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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 | * | |
20 | * Usage: | |
21 | * $ # for 4.5/4.6/C based 4.7 | |
22 | * $ 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 | |
23 | * $ # for C++ based 4.7/4.8+ | |
24 | * $ 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 | |
25 | * $ gcc -fplugin=./structleak_plugin.so test.c -O2 | |
26 | * | |
27 | * TODO: eliminate redundant initializers | |
28 | * increase type coverage | |
29 | */ | |
30 | ||
31 | #include "gcc-common.h" | |
32 | ||
33 | /* unused C type flag in all versions 4.5-6 */ | |
34 | #define TYPE_USERSPACE(TYPE) TYPE_LANG_FLAG_5(TYPE) | |
35 | ||
36 | __visible int plugin_is_GPL_compatible; | |
37 | ||
38 | static struct plugin_info structleak_plugin_info = { | |
39 | .version = "201607271510vanilla", | |
40 | .help = "disable\tdo not activate plugin\n" | |
41 | "verbose\tprint all initialized variables\n", | |
42 | }; | |
43 | ||
44 | static bool verbose; | |
45 | ||
46 | static tree handle_user_attribute(tree *node, tree name, tree args, int flags, bool *no_add_attrs) | |
47 | { | |
48 | *no_add_attrs = true; | |
49 | ||
50 | /* check for types? for now accept everything linux has to offer */ | |
51 | if (TREE_CODE(*node) != FIELD_DECL) | |
52 | return NULL_TREE; | |
53 | ||
54 | *no_add_attrs = false; | |
55 | return NULL_TREE; | |
56 | } | |
57 | ||
58 | static struct attribute_spec user_attr = { | |
59 | .name = "user", | |
60 | .min_length = 0, | |
61 | .max_length = 0, | |
62 | .decl_required = false, | |
63 | .type_required = false, | |
64 | .function_type_required = false, | |
65 | .handler = handle_user_attribute, | |
66 | #if BUILDING_GCC_VERSION >= 4007 | |
67 | .affects_type_identity = true | |
68 | #endif | |
69 | }; | |
70 | ||
71 | static void register_attributes(void *event_data, void *data) | |
72 | { | |
73 | register_attribute(&user_attr); | |
74 | } | |
75 | ||
76 | static tree get_field_type(tree field) | |
77 | { | |
78 | return strip_array_types(TREE_TYPE(field)); | |
79 | } | |
80 | ||
81 | static 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 | ||
99 | static 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 BUILDING_GCC_VERSION >= 5000 | |
107 | if (TREE_CODE(type) == ENUMERAL_TYPE) | |
108 | return; | |
109 | #endif | |
110 | ||
111 | if (TYPE_USERSPACE(type)) | |
112 | return; | |
113 | ||
114 | if (is_userspace_type(type)) | |
115 | TYPE_USERSPACE(type) = 1; | |
116 | } | |
117 | ||
118 | static void initialize(tree var) | |
119 | { | |
120 | basic_block bb; | |
121 | gimple_stmt_iterator gsi; | |
122 | tree initializer; | |
123 | gimple init_stmt; | |
124 | ||
125 | /* this is the original entry bb before the forced split */ | |
126 | bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); | |
127 | ||
128 | /* first check if variable is already initialized, warn otherwise */ | |
129 | for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) { | |
130 | gimple stmt = gsi_stmt(gsi); | |
131 | tree rhs1; | |
132 | ||
133 | /* we're looking for an assignment of a single rhs... */ | |
134 | if (!gimple_assign_single_p(stmt)) | |
135 | continue; | |
136 | rhs1 = gimple_assign_rhs1(stmt); | |
137 | #if BUILDING_GCC_VERSION >= 4007 | |
138 | /* ... of a non-clobbering expression... */ | |
139 | if (TREE_CLOBBER_P(rhs1)) | |
140 | continue; | |
141 | #endif | |
142 | /* ... to our variable... */ | |
143 | if (gimple_get_lhs(stmt) != var) | |
144 | continue; | |
145 | /* if it's an initializer then we're good */ | |
146 | if (TREE_CODE(rhs1) == CONSTRUCTOR) | |
147 | return; | |
148 | } | |
149 | ||
150 | /* these aren't the 0days you're looking for */ | |
151 | if (verbose) | |
152 | inform(DECL_SOURCE_LOCATION(var), | |
153 | "userspace variable will be forcibly initialized"); | |
154 | ||
155 | /* build the initializer expression */ | |
156 | initializer = build_constructor(TREE_TYPE(var), NULL); | |
157 | ||
158 | /* build the initializer stmt */ | |
159 | init_stmt = gimple_build_assign(var, initializer); | |
160 | gsi = gsi_after_labels(single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun))); | |
161 | gsi_insert_before(&gsi, init_stmt, GSI_NEW_STMT); | |
162 | update_stmt(init_stmt); | |
163 | } | |
164 | ||
165 | static unsigned int structleak_execute(void) | |
166 | { | |
167 | basic_block bb; | |
168 | unsigned int ret = 0; | |
169 | tree var; | |
170 | unsigned int i; | |
171 | ||
172 | /* split the first bb where we can put the forced initializers */ | |
173 | gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun))); | |
174 | bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); | |
175 | if (!single_pred_p(bb)) { | |
176 | split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun))); | |
177 | gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun))); | |
178 | } | |
179 | ||
180 | /* enumerate all local variables and forcibly initialize our targets */ | |
181 | FOR_EACH_LOCAL_DECL(cfun, i, var) { | |
182 | tree type = TREE_TYPE(var); | |
183 | ||
184 | gcc_assert(DECL_P(var)); | |
185 | if (!auto_var_in_fn_p(var, current_function_decl)) | |
186 | continue; | |
187 | ||
188 | /* only care about structure types */ | |
189 | if (TREE_CODE(type) != RECORD_TYPE && TREE_CODE(type) != UNION_TYPE) | |
190 | continue; | |
191 | ||
192 | /* if the type is of interest, examine the variable */ | |
193 | if (TYPE_USERSPACE(type)) | |
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 | error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key); | |
236 | } | |
237 | ||
238 | register_callback(plugin_name, PLUGIN_INFO, NULL, &structleak_plugin_info); | |
239 | if (enable) { | |
240 | register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, &structleak_pass_info); | |
241 | register_callback(plugin_name, PLUGIN_FINISH_TYPE, finish_type, NULL); | |
242 | } | |
243 | register_callback(plugin_name, PLUGIN_ATTRIBUTES, register_attributes, NULL); | |
244 | ||
245 | return 0; | |
246 | } |