xref: /openbmc/linux/kernel/kcov.c (revision 8bd1369b) 
1 // SPDX-License-Identifier: GPL-2.0
2 #define pr_fmt(fmt) "kcov: " fmt
3 
4 #define DISABLE_BRANCH_PROFILING
5 #include <linux/atomic.h>
6 #include <linux/compiler.h>
7 #include <linux/errno.h>
8 #include <linux/export.h>
9 #include <linux/types.h>
10 #include <linux/file.h>
11 #include <linux/fs.h>
12 #include <linux/init.h>
13 #include <linux/mm.h>
14 #include <linux/preempt.h>
15 #include <linux/printk.h>
16 #include <linux/sched.h>
17 #include <linux/slab.h>
18 #include <linux/spinlock.h>
19 #include <linux/vmalloc.h>
20 #include <linux/debugfs.h>
21 #include <linux/uaccess.h>
22 #include <linux/kcov.h>
23 #include <asm/setup.h>
24 
25 /* Number of 64-bit words written per one comparison: */
26 #define KCOV_WORDS_PER_CMP 4
27 
28 /*
29  * kcov descriptor (one per opened debugfs file).
30  * State transitions of the descriptor:
31  *  - initial state after open()
32  *  - then there must be a single ioctl(KCOV_INIT_TRACE) call
33  *  - then, mmap() call (several calls are allowed but not useful)
34  *  - then, ioctl(KCOV_ENABLE, arg), where arg is
35  *	KCOV_TRACE_PC - to trace only the PCs
36  *	or
37  *	KCOV_TRACE_CMP - to trace only the comparison operands
38  *  - then, ioctl(KCOV_DISABLE) to disable the task.
39  * Enabling/disabling ioctls can be repeated (only one task a time allowed).
40  */
41 struct kcov {
42 	/*
43 	 * Reference counter. We keep one for:
44 	 *  - opened file descriptor
45 	 *  - task with enabled coverage (we can't unwire it from another task)
46 	 */
47 	atomic_t		refcount;
48 	/* The lock protects mode, size, area and t. */
49 	spinlock_t		lock;
50 	enum kcov_mode		mode;
51 	/* Size of arena (in long's for KCOV_MODE_TRACE). */
52 	unsigned		size;
53 	/* Coverage buffer shared with user space. */
54 	void			*area;
55 	/* Task for which we collect coverage, or NULL. */
56 	struct task_struct	*t;
57 };
58 
59 static bool check_kcov_mode(enum kcov_mode needed_mode, struct task_struct *t)
60 {
61 	unsigned int mode;
62 
63 	/*
64 	 * We are interested in code coverage as a function of a syscall inputs,
65 	 * so we ignore code executed in interrupts.
66 	 */
67 	if (!in_task())
68 		return false;
69 	mode = READ_ONCE(t->kcov_mode);
70 	/*
71 	 * There is some code that runs in interrupts but for which
72 	 * in_interrupt() returns false (e.g. preempt_schedule_irq()).
73 	 * READ_ONCE()/barrier() effectively provides load-acquire wrt
74 	 * interrupts, there are paired barrier()/WRITE_ONCE() in
75 	 * kcov_ioctl_locked().
76 	 */
77 	barrier();
78 	return mode == needed_mode;
79 }
80 
81 static unsigned long canonicalize_ip(unsigned long ip)
82 {
83 #ifdef CONFIG_RANDOMIZE_BASE
84 	ip -= kaslr_offset();
85 #endif
86 	return ip;
87 }
88 
89 /*
90  * Entry point from instrumented code.
91  * This is called once per basic-block/edge.
