1 // SPDX-License-Identifier: GPL-2.0
3 * Test cases for compiler-based stack variable zeroing via future
4 * compiler flags or CONFIG_GCC_PLUGIN_STRUCTLEAK*.
6 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
8 #include <linux/init.h>
9 #include <linux/kernel.h>
10 #include <linux/module.h>
11 #include <linux/string.h>
13 /* Exfiltration buffer. */
14 #define MAX_VAR_SIZE 128
15 static u8 check_buf[MAX_VAR_SIZE];
17 /* Character array to trigger stack protector in all functions. */
20 /* Volatile mask to convince compiler to copy memory with 0xff. */
21 static volatile u8 forced_mask = 0xff;
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;
27 static bool range_contains(char *haystack_start, size_t haystack_size,
28 char *needle_start, size_t needle_size)
30 if (needle_start >= haystack_start &&
31 needle_start + needle_size <= haystack_start + haystack_size)
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
40 #define DO_NOTHING_RETURN_SCALAR(ptr) *(ptr)
41 #define DO_NOTHING_RETURN_STRING(ptr) /**/
42 #define DO_NOTHING_RETURN_STRUCT(ptr) /**/
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))
51 #define FETCH_ARG_SCALAR(var) &var
52 #define FETCH_ARG_STRING(var) var
53 #define FETCH_ARG_STRUCT(var) &var
55 #define FILL_SIZE_STRING 16
57 #define INIT_CLONE_SCALAR /**/
58 #define INIT_CLONE_STRING [FILL_SIZE_STRING]
59 #define INIT_CLONE_STRUCT /**/
61 #define INIT_SCALAR_none /**/
62 #define INIT_SCALAR_zero = 0
64 #define INIT_STRING_none [FILL_SIZE_STRING] /**/
65 #define INIT_STRING_zero [FILL_SIZE_STRING] = { }
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, \
75 #define INIT_STRUCT_dynamic_partial = { .two = arg->two, }
76 #define INIT_STRUCT_dynamic_all = { .one = arg->one, \
78 .three = arg->three, \
81 #define INIT_STRUCT_runtime_partial ; \
83 #define INIT_STRUCT_runtime_all ; \
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?
96 #define DEFINE_TEST_DRIVER(name, var_type, which, xfail) \
97 /* Returns 0 on success, 1 on failure. */ \
98 static noinline __init int test_ ## name (void) \
100 var_type zero INIT_CLONE_ ## which; \
104 /* Notice when a new test is larger than expected. */ \
105 BUILD_BUG_ON(sizeof(zero) > MAX_VAR_SIZE); \
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); \
118 pr_err(#name ": leaf fill was not 0xFF!?\n"); \
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)); \
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)); \
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); \
143 pr_info(#name " ok\n"); \
146 pr_warn(#name " %sFAIL (uninit bytes: %d)\n", \
147 (xfail) ? "X" : "", sum); \
148 return (xfail) ? 0 : 1; \
151 #define DEFINE_TEST(name, var_type, which, init_level) \
152 /* no-op to force compiler into ignoring "uninitialized" vars */\
153 static noinline __init DO_NOTHING_TYPE_ ## which(var_type) \
154 do_nothing_ ## name(var_type *ptr) \
156 /* Will always be true, but compiler doesn't know. */ \
157 if ((unsigned long)ptr > 0x2) \
158 return DO_NOTHING_RETURN_ ## which(ptr); \
160 return DO_NOTHING_RETURN_ ## which(ptr + 1); \
162 static noinline __init int leaf_ ## name(unsigned long sp, \
166 char buf[VAR_BUFFER]; \
167 var_type var INIT_ ## which ## _ ## init_level; \
169 target_start = &var; \
170 target_size = sizeof(var); \
172 * Keep this buffer around to make sure we've got a \
173 * stack frame of SOME kind... \
175 memset(buf, (char)(sp & 0xff), sizeof(buf)); \
176 /* Fill variable with 0xFF. */ \
179 fill_size = sizeof(var); \
181 (char)((sp & 0xff) | forced_mask), \
185 /* Silence "never initialized" warnings. */ \
