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 | |
39 | static 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 | |
50 | static bool verbose; |
51 | static int byref; |
52 | |
53 | static 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 | |
65 | static struct attribute_spec user_attr = { }; |
66 | |
67 | static 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 | |
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 (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 | |
116 | static 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 | |
168 | static 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 | |