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 handle_user_attribute(tree * node,tree name,tree args,int flags,bool * no_add_attrs)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 register_attributes(void * event_data,void * data)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 get_field_type(tree field)76 static tree get_field_type(tree field) 77 { 78 return strip_array_types(TREE_TYPE(field)); 79 } 80 is_userspace_type(tree type)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 finish_type(void * event_data,void * data)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 (TREE_CODE(type) == ENUMERAL_TYPE) 107 return; 108 109 if (TYPE_USERSPACE(type)) 110 return; 111 112 if (is_userspace_type(type)) 113 TYPE_USERSPACE(type) = 1; 114 } 115 initialize(tree var)116 static void initialize(tree var) 117 { 118 basic_block bb; 119 gimple_stmt_iterator gsi; 120 tree initializer; 121 gimple init_stmt; 122 tree type; 123 124 /* this is the original entry bb before the forced split */ 125 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); 126 127 /* first check if variable is already initialized, warn otherwise */ 128 for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) { 129 gimple stmt = gsi_stmt(gsi); 130 tree rhs1; 131 132 /* we're looking for an assignment of a single rhs... */ 133 if (!gimple_assign_single_p(stmt)) 134 continue; 135 rhs1 = gimple_assign_rhs1(stmt); 136 /* ... of a non-clobbering expression... */ 137 if (TREE_CLOBBER_P(rhs1)) 138 continue; 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 && TREE_ADDRESSABLE(var)) ? "byref" 152 : "userspace"); 153 154 /* build the initializer expression */ 155 type = TREE_TYPE(var); 156 if (AGGREGATE_TYPE_P(type)) 157 initializer = build_constructor(type, NULL); 158 else 159 initializer = fold_convert(type, integer_zero_node); 160 161 /* build the initializer stmt */ 162 init_stmt = gimple_build_assign(var, initializer); 163 gsi = gsi_after_labels(single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 164 gsi_insert_before(&gsi, init_stmt, GSI_NEW_STMT); 165 update_stmt(init_stmt); 166 } 167 structleak_execute(void)168 static unsigned int structleak_execute(void) 169 { 170 basic_block bb; 171 tree var; 172 unsigned int i; 173 174 /* split the first bb where we can put the forced initializers */ 175 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 176 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); 177 if (!single_pred_p(bb)) { 178 split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 179 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun))); 180 } 181 182 /* enumerate all local variables and forcibly initialize our targets */ 183 FOR_EACH_LOCAL_DECL(cfun, i, var) { 184 tree type = TREE_TYPE(var); 185 186 gcc_assert(DECL_P(var)); 187 if (!auto_var_in_fn_p(var, current_function_decl)) 188 continue; 189 190 /* only care about structure types unless byref-all */ 191 if (byref != BYREF_ALL && TREE_CODE(type) != RECORD_TYPE && TREE_CODE(type) != UNION_TYPE) 192 continue; 193 194 /* if the type is of interest, examine the variable */ 195 if (TYPE_USERSPACE(type) || 196 (byref && TREE_ADDRESSABLE(var))) 197 initialize(var); 198 } 199 200 return 0; 201 } 202 203 #define PASS_NAME structleak 204 #define NO_GATE 205 #define PROPERTIES_REQUIRED PROP_cfg 206 #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 207 #include "gcc-generate-gimple-pass.h" 208 plugin_init(struct plugin_name_args * plugin_info,struct plugin_gcc_version * version)209 __visible int plugin_init(struct plugin_name_args *plugin_info, struct plugin_gcc_version *version) 210 { 211 int i; 212 const char * const plugin_name = plugin_info->base_name; 213 const int argc = plugin_info->argc; 214 const struct plugin_argument * const argv = plugin_info->argv; 215 bool enable = true; 216 217 PASS_INFO(structleak, "early_optimizations", 1, PASS_POS_INSERT_BEFORE); 218 219 if (!plugin_default_version_check(version, &gcc_version)) { 220 error(G_("incompatible gcc/plugin versions")); 221 return 1; 222 } 223 224 if (strncmp(lang_hooks.name, "GNU C", 5) && !strncmp(lang_hooks.name, "GNU C+", 6)) { 225 inform(UNKNOWN_LOCATION, G_("%s supports C only, not %s"), plugin_name, lang_hooks.name); 226 enable = false; 227 } 228 229 for (i = 0; i < argc; ++i) { 230 if (!strcmp(argv[i].key, "disable")) { 231 enable = false; 232 continue; 233 } 234 if (!strcmp(argv[i].key, "verbose")) { 235 verbose = true; 236 continue; 237 } 238 if (!strcmp(argv[i].key, "byref")) { 239 byref = BYREF_STRUCT; 240 continue; 241 } 242 if (!strcmp(argv[i].key, "byref-all")) { 243 byref = BYREF_ALL; 244 continue; 245 } 246 error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key); 247 } 248 249 register_callback(plugin_name, PLUGIN_INFO, NULL, &structleak_plugin_info); 250 if (enable) { 251 register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, &structleak_pass_info); 252 register_callback(plugin_name, PLUGIN_FINISH_TYPE, finish_type, NULL); 253 } 254 register_callback(plugin_name, PLUGIN_ATTRIBUTES, register_attributes, NULL); 255 256 return 0; 257 } 258