name : structleak_plugin.c // SPDX-License-Identifier: GPL-2.0-only /* * Copyright 2013-2017 by PaX Team <pageexec@freemail.hu> * * Note: the choice of the license means that the compilation process is * NOT 'eligible' as defined by gcc's library exception to the GPL v3, * but for the kernel it doesn't matter since it doesn't link against * any of the gcc libraries * * gcc plugin to forcibly initialize certain local variables that could * otherwise leak kernel stack to userland if they aren't properly initialized * by later code * * Homepage: https://pax.grsecurity.net/ * * Options: * -fplugin-arg-structleak_plugin-disable * -fplugin-arg-structleak_plugin-verbose * -fplugin-arg-structleak_plugin-byref * -fplugin-arg-structleak_plugin-byref-all * * Usage: * $ # for 4.5/4.6/C based 4.7 * $ 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 * $ # for C++ based 4.7/4.8+ * $ 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 * $ gcc -fplugin=./structleak_plugin.so test.c -O2 * * TODO: eliminate redundant initializers */ #include "gcc-common.h" /* unused C type flag in all versions 4.5-6 */ #define TYPE_USERSPACE(TYPE) TYPE_LANG_FLAG_5(TYPE) __visible int plugin_is_GPL_compatible; static struct plugin_info structleak_plugin_info = { .version = PLUGIN_VERSION, .help = "disable\tdo not activate plugin\n" "byref\tinit structs passed by reference\n" "byref-all\tinit anything passed by reference\n" "verbose\tprint all initialized variables\n", }; #define BYREF_STRUCT 1 #define BYREF_ALL 2 static bool verbose; static int byref; static tree handle_user_attribute(tree *node, tree name, tree args, int flags, bool *no_add_attrs) { *no_add_attrs = true; /* check for types? for now accept everything linux has to offer */ if (TREE_CODE(*node) != FIELD_DECL) return NULL_TREE; *no_add_attrs = false; return NULL_TREE; } static struct attribute_spec user_attr = { }; static void register_attributes(void *event_data, void *data) { user_attr.name = "user"; user_attr.handler = handle_user_attribute; user_attr.affects_type_identity = true; register_attribute(&user_attr); } static tree get_field_type(tree field) { return strip_array_types(TREE_TYPE(field)); } static bool is_userspace_type(tree type) { tree field; for (field = TYPE_FIELDS(type); field; field = TREE_CHAIN(field)) { tree fieldtype = get_field_type(field); enum tree_code code = TREE_CODE(fieldtype); if (code == RECORD_TYPE || code == UNION_TYPE) if (is_userspace_type(fieldtype)) return true; if (lookup_attribute("user", DECL_ATTRIBUTES(field))) return true; } return false; } static void finish_type(void *event_data, void *data) { tree type = (tree)event_data; if (type == NULL_TREE || type == error_mark_node) return; if (TREE_CODE(type) == ENUMERAL_TYPE) return; if (TYPE_USERSPACE(type)) return; if (is_userspace_type(type)) TYPE_USERSPACE(type) = 1; } static void initialize(tree var) { basic_block bb; gimple_stmt_iterator gsi; tree initializer; gimple init_stmt; tree type; /* this is the original entry bb before the forced split */ bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); /* first check if variable is already initialized, warn otherwise */ for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) { gimple stmt = gsi_stmt(gsi); tree rhs1; /* we're looking for an assignment of a single rhs... */ if (!gimple_assign_single_p(stmt)) continue; rhs1 = gimple_assign_rhs1(stmt); /* ... of a non-clobbering expression... */ if (TREE_CLOBBER_P(rhs1)) continue; /* ... to our variable... */ if (gimple_get_lhs(stmt) != var) continue; /* if it's an initializer then we're good */ if (TREE_CODE(rhs1) == CONSTRUCTOR) return; } /* these aren't the 0days you're looking for */ if (verbose) inform(DECL_SOURCE_LOCATION(var), "%s variable will be forcibly initialized", (byref && TREE_ADDRESSABLE(var)) ? "byref" : "userspace"); /* build the initializer expression */ type = TREE_TYPE(var); if (AGGREGATE_TYPE_P(type)) initializer = build_constructor(type, NULL); else initializer = fold_convert(type, integer_zero_node); /* build the initializer stmt */ init_stmt = gimple_build_assign(var, initializer); gsi = gsi_after_labels(single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun))); gsi_insert_before(&gsi, init_stmt, GSI_NEW_STMT); update_stmt(init_stmt); } static unsigned int structleak_execute(void) { basic_block bb; tree var; unsigned int i; /* split the first bb where we can put the forced initializers */ gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun))); bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); if (!single_pred_p(bb)) { split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun))); gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun))); } /* enumerate all local variables and forcibly initialize our targets */ FOR_EACH_LOCAL_DECL(cfun, i, var) { tree type = TREE_TYPE(var); gcc_assert(DECL_P(var)); if (!auto_var_in_fn_p(var, current_function_decl)) continue; /* only care about structure types unless byref-all */ if (byref != BYREF_ALL && TREE_CODE(type) != RECORD_TYPE && TREE_CODE(type) != UNION_TYPE) continue; /* if the type is of interest, examine the variable */ if (TYPE_USERSPACE(type) || (byref && TREE_ADDRESSABLE(var))) initialize(var); } return 0; } #define PASS_NAME structleak #define NO_GATE #define PROPERTIES_REQUIRED PROP_cfg #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 #include "gcc-generate-gimple-pass.h" __visible int plugin_init(struct plugin_name_args *plugin_info, struct plugin_gcc_version *version) { int i; const char * const plugin_name = plugin_info->base_name; const int argc = plugin_info->argc; const struct plugin_argument * const argv = plugin_info->argv; bool enable = true; PASS_INFO(structleak, "early_optimizations", 1, PASS_POS_INSERT_BEFORE); if (!plugin_default_version_check(version, &gcc_version)) { error(G_("incompatible gcc/plugin versions")); return 1; } if (strncmp(lang_hooks.name, "GNU C", 5) && !strncmp(lang_hooks.name, "GNU C+", 6)) { inform(UNKNOWN_LOCATION, G_("%s supports C only, not %s"), plugin_name, lang_hooks.name); enable = false; } for (i = 0; i < argc; ++i) { if (!strcmp(argv[i].key, "disable")) { enable = false; continue; } if (!strcmp(argv[i].key, "verbose")) { verbose = true; continue; } if (!strcmp(argv[i].key, "byref")) { byref = BYREF_STRUCT; continue; } if (!strcmp(argv[i].key, "byref-all")) { byref = BYREF_ALL; continue; } error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key); } register_callback(plugin_name, PLUGIN_INFO, NULL, &structleak_plugin_info); if (enable) { register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, &structleak_pass_info); register_callback(plugin_name, PLUGIN_FINISH_TYPE, finish_type, NULL); } register_callback(plugin_name, PLUGIN_ATTRIBUTES, register_attributes, NULL); return 0; }