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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
15static 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. */
21static volatile u8 forced_mask = 0xff;
22
23/* Location and size tracking to validate fill and test are colocated. */
24static void *fill_start, *target_start;
25static size_t fill_size, target_size;
26
27static 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 = 0, \
71 .two = 0, \
72 .three = 0, \
73 .four = 0, \
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 var.four = 0
88
89/*
90 * @name: unique string name for the test
91 * @var_type: type to be tested for zeroing initialization
92 * @which: is this a SCALAR, STRING, or STRUCT type?
93 * @init_level: what kind of initialization is performed
94 * @xfail: is this test expected to fail?
95 */
96#define DEFINE_TEST_DRIVER(name, var_type, which, xfail) \
97/* Returns 0 on success, 1 on failure. */ \
98static 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 return 0; \
145 } else { \
146 pr_warn(#name " %sFAIL (uninit bytes: %d)\n", \
147 (xfail) ? "X" : "", sum); \
148 return (xfail) ? 0 : 1; \
149 } \
150}
151#define DEFINE_TEST(name, var_type, which, init_level) \
152/* no-op to force compiler into ignoring "uninitialized" vars */\
153static noinline __init DO_NOTHING_TYPE_ ## which(var_type) \
154do_nothing_ ## name(var_type *ptr) \
155{ \
156 /* Will always be true, but compiler doesn't know. */ \
157 if ((unsigned long)ptr > 0x2) \
158 return DO_NOTHING_RETURN_ ## which(ptr); \
159 else \
160 return DO_NOTHING_RETURN_ ## which(ptr + 1); \
161} \
162static noinline __init int leaf_ ## name(unsigned long sp, \
163 bool fill, \
164 var_type *arg) \
165{ \
166 char buf[VAR_BUFFER]; \
167 var_type var INIT_ ## which ## _ ## init_level; \
168 \
169 target_start = &var; \
170 target_size = sizeof(var); \
171 /* \
172 * Keep this buffer around to make sure we've got a \
173 * stack frame of SOME kind... \
174 */ \
175 memset(buf, (char)(sp & 0xff), sizeof(buf)); \
176 /* Fill variable with 0xFF. */ \
177 if (fill) { \
178 fill_start = &var; \
179 fill_size = sizeof(var); \
180 memset(fill_start, \
181 (char)((sp & 0xff) | forced_mask), \
182 fill_size); \
183 } \
184 \
185 /* Silence "never initialized" warnings. */ \
186 DO_NOTHING_CALL_ ## which(var, name); \
187 \
188 /* Exfiltrate "var". */ \
189 memcpy(check_buf, target_start, target_size); \
190 \
191 return (int)buf[0] | (int)buf[sizeof(buf) - 1]; \
192} \
193DEFINE_TEST_DRIVER(name, var_type, which, 0)
194
195/* Structure with no padding. */
196struct test_packed {
197 unsigned long one;
198 unsigned long two;
199 unsigned long three;
200 unsigned long four;
201};
202
203/* Simple structure with padding likely to be covered by compiler. */
204struct test_small_hole {
205 size_t one;
206 char two;
207 /* 3 byte padding hole here. */
208 int three;
209 unsigned long four;
210};
211
212/* Trigger unhandled padding in a structure. */
213struct test_big_hole {
214 u8 one;
215 u8 two;
216 u8 three;
217 /* 61 byte padding hole here. */
218 u8 four __aligned(64);
219} __aligned(64);
220
221struct test_trailing_hole {
222 char *one;
223 char *two;
224 char *three;
225 char four;
226 /* "sizeof(unsigned long) - 1" byte padding hole here. */
227};
228
229/* Test if STRUCTLEAK is clearing structs with __user fields. */
230struct test_user {
231 u8 one;
232 unsigned long two;
233 char __user *three;
234 unsigned long four;
235};
236
237#define DEFINE_SCALAR_TEST(name, init) \
238 DEFINE_TEST(name ## _ ## init, name, SCALAR, init)
239
240#define DEFINE_SCALAR_TESTS(init) \
241 DEFINE_SCALAR_TEST(u8, init); \
242 DEFINE_SCALAR_TEST(u16, init); \
243 DEFINE_SCALAR_TEST(u32, init); \
244 DEFINE_SCALAR_TEST(u64, init); \
245 DEFINE_TEST(char_array_ ## init, unsigned char, STRING, init)
246
247#define DEFINE_STRUCT_TEST(name, init) \
248 DEFINE_TEST(name ## _ ## init, \
249 struct test_ ## name, STRUCT, init)
250
251#define DEFINE_STRUCT_TESTS(init) \
252 DEFINE_STRUCT_TEST(small_hole, init); \
253 DEFINE_STRUCT_TEST(big_hole, init); \
254 DEFINE_STRUCT_TEST(trailing_hole, init); \
255 DEFINE_STRUCT_TEST(packed, init)
256
257/* These should be fully initialized all the time! */
258DEFINE_SCALAR_TESTS(zero);
259DEFINE_STRUCT_TESTS(zero);
260/* Static initialization: padding may be left uninitialized. */
261DEFINE_STRUCT_TESTS(static_partial);
262DEFINE_STRUCT_TESTS(static_all);
263/* Dynamic initialization: padding may be left uninitialized. */
264DEFINE_STRUCT_TESTS(dynamic_partial);
265DEFINE_STRUCT_TESTS(dynamic_all);
266/* Runtime initialization: padding may be left uninitialized. */
267DEFINE_STRUCT_TESTS(runtime_partial);
268DEFINE_STRUCT_TESTS(runtime_all);
269/* No initialization without compiler instrumentation. */
270DEFINE_SCALAR_TESTS(none);
271DEFINE_STRUCT_TESTS(none);
272DEFINE_TEST(user, struct test_user, STRUCT, none);
273
274/*
275 * Check two uses through a variable declaration outside either path,
276 * which was noticed as a special case in porting earlier stack init
277 * compiler logic.
