1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright 2013-2017 by PaX Team <pageexec@freemail.hu>
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
39static struct plugin_info structleak_plugin_info = {
40	.version	= PLUGIN_VERSION,
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
50static bool verbose;
51static int byref;
52
53static 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
65static struct attribute_spec user_attr = { };
66
67static void register_attributes(void *event_data, void *data)
68{
69	user_attr.name			= "user";
70	user_attr.handler		= handle_user_attribute;
71	user_attr.affects_type_identity	= true;
72
73	register_attribute(&user_attr);
74}
75
76static tree get_field_type(tree field)
77{
78	return strip_array_types(TREE_TYPE(field));
79}
80
81static 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
99static 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 (TREE_CODE(type) == ENUMERAL_TYPE)
107		return;
108
109	if (TYPE_USERSPACE(type))
110		return;
111
112	if (is_userspace_type(type))
113		TYPE_USERSPACE(type) = 1;
114}
115
116static void initialize(tree var)
117{
118	basic_block bb;
119	gimple_stmt_iterator gsi;
120	tree initializer;
121	gimple init_stmt;
122	tree type;
123
124	/* this is the original entry bb before the forced split */
125	bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
126
127	/* first check if variable is already initialized, warn otherwise */
128	for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) {
129		gimple stmt = gsi_stmt(gsi);
130		tree rhs1;
131
132		/* we're looking for an assignment of a single rhs... */
133		if (!gimple_assign_single_p(stmt))
134			continue;
135		rhs1 = gimple_assign_rhs1(stmt);
136		/* ... of a non-clobbering expression... */
137		if (TREE_CLOBBER_P(rhs1))
138			continue;
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 && TREE_ADDRESSABLE(var)) ? "byref"
152							 : "userspace");
153
154	/* build the initializer expression */
155	type = TREE_TYPE(var);
156	if (AGGREGATE_TYPE_P(type))
157		initializer = build_constructor(type, NULL);
158	else
159		initializer = fold_convert(type, integer_zero_node);
160
161	/* build the initializer stmt */
162	init_stmt = gimple_build_assign(var, initializer);
163	gsi = gsi_after_labels(single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
164	gsi_insert_before(&gsi, init_stmt, GSI_NEW_STMT);
165	update_stmt(init_stmt);
166}
167
168static unsigned int structleak_execute(void)
169{
170	basic_block bb;
171	tree var;
172	unsigned int i;
173
174	/* split the first bb where we can put the forced initializers */
175	gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
176	bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
177	if (!single_pred_p(bb)) {
178		split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
179		gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
180	}
181
182	/* enumerate all local variables and forcibly initialize our targets */
183	FOR_EACH_LOCAL_DECL(cfun, i, var) {
184		tree type = TREE_TYPE(var);
185
186		gcc_assert(DECL_P(var));
187		if (!auto_var_in_fn_p(var, current_function_decl))
188			continue;
189
190		/* only care about structure types unless byref-all */
191		if (byref != BYREF_ALL && TREE_CODE(type) != RECORD_TYPE && TREE_CODE(type) != UNION_TYPE)
192			continue;
193
194		/* if the type is of interest, examine the variable */
195		if (TYPE_USERSPACE(type) ||
196		    (byref && TREE_ADDRESSABLE(var)))
197			initialize(var);
198	}
199
200	return 0;
201}
202
203#define PASS_NAME structleak
204#define NO_GATE
205#define PROPERTIES_REQUIRED PROP_cfg
206#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
207#include "gcc-generate-gimple-pass.h"
208
209__visible int plugin_init(struct plugin_name_args *plugin_info, struct plugin_gcc_version *version)
210{
211	int i;
212	const char * const plugin_name = plugin_info->base_name;
213	const int argc = plugin_info->argc;
214	const struct plugin_argument * const argv = plugin_info->argv;
215	bool enable = true;
216
217	PASS_INFO(structleak, "early_optimizations", 1, PASS_POS_INSERT_BEFORE);
218
219	if (!plugin_default_version_check(version, &gcc_version)) {
220		error(G_("incompatible gcc/plugin versions"));
221		return 1;
222	}
223
224	if (strncmp(lang_hooks.name, "GNU C", 5) && !strncmp(lang_hooks.name, "GNU C+", 6)) {
225		inform(UNKNOWN_LOCATION, G_("%s supports C only, not %s"), plugin_name, lang_hooks.name);
226		enable = false;
227	}
228
229	for (i = 0; i < argc; ++i) {
230		if (!strcmp(argv[i].key, "disable")) {
231			enable = false;
232			continue;
233		}
234		if (!strcmp(argv[i].key, "verbose")) {
235			verbose = true;
236			continue;
237		}
238		if (!strcmp(argv[i].key, "byref")) {
239			byref = BYREF_STRUCT;
240			continue;
241		}
242		if (!strcmp(argv[i].key, "byref-all")) {
243			byref = BYREF_ALL;
244			continue;
245		}
246		error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key);
247	}
248
249	register_callback(plugin_name, PLUGIN_INFO, NULL, &structleak_plugin_info);
250	if (enable) {
251		register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, &structleak_pass_info);
252		register_callback(plugin_name, PLUGIN_FINISH_TYPE, finish_type, NULL);
253	}
254	register_callback(plugin_name, PLUGIN_ATTRIBUTES, register_attributes, NULL);
255
256	return 0;
257}
258