summaryrefslogtreecommitdiffstats
path: root/drivers/misc/lkdtm/bugs.c
blob: 24245ccdba7207f9bb021708de67fd422d04cacb (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
// SPDX-License-Identifier: GPL-2.0
/*
 * This is for all the tests related to logic bugs (e.g. bad dereferences,
 * bad alignment, bad loops, bad locking, bad scheduling, deep stacks, and
 * lockups) along with other things that don't fit well into existing LKDTM
 * test source files.
 */
#include "lkdtm.h"
#include <linux/list.h>
#include <linux/sched.h>
#include <linux/sched/signal.h>
#include <linux/sched/task_stack.h>
#include <linux/uaccess.h>

struct lkdtm_list {
	struct list_head node;
};

/*
 * Make sure our attempts to over run the kernel stack doesn't trigger
 * a compiler warning when CONFIG_FRAME_WARN is set. Then make sure we
 * recurse past the end of THREAD_SIZE by default.
 */
#if defined(CONFIG_FRAME_WARN) && (CONFIG_FRAME_WARN > 0)
#define REC_STACK_SIZE (_AC(CONFIG_FRAME_WARN, UL) / 2)
#else
#define REC_STACK_SIZE (THREAD_SIZE / 8)
#endif
#define REC_NUM_DEFAULT ((THREAD_SIZE / REC_STACK_SIZE) * 2)

static int recur_count = REC_NUM_DEFAULT;

static DEFINE_SPINLOCK(lock_me_up);

/*
 * Make sure compiler does not optimize this function or stack frame away:
 * - function marked noinline
 * - stack variables are marked volatile
 * - stack variables are written (memset()) and read (pr_info())
 * - function has external effects (pr_info())
 * */
static int noinline recursive_loop(int remaining)
{
	volatile char buf[REC_STACK_SIZE];

	memset((void *)buf, remaining & 0xFF, sizeof(buf));
	pr_info("loop %d/%d ...\n", (int)buf[remaining % sizeof(buf)],
		recur_count);
	if (!remaining)
		return 0;
	else
		return recursive_loop(remaining - 1);
}

/* If the depth is negative, use the default, otherwise keep parameter. */
void __init lkdtm_bugs_init(int *recur_param)
{
	if (*recur_param < 0)
		*recur_param = recur_count;
	else
		recur_count = *recur_param;
}

void lkdtm_PANIC(void)
{
	panic("dumptest");
}

void lkdtm_BUG(void)
{
	BUG();
}

static int warn_counter;

void lkdtm_WARNING(void)
{
	WARN(1, "Warning message trigger count: %d\n", warn_counter++);
}

void lkdtm_EXCEPTION(void)
{
	*((volatile int *) 0) = 0;
}

void lkdtm_LOOP(void)
{
	for (;;)
		;
}

void lkdtm_EXHAUST_STACK(void)
{
	pr_info("Calling function with %lu frame size to depth %d ...\n",
		REC_STACK_SIZE, recur_count);
	recursive_loop(recur_count);
	pr_info("FAIL: survived without exhausting stack?!\n");
}

static noinline void __lkdtm_CORRUPT_STACK(void *stack)
{
	memset(stack, '\xff', 64);
}

/* This should trip the stack canary, not corrupt the return address. */
noinline void lkdtm_CORRUPT_STACK(void)
{
	/* Use default char array length that triggers stack protection. */
	char data[8] __aligned(sizeof(void *));

	__lkdtm_CORRUPT_STACK(&data);

	pr_info("Corrupted stack containing char array ...\n");
}

/* Same as above but will only get a canary with -fstack-protector-strong */
noinline void lkdtm_CORRUPT_STACK_STRONG(void)
{
	union {
		unsigned short shorts[4];
		unsigned long *ptr;
	} data __aligned(sizeof(void *));

	__lkdtm_CORRUPT_STACK(&data);

	pr_info("Corrupted stack containing union ...\n");
}

void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void)
{
	static u8 data[5] __attribute__((aligned(4))) = {1, 2, 3, 4, 5};
	u32 *p;
	u32 val = 0x12345678;

	p = (u32 *)(data + 1);
	if (*p == 0)
		val = 0x87654321;
	*p = val;
}

void lkdtm_SOFTLOCKUP(void)
{
	preempt_disable();
	for (;;)
		cpu_relax();
}

void lkdtm_HARDLOCKUP(void)
{
	local_irq_disable();
	for (;;)
		cpu_relax();
}

void lkdtm_SPINLOCKUP(void)
{
	/* Must be called twice to trigger. */
	spin_lock(&lock_me_up);
	/* Let sparse know we intended to exit holding the lock. */
	__release(&lock_me_up);
}

void lkdtm_HUNG_TASK(void)
{
	set_current_state(TASK_UNINTERRUPTIBLE);
	schedule();
}

void lkdtm_CORRUPT_LIST_ADD(void)
{
	/*
	 * Initially, an empty list via LIST_HEAD:
	 *	test_head.next = &test_head
	 *	test_head.prev = &test_head
	 */
	LIST_HEAD(test_head);
	struct lkdtm_list good, bad;
	void *target[2] = { };
	void *redirection = &target;

	pr_info("attempting good list addition\n");

