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 * @xfail: is this test expected to fail?
96 */
97 #define DEFINE_TEST_DRIVER(name, var_type, which, xfail) \
98 /* Returns 0 on success, 1 on failure. */ \
99 static noinline __init int test_ ## name (void) \
100 { \
101 var_type zero INIT_CLONE_ ## which; \
102 int ignored; \
103 u8 sum = 0, i; \
104 \
105 /* Notice when a new test is larger than expected. */ \
106 BUILD_BUG_ON(sizeof(zero) > MAX_VAR_SIZE); \
107 \
108 /* Fill clone type with zero for per-field init. */ \
109 memset(&zero, 0x00, sizeof(zero)); \
110 /* Clear entire check buffer for 0xFF overlap test. */ \
111 memset(check_buf, 0x00, sizeof(check_buf)); \
112 /* Fill stack with 0xFF. */ \
113 ignored = leaf_ ##name((unsigned long)&ignored, 1, \
114 FETCH_ARG_ ## which(zero)); \
115 /* Verify all bytes overwritten with 0xFF. */ \
116 for (sum = 0, i = 0; i < target_size; i++) \
117 sum += (check_buf[i] != 0xFF); \
118 if (sum) { \
119 pr_err(#name ": leaf fill was not 0xFF!?\n"); \
120 return 1; \
121 } \
122 /* Clear entire check buffer for later bit tests. */ \
123 memset(check_buf, 0x00, sizeof(check_buf)); \
124 /* Extract stack-defined variable contents. */ \
125 ignored = leaf_ ##name((unsigned long)&ignored, 0, \
126 FETCH_ARG_ ## which(zero)); \
127 \
128 /* Validate that compiler lined up fill and target. */ \
129 if (!range_contains(fill_start, fill_size, \
130 target_start, target_size)) { \
131 pr_err(#name ": stack fill missed target!?\n"); \
132 pr_err(#name ": fill %zu wide\n", fill_size); \
133 pr_err(#name ": target offset by %d\n", \
134 (int)((ssize_t)(uintptr_t)fill_start - \
135 (ssize_t)(uintptr_t)target_start)); \
136 return 1; \
137 } \
138 \
139 /* Look for any bytes still 0xFF in check region. */ \
140 for (sum = 0, i = 0; i < target_size; i++) \
141 sum += (check_buf[i] == 0xFF); \
142 \
143 if (sum == 0) { \
144 pr_info(#name " ok\n"); \
145 return 0; \
146 } else { \
147 pr_warn(#name " %sFAIL (uninit bytes: %d)\n", \
148 (xfail) ? "X" : "", sum); \
149 return (xfail) ? 0 : 1; \
150 } \
151 }
152 #define DEFINE_TEST(name, var_type, which, init_level) \
153 /* no-op to force compiler into ignoring "uninitialized" vars */\
154 static noinline __init DO_NOTHING_TYPE_ ## which(var_type) \
155 do_nothing_ ## name(var_type *ptr) \
156 { \
157 /* Will always be true, but compiler doesn't know. */ \
158 if ((unsigned long)ptr > 0x2) \
159 return DO_NOTHING_RETURN_ ## which(ptr); \
160 else \
161 return DO_NOTHING_RETURN_ ## which(ptr + 1); \
162 } \
163 static noinline __init int leaf_ ## name(unsigned long sp, \
164 bool fill, \
165 var_type *arg) \
166 { \
167 char buf[VAR_BUFFER]; \
168 var_type var INIT_ ## which ## _ ## init_level; \
169 \
170 target_start = &var; \
171 target_size = sizeof(var); \
172 /* \
173 * Keep this buffer around to make sure we've got a \
174 * stack frame of SOME kind... \
175 */ \
176 memset(buf, (char)(sp & 0xff), sizeof(buf)); \
177 /* Fill variable with 0xFF. */ \
178 if (fill) { \
179 fill_start = &var; \
180 fill_size = sizeof(var); \