92  */
93 void notrace __sanitizer_cov_trace_pc(void)
94 {
95 	struct task_struct *t;
96 	unsigned long *area;
97 	unsigned long ip = canonicalize_ip(_RET_IP_);
98 	unsigned long pos;
99 
100 	t = current;
101 	if (!check_kcov_mode(KCOV_MODE_TRACE_PC, t))
102 		return;
103 
104 	area = t->kcov_area;
105 	/* The first 64-bit word is the number of subsequent PCs. */
106 	pos = READ_ONCE(area[0]) + 1;
107 	if (likely(pos < t->kcov_size)) {
108 		area[pos] = ip;
109 		WRITE_ONCE(area[0], pos);
110 	}
111 }
112 EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
113 
114 #ifdef CONFIG_KCOV_ENABLE_COMPARISONS
115 static void write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
116 {
117 	struct task_struct *t;
118 	u64 *area;
119 	u64 count, start_index, end_pos, max_pos;
120 
121 	t = current;
122 	if (!check_kcov_mode(KCOV_MODE_TRACE_CMP, t))
123 		return;
124 
125 	ip = canonicalize_ip(ip);
126 
127 	/*
128 	 * We write all comparison arguments and types as u64.
129 	 * The buffer was allocated for t->kcov_size unsigned longs.
130 	 */
131 	area = (u64 *)t->kcov_area;
132 	max_pos = t->kcov_size * sizeof(unsigned long);
133 
134 	count = READ_ONCE(area[0]);
135 
136 	/* Every record is KCOV_WORDS_PER_CMP 64-bit words. */
137 	start_index = 1 + count * KCOV_WORDS_PER_CMP;
138 	end_pos = (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64);
139 	if (likely(end_pos <= max_pos)) {
140 		area[start_index] = type;
141 		area[start_index + 1] = arg1;
142 		area[start_index + 2] = arg2;
143 		area[start_index + 3] = ip;
144 		WRITE_ONCE(area[0], count + 1);
145 	}
146 }
147 
148 void notrace __sanitizer_cov_trace_cmp1(u8 arg1, u8 arg2)
149 {
150 	write_comp_data(KCOV_CMP_SIZE(0), arg1, arg2, _RET_IP_);
151 }
152 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp1);
153 
154 void notrace __sanitizer_cov_trace_cmp2(u16 arg1, u16 arg2)
155 {
156 	write_comp_data(KCOV_CMP_SIZE(1), arg1, arg2, _RET_IP_);
157 }
158 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp2);
159 
160 void notrace __sanitizer_cov_trace_cmp4(u32 arg1, u32 arg2)
161 {
162 	write_comp_data(KCOV_CMP_SIZE(2), arg1, arg2, _RET_IP_);
163 }
164 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp4);
165 
166 void notrace __sanitizer_cov_trace_cmp8(u64 arg1, u64 arg2)
167 {
168 	write_comp_data(KCOV_CMP_SIZE(3), arg1, arg2, _RET_IP_);
169 }
170 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp8);
171 
172 void notrace __sanitizer_cov_trace_const_cmp1(u8 arg1, u8 arg2)
173 {
174 	write_comp_data(KCOV_CMP_SIZE(0) | KCOV_CMP_CONST, arg1, arg2,
175 			_RET_IP_);
176 }
177 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp1);
178 
179 void notrace __sanitizer_cov_trace_const_cmp2(u16 arg1, u16 arg2)
180 {
181 	write_comp_data(KCOV_CMP_SIZE(1) | KCOV_CMP_CONST, arg1, arg2,
182 			_RET_IP_);
183 }
184 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp2);
185 
186 void notrace __sanitizer_cov_trace_const_cmp4(u32 arg1, u32 arg2)
187 {
188 	write_comp_data(KCOV_CMP_SIZE(2) | KCOV_CMP_CONST, arg1, arg2,
189 			_RET_IP_);
190 }
191 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp4);
192 
193 void notrace __sanitizer_cov_trace_const_cmp8(u64 arg1, u64 arg2)
194 {
195 	write_comp_data(KCOV_CMP_SIZE(3) | KCOV_CMP_CONST, arg1, arg2,
196 			_RET_IP_);
197 }
198 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp8);
