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: 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 #if BUILDING_GCC_VERSION >= 4007
  72         user_attr.affects_type_identity = true;
  73 #endif
  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         tree type;
 127
 128         /* this is the original entry bb before the forced split */
 129         bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
 130
 131         /* first check if variable is already initialized, warn otherwise */
 132         for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) {
 133                 gimple stmt = gsi_stmt(gsi);
 134                 tree rhs1;
 135
 136                 /* we're looking for an assignment of a single rhs... */
 137                 if (!gimple_assign_single_p(stmt))
 138                         continue;
 139                 rhs1 = gimple_assign_rhs1(stmt);
 140 #if BUILDING_GCC_VERSION >= 4007
 141                 /* ... of a non-clobbering expression... */
 142                 if (TREE_CLOBBER_P(rhs1))
 143                         continue;
 144 #endif
 145                 /* ... to our variable... */
 146                 if (gimple_get_lhs(stmt) != var)
 147                         continue;
 148                 /* if it's an initializer then we're good */
 149                 if (TREE_CODE(rhs1) == CONSTRUCTOR)
 150                         return;
 151         }
 152
 153         /* these aren't the 0days you're looking for */
 154         if (verbose)
 155                 inform(DECL_SOURCE_LOCATION(var),
 156                         "%s variable will be forcibly initialized",
 157                         (byref && TREE_ADDRESSABLE(var)) ? "byref"
 158                                                          : "userspace");
 159
 160         /* build the initializer expression */
 161         type = TREE_TYPE(var);
 162         if (AGGREGATE_TYPE_P(type))
 163                 initializer = build_constructor(type, NULL);
 164         else
 165                 initializer = fold_convert(type, integer_zero_node);
 166
 167         /* build the initializer stmt */
 168         init_stmt = gimple_build_assign(var, initializer);
 169         gsi = gsi_after_labels(single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
 170         gsi_insert_before(&gsi, init_stmt, GSI_NEW_STMT);
 171         update_stmt(init_stmt);
 172 }
 173
 174 static unsigned int structleak_execute(void)
 175 {
 176         basic_block bb;
 177         unsigned int ret = 0;
 178         tree var;
 179         unsigned int i;
 180
 181         /* split the first bb where we can put the forced initializers */
 182         gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
 183         bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
 184         if (!single_pred_p(bb)) {
 185                 split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
 186                 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
 187         }
 188
 189         /* enumerate all local variables and forcibly initialize our targets */
 190         FOR_EACH_LOCAL_DECL(cfun, i, var) {
 191                 tree type = TREE_TYPE(var);
 192
 193                 gcc_assert(DECL_P(var));
 194                 if (!auto_var_in_fn_p(var, current_function_decl))
 195                         continue;
 196
 197                 /* only care about structure types unless byref-all */
 198                 if (byref != BYREF_ALL && TREE_CODE(type) != RECORD_TYPE && TREE_CODE(type) != UNION_TYPE)
 199                         continue;
 200
 201                 /* if the type is of interest, examine the variable */
 202                 if (TYPE_USERSPACE(type) ||
 203                     (byref && TREE_ADDRESSABLE(var)))
 204                         initialize(var);
 205         }
 206
 207         return ret;
 208 }
 209
 210 #define PASS_NAME structleak
 211 #define NO_GATE
 212 #define PROPERTIES_REQUIRED PROP_cfg
 213 #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
 214 #include "gcc-generate-gimple-pass.h"
 215
 216 __visible int plugin_init(struct plugin_name_args *plugin_info, struct plugin_gcc_version *version)
 217 {
 218         int i;
 219         const char * const plugin_name = plugin_info->base_name;
 220         const int argc = plugin_info->argc;
 221         const struct plugin_argument * const argv = plugin_info->argv;
 222         bool enable = true;
 223
 224         PASS_INFO(structleak, "early_optimizations", 1, PASS_POS_INSERT_BEFORE);
 225
 226         if (!plugin_default_version_check(version, &gcc_version)) {
 227                 error(G_("incompatible gcc/plugin versions"));
 228                 return 1;
 229         }
 230
 231         if (strncmp(lang_hooks.name, "GNU C", 5) && !strncmp(lang_hooks.name, "GNU C+", 6)) {
 232                 inform(UNKNOWN_LOCATION, G_("%s supports C only, not %s"), plugin_name, lang_hooks.name);
 233                 enable = false;
 234         }
 235
 236         for (i = 0; i < argc; ++i) {
 237                 if (!strcmp(argv[i].key, "disable")) {
 238                         enable = false;
 239                         continue;
 240                 }
 241                 if (!strcmp(argv[i].key, "verbose")) {
 242                         verbose = true;
 243                         continue;
 244                 }
 245                 if (!strcmp(argv[i].key, "byref")) {
 246                         byref = BYREF_STRUCT;
 247                         continue;
 248                 }
 249                 if (!strcmp(argv[i].key, "byref-all")) {
 250                         byref = BYREF_ALL;
 251                         continue;
 252                 }
 253                 error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key);
 254         }
 255
 256         register_callback(plugin_name, PLUGIN_INFO, NULL, &structleak_plugin_info);
 257         if (enable) {
 258                 register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, &structleak_pass_info);
 259                 register_callback(plugin_name, PLUGIN_FINISH_TYPE, finish_type, NULL);
 260         }
 261         register_callback(plugin_name, PLUGIN_ATTRIBUTES, register_attributes, NULL);
 262
 263         return 0;
 264 }