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");
390