181 memset(fill_start, \
182 (char)((sp & 0xff) | forced_mask), \
183 fill_size); \
184 } \
185 \
186 /* Silence "never initialized" warnings. */ \
187 DO_NOTHING_CALL_ ## which(var, name); \
188 \
189 /* Exfiltrate "var". */ \
190 memcpy(check_buf, target_start, target_size); \
191 \
192 return (int)buf[0] | (int)buf[sizeof(buf) - 1]; \
193 } \
194 DEFINE_TEST_DRIVER(name, var_type, which, 0)
195
196 /* Structure with no padding. */
197 struct test_packed {
198 unsigned long one;
199 unsigned long two;
200 unsigned long three;
201 unsigned long four;
202 };
203
204 /* Simple structure with padding likely to be covered by compiler. */
205 struct test_small_hole {
206 size_t one;
207 char two;
208 /* 3 byte padding hole here. */
209 int three;
210 unsigned long four;
211 };
212
213 /* Try to trigger unhandled padding in a structure. */
214 struct test_aligned {
215 u32 internal1;
216 u64 internal2;
217 } __aligned(64);
218
219 struct test_big_hole {
220 u8 one;
221 u8 two;
222 u8 three;
223 /* 61 byte padding hole here. */
224 struct test_aligned four;
225 } __aligned(64);
226
227 struct test_trailing_hole {
228 char *one;
229 char *two;
230 char *three;
231 char four;
232 /* "sizeof(unsigned long) - 1" byte padding hole here. */
233 };
234
235 /* Test if STRUCTLEAK is clearing structs with __user fields. */
236 struct test_user {
237 u8 one;
238 unsigned long two;
239 char __user *three;
240 unsigned long four;
241 };
242
243 #define DEFINE_SCALAR_TEST(name, init) \
244 DEFINE_TEST(name ## _ ## init, name, SCALAR, init)
245
246 #define DEFINE_SCALAR_TESTS(init) \
247 DEFINE_SCALAR_TEST(u8, init); \
248 DEFINE_SCALAR_TEST(u16, init); \
249 DEFINE_SCALAR_TEST(u32, init); \
250 DEFINE_SCALAR_TEST(u64, init); \
251 DEFINE_TEST(char_array_ ## init, unsigned char, STRING, init)
252
253 #define DEFINE_STRUCT_TEST(name, init) \
254 DEFINE_TEST(name ## _ ## init, \
255 struct test_ ## name, STRUCT, init)
256
257 #define DEFINE_STRUCT_TESTS(init) \
258 DEFINE_STRUCT_TEST(small_hole, init); \
259 DEFINE_STRUCT_TEST(big_hole, init); \
260 DEFINE_STRUCT_TEST(trailing_hole, init); \
261 DEFINE_STRUCT_TEST(packed, init)
262
263 /* These should be fully initialized all the time! */
264 DEFINE_SCALAR_TESTS(zero);
265 DEFINE_STRUCT_TESTS(zero);
266 /* Static initialization: padding may be left uninitialized. */
267 DEFINE_STRUCT_TESTS(static_partial);
268 DEFINE_STRUCT_TESTS(static_all);
269 /* Dynamic initialization: padding may be left uninitialized. */
270 DEFINE_STRUCT_TESTS(dynamic_partial);
271 DEFINE_STRUCT_TESTS(dynamic_all);
272 /* Runtime initialization: padding may be left uninitialized. */
273 DEFINE_STRUCT_TESTS(runtime_partial);
274 DEFINE_STRUCT_TESTS(runtime_all);
275 /* No initialization without compiler instrumentation. */
276 DEFINE_SCALAR_TESTS(none);
277 DEFINE_STRUCT_TESTS(none);
278 DEFINE_TEST(user, struct test_user, STRUCT, none);
279
280 /*
281 * Check two uses through a variable declaration outside either path,
282 * which was noticed as a special case in porting earlier stack init
283 * compiler logic.
