scripts/gcc-plugins/stackleak_plugin.c

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