_function_decl)); 208 } 209 210 /* Insert stackleak_track_stack() call after alloca() */ 211 add_stack_tracking(&gsi, true); 212 if (bb == entry_bb) 213 prologue_instrumented = true; 214 } 215 } 216 217 if (prologue_instrumented) 218 return 0; 219 220 /* 221 * Special cases to skip the instrumentation. 222 * 223 * Taking the address of static inline functions materializes them, 224 * but we mustn't instrument some of them as the resulting stack 225 * alignment required by the function call ABI will break other 226 * assumptions regarding the expected (but not otherwise enforced) 227 * register clobbering ABI. 228 * 229 * Case in point: native_save_fl on amd64 when optimized for size 230 * clobbers rdx if it were instrumented here. 231 * 232 * TODO: any more special cases? 233 */ 234 if (is_leaf && 235 !TREE_PUBLIC(current_function_decl) && 236 DECL_DECLARED_INLINE_P(current_function_decl)) { 237 return 0; 238 } 239 240 if (is_leaf && 241 !strncmp(IDENTIFIER_POINTER(DECL_NAME(current_function_decl)), 242 "_paravirt_", 10)) { 243 return 0; 244 } 245 246 /* Insert stackleak_track_stack() call at the function beginning */ 247 bb = entry_bb; 248 if (!single_pred_p(bb)) { 249 /* gcc_assert(bb_loop_depth(bb) || 250 (bb->flags & BB_IRREDUCIBLE_LOOP)); */ 251 split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 252 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 253 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); 254 } 255 gsi = gsi_after_labels(bb); 256 add_stack_tracking(&gsi, false); 257 258 return 0; 259 } 260 261 static bool large_stack_frame(void) 262 { 263 #if BUILDING_GCC_VERSION >= 8000 264 return maybe_ge(get_frame_size(), track_frame_size); 265 #else 266 return (get_frame_size() >= track_frame_size); 267 #endif 268 } 269 270 static void remove_stack_tracking_gcall(void) 271 { 272 rtx_insn *insn, *next; 273 274 /* 275 * Find stackleak_track_stack() calls. Loop through the chain of insns, 276 * which is an RTL representation of the code for a function. 277 * 278 * The example of a matching insn: 279 * (call_insn 8 4 10 2 (call (mem (symbol_ref ("stackleak_track_stack") 280 * [flags 0x41] <function_decl 0x7f7cd3302a80 stackleak_track_stack>) 281 * [0 stackleak_track_stack S1 A8]) (0)) 675 {*call} (expr_list 282 * (symbol_ref ("stackleak_track_stack") [flags 0x41] <function_decl 283 * 0x7f7cd3302a80 stackleak_track_stack>) (expr_list (0) (nil))) (nil)) 284 */ 285 for (insn = get_insns(); insn; insn = next) { 286 rtx body; 287 288 next = NEXT_INSN(insn); 289 290 /* Check the expression code of the insn */ 291 if (!CALL_P(insn)) 292 continue; 293 294 /* 295 * Check the expression code of the insn body, which is an RTL 296 * Expression (RTX) describing the side effect performed by 297 * that insn. 298 */ 299 body = PATTERN(insn); 300 301 if (GET_CODE(body) == PARALLEL) 302 body = XVECEXP(body, 0, 0); 303 304 if (GET_CODE(body) != CALL) 305 continue; 306 307 /* 308 * Check the first operand of the call expression. It should 309 * be a mem RTX describing the needed subroutine with a 310 * symbol_ref RTX. 311 */ 312 body = XEXP(body, 0); 313 if (GET_CODE(body) != MEM) 314 continue; 315 316 body = XEXP(body, 0); 317 if (GET_CODE(body) != SYMBOL_REF) 318 continue; 319 320 if (SYMBOL_REF_DECL(body) != track_function_decl) 321 continue; 322 323 /* Delete the stackleak_track_stack() call */ 324 delete_insn_and_edges(insn); 325 #if BUILDING_GCC_VERSION >= 4007 && BUILDING_GCC_VERSION < 8000 326 if (GET_CODE(next) == NOTE && 327 NOTE_KIND(next) == NOTE_INSN_CALL_ARG_LOCATION) { 328 insn = next; 329 next = NEXT_INSN(insn); 330 delete_insn_and_edges(insn); 331 } 332 #endif 333 } 334 } 335 336 static bool remove_stack_tracking_gasm(void) 337 { 338 bool removed = false; 339 rtx_insn *insn, *next; 340 341 /* 'no_caller_saved_registers' is currently supported only for x86 */ 342 gcc_assert(build_for_x86); 343 344 /* 345 * Find stackleak_track_stack() asm calls. Loop through the chain of 346 * insns, which is an RTL representation of the code for a function. 