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 * 20 * Usage: 21 * $ # for 4.5/4.6/C based 4.7 22 * $ 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 23 * $ # for C++ based 4.7/4.8+ 24 * $ 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 25 * $ gcc -fplugin=./structleak_plugin.so test.c -O2 26 * 27 * TODO: eliminate redundant initializers 28 * increase type coverage 29 */ 30 31 #include "gcc-common.h" 32 33 /* unused C type flag in all versions 4.5-6 */ 34 #define TYPE_USERSPACE(TYPE) TYPE_LANG_FLAG_5(TYPE) 35 36 __visible int plugin_is_GPL_compatible; 37 38 static struct plugin_info structleak_plugin_info = { 39 .version = "201607271510vanilla", 40 .help = "disable\tdo not activate plugin\n" 41 "verbose\tprint all initialized variables\n", 42 }; 43 44 static bool verbose; 45 46 static tree handle_user_attribute(tree *node, tree name, tree args, int flags, bool *no_add_attrs) 47 { 48 *no_add_attrs = true; 49 50 /* check for types? for now accept everything linux has to offer */ 51 if (TREE_CODE(*node) != FIELD_DECL) 52 return NULL_TREE; 53 54 *no_add_attrs = false; 55 return NULL_TREE; 56 } 57 58 static struct attribute_spec user_attr = { 59 .name = "user", 60 .min_length = 0, 61 .max_length = 0, 62 .decl_required = false, 63 .type_required = false, 64 .function_type_required = false, 65 .handler = handle_user_attribute, 66 #if BUILDING_GCC_VERSION >= 4007 67 .affects_type_identity = true 68 #endif 69 }; 70 71 static void register_attributes(void *event_data, void *data) 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; 124 125 /* this is the original entry bb before the forced split */ 126 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); 127 128 /* first check if variable is already initialized, warn otherwise */ 129 for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) { 130 gimple stmt = gsi_stmt(gsi); 131 tree rhs1; 132 133 /* we're looking for an assignment of a single rhs... */ 134 if (!gimple_assign_single_p(stmt)) 135 continue; 136 rhs1 = gimple_assign_rhs1(stmt); 137 #if BUILDING_GCC_VERSION >= 4007 138 /* ... of a non-clobbering expression... */ 139 if (TREE_CLOBBER_P(rhs1)) 140 continue; 141 #endif 142 /* ... to our variable... */ 143 if (gimple_get_lhs(stmt) != var) 144 continue; 145 /* if it's an initializer then we're good */ 146 if (TREE_CODE(rhs1) == CONSTRUCTOR) 147 return; 148 } 149 150 /* these aren't the 0days you're looking for */ 151 if (verbose) 152 inform(DECL_SOURCE_LOCATION(var), 153 "userspace variable will be forcibly initialized"); 154 155 /* build the initializer expression */ 156 initializer = build_constructor(TREE_TYPE(var), NULL); 157 158 /* build the initializer stmt */ 159 init_stmt = gimple_build_assign(var, initializer); 160 gsi = gsi_after_labels(single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 161 gsi_insert_before(&gsi, init_stmt, GSI_NEW_STMT); 162 update_stmt(init_stmt); 163 } 164 165 static unsigned int structleak_execute(void) 166 { 167 basic_block bb; 168 unsigned int ret = 0; 169 tree var; 170 unsigned int i; 171 172 /* split the first bb where we can put the forced initializers */ 173 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 174 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); 175 if (!single_pred_p(bb)) { 176 split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 177 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 178 } 179 180 /* enumerate all local variables and forcibly initialize our targets */ 181 FOR_EACH_LOCAL_DECL(cfun, i, var) { 182 tree type = TREE_TYPE(var); 183 184 gcc_assert(DECL_P(var)); 185 if (!auto_var_in_fn_p(var, current_function_decl)) 186 continue; 187 188 /* only care about structure types */ 189 if (TREE_CODE(type) != RECORD_TYPE && TREE_CODE(type) != UNION_TYPE) 190 continue; 191 192 /* if the type is of interest, examine the variable */ 193 if (TYPE_USERSPACE(type)) 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 error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key); 236 } 237 238 register_callback(plugin_name, PLUGIN_INFO, NULL, &structleak_plugin_info); 239 if (enable) { 240 register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, &structleak_pass_info); 241 register_callback(plugin_name, PLUGIN_FINISH_TYPE, finish_type, NULL); 242 } 243 register_callback(plugin_name, PLUGIN_ATTRIBUTES, register_attributes, NULL); 244 245 return 0; 246 } 247