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: https://pax.grsecurity.net/ 15 * 16 * Options: 17 * -fplugin-arg-structleak_plugin-disable 18 * -fplugin-arg-structleak_plugin-verbose 19 * -fplugin-arg-structleak_plugin-byref 20 * -fplugin-arg-structleak_plugin-byref-all 21 * 22 * Usage: 23 * $ # for 4.5/4.6/C based 4.7 24 * $ 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 25 * $ # for C++ based 4.7/4.8+ 26 * $ 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 27 * $ gcc -fplugin=./structleak_plugin.so test.c -O2 28 * 29 * TODO: eliminate redundant initializers 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 = "20190125vanilla", 41 .help = "disable\tdo not activate plugin\n" 42 "byref\tinit structs passed by reference\n" 43 "byref-all\tinit anything passed by reference\n" 44 "verbose\tprint all initialized variables\n", 45 }; 46 47 #define BYREF_STRUCT 1 48 #define BYREF_ALL 2 49 50 static bool verbose; 51 static int byref; 52 53 static tree handle_user_attribute(tree *node, tree name, tree args, int flags, bool *no_add_attrs) 54 { 55 *no_add_attrs = true; 56 57 /* check for types? for now accept everything linux has to offer */ 58 if (TREE_CODE(*node) != FIELD_DECL) 59 return NULL_TREE; 60 61 *no_add_attrs = false; 62 return NULL_TREE; 63 } 64 65 static struct attribute_spec user_attr = { }; 66 67 static void register_attributes(void *event_data, void *data) 68 { 69 user_attr.name = "user"; 70 user_attr.handler = handle_user_attribute; 71 user_attr.affects_type_identity = true; 72 73 register_attribute(&user_attr); 74 } 75 76 static tree get_field_type(tree field) 77 { 78 return strip_array_types(TREE_TYPE(field)); 79 } 80 81 static bool is_userspace_type(tree type) 82 { 83 tree field; 84 85 for (field = TYPE_FIELDS(type); field; field = TREE_CHAIN(field)) { 86 tree fieldtype = get_field_type(field); 87 enum tree_code code = TREE_CODE(fieldtype); 88 89 if (code == RECORD_TYPE || code == UNION_TYPE) 90 if (is_userspace_type(fieldtype)) 91 return true; 92 93 if (lookup_attribute("user", DECL_ATTRIBUTES(field))) 94 return true; 95 } 96 return false; 97 } 98 99 static void finish_type(void *event_data, void *data) 100 { 101 tree type = (tree)event_data; 102 103 if (type == NULL_TREE || type == error_mark_node) 104 return; 105 106 #if BUILDING_GCC_VERSION >= 5000 107 if (TREE_CODE(type) == ENUMERAL_TYPE) 108 return; 109 #endif 110 111 if (TYPE_USERSPACE(type)) 112 return; 113 114 if (is_userspace_type(type)) 115 TYPE_USERSPACE(type) = 1; 116 } 117 118 static void initialize(tree var) 119 { 120 basic_block bb; 121 gimple_stmt_iterator gsi; 122 tree initializer; 123 gimple init_stmt; 124 tree type; 125 126 /* this is the original entry bb before the forced split */ 127 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); 128 129 /* first check if variable is already initialized, warn otherwise */ 130 for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) { 131 gimple stmt = gsi_stmt(gsi); 132 tree rhs1; 133 134 /* we're looking for an assignment of a single rhs... */ 135 if (!gimple_assign_single_p(stmt)) 136 continue; 137 rhs1 = gimple_assign_rhs1(stmt); 138 /* ... of a non-clobbering expression... */ 139 if (TREE_CLOBBER_P(rhs1)) 140 continue; 141 /* ... to our variable... */ 142 if (gimple_get_lhs(stmt) != var) 143 continue; 144 /* if it's an initializer then we're good */ 145 if (TREE_CODE(rhs1) == CONSTRUCTOR) 146 return; 147 } 148 149 /* these aren't the 0days you're looking for */ 150 if (verbose) 151 inform(DECL_SOURCE_LOCATION(var), 152 "%s variable will be forcibly initialized", 153 (byref && TREE_ADDRESSABLE(var)) ? "byref" 154 : "userspace"); 155 156 /* build the initializer expression */ 157 type = TREE_TYPE(var); 158 if (AGGREGATE_TYPE_P(type)) 159 initializer = build_constructor(type, NULL); 160 else 161 initializer = fold_convert(type, integer_zero_node); 162 163 /* build the initializer stmt */ 164 init_stmt = gimple_build_assign(var, initializer); 165 gsi = gsi_after_labels(single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 166 gsi_insert_before(&gsi, init_stmt, GSI_NEW_STMT); 167 update_stmt(init_stmt); 168 } 169 170 static unsigned int structleak_execute(void) 171 { 172 basic_block bb; 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 unless byref-all */ 193 if (byref != BYREF_ALL && 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 && TREE_ADDRESSABLE(var))) 199 initialize(var); 200 } 201 202 return 0; 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")) { 241 byref = BYREF_STRUCT; 242 continue; 243 } 244 if (!strcmp(argv[i].key, "byref-all")) { 245 byref = BYREF_ALL; 246 continue; 247 } 248 error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key); 249 } 250 251 register_callback(plugin_name, PLUGIN_INFO, NULL, &structleak_plugin_info); 252 if (enable) { 253 register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, &structleak_pass_info); 254 register_callback(plugin_name, PLUGIN_FINISH_TYPE, finish_type, NULL); 255 } 256 register_callback(plugin_name, PLUGIN_ATTRIBUTES, register_attributes, NULL); 257 258 return 0; 259 } 260