284 */
__leaf_switch_none(int path,bool fill)285 static int noinline __leaf_switch_none(int path, bool fill)
286 {
287 switch (path) {
288 uint64_t var;
289
290 case 1:
291 target_start = &var;
292 target_size = sizeof(var);
293 if (fill) {
294 fill_start = &var;
295 fill_size = sizeof(var);
296
297 memset(fill_start, forced_mask | 0x55, fill_size);
298 }
299 memcpy(check_buf, target_start, target_size);
300 break;
301 case 2:
302 target_start = &var;
303 target_size = sizeof(var);
304 if (fill) {
305 fill_start = &var;
306 fill_size = sizeof(var);
307
308 memset(fill_start, forced_mask | 0xaa, fill_size);
309 }
310 memcpy(check_buf, target_start, target_size);
311 break;
312 default:
313 var = 5;
314 return var & forced_mask;
315 }
316 return 0;
317 }
318
leaf_switch_1_none(unsigned long sp,bool fill,uint64_t * arg)319 static noinline __init int leaf_switch_1_none(unsigned long sp, bool fill,
320 uint64_t *arg)
321 {
322 return __leaf_switch_none(1, fill);
323 }
324
leaf_switch_2_none(unsigned long sp,bool fill,uint64_t * arg)325 static noinline __init int leaf_switch_2_none(unsigned long sp, bool fill,
326 uint64_t *arg)
327 {
328 return __leaf_switch_none(2, fill);
329 }
330
331 /*
332 * These are expected to fail for most configurations because neither
333 * GCC nor Clang have a way to perform initialization of variables in
334 * non-code areas (i.e. in a switch statement before the first "case").
335 * https://bugs.llvm.org/show_bug.cgi?id=44916
336 */
337 DEFINE_TEST_DRIVER(switch_1_none, uint64_t, SCALAR, 1);
338 DEFINE_TEST_DRIVER(switch_2_none, uint64_t, SCALAR, 1);
339
test_stackinit_init(void)340 static int __init test_stackinit_init(void)
341 {
342 unsigned int failures = 0;
343
344 #define test_scalars(init) do { \
345 failures += test_u8_ ## init (); \
346 failures += test_u16_ ## init (); \
347 failures += test_u32_ ## init (); \
348 failures += test_u64_ ## init (); \
349 failures += test_char_array_ ## init (); \
350 } while (0)
351
352 #define test_structs(init) do { \
353 failures += test_small_hole_ ## init (); \
354 failures += test_big_hole_ ## init (); \
355 failures += test_trailing_hole_ ## init (); \
356 failures += test_packed_ ## init (); \
357 } while (0)
358
359 /* These are explicitly initialized and should always pass. */
360 test_scalars(zero);
361 test_structs(zero);
362 /* Padding here appears to be accidentally always initialized? */
363 test_structs(dynamic_partial);
364 /* Padding initialization depends on compiler behaviors. */
365 test_structs(static_partial);
366 test_structs(static_all);
367 test_structs(dynamic_all);
368 test_structs(runtime_partial);
369 test_structs(runtime_all);
370
371 /* STRUCTLEAK_BYREF_ALL should cover everything from here down. */
372 test_scalars(none);
373 failures += test_switch_1_none();
374 failures += test_switch_2_none();
375
376 /* STRUCTLEAK_BYREF should cover from here down. */
377 test_structs(none);
378
379 /* STRUCTLEAK will only cover this. */
380 failures += test_user();
381
382 if (failures == 0)
383 pr_info("all tests passed!\n");
384 else
385 pr_err("failures: %u\n", failures);
386
387 return failures ? -EINVAL : 0;
388 }
389 module_init(test_stackinit_init);
390
test_stackinit_exit(void)391 static void __exit test_stackinit_exit(void)
392 { }
393 module_exit(test_stackinit_exit);
394
395 MODULE_LICENSE("GPL");
396