199 
200 void notrace __sanitizer_cov_trace_switch(u64 val, u64 *cases)
201 {
202 	u64 i;
203 	u64 count = cases[0];
204 	u64 size = cases[1];
205 	u64 type = KCOV_CMP_CONST;
206 
207 	switch (size) {
208 	case 8:
209 		type |= KCOV_CMP_SIZE(0);
210 		break;
211 	case 16:
212 		type |= KCOV_CMP_SIZE(1);
213 		break;
214 	case 32:
215 		type |= KCOV_CMP_SIZE(2);
216 		break;
217 	case 64:
218 		type |= KCOV_CMP_SIZE(3);
219 		break;
220 	default:
221 		return;
222 	}
223 	for (i = 0; i < count; i++)
224 		write_comp_data(type, cases[i + 2], val, _RET_IP_);
225 }
226 EXPORT_SYMBOL(__sanitizer_cov_trace_switch);
227 #endif /* ifdef CONFIG_KCOV_ENABLE_COMPARISONS */
228 
229 static void kcov_get(struct kcov *kcov)
230 {
231 	atomic_inc(&kcov->refcount);
232 }
233 
234 static void kcov_put(struct kcov *kcov)
235 {
236 	if (atomic_dec_and_test(&kcov->refcount)) {
237 		vfree(kcov->area);
238 		kfree(kcov);
239 	}
240 }
241 
242 void kcov_task_init(struct task_struct *t)
243 {
244 	WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED);
245 	barrier();
246 	t->kcov_size = 0;
247 	t->kcov_area = NULL;
248 	t->kcov = NULL;
249 }
250 
251 void kcov_task_exit(struct task_struct *t)
252 {
253 	struct kcov *kcov;
254 
255 	kcov = t->kcov;
256 	if (kcov == NULL)
257 		return;
258 	spin_lock(&kcov->lock);
259 	if (WARN_ON(kcov->t != t)) {
260 		spin_unlock(&kcov->lock);
261 		return;
262 	}
263 	/* Just to not leave dangling references behind. */
264 	kcov_task_init(t);
265 	kcov->t = NULL;
266 	kcov->mode = KCOV_MODE_INIT;
267 	spin_unlock(&kcov->lock);
268 	kcov_put(kcov);
269 }
270 
271 static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
272 {
273 	int res = 0;
274 	void *area;
275 	struct kcov *kcov = vma->vm_file->private_data;
276 	unsigned long size, off;
277 	struct page *page;
278 
279 	area = vmalloc_user(vma->vm_end - vma->vm_start);
280 	if (!area)
281 		return -ENOMEM;
282 
283 	spin_lock(&kcov->lock);
284 	size = kcov->size * sizeof(unsigned long);
285 	if (kcov->mode != KCOV_MODE_INIT || vma->vm_pgoff != 0 ||
286 	    vma->vm_end - vma->vm_start != size) {
287 		res = -EINVAL;
288 		goto exit;
289 	}
290 	if (!kcov->area) {
291 		kcov->area = area;
292 		vma->vm_flags |= VM_DONTEXPAND;
293 		spin_unlock(&kcov->lock);
294 		for (off = 0; off < size; off += PAGE_SIZE) {
295 			page = vmalloc_to_page(kcov->area + off);
296 			if (vm_insert_page(vma, vma->vm_start + off, page))
297 				WARN_ONCE(1, "vm_insert_page() failed");
298 		}
299 		return 0;
300 	}
301 exit:
302 	spin_unlock(&kcov->lock);
303 	vfree(area);
304 	return res;
305 }
306 
307 static int kcov_open(struct inode *inode, struct file *filep)
308 {
309 	struct kcov *kcov;
310 
311 	kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
312 	if (!kcov)
313 		return -ENOMEM;
314 	kcov->mode = KCOV_MODE_DISABLED;
315 	atomic_set(&kcov->refcount, 1);
316 	spin_lock_init(&kcov->lock);
317 	filep->private_data = kcov;
318 	return nonseekable_open(inode, filep);
319 }
320 
321 static int kcov_close(struct inode *inode, struct file *filep)
322 {
323 	kcov_put(filep->private_data);
324 	return 0;
325 }
326 
327 /*
328  * Fault in a lazily-faulted vmalloc area before it can be used by
329  * __santizer_cov_trace_pc(), to avoid recursion issues if any code on the
330  * vmalloc fault handling path is instrumented.
