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  *
  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 }