347 * 348 * The example of a matching insn: 349 * (insn 11 5 12 2 (parallel [ (asm_operands/v 350 * ("call stackleak_track_stack") ("") 0 351 * [ (reg/v:DI 7 sp [ current_stack_pointer ]) ] 352 * [ (asm_input:DI ("r")) ] []) 353 * (clobber (reg:CC 17 flags)) ]) -1 (nil)) 354 */ 355 for (insn = get_insns(); insn; insn = next) { 356 rtx body; 357 358 next = NEXT_INSN(insn); 359 360 /* Check the expression code of the insn */ 361 if (!NONJUMP_INSN_P(insn)) 362 continue; 363 364 /* 365 * Check the expression code of the insn body, which is an RTL 366 * Expression (RTX) describing the side effect performed by 367 * that insn. 368 */ 369 body = PATTERN(insn); 370 371 if (GET_CODE(body) != PARALLEL) 372 continue; 373 374 body = XVECEXP(body, 0, 0); 375 376 if (GET_CODE(body) != ASM_OPERANDS) 377 continue; 378 379 if (strcmp(ASM_OPERANDS_TEMPLATE(body), 380 "call stackleak_track_stack")) { 381 continue; 382 } 383 384 delete_insn_and_edges(insn); 385 gcc_assert(!removed); 386 removed = true; 387 } 388 389 return removed; 390 } 391 392 /* 393 * Work with the RTL representation of the code. 394 * Remove the unneeded stackleak_track_stack() calls from the functions 395 * which don't call alloca() and don't have a large enough stack frame size. 396 */ 397 static unsigned int stackleak_cleanup_execute(void) 398 { 399 const char *fn = DECL_NAME_POINTER(current_function_decl); 400 bool removed = false; 401 402 /* 403 * Leave stack tracking in functions that call alloca(). 404 * Additional case: 405 * gcc before version 7 called allocate_dynamic_stack_space() from 406 * expand_stack_vars() for runtime alignment of constant-sized stack 407 * variables. That caused cfun->calls_alloca to be set for functions 408 * that in fact don't use alloca(). 409 * For more info see gcc commit 7072df0aae0c59ae437e. 410 * Let's leave such functions instrumented as well. 411 */ 412 if (cfun->calls_alloca) { 413 if (verbose) 414 fprintf(stderr, "stackleak: instrument %s(): calls_alloca\n", fn); 415 return 0; 416 } 417 418 /* Leave stack tracking in functions with large stack frame */ 419 if (large_stack_frame()) { 420 if (verbose) 421 fprintf(stderr, "stackleak: instrument %s()\n", fn); 422 return 0; 423 } 424 425 if (lookup_attribute_spec(get_identifier("no_caller_saved_registers"))) 426 removed = remove_stack_tracking_gasm(); 427 428 if (!removed) 429 remove_stack_tracking_gcall(); 430 431 return 0; 432 } 433 434 static bool stackleak_gate(void) 435 { 436 tree section; 437 438 section = lookup_attribute("section", 439 DECL_ATTRIBUTES(current_function_decl)); 440 if (section && TREE_VALUE(section)) { 441 section = TREE_VALUE(TREE_VALUE(section)); 442 443 if (!strncmp(TREE_STRING_POINTER(section), ".init.text", 10)) 444 return false; 445 if (!strncmp(TREE_STRING_POINTER(section), ".devinit.text", 13)) 446 return false; 447 if (!strncmp(TREE_STRING_POINTER(section), ".cpuinit.text", 13)) 448 return false; 449 if (!strncmp(TREE_STRING_POINTER(section), ".meminit.text", 13)) 450 return false; 451 } 452 453 return track_frame_size >= 0; 454 } 455 456 /* Build the function declaration for stackleak_track_stack() */ 457 static void stackleak_start_unit(void *gcc_data __unused, 458 void *user_data __unused) 459 { 460 tree fntype; 461 462 /* void stackleak_track_stack(void) */ 463 fntype = build_function_type_list(void_type_node, NULL_TREE); 464 track_function_decl = build_fn_decl(track_function, fntype); 465 DECL_ASSEMBLER_NAME(track_function_decl); /* for LTO */ 466 TREE_PUBLIC(track_function_decl) = 1; 467 TREE_USED(track_function_decl) = 1; 468 DECL_EXTERNAL(track_function_decl) = 1; 469 DECL_ARTIFICIAL(track_function_decl) = 1; 470 DECL_PRESERVE_P(track_function_decl) = 1; 471 } 472 473 /* 474 * Pass gate function is a predicate function that gets executed before the 475 * corresponding pass. If the return value is 'true' the pass gets executed, 476 * otherwise, it is skipped. 477 */ 478 static bool stackleak_instrument_gate(void) 479 { 480 return stackleak_gate(); 481 } 482 483 #define PASS_NAME stackleak_instrument 484 #define PROPERTIES_REQUIRED PROP_gimple_leh | PROP_cfg 485 #define TODO_FLAGS_START TODO_verify_ssa | TODO_verify_flow | TODO_verify_stmts 486 #define TODO_FLAGS_FINISH TODO_verify_ssa | TODO_verify_stmts | TODO_dump_func \ 487 | TODO_update_ssa | TODO_rebuild_cgraph_edges 488 #include "gcc-generate-gimple-pass.h" 489 490 static bool stackleak_cleanup_gate(void) 491 { 492 return stackleak_gate(); 493 } 494 495 #define PASS_NAME stackleak_cleanup 496 #define TODO_FLAGS_FINISH TODO_dump_func 497 #include "gcc-generate-rtl-pass.h" 498 499 /* 500 * Every gcc plugin exports a plugin_init() function that is called right 501 * after the plugin is loaded. This function is responsible for registering 502 * the plugin callbacks and doing other required initialization. 