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 = >_ggc_mx_tree_node, 349 .pchw = >_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 *)>_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 } 429