1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Test cases for compiler-based stack variable zeroing via future
4 * compiler flags or CONFIG_GCC_PLUGIN_STRUCTLEAK*.
5 */
6 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
7
8 #include <linux/init.h>
9 #include <linux/kernel.h>
10 #include <linux/module.h>
11 #include <linux/string.h>
12
13 /* Exfiltration buffer. */
14 #define MAX_VAR_SIZE 128
15 static u8 check_buf[MAX_VAR_SIZE];
16
17 /* Character array to trigger stack protector in all functions. */
18 #define VAR_BUFFER 32
19
20 /* Volatile mask to convince compiler to copy memory with 0xff. */
21 static volatile u8 forced_mask = 0xff;
22
23 /* Location and size tracking to validate fill and test are colocated. */
24 static void *fill_start, *target_start;
25 static size_t fill_size, target_size;
26
range_contains(char * haystack_start,size_t haystack_size,char * needle_start,size_t needle_size)27 static bool range_contains(char *haystack_start, size_t haystack_size,
28 char *needle_start, size_t needle_size)
29 {
30 if (needle_start >= haystack_start &&
31 needle_start + needle_size <= haystack_start + haystack_size)
32 return true;
33 return false;
34 }
35
36 #define DO_NOTHING_TYPE_SCALAR(var_type) var_type
37 #define DO_NOTHING_TYPE_STRING(var_type) void
38 #define DO_NOTHING_TYPE_STRUCT(var_type) void
39
40 #define DO_NOTHING_RETURN_SCALAR(ptr) *(ptr)
41 #define DO_NOTHING_RETURN_STRING(ptr) /**/
42 #define DO_NOTHING_RETURN_STRUCT(ptr) /**/
43
44 #define DO_NOTHING_CALL_SCALAR(var, name) \
45 (var) = do_nothing_ ## name(&(var))
46 #define DO_NOTHING_CALL_STRING(var, name) \
47 do_nothing_ ## name(var)
48 #define DO_NOTHING_CALL_STRUCT(var, name) \
49 do_nothing_ ## name(&(var))
50
51 #define FETCH_ARG_SCALAR(var) &var
52 #define FETCH_ARG_STRING(var) var
53 #define FETCH_ARG_STRUCT(var) &var
54
55 #define FILL_SIZE_STRING 16
56
57 #define INIT_CLONE_SCALAR /**/
58 #define INIT_CLONE_STRING [FILL_SIZE_STRING]
59 #define INIT_CLONE_STRUCT /**/
60
61 #define INIT_SCALAR_none /**/
62 #define INIT_SCALAR_zero = 0
63
64 #define INIT_STRING_none [FILL_SIZE_STRING] /**/
65 #define INIT_STRING_zero [FILL_SIZE_STRING] = { }
66
67 #define INIT_STRUCT_none /**/
68 #define INIT_STRUCT_zero = { }
69 #define INIT_STRUCT_static_partial = { .two = 0, }
70 #define INIT_STRUCT_static_all = { .one = arg->one, \
71 .two = arg->two, \
72 .three = arg->three, \
73 .four = arg->four, \
74 }
75 #define INIT_STRUCT_dynamic_partial = { .two = arg->two, }
76 #define INIT_STRUCT_dynamic_all = { .one = arg->one, \
77 .two = arg->two, \
78 .three = arg->three, \
79 .four = arg->four, \
80 }
81 #define INIT_STRUCT_runtime_partial ; \
82 var.two = 0
83 #define INIT_STRUCT_runtime_all ; \
84 var.one = 0; \
85 var.two = 0; \
86 var.three = 0; \
87 memset(&var.four, 0, \
88 sizeof(var.four))
89
90 /*
91 * @name: unique string name for the test
92 * @var_type: type to be tested for zeroing initialization
93 * @which: is this a SCALAR, STRING, or STRUCT type?
