scripts/gcc-plugins/structleak_plugin.c

   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 }