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() and print_simple_rtl();
  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 const char track_function[] = "stackleak_track_stack";
  36
  37 /*
  38  * Mark these global variables (roots) for gcc garbage collector since
  39  * they point to the garbage-collected memory.
  40  */
  41 static GTY(()) tree track_function_decl;
  42
  43 static struct plugin_info stackleak_plugin_info = {
  44         .version = "201707101337",
  45         .help = "track-min-size=nn\ttrack stack for functions with a stack frame size >= nn bytes\n"
  46                 "disable\t\tdo not activate the plugin\n"
  47 };
  48
  49 static void stackleak_add_track_stack(gimple_stmt_iterator *gsi, bool after)
  50 {
  51         gimple stmt;
  52         gcall *stackleak_track_stack;
  53         cgraph_node_ptr node;
  54         basic_block bb;
  55
  56         /* Insert call to void stackleak_track_stack(void) */
  57         stmt = gimple_build_call(track_function_decl, 0);
  58         stackleak_track_stack = as_a_gcall(stmt);
  59         if (after) {
  60                 gsi_insert_after(gsi, stackleak_track_stack,
  61                                                 GSI_CONTINUE_LINKING);
  62         } else {
  63                 gsi_insert_before(gsi, stackleak_track_stack, GSI_SAME_STMT);
  64         }
  65
  66         /* Update the cgraph */
  67         bb = gimple_bb(stackleak_track_stack);
  68         node = cgraph_get_create_node(track_function_decl);
  69         gcc_assert(node);
  70         cgraph_create_edge(cgraph_get_node(current_function_decl), node,
  71                         stackleak_track_stack, bb->count,
  72                         compute_call_stmt_bb_frequency(current_function_decl, bb));
  73 }
  74
  75 static bool is_alloca(gimple stmt)
  76 {
  77         if (gimple_call_builtin_p(stmt, BUILT_IN_ALLOCA))
  78                 return true;
  79
  80 #if BUILDING_GCC_VERSION >= 4007
  81         if (gimple_call_builtin_p(stmt, BUILT_IN_ALLOCA_WITH_ALIGN))
  82                 return true;
  83 #endif
  84
  85         return false;
  86 }
  87
  88 /*
  89  * Work with the GIMPLE representation of the code. Insert the
  90  * stackleak_track_stack() call after alloca() and into the beginning
  91  * of the function if it is not instrumented.
  92  */
  93 static unsigned int stackleak_instrument_execute(void)
  94 {
  95         basic_block bb, entry_bb;
  96         bool prologue_instrumented = false, is_leaf = true;
  97         gimple_stmt_iterator gsi;
  98
  99         /*
 100          * ENTRY_BLOCK_PTR is a basic block which represents possible entry
 101          * point of a function. This block does not contain any code and
 102          * has a CFG edge to its successor.
 103          */
 104         gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
 105         entry_bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
 106
 107         /*
 108          * Loop through the GIMPLE statements in each of cfun basic blocks.
 109          * cfun is a global variable which represents the function that is
 110          * currently processed.
 111          */
 112         FOR_EACH_BB_FN(bb, cfun) {
 113                 for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) {
 114                         gimple stmt;
 115
 116                         stmt = gsi_stmt(gsi);
 117
 118                         /* Leaf function is a function which makes no calls */
 119                         if (is_gimple_call(stmt))
 120                                 is_leaf = false;
 121
 122                         if (!is_alloca(stmt))
 123                                 continue;
 124
 125                         /* Insert stackleak_track_stack() call after alloca() */
 126                         stackleak_add_track_stack(&gsi, true);
 127                         if (bb == entry_bb)
 128                                 prologue_instrumented = true;
 129                 }
 130         }
 131
 132         if (prologue_instrumented)
 133                 return 0;
 134
 135         /*
 136          * Special cases to skip the instrumentation.
