1 /* 2 * Copyright 2013-2017 by PaX Team <pageexec@freemail.hu> 3 * Licensed under the GPL v2 4 * 5 * Note: the choice of the license means that the compilation process is 6 * NOT 'eligible' as defined by gcc's library exception to the GPL v3, 7 * but for the kernel it doesn't matter since it doesn't link against 8 * any of the gcc libraries 9 * 10 * gcc plugin to forcibly initialize certain local variables that could 11 * otherwise leak kernel stack to userland if they aren't properly initialized 12 * by later code 13 * 14 * Homepage: http://pax.grsecurity.net/ 15 * 16 * Options: 17 * -fplugin-arg-structleak_plugin-disable 18 * -fplugin-arg-structleak_plugin-verbose 19 * -fplugin-arg-structleak_plugin-byref-all 20 * 21 * Usage: 22 * $ # for 4.5/4.6/C based 4.7 23 * $ gcc -I`gcc -print-file-name=plugin`/include -I`gcc -print-file-name=plugin`/include/c-family -fPIC -shared -O2 -o structleak_plugin.so structleak_plugin.c 24 * $ # for C++ based 4.7/4.8+ 25 * $ g++ -I`g++ -print-file-name=plugin`/include -I`g++ -print-file-name=plugin`/include/c-family -fPIC -shared -O2 -o structleak_plugin.so structleak_plugin.c 26 * $ gcc -fplugin=./structleak_plugin.so test.c -O2 27 * 28 * TODO: eliminate redundant initializers 29 * increase type coverage 30 */ 31 32 #include "gcc-common.h" 33 34 /* unused C type flag in all versions 4.5-6 */ 35 #define TYPE_USERSPACE(TYPE) TYPE_LANG_FLAG_5(TYPE) 36 37 __visible int plugin_is_GPL_compatible; 38 39 static struct plugin_info structleak_plugin_info = { 40 .version = "201607271510vanilla", 41 .help = "disable\tdo not activate plugin\n" 42 "verbose\tprint all initialized variables\n", 43 }; 44 45 static bool verbose; 46 static bool byref_all; 47 48 static tree handle_user_attribute(tree *node, tree name, tree args, int flags, bool *no_add_attrs) 49 { 50 *no_add_attrs = true; 51 52 /* check for types? for now accept everything linux has to offer */ 53 if (TREE_CODE(*node) != FIELD_DECL) 54 return NULL_TREE; 55 56 *no_add_attrs = false; 57 return NULL_TREE; 58 } 59 60 static struct attribute_spec user_attr = { 61 .name = "user", 62 .min_length = 0, 63 .max_length = 0, 64 .decl_required = false, 65 .type_required = false, 66 .function_type_required = false, 67 .handler = handle_user_attribute, 68 #if BUILDING_GCC_VERSION >= 4007 69 .affects_type_identity = true 70 #endif 71 }; 72 73 static void register_attributes(void *event_data, void *data) 74 { 75 register_attribute(&user_attr); 76 } 77 78 static tree get_field_type(tree field) 79 { 80 return strip_array_types(TREE_TYPE(field)); 81 } 82 83 static bool is_userspace_type(tree type) 84 { 85 tree field; 86 87 for (field = TYPE_FIELDS(type); field; field = TREE_CHAIN(field)) { 88 tree fieldtype = get_field_type(field); 89 enum tree_code code = TREE_CODE(fieldtype); 90 91 if (code == RECORD_TYPE || code == UNION_TYPE) 92 if (is_userspace_type(fieldtype)) 93 return true; 94 95 if (lookup_attribute("user", DECL_ATTRIBUTES(field))) 96 return true; 97 } 98 return false; 99 } 100 101 static void finish_type(void *event_data, void *data) 102 { 103 tree type = (tree)event_data; 104 105 if (type == NULL_TREE || type == error_mark_node) 106 return; 107 108 #if BUILDING_GCC_VERSION >= 5000 109 if (TREE_CODE(type) == ENUMERAL_TYPE) 110 return; 111 #endif 112 113 if (TYPE_USERSPACE(type)) 114 return; 115 116 if (is_userspace_type(type)) 117 TYPE_USERSPACE(type) = 1; 118 } 119 120 static void initialize(tree var) 121 { 122 basic_block bb; 123 gimple_stmt_iterator gsi; 124 tree initializer; 125 gimple init_stmt; 126 127 /* this is the original entry bb before the forced split */ 128 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); 129 130 /* first check if variable is already initialized, warn otherwise */ 131 for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) { 132 gimple stmt = gsi_stmt(gsi); 133 tree rhs1; 134 135 /* we're looking for an assignment of a single rhs... */ 