94 * @init_level: what kind of initialization is performed
95 */
96 #define DEFINE_TEST_DRIVER(name, var_type, which) \
97 /* Returns 0 on success, 1 on failure. */ \
98 static noinline __init int test_ ## name (void) \
99 { \
100 var_type zero INIT_CLONE_ ## which; \
101 int ignored; \
102 u8 sum = 0, i; \
103 \
104 /* Notice when a new test is larger than expected. */ \
105 BUILD_BUG_ON(sizeof(zero) > MAX_VAR_SIZE); \
106 \
107 /* Fill clone type with zero for per-field init. */ \
108 memset(&zero, 0x00, sizeof(zero)); \
109 /* Clear entire check buffer for 0xFF overlap test. */ \
110 memset(check_buf, 0x00, sizeof(check_buf)); \
111 /* Fill stack with 0xFF. */ \
112 ignored = leaf_ ##name((unsigned long)&ignored, 1, \
113 FETCH_ARG_ ## which(zero)); \
114 /* Verify all bytes overwritten with 0xFF. */ \
115 for (sum = 0, i = 0; i < target_size; i++) \
116 sum += (check_buf[i] != 0xFF); \
117 if (sum) { \
118 pr_err(#name ": leaf fill was not 0xFF!?\n"); \
119 return 1; \
120 } \
121 /* Clear entire check buffer for later bit tests. */ \
122 memset(check_buf, 0x00, sizeof(check_buf)); \
123 /* Extract stack-defined variable contents. */ \
124 ignored = leaf_ ##name((unsigned long)&ignored, 0, \
125 FETCH_ARG_ ## which(zero)); \
126 \
127 /* Validate that compiler lined up fill and target. */ \
128 if (!range_contains(fill_start, fill_size, \
129 target_start, target_size)) { \
130 pr_err(#name ": stack fill missed target!?\n"); \
131 pr_err(#name ": fill %zu wide\n", fill_size); \
132 pr_err(#name ": target offset by %d\n", \
133 (int)((ssize_t)(uintptr_t)fill_start - \
134 (ssize_t)(uintptr_t)target_start)); \
135 return 1; \
136 } \
137 \
138 /* Look for any bytes still 0xFF in check region. */ \
139 for (sum = 0, i = 0; i < target_size; i++) \
140 sum += (check_buf[i] == 0xFF); \
141 \
142 if (sum == 0) \
143 pr_info(#name " ok\n"); \
144 else \
145 pr_warn(#name " FAIL (uninit bytes: %d)\n", \
146 sum); \
147 \
148 return (sum != 0); \
149 }
150 #define DEFINE_TEST(name, var_type, which, init_level) \
151 /* no-op to force compiler into ignoring "uninitialized" vars */\
152 static noinline __init DO_NOTHING_TYPE_ ## which(var_type) \
153 do_nothing_ ## name(var_type *ptr) \
154 { \
155 /* Will always be true, but compiler doesn't know. */ \
156 if ((unsigned long)ptr > 0x2) \
157 return DO_NOTHING_RETURN_ ## which(ptr); \
158 else \
159 return DO_NOTHING_RETURN_ ## which(ptr + 1); \
160 } \
161 static noinline __init int leaf_ ## name(unsigned long sp, \
162 bool fill, \
163 var_type *arg) \
164 { \
165 char buf[VAR_BUFFER]; \
166 var_type var INIT_ ## which ## _ ## init_level; \
167 \
168 target_start = &var; \
169 target_size = sizeof(var); \
170 /* \
171 * Keep this buffer around to make sure we've got a \
172 * stack frame of SOME kind... \
173 */ \
174 memset(buf, (char)(sp & 0xff), sizeof(buf)); \
175 /* Fill variable with 0xFF. */ \
176 if (fill) { \
177 fill_start = &var; \
178 fill_size = sizeof(var); \
179 memset(fill_start, \
180 (char)((sp & 0xff) | forced_mask), \
181 fill_size); \
182 } \
183 \
184 /* Silence "never initialized" warnings. */ \
185 DO_NOTHING_CALL_ ## which(var, name); \
186 \
187 /* Exfiltrate "var". */ \
188 memcpy(check_buf, target_start, target_size); \
189 \
190 return (int)buf[0] | (int)buf[sizeof(buf) - 1]; \
191 } \
192 DEFINE_TEST_DRIVER(name, var_type, which)
193
194 /* Structure with no padding. */
195 struct test_packed {
196 unsigned long one;
197 unsigned long two;
198 unsigned long three;
199 unsigned long four;
200 };
201
202 /* Simple structure with padding likely to be covered by compiler. */
203 struct test_small_hole {
204 size_t one;
205 char two;
206 /* 3 byte padding hole here. */
207 int three;
208 unsigned long four;
209 };
210
211 /* Try to trigger unhandled padding in a structure. */
212 struct test_aligned {
213 u32 internal1;
214 u64 internal2;
215 } __aligned(64);
216
217 struct test_big_hole {
218 u8 one;
219 u8 two;
220 u8 three;
221 /* 61 byte padding hole here. */
222 struct test_aligned four;
223 } __aligned(64);
224
225 struct test_trailing_hole {
226 char *one;
227 char *two;
228 char *three;
229 char four;
230 /* "sizeof(unsigned long) - 1" byte padding hole here. */
231 };
232
233 /* Test if STRUCTLEAK is clearing structs with __user fields. */
234 struct test_user {
235 u8 one;
236 unsigned long two;
237 char __user *three;
238 unsigned long four;
239 };
240
241 #define DEFINE_SCALAR_TEST(name, init) \
242 DEFINE_TEST(name ## _ ## init, name, SCALAR, init)
243
244 #define DEFINE_SCALAR_TESTS(init) \
245 DEFINE_SCALAR_TEST(u8, init); \
246 DEFINE_SCALAR_TEST(u16, init); \
247 DEFINE_SCALAR_TEST(u32, init); \
248 DEFINE_SCALAR_TEST(u64, init); \
249 DEFINE_TEST(char_array_ ## init, unsigned char, STRING, init)
250
251 #define DEFINE_STRUCT_TEST(name, init) \
252 DEFINE_TEST(name ## _ ## init, \
253 struct test_ ## name, STRUCT, init)
254
255 #define DEFINE_STRUCT_TESTS(init) \
256 DEFINE_STRUCT_TEST(small_hole, init); \
257 DEFINE_STRUCT_TEST(big_hole, init); \
258 DEFINE_STRUCT_TEST(trailing_hole, init); \
259 DEFINE_STRUCT_TEST(packed, init)
260
261 /* These should be fully initialized all the time! */
262 DEFINE_SCALAR_TESTS(zero);
263 DEFINE_STRUCT_TESTS(zero);
264 /* Static initialization: padding may be left uninitialized. */
265 DEFINE_STRUCT_TESTS(static_partial);
266 DEFINE_STRUCT_TESTS(static_all);
267 /* Dynamic initialization: padding may be left uninitialized. */
268 DEFINE_STRUCT_TESTS(dynamic_partial);
269 DEFINE_STRUCT_TESTS(dynamic_all);
270 /* Runtime initialization: padding may be left uninitialized. */
271 DEFINE_STRUCT_TESTS(runtime_partial);
272 DEFINE_STRUCT_TESTS(runtime_all);
273 /* No initialization without compiler instrumentation. */
274 DEFINE_SCALAR_TESTS(none);
275 DEFINE_STRUCT_TESTS(none);
276 DEFINE_TEST(user, struct test_user, STRUCT, none);
277
278 /*
279 * Check two uses through a variable declaration outside either path,
280 * which was noticed as a special case in porting earlier stack init
281 * compiler logic.