 137          *
 138          * Taking the address of static inline functions materializes them,
 139          * but we mustn't instrument some of them as the resulting stack
 140          * alignment required by the function call ABI will break other
 141          * assumptions regarding the expected (but not otherwise enforced)
 142          * register clobbering ABI.
 143          *
 144          * Case in point: native_save_fl on amd64 when optimized for size
 145          * clobbers rdx if it were instrumented here.
 146          *
 147          * TODO: any more special cases?
 148          */
 149         if (is_leaf &&
 150             !TREE_PUBLIC(current_function_decl) &&
 151             DECL_DECLARED_INLINE_P(current_function_decl)) {
 152                 return 0;
 153         }
 154
 155         if (is_leaf &&
 156             !strncmp(IDENTIFIER_POINTER(DECL_NAME(current_function_decl)),
 157                      "_paravirt_", 10)) {
 158                 return 0;
 159         }
 160
 161         /* Insert stackleak_track_stack() call at the function beginning */
 162         bb = entry_bb;
 163         if (!single_pred_p(bb)) {
 164                 /* gcc_assert(bb_loop_depth(bb) ||
 165                                 (bb->flags & BB_IRREDUCIBLE_LOOP)); */
 166                 split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
 167                 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
 168                 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
 169         }
 170         gsi = gsi_after_labels(bb);
 171         stackleak_add_track_stack(&gsi, false);
 172
 173         return 0;
 174 }
 175
 176 static bool large_stack_frame(void)
 177 {
 178 #if BUILDING_GCC_VERSION >= 8000
 179         return maybe_ge(get_frame_size(), track_frame_size);
 180 #else
 181         return (get_frame_size() >= track_frame_size);
 182 #endif
 183 }
 184
 185 /*
 186  * Work with the RTL representation of the code.
 187  * Remove the unneeded stackleak_track_stack() calls from the functions
 188  * which don't call alloca() and don't have a large enough stack frame size.
 189  */
 190 static unsigned int stackleak_cleanup_execute(void)
 191 {
 192         rtx_insn *insn, *next;
 193
 194         if (cfun->calls_alloca)
 195                 return 0;
 196
 197         if (large_stack_frame())
 198                 return 0;
 199
 200         /*
 201          * Find stackleak_track_stack() calls. Loop through the chain of insns,
 202          * which is an RTL representation of the code for a function.
 203          *
 204          * The example of a matching insn:
 205          *  (call_insn 8 4 10 2 (call (mem (symbol_ref ("stackleak_track_stack")
 206          *  [flags 0x41] <function_decl 0x7f7cd3302a80 stackleak_track_stack>)
 207          *  [0 stackleak_track_stack S1 A8]) (0)) 675 {*call} (expr_list
 208          *  (symbol_ref ("stackleak_track_stack") [flags 0x41] <function_decl
 209          *  0x7f7cd3302a80 stackleak_track_stack>) (expr_list (0) (nil))) (nil))
 210          */
 211         for (insn = get_insns(); insn; insn = next) {
 212                 rtx body;
 213
 214                 next = NEXT_INSN(insn);
 215
 216                 /* Check the expression code of the insn */
 217                 if (!CALL_P(insn))
 218                         continue;
 219
 220                 /*
 221                  * Check the expression code of the insn body, which is an RTL
 222                  * Expression (RTX) describing the side effect performed by
 223                  * that insn.
 224                  */
 225                 body = PATTERN(insn);
 226
 227                 if (GET_CODE(body) == PARALLEL)
 228                         body = XVECEXP(body, 0, 0);
 229
 230                 if (GET_CODE(body) != CALL)
 231                         continue;
 232
 233                 /*
 234                  * Check the first operand of the call expression. It should
 235                  * be a mem RTX describing the needed subroutine with a
 236                  * symbol_ref RTX.
