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 62 static void register_attributes(void *event_data, void *data) 63 { 64 user_attr.name = "user"; 65 user_attr.handler = handle_user_attribute; 66 #if BUILDING_GCC_VERSION >= 4007 67 user_attr.affects_type_identity = true; 68 #endif 69 70 register_attribute(&user_attr); 71 } 72 73 static tree get_field_type(tree field) 74 { 75 return strip_array_types(TREE_TYPE(field)); 76 } 77 78 static bool is_userspace_type(tree type) 79 { 80 tree field; 81 82 for (field = TYPE_FIELDS(type); field; field = TREE_CHAIN(field)) { 83 tree fieldtype = get_field_type(field); 84 enum tree_code code = TREE_CODE(fieldtype); 85 86 if (code == RECORD_TYPE || code == UNION_TYPE) 87 if (is_userspace_type(fieldtype)) 88 return true; 89 90 if (lookup_attribute("user", DECL_ATTRIBUTES(field))) 91 return true; 92 } 93 return false; 94 } 95 96 static void finish_type(void *event_data, void *data) 97 { 98 tree type = (tree)event_data; 99 100 if (type == NULL_TREE || type == error_mark_node) 101 return; 102 103 #if BUILDING_GCC_VERSION >= 5000 104 if (TREE_CODE(type) == ENUMERAL_TYPE) 105 return; 106 #endif 107 108 if (TYPE_USERSPACE(type)) 109 return; 110 111 if (is_userspace_type(type)) 112 TYPE_USERSPACE(type) = 1; 113 } 114 115 static void initialize(tree var) 116 { 117 basic_block bb; 118 gimple_stmt_iterator gsi; 119 tree initializer; 120 gimple init_stmt; 121 122 /* this is the original entry bb before the forced split */ 123 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); 124 125 /* first check if variable is already initialized, warn otherwise */ 126 for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) { 127 gimple stmt = gsi_stmt(gsi); 128 tree rhs1; 129 130 /* we're looking for an assignment of a single rhs... */ 131 if (!gimple_assign_single_p(stmt)) 132 continue; 133 rhs1 = gimple_assign_rhs1(stmt); 134 #if BUILDING_GCC_VERSION >= 4007 135 /* ... of a non-clobbering expression... */ 136 if (TREE_CLOBBER_P(rhs1)) 137 continue; 138 #endif 139 /* ... to our variable... */ 140 if (gimple_get_lhs(stmt) != var) 141 continue; 142 /* if it's an initializer then we're good */ 143 if (TREE_CODE(rhs1) == CONSTRUCTOR) 144 return; 145 } 146 147 /* these aren't the 0days you're looking for */ 148 if (verbose) 149 inform(DECL_SOURCE_LOCATION(var), 150 "%s variable will be forcibly initialized", 151 (byref_all && TREE_ADDRESSABLE(var)) ? "byref" 152 : "userspace"); 153 154 /* build the initializer expression */ 155 initializer = build_constructor(TREE_TYPE(var), NULL); 156 157 /* build the initializer stmt */ 158 init_stmt = gimple_build_assign(var, initializer); 159 gsi = gsi_after_labels(single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 160 gsi_insert_before(&gsi, init_stmt, GSI_NEW_STMT); 161 update_stmt(init_stmt); 162 } 163 164 static unsigned int structleak_execute(void) 165 { 166 basic_block bb; 167 unsigned int ret = 0; 168 tree var; 169 unsigned int i; 170 171 /* split the first bb where we can put the forced initializers */ 172 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 173 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); 174 if (!single_pred_p(bb)) { 175 split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 176 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 177 } 178 179 /* enumerate all local variables and forcibly initialize our targets */ 180 FOR_EACH_LOCAL_DECL(cfun, i, var) { 181 tree type = TREE_TYPE(var); 182 183 gcc_assert(DECL_P(var)); 184 if (!auto_var_in_fn_p(var, current_function_decl)) 185 continue; 186 187 /* only care about structure types */ 188 if (TREE_CODE(type) != RECORD_TYPE && TREE_CODE(type) != UNION_TYPE) 189 continue; 190 191 /* if the type is of interest, examine the variable */ 192 if (TYPE_USERSPACE(type) || 193 (byref_all && TREE_ADDRESSABLE(var))) 194 initialize(var); 195 } 196 197 return ret; 198 } 199 200 #define PASS_NAME structleak 201 #define NO_GATE 202 #define PROPERTIES_REQUIRED PROP_cfg 203 #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 204 #include "gcc-generate-gimple-pass.h" 205 206 __visible int plugin_init(struct plugin_name_args *plugin_info, struct plugin_gcc_version *version) 207 { 208 int i; 209 const char * const plugin_name = plugin_info->base_name; 210 const int argc = plugin_info->argc; 211 const struct plugin_argument * const argv = plugin_info->argv; 212 bool enable = true; 213 214 PASS_INFO(structleak, "early_optimizations", 1, PASS_POS_INSERT_BEFORE); 215 216 if (!plugin_default_version_check(version, &gcc_version)) { 217 error(G_("incompatible gcc/plugin versions")); 218 return 1; 219 } 220 221 if (strncmp(lang_hooks.name, "GNU C", 5) && !strncmp(lang_hooks.name, "GNU C+", 6)) { 222 inform(UNKNOWN_LOCATION, G_("%s supports C only, not %s"), plugin_name, lang_hooks.name); 223 enable = false; 224 } 225 226 for (i = 0; i < argc; ++i) { 227 if (!strcmp(argv[i].key, "disable")) { 228 enable = false; 229 continue; 230 } 231 if (!strcmp(argv[i].key, "verbose")) { 232 verbose = true; 233 continue; 234 } 235 if (!strcmp(argv[i].key, "byref-all")) { 236 byref_all = true; 237 continue; 238 } 239 error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key); 240 } 241 242 register_callback(plugin_name, PLUGIN_INFO, NULL, &structleak_plugin_info); 243 if (enable) { 244 register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, &structleak_pass_info); 245 register_callback(plugin_name, PLUGIN_FINISH_TYPE, finish_type, NULL); 246 } 247 register_callback(plugin_name, PLUGIN_ATTRIBUTES, register_attributes, NULL); 248 249 return 0; 250 } 251