projects/linux·blob 4563243e · refs

257 lines · 7.2 KiB

1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright 2013-2017 by PaX Team <[email protected]>
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}