282 */
__leaf_switch_none(int path,bool fill)283 static int noinline __leaf_switch_none(int path, bool fill)
284 {
285 switch (path) {
286 uint64_t var;
287
288 case 1:
289 target_start = &var;
290 target_size = sizeof(var);
291 if (fill) {
292 fill_start = &var;
293 fill_size = sizeof(var);
294
295 memset(fill_start, forced_mask | 0x55, fill_size);
296 }
297 memcpy(check_buf, target_start, target_size);
298 break;
299 case 2:
300 target_start = &var;
301 target_size = sizeof(var);
302 if (fill) {
303 fill_start = &var;
304 fill_size = sizeof(var);
305
306 memset(fill_start, forced_mask | 0xaa, fill_size);
307 }
308 memcpy(check_buf, target_start, target_size);
309 break;
310 default:
311 var = 5;
312 return var & forced_mask;
313 }
314 return 0;
315 }
316
leaf_switch_1_none(unsigned long sp,bool fill,uint64_t * arg)317 static noinline __init int leaf_switch_1_none(unsigned long sp, bool fill,
318 uint64_t *arg)
319 {
320 return __leaf_switch_none(1, fill);
321 }
322
leaf_switch_2_none(unsigned long sp,bool fill,uint64_t * arg)323 static noinline __init int leaf_switch_2_none(unsigned long sp, bool fill,
324 uint64_t *arg)
325 {
326 return __leaf_switch_none(2, fill);
327 }
328
329 DEFINE_TEST_DRIVER(switch_1_none, uint64_t, SCALAR);
330 DEFINE_TEST_DRIVER(switch_2_none, uint64_t, SCALAR);
331
test_stackinit_init(void)332 static int __init test_stackinit_init(void)
333 {
334 unsigned int failures = 0;
335
336 #define test_scalars(init) do { \
337 failures += test_u8_ ## init (); \
338 failures += test_u16_ ## init (); \
339 failures += test_u32_ ## init (); \
340 failures += test_u64_ ## init (); \
341 failures += test_char_array_ ## init (); \
342 } while (0)
343
344 #define test_structs(init) do { \
345 failures += test_small_hole_ ## init (); \
346 failures += test_big_hole_ ## init (); \
347 failures += test_trailing_hole_ ## init (); \
348 failures += test_packed_ ## init (); \
349 } while (0)
350
351 /* These are explicitly initialized and should always pass. */
352 test_scalars(zero);
353 test_structs(zero);
354 /* Padding here appears to be accidentally always initialized? */
355 test_structs(dynamic_partial);
356 /* Padding initialization depends on compiler behaviors. */
357 test_structs(static_partial);
358 test_structs(static_all);
359 test_structs(dynamic_all);
360 test_structs(runtime_partial);
361 test_structs(runtime_all);
362
363 /* STRUCTLEAK_BYREF_ALL should cover everything from here down. */
364 test_scalars(none);
365 failures += test_switch_1_none();
366 failures += test_switch_2_none();
367
368 /* STRUCTLEAK_BYREF should cover from here down. */
369 test_structs(none);
370
371 /* STRUCTLEAK will only cover this. */
372 failures += test_user();
373
374 if (failures == 0)
375 pr_info("all tests passed!\n");
376 else
377 pr_err("failures: %u\n", failures);
378
379 return failures ? -EINVAL : 0;
380 }
381 module_init(test_stackinit_init);
382
test_stackinit_exit(void)383 static void __exit test_stackinit_exit(void)
384 { }
385 module_exit(test_stackinit_exit);
386
387 MODULE_LICENSE("GPL");
388