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
 39static 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
 45static bool verbose;
 46static bool byref_all;
 47
 48static 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
 60static struct attribute_spec user_attr = { };
 61
 62static void register_attributes(void *event_data, void *data)
 63{
 64	user_attr.name			= "user";
 65	user_attr.handler		= handle_user_attribute;
 66#if BUILDING_GCC_VERSION >= 4007
 67	user_attr.affects_type_identity	= true;
 68#endif
 69
 70	register_attribute(&user_attr);
 71}
 72
 73static tree get_field_type(tree field)
 74{
 75	return strip_array_types(TREE_TYPE(field));
 76}
 77
 78static bool is_userspace_type(tree type)
 79{
 80	tree field;
 81
 82	for (field = TYPE_FIELDS(type); field; field = TREE_CHAIN(field)) {
 83		tree fieldtype = get_field_type(field);
 84		enum tree_code code = TREE_CODE(fieldtype);
 85
 86		if (code == RECORD_TYPE || code == UNION_TYPE)
 87			if (is_userspace_type(fieldtype))
 88				return true;
 89
 90		if (lookup_attribute("user", DECL_ATTRIBUTES(field)))
 91			return true;
 92	}
 93	return false;
 94}
 95
 96static void finish_type(void *event_data, void *data)
 97{
 98	tree type = (tree)event_data;
 99
100	if (type == NULL_TREE || type == error_mark_node)
101		return;
102
103#if BUILDING_GCC_VERSION >= 5000
104	if (TREE_CODE(type) == ENUMERAL_TYPE)
105		return;
106#endif
107
108	if (TYPE_USERSPACE(type))
109		return;
110
111	if (is_userspace_type(type))
112		TYPE_USERSPACE(type) = 1;
113}
114
115static void initialize(tree var)
116{
117	basic_block bb;
118	gimple_stmt_iterator gsi;
119	tree initializer;
120	gimple init_stmt;
121
122	/* this is the original entry bb before the forced split */
123	bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
124
125	/* first check if variable is already initialized, warn otherwise */
126	for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) {
127		gimple stmt = gsi_stmt(gsi);
128		tree rhs1;
129
130		/* we're looking for an assignment of a single rhs... */
131		if (!gimple_assign_single_p(stmt))
132			continue;
133		rhs1 = gimple_assign_rhs1(stmt);
134#if BUILDING_GCC_VERSION >= 4007
135		/* ... of a non-clobbering expression... */
136		if (TREE_CLOBBER_P(rhs1))
137			continue;
138#endif
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_all && TREE_ADDRESSABLE(var)) ? "byref"
152							     : "userspace");
153
154	/* build the initializer expression */
155	initializer = build_constructor(TREE_TYPE(var), NULL);
156
157	/* build the initializer stmt */
158	init_stmt = gimple_build_assign(var, initializer);
159	gsi = gsi_after_labels(single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
160	gsi_insert_before(&gsi, init_stmt, GSI_NEW_STMT);
161	update_stmt(init_stmt);
162}
163
164static unsigned int structleak_execute(void)
165{
166	basic_block bb;
167	unsigned int ret = 0;
168	tree var;
169	unsigned int i;
170
171	/* split the first bb where we can put the forced initializers */
172	gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
173	bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
174	if (!single_pred_p(bb)) {
175		split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
176		gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
177	}
178
179	/* enumerate all local variables and forcibly initialize our targets */
180	FOR_EACH_LOCAL_DECL(cfun, i, var) {
181		tree type = TREE_TYPE(var);
182
183		gcc_assert(DECL_P(var));
184		if (!auto_var_in_fn_p(var, current_function_decl))
185			continue;
186
187		/* only care about structure types */
188		if (TREE_CODE(type) != RECORD_TYPE && TREE_CODE(type) != UNION_TYPE)
189			continue;
190
191		/* if the type is of interest, examine the variable */
192		if (TYPE_USERSPACE(type) ||
193		    (byref_all && TREE_ADDRESSABLE(var)))
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		if (!strcmp(argv[i].key, "byref-all")) {
236			byref_all = true;
237			continue;
238		}
239		error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key);
240	}
241
242	register_callback(plugin_name, PLUGIN_INFO, NULL, &structleak_plugin_info);
243	if (enable) {
244		register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, &structleak_pass_info);
245		register_callback(plugin_name, PLUGIN_FINISH_TYPE, finish_type, NULL);
246	}
247	register_callback(plugin_name, PLUGIN_ATTRIBUTES, register_attributes, NULL);
248
249	return 0;
250}