278 */
279static int noinline __leaf_switch_none(int path, bool fill)
280{
281 switch (path) {
282 uint64_t var;
283
284 case 1:
285 target_start = &var;
286 target_size = sizeof(var);
287 if (fill) {
288 fill_start = &var;
289 fill_size = sizeof(var);
290
291 memset(fill_start, forced_mask | 0x55, fill_size);
292 }
293 memcpy(check_buf, target_start, target_size);
294 break;
295 case 2:
296 target_start = &var;
297 target_size = sizeof(var);
298 if (fill) {
299 fill_start = &var;
300 fill_size = sizeof(var);
301
302 memset(fill_start, forced_mask | 0xaa, fill_size);
303 }
304 memcpy(check_buf, target_start, target_size);
305 break;
306 default:
307 var = 5;
308 return var & forced_mask;
309 }
310 return 0;
311}
312
313static noinline __init int leaf_switch_1_none(unsigned long sp, bool fill,
314 uint64_t *arg)
315{
316 return __leaf_switch_none(1, fill);
317}
318
319static noinline __init int leaf_switch_2_none(unsigned long sp, bool fill,
320 uint64_t *arg)
321{
322 return __leaf_switch_none(2, fill);
323}
324
325/*
326 * These are expected to fail for most configurations because neither
327 * GCC nor Clang have a way to perform initialization of variables in
328 * non-code areas (i.e. in a switch statement before the first "case").
329 * https://bugs.llvm.org/show_bug.cgi?id=44916
330 */
331DEFINE_TEST_DRIVER(switch_1_none, uint64_t, SCALAR, 1);
332DEFINE_TEST_DRIVER(switch_2_none, uint64_t, SCALAR, 1);
333
334static int __init test_stackinit_init(void)
335{
336 unsigned int failures = 0;
337
338#define test_scalars(init) do { \
339 failures += test_u8_ ## init (); \
340 failures += test_u16_ ## init (); \
341 failures += test_u32_ ## init (); \
342 failures += test_u64_ ## init (); \
343 failures += test_char_array_ ## init (); \
344 } while (0)
345
346#define test_structs(init) do { \
347 failures += test_small_hole_ ## init (); \
348 failures += test_big_hole_ ## init (); \
349 failures += test_trailing_hole_ ## init (); \
350 failures += test_packed_ ## init (); \
351 } while (0)
352
353 /* These are explicitly initialized and should always pass. */
354 test_scalars(zero);
355 test_structs(zero);
356 /* Padding here appears to be accidentally always initialized? */
357 test_structs(dynamic_partial);
358 /* Padding initialization depends on compiler behaviors. */
359 test_structs(static_partial);
360 test_structs(static_all);
361 test_structs(dynamic_all);
362 test_structs(runtime_partial);
363 test_structs(runtime_all);
364
365 /* STRUCTLEAK_BYREF_ALL should cover everything from here down. */
366 test_scalars(none);
367 failures += test_switch_1_none();
368 failures += test_switch_2_none();
369
370 /* STRUCTLEAK_BYREF should cover from here down. */
371 test_structs(none);
372
373 /* STRUCTLEAK will only cover this. */
374 failures += test_user();
375
376 if (failures == 0)
377 pr_info("all tests passed!\n");
378 else
379 pr_err("failures: %u\n", failures);
380
381 return failures ? -EINVAL : 0;
382}
383module_init(test_stackinit_init);
384
385static void __exit test_stackinit_exit(void)
386{ }
387module_exit(test_stackinit_exit);
388
389MODULE_LICENSE("GPL");