136 if (!gimple_assign_single_p(stmt)) 137 continue; 138 rhs1 = gimple_assign_rhs1(stmt); 139 #if BUILDING_GCC_VERSION >= 4007 140 /* ... of a non-clobbering expression... */ 141 if (TREE_CLOBBER_P(rhs1)) 142 continue; 143 #endif 144 /* ... to our variable... */ 145 if (gimple_get_lhs(stmt) != var) 146 continue; 147 /* if it's an initializer then we're good */ 148 if (TREE_CODE(rhs1) == CONSTRUCTOR) 149 return; 150 } 151 152 /* these aren't the 0days you're looking for */ 153 if (verbose) 154 inform(DECL_SOURCE_LOCATION(var), 155 "%s variable will be forcibly initialized", 156 (byref_all && TREE_ADDRESSABLE(var)) ? "byref" 157 : "userspace"); 158 159 /* build the initializer expression */ 160 initializer = build_constructor(TREE_TYPE(var), NULL); 161 162 /* build the initializer stmt */ 163 init_stmt = gimple_build_assign(var, initializer); 164 gsi = gsi_after_labels(single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 165 gsi_insert_before(&gsi, init_stmt, GSI_NEW_STMT); 166 update_stmt(init_stmt); 167 } 168 169 static unsigned int structleak_execute(void) 170 { 171 basic_block bb; 172 unsigned int ret = 0; 173 tree var; 174 unsigned int i; 175 176 /* split the first bb where we can put the forced initializers */ 177 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 178 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); 179 if (!single_pred_p(bb)) { 180 split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 181 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 182 } 183 184 /* enumerate all local variables and forcibly initialize our targets */ 185 FOR_EACH_LOCAL_DECL(cfun, i, var) { 186 tree type = TREE_TYPE(var); 187 188 gcc_assert(DECL_P(var)); 189 if (!auto_var_in_fn_p(var, current_function_decl)) 190 continue; 191 192 /* only care about structure types */ 193 if (TREE_CODE(type) != RECORD_TYPE && TREE_CODE(type) != UNION_TYPE) 194 continue; 195 196 /* if the type is of interest, examine the variable */ 197 if (TYPE_USERSPACE(type) || 198 (byref_all && TREE_ADDRESSABLE(var))) 199 initialize(var); 200 } 201 202 return ret; 203 } 204 205 #define PASS_NAME structleak 206 #define NO_GATE 207 #define PROPERTIES_REQUIRED PROP_cfg 208 #define TODO_FLAGS_FINISH TODO_verify_il | TODO_verify_ssa | TODO_verify_stmts | TODO_dump_func | TODO_remove_unused_locals | TODO_update_ssa | TODO_ggc_collect | TODO_verify_flow 209 #include "gcc-generate-gimple-pass.h" 210 211 __visible int plugin_init(struct plugin_name_args *plugin_info, struct plugin_gcc_version *version) 212 { 213 int i; 214 const char * const plugin_name = plugin_info->base_name; 215 const int argc = plugin_info->argc; 216 const struct plugin_argument * const argv = plugin_info->argv; 217 bool enable = true; 218 219 PASS_INFO(structleak, "early_optimizations", 1, PASS_POS_INSERT_BEFORE); 220 221 if (!plugin_default_version_check(version, &gcc_version)) { 222 error(G_("incompatible gcc/plugin versions")); 223 return 1; 224 } 225 226 if (strncmp(lang_hooks.name, "GNU C", 5) && !strncmp(lang_hooks.name, "GNU C+", 6)) { 227 inform(UNKNOWN_LOCATION, G_("%s supports C only, not %s"), plugin_name, lang_hooks.name); 228 enable = false; 229 } 230 231 for (i = 0; i < argc; ++i) { 232 if (!strcmp(argv[i].key, "disable")) { 233 enable = false; 234 continue; 235 } 236 if (!strcmp(argv[i].key, "verbose")) { 237 verbose = true; 238 continue; 239 } 240 if (!strcmp(argv[i].key, "byref-all")) { 241 byref_all = true; 242 continue; 243 } 244 error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key); 245 } 246 247 register_callback(plugin_name, PLUGIN_INFO, NULL, &structleak_plugin_info); 248 if (enable) { 249 register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, &structleak_pass_info); 250 register_callback(plugin_name, PLUGIN_FINISH_TYPE, finish_type, NULL); 251 } 252 register_callback(plugin_name, PLUGIN_ATTRIBUTES, register_attributes, NULL); 253 254 return 0; 255 } 256