	/*
	 * Adding to the list performs these actions:
	 *	test_head.next->prev = &good.node
	 *	good.node.next = test_head.next
	 *	good.node.prev = test_head
	 *	test_head.next = good.node
	 */
	list_add(&good.node, &test_head);

	pr_info("attempting corrupted list addition\n");
	/*
	 * In simulating this "write what where" primitive, the "what" is
	 * the address of &bad.node, and the "where" is the address held
	 * by "redirection".
	 */
	test_head.next = redirection;
	list_add(&bad.node, &test_head);

	if (target[0] == NULL && target[1] == NULL)
		pr_err("Overwrite did not happen, but no BUG?!\n");
	else
		pr_err("list_add() corruption not detected!\n");
}

void lkdtm_CORRUPT_LIST_DEL(void)
{
	LIST_HEAD(test_head);
	struct lkdtm_list item;
	void *target[2] = { };
	void *redirection = &target;

	list_add(&item.node, &test_head);

	pr_info("attempting good list removal\n");
	list_del(&item.node);

	pr_info("attempting corrupted list removal\n");
	list_add(&item.node, &test_head);

	/* As with the list_add() test above, this corrupts "next". */
	item.node.next = redirection;
	list_del(&item.node);

	if (target[0] == NULL && target[1] == NULL)
		pr_err("Overwrite did not happen, but no BUG?!\n");
	else
		pr_err("list_del() corruption not detected!\n");
}

/* Test if unbalanced set_fs(KERNEL_DS)/set_fs(USER_DS) check exists. */
void lkdtm_CORRUPT_USER_DS(void)
{
	pr_info("setting bad task size limit\n");
	set_fs(KERNEL_DS);

	/* Make sure we do not keep running with a KERNEL_DS! */
	force_sig(SIGKILL);
}

/* Test that VMAP_STACK is actually allocating with a leading guard page */
void lkdtm_STACK_GUARD_PAGE_LEADING(void)
{
	const unsigned char *stack = task_stack_page(current);
	const unsigned char *ptr = stack - 1;
	volatile unsigned char byte;

	pr_info("attempting bad read from page below current stack\n");

	byte = *ptr;

	pr_err("FAIL: accessed page before stack!\n");
}

/* Test that VMAP_STACK is actually allocating with a trailing guard page */
void lkdtm_STACK_GUARD_PAGE_TRAILING(void)
{
	const unsigned char *stack = task_stack_page(current);
	const unsigned char *ptr = stack + THREAD_SIZE;
	volatile unsigned char byte;

	pr_info("attempting bad read from page above current stack\n");

	byte = *ptr;

	pr_err("FAIL: accessed page after stack!\n");
}

void lkdtm_UNSET_SMEP(void)
{
#ifdef CONFIG_X86_64
#define MOV_CR4_DEPTH	64
	void (*direct_write_cr4)(unsigned long val);
	unsigned char *insn;
	unsigned long cr4;
	int i;

	cr4 = native_read_cr4();

	if ((cr4 & X86_CR4_SMEP) != X86_CR4_SMEP) {
		pr_err("FAIL: SMEP not in use\n");
		return;
	}
	cr4 &= ~(X86_CR4_SMEP);

	pr_info("trying to clear SMEP normally\n");
	native_write_cr4(cr4);
	if (cr4 == native_read_cr4()) {
		pr_err("FAIL: pinning SMEP failed!\n");
		cr4 |= X86_CR4_SMEP;
		pr_info("restoring SMEP\n");
		native_write_cr4(cr4);
		return;
	}
	pr_info("ok: SMEP did not get cleared\n");

	/*
	 * To test the post-write pinning verification we need to call
	 * directly into the middle of native_write_cr4() where the
	 * cr4 write happens, skipping any pinning. This searches for
	 * the cr4 writing instruction.
	 */
	insn = (unsigned char *)native_write_cr4;
	for (i = 0; i < MOV_CR4_DEPTH; i++) {
		/* mov %rdi, %cr4 */
		if (insn[i] == 0x0f && insn[i+1] == 0x22 && insn[i+2] == 0xe7)
			break;
		/* mov %rdi,%rax; mov %rax, %cr4 */
		if (insn[i]   == 0x48 && insn[i+1] == 0x89 &&
		    insn[i+2] == 0xf8 && insn[i+3] == 0x0f &&
		    insn[i+4] == 0x22 && insn[i+5] == 0xe0)
			break;
	}
	if (i >= MOV_CR4_DEPTH) {
		pr_info("ok: cannot locate cr4 writing call gadget\n");
		return;
	}
	direct_write_cr4 = (void *)(insn + i);

	pr_info("trying to clear SMEP with call gadget\n");
	direct_write_cr4(cr4);
	if (native_read_cr4() & X86_CR4_SMEP) {
		pr_info("ok: SMEP removal was reverted\n");
	} else {
		pr_err("FAIL: cleared SMEP not detected!\n");
		cr4 |= X86_CR4_SMEP;
		pr_info("restoring SMEP\n");
		native_write_cr4(cr4);
	}
#else
	pr_err("FAIL: this test is x86_64-only\n");
#endif
}