331  */
332 static void kcov_fault_in_area(struct kcov *kcov)
333 {
334 	unsigned long stride = PAGE_SIZE / sizeof(unsigned long);
335 	unsigned long *area = kcov->area;
336 	unsigned long offset;
337 
338 	for (offset = 0; offset < kcov->size; offset += stride)
339 		READ_ONCE(area[offset]);
340 }
341 
342 static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
343 			     unsigned long arg)
344 {
345 	struct task_struct *t;
346 	unsigned long size, unused;
347 
348 	switch (cmd) {
349 	case KCOV_INIT_TRACE:
350 		/*
351 		 * Enable kcov in trace mode and setup buffer size.
352 		 * Must happen before anything else.
353 		 */
354 		if (kcov->mode != KCOV_MODE_DISABLED)
355 			return -EBUSY;
356 		/*
357 		 * Size must be at least 2 to hold current position and one PC.
358 		 * Later we allocate size * sizeof(unsigned long) memory,
359 		 * that must not overflow.
360 		 */
361 		size = arg;
362 		if (size < 2 || size > INT_MAX / sizeof(unsigned long))
363 			return -EINVAL;
364 		kcov->size = size;
365 		kcov->mode = KCOV_MODE_INIT;
366 		return 0;
367 	case KCOV_ENABLE:
368 		/*
369 		 * Enable coverage for the current task.
370 		 * At this point user must have been enabled trace mode,
371 		 * and mmapped the file. Coverage collection is disabled only
372 		 * at task exit or voluntary by KCOV_DISABLE. After that it can
373 		 * be enabled for another task.
374 		 */
375 		if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
376 			return -EINVAL;
377 		t = current;
378 		if (kcov->t != NULL || t->kcov != NULL)
379 			return -EBUSY;
380 		if (arg == KCOV_TRACE_PC)
381 			kcov->mode = KCOV_MODE_TRACE_PC;
382 		else if (arg == KCOV_TRACE_CMP)
383 #ifdef CONFIG_KCOV_ENABLE_COMPARISONS
384 			kcov->mode = KCOV_MODE_TRACE_CMP;
385 #else
386 		return -ENOTSUPP;
387 #endif
388 		else
389 			return -EINVAL;
390 		kcov_fault_in_area(kcov);
391 		/* Cache in task struct for performance. */
392 		t->kcov_size = kcov->size;
393 		t->kcov_area = kcov->area;
394 		/* See comment in check_kcov_mode(). */
395 		barrier();
396 		WRITE_ONCE(t->kcov_mode, kcov->mode);
397 		t->kcov = kcov;
398 		kcov->t = t;
399 		/* This is put either in kcov_task_exit() or in KCOV_DISABLE. */
400 		kcov_get(kcov);
401 		return 0;
402 	case KCOV_DISABLE:
403 		/* Disable coverage for the current task. */
404 		unused = arg;
405 		if (unused != 0 || current->kcov != kcov)
406 			return -EINVAL;
407 		t = current;
408 		if (WARN_ON(kcov->t != t))
409 			return -EINVAL;
410 		kcov_task_init(t);
411 		kcov->t = NULL;
412 		kcov->mode = KCOV_MODE_INIT;
413 		kcov_put(kcov);
414 		return 0;
415 	default:
416 		return -ENOTTY;
417 	}
418 }
419 
420 static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
421 {
422 	struct kcov *kcov;
423 	int res;
424 
425 	kcov = filep->private_data;
426 	spin_lock(&kcov->lock);
427 	res = kcov_ioctl_locked(kcov, cmd, arg);
428 	spin_unlock(&kcov->lock);
429 	return res;
430 }
431 
432 static const struct file_operations kcov_fops = {
433 	.open		= kcov_open,
434 	.unlocked_ioctl	= kcov_ioctl,
435 	.compat_ioctl	= kcov_ioctl,
436 	.mmap		= kcov_mmap,
437 	.release        = kcov_close,
438 };
439 
440 static int __init kcov_init(void)
441 {
442 	/*
443 	 * The kcov debugfs file won't ever get removed and thus,
444 	 * there is no need to protect it against removal races. The
445 	 * use of debugfs_create_file_unsafe() is actually safe here.
446 	 */
447 	if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) {
448 		pr_err("failed to create kcov in debugfs\n");
449 		return -ENOMEM;
450 	}
451 	return 0;
452 }
453 
454 device_initcall(kcov_init);
455