 237                  */
 238                 body = XEXP(body, 0);
 239                 if (GET_CODE(body) != MEM)
 240                         continue;
 241
 242                 body = XEXP(body, 0);
 243                 if (GET_CODE(body) != SYMBOL_REF)
 244                         continue;
 245
 246                 if (SYMBOL_REF_DECL(body) != track_function_decl)
 247                         continue;
 248
 249                 /* Delete the stackleak_track_stack() call */
 250                 delete_insn_and_edges(insn);
 251 #if BUILDING_GCC_VERSION >= 4007 && BUILDING_GCC_VERSION < 8000
 252                 if (GET_CODE(next) == NOTE &&
 253                     NOTE_KIND(next) == NOTE_INSN_CALL_ARG_LOCATION) {
 254                         insn = next;
 255                         next = NEXT_INSN(insn);
 256                         delete_insn_and_edges(insn);
 257                 }
 258 #endif
 259         }
 260
 261         return 0;
 262 }
 263
 264 static bool stackleak_gate(void)
 265 {
 266         tree section;
 267
 268         section = lookup_attribute("section",
 269                                    DECL_ATTRIBUTES(current_function_decl));
 270         if (section && TREE_VALUE(section)) {
 271                 section = TREE_VALUE(TREE_VALUE(section));
 272
 273                 if (!strncmp(TREE_STRING_POINTER(section), ".init.text", 10))
 274                         return false;
 275                 if (!strncmp(TREE_STRING_POINTER(section), ".devinit.text", 13))
 276                         return false;
 277                 if (!strncmp(TREE_STRING_POINTER(section), ".cpuinit.text", 13))
 278                         return false;
 279                 if (!strncmp(TREE_STRING_POINTER(section), ".meminit.text", 13))
 280                         return false;
 281         }
 282
 283         return track_frame_size >= 0;
 284 }
 285
 286 /* Build the function declaration for stackleak_track_stack() */
 287 static void stackleak_start_unit(void *gcc_data __unused,
 288                                  void *user_data __unused)
 289 {
 290         tree fntype;
 291
 292         /* void stackleak_track_stack(void) */
 293         fntype = build_function_type_list(void_type_node, NULL_TREE);
 294         track_function_decl = build_fn_decl(track_function, fntype);
 295         DECL_ASSEMBLER_NAME(track_function_decl); /* for LTO */
 296         TREE_PUBLIC(track_function_decl) = 1;
 297         TREE_USED(track_function_decl) = 1;
 298         DECL_EXTERNAL(track_function_decl) = 1;
 299         DECL_ARTIFICIAL(track_function_decl) = 1;
 300         DECL_PRESERVE_P(track_function_decl) = 1;
 301 }
 302
 303 /*
 304  * Pass gate function is a predicate function that gets executed before the
 305  * corresponding pass. If the return value is 'true' the pass gets executed,
 306  * otherwise, it is skipped.
 307  */
 308 static bool stackleak_instrument_gate(void)
 309 {
 310         return stackleak_gate();
 311 }
 312
 313 #define PASS_NAME stackleak_instrument
 314 #define PROPERTIES_REQUIRED PROP_gimple_leh | PROP_cfg
 315 #define TODO_FLAGS_START TODO_verify_ssa | TODO_verify_flow | TODO_verify_stmts
 316 #define TODO_FLAGS_FINISH TODO_verify_ssa | TODO_verify_stmts | TODO_dump_func \
 317                         | TODO_update_ssa | TODO_rebuild_cgraph_edges
 318 #include "gcc-generate-gimple-pass.h"
 319
 320 static bool stackleak_cleanup_gate(void)
 321 {
 322         return stackleak_gate();
 323 }
 324
 325 #define PASS_NAME stackleak_cleanup
 326 #define TODO_FLAGS_FINISH TODO_dump_func
 327 #include "gcc-generate-rtl-pass.h"
 328
 329 /*
 330  * Every gcc plugin exports a plugin_init() function that is called right
 331  * after the plugin is loaded. This function is responsible for registering
 332  * the plugin callbacks and doing other required initialization.