503 */ 504 __visible int plugin_init(struct plugin_name_args *plugin_info, 505 struct plugin_gcc_version *version) 506 { 507 const char * const plugin_name = plugin_info->base_name; 508 const int argc = plugin_info->argc; 509 const struct plugin_argument * const argv = plugin_info->argv; 510 int i = 0; 511 512 /* Extra GGC root tables describing our GTY-ed data */ 513 static const struct ggc_root_tab gt_ggc_r_gt_stackleak[] = { 514 { 515 .base = &track_function_decl, 516 .nelt = 1, 517 .stride = sizeof(track_function_decl), 518 .cb = >_ggc_mx_tree_node, 519 .pchw = >_pch_nx_tree_node 520 }, 521 LAST_GGC_ROOT_TAB 522 }; 523 524 /* 525 * The stackleak_instrument pass should be executed before the 526 * "optimized" pass, which is the control flow graph cleanup that is 527 * performed just before expanding gcc trees to the RTL. In former 528 * versions of the plugin this new pass was inserted before the 529 * "tree_profile" pass, which is currently called "profile". 530 */ 531 PASS_INFO(stackleak_instrument, "optimized", 1, 532 PASS_POS_INSERT_BEFORE); 533 534 /* 535 * The stackleak_cleanup pass should be executed before the "*free_cfg" 536 * pass. It's the moment when the stack frame size is already final, 537 * function prologues and epilogues are generated, and the 538 * machine-dependent code transformations are not done. 539 */ 540 PASS_INFO(stackleak_cleanup, "*free_cfg", 1, PASS_POS_INSERT_BEFORE); 541 542 if (!plugin_default_version_check(version, &gcc_version)) { 543 error(G_("incompatible gcc/plugin versions")); 544 return 1; 545 } 546 547 /* Parse the plugin arguments */ 548 for (i = 0; i < argc; i++) { 549 if (!strcmp(argv[i].key, "track-min-size")) { 550 if (!argv[i].value) { 551 error(G_("no value supplied for option '-fplugin-arg-%s-%s'"), 552 plugin_name, argv[i].key); 553 return 1; 554 } 555 556 track_frame_size = atoi(argv[i].value); 557 if (track_frame_size < 0) { 558 error(G_("invalid option argument '-fplugin-arg-%s-%s=%s'"), 559 plugin_name, argv[i].key, argv[i].value); 560 return 1; 561 } 562 } else if (!strcmp(argv[i].key, "arch")) { 563 if (!argv[i].value) { 564 error(G_("no value supplied for option '-fplugin-arg-%s-%s'"), 565 plugin_name, argv[i].key); 566 return 1; 567 } 568 569 if (!strcmp(argv[i].value, "x86")) 570 build_for_x86 = true; 571 } else if (!strcmp(argv[i].key, "disable")) { 572 disable = true; 573 } else if (!strcmp(argv[i].key, "verbose")) { 574 verbose = true; 575 } else { 576 error(G_("unknown option '-fplugin-arg-%s-%s'"), 577 plugin_name, argv[i].key); 578 return 1; 579 } 580 } 581 582 if (disable) { 583 if (verbose) 584 fprintf(stderr, "stackleak: disabled for this translation unit\n"); 585 return 0; 586 } 587 588 /* Give the information about the plugin */ 589 register_callback(plugin_name, PLUGIN_INFO, NULL, 590 &stackleak_plugin_info); 591 592 /* Register to be called before processing a translation unit */ 593 register_callback(plugin_name, PLUGIN_START_UNIT, 594 &stackleak_start_unit, NULL); 595 596 /* Register an extra GCC garbage collector (GGC) root table */ 597 register_callback(plugin_name, PLUGIN_REGISTER_GGC_ROOTS, NULL, 598 (void *)>_ggc_r_gt_stackleak); 599 600 /* 601 * Hook into the Pass Manager to register new gcc passes. 602 * 603 * The stack frame size info is available only at the last RTL pass, 604 * when it's too late to insert complex code like a function call. 605 * So we register two gcc passes to instrument every function at first 606 * and remove the unneeded instrumentation later. 607 */ 608 register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, 609 &stackleak_instrument_pass_info); 610 register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, 611 &stackleak_cleanup_pass_info); 612 613 return 0; 614 } 615