gcc-plugins: Use dynamic initializers
[muen/linux.git] / 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  * -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
39 static 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
45 static bool verbose;
46 static bool byref_all;
47
48 static 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
60 static struct attribute_spec user_attr = { };
61
62 static 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
73 static tree get_field_type(tree field)
74 {
75         return strip_array_types(TREE_TYPE(field));
76 }
77
78 static 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
96 static 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
115 static 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
164 static 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 }