 333  */
 334 __visible int plugin_init(struct plugin_name_args *plugin_info,
 335                           struct plugin_gcc_version *version)
 336 {
 337         const char * const plugin_name = plugin_info->base_name;
 338         const int argc = plugin_info->argc;
 339         const struct plugin_argument * const argv = plugin_info->argv;
 340         int i = 0;
 341
 342         /* Extra GGC root tables describing our GTY-ed data */
 343         static const struct ggc_root_tab gt_ggc_r_gt_stackleak[] = {
 344                 {
 345                         .base = &track_function_decl,
 346                         .nelt = 1,
 347                         .stride = sizeof(track_function_decl),
 348                         .cb = &gt_ggc_mx_tree_node,
 349                         .pchw = &gt_pch_nx_tree_node
 350                 },
 351                 LAST_GGC_ROOT_TAB
 352         };
 353
 354         /*
 355          * The stackleak_instrument pass should be executed before the
 356          * "optimized" pass, which is the control flow graph cleanup that is
 357          * performed just before expanding gcc trees to the RTL. In former
 358          * versions of the plugin this new pass was inserted before the
 359          * "tree_profile" pass, which is currently called "profile".
 360          */
 361         PASS_INFO(stackleak_instrument, "optimized", 1,
 362                                                 PASS_POS_INSERT_BEFORE);
 363
 364         /*
 365          * The stackleak_cleanup pass should be executed before the "*free_cfg"
 366          * pass. It's the moment when the stack frame size is already final,
 367          * function prologues and epilogues are generated, and the
 368          * machine-dependent code transformations are not done.
 369          */
 370         PASS_INFO(stackleak_cleanup, "*free_cfg", 1, PASS_POS_INSERT_BEFORE);
 371
 372         if (!plugin_default_version_check(version, &gcc_version)) {
 373                 error(G_("incompatible gcc/plugin versions"));
 374                 return 1;
 375         }
 376
 377         /* Parse the plugin arguments */
 378         for (i = 0; i < argc; i++) {
 379                 if (!strcmp(argv[i].key, "disable"))
 380                         return 0;
 381
 382                 if (!strcmp(argv[i].key, "track-min-size")) {
 383                         if (!argv[i].value) {
 384                                 error(G_("no value supplied for option '-fplugin-arg-%s-%s'"),
 385                                         plugin_name, argv[i].key);
 386                                 return 1;
 387                         }
 388
 389                         track_frame_size = atoi(argv[i].value);
 390                         if (track_frame_size < 0) {
 391                                 error(G_("invalid option argument '-fplugin-arg-%s-%s=%s'"),
 392                                         plugin_name, argv[i].key, argv[i].value);
 393                                 return 1;
 394                         }
 395                 } else {
 396                         error(G_("unknown option '-fplugin-arg-%s-%s'"),
 397                                         plugin_name, argv[i].key);
 398                         return 1;
 399                 }
 400         }
 401
 402         /* Give the information about the plugin */
 403         register_callback(plugin_name, PLUGIN_INFO, NULL,
 404                                                 &stackleak_plugin_info);
 405
 406         /* Register to be called before processing a translation unit */
 407         register_callback(plugin_name, PLUGIN_START_UNIT,
 408                                         &stackleak_start_unit, NULL);
 409
 410         /* Register an extra GCC garbage collector (GGC) root table */
 411         register_callback(plugin_name, PLUGIN_REGISTER_GGC_ROOTS, NULL,
 412                                         (void *)&gt_ggc_r_gt_stackleak);
 413
 414         /*
 415          * Hook into the Pass Manager to register new gcc passes.
 416          *
 417          * The stack frame size info is available only at the last RTL pass,
 418          * when it's too late to insert complex code like a function call.
 419          * So we register two gcc passes to instrument every function at first
 420          * and remove the unneeded instrumentation later.
 421          */
 422         register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL,
 423                                         &stackleak_instrument_pass_info);
 424         register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL,
 425                                         &stackleak_cleanup_pass_info);
 426
 427         return 0;
 428 }