186 DO_NOTHING_CALL_ ## which(var, name); \
188 /* Exfiltrate "var". */ \
189 memcpy(check_buf, target_start, target_size); \
191 return (int)buf[0] | (int)buf[sizeof(buf) - 1]; \
193 DEFINE_TEST_DRIVER(name, var_type, which, 0)
195 /* Structure with no padding. */
203 /* Simple structure with padding likely to be covered by compiler. */
204 struct test_small_hole {
207 /* 3 byte padding hole here. */
212 /* Trigger unhandled padding in a structure. */
213 struct test_big_hole {
217 /* 61 byte padding hole here. */
218 u8 four __aligned(64);
221 struct test_trailing_hole {
226 /* "sizeof(unsigned long) - 1" byte padding hole here. */
229 /* Test if STRUCTLEAK is clearing structs with __user fields. */
237 #define DEFINE_SCALAR_TEST(name, init) \
238 DEFINE_TEST(name ## _ ## init, name, SCALAR, init)
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)
247 #define DEFINE_STRUCT_TEST(name, init) \
248 DEFINE_TEST(name ## _ ## init, \
249 struct test_ ## name, STRUCT, init)
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)
257 /* These should be fully initialized all the time! */
258 DEFINE_SCALAR_TESTS(zero);
259 DEFINE_STRUCT_TESTS(zero);
260 /* Static initialization: padding may be left uninitialized. */
261 DEFINE_STRUCT_TESTS(static_partial);
262 DEFINE_STRUCT_TESTS(static_all);
263 /* Dynamic initialization: padding may be left uninitialized. */
264 DEFINE_STRUCT_TESTS(dynamic_partial);
265 DEFINE_STRUCT_TESTS(dynamic_all);
266 /* Runtime initialization: padding may be left uninitialized. */
267 DEFINE_STRUCT_TESTS(runtime_partial);
268 DEFINE_STRUCT_TESTS(runtime_all);
269 /* No initialization without compiler instrumentation. */
270 DEFINE_SCALAR_TESTS(none);
271 DEFINE_STRUCT_TESTS(none);
272 DEFINE_TEST(user, struct test_user, STRUCT, none);
275 * Check two uses through a variable declaration outside either path,
276 * which was noticed as a special case in porting earlier stack init
279 static int noinline __leaf_switch_none(int path, bool fill)
286 target_size = sizeof(var);
289 fill_size = sizeof(var);
291 memset(fill_start, forced_mask | 0x55, fill_size);
293 memcpy(check_buf, target_start, target_size);
297 target_size = sizeof(var);
300 fill_size = sizeof(var);
302 memset(fill_start, forced_mask | 0xaa, fill_size);
304 memcpy(check_buf, target_start, target_size);
308 return var & forced_mask;
313 static noinline __init int leaf_switch_1_none(unsigned long sp, bool fill,
316 return __leaf_switch_none(1, fill);
319 static noinline __init int leaf_switch_2_none(unsigned long sp, bool fill,
322 return __leaf_switch_none(2, fill);
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
331 DEFINE_TEST_DRIVER(switch_1_none, uint64_t, SCALAR, 1);
332 DEFINE_TEST_DRIVER(switch_2_none, uint64_t, SCALAR, 1);
334 static int __init test_stackinit_init(void)
336 unsigned int failures = 0;
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 (); \
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 (); \
353 /* These are explicitly initialized and should always pass. */
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);
365 /* STRUCTLEAK_BYREF_ALL should cover everything from here down. */
367 failures += test_switch_1_none();
368 failures += test_switch_2_none();
370 /* STRUCTLEAK_BYREF should cover from here down. */
373 /* STRUCTLEAK will only cover this. */
374 failures += test_user();
377 pr_info("all tests passed!\n");
379 pr_err("failures: %u\n", failures);
381 return failures ? -EINVAL : 0;
383 module_init(test_stackinit_init);
385 static void __exit test_stackinit_exit(void)
387 module_exit(test_stackinit_exit);
389 MODULE_LICENSE("GPL");