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/hashtable.h>
13 #include <linux/init.h>
14 #include <linux/mm.h>
15 #include <linux/preempt.h>
16 #include <linux/printk.h>
17 #include <linux/sched.h>
18 #include <linux/slab.h>
19 #include <linux/spinlock.h>
20 #include <linux/vmalloc.h>
21 #include <linux/debugfs.h>
22 #include <linux/uaccess.h>
23 #include <linux/kcov.h>
24 #include <linux/refcount.h>
25 #include <linux/log2.h>
26 #include <asm/setup.h>
27
28 #define kcov_debug(fmt, ...) pr_debug("%s: " fmt, __func__, ##__VA_ARGS__)
29
30 /* Number of 64-bit words written per one comparison: */
31 #define KCOV_WORDS_PER_CMP 4
32
33 /*
34 * kcov descriptor (one per opened debugfs file).
35 * State transitions of the descriptor:
36 * - initial state after open()
37 * - then there must be a single ioctl(KCOV_INIT_TRACE) call
38 * - then, mmap() call (several calls are allowed but not useful)
39 * - then, ioctl(KCOV_ENABLE, arg), where arg is
40 * KCOV_TRACE_PC - to trace only the PCs
41 * or
42 * KCOV_TRACE_CMP - to trace only the comparison operands
43 * - then, ioctl(KCOV_DISABLE) to disable the task.
44 * Enabling/disabling ioctls can be repeated (only one task a time allowed).
45 */
46 struct kcov {
47 /*
48 * Reference counter. We keep one for:
49 * - opened file descriptor
50 * - task with enabled coverage (we can't unwire it from another task)
51 * - each code section for remote coverage collection
52 */
53 refcount_t refcount;
54 /* The lock protects mode, size, area and t. */
55 spinlock_t lock;
56 enum kcov_mode mode;
57 /* Size of arena (in long's). */
58 unsigned int size;
59 /* Coverage buffer shared with user space. */
60 void *area;
61 /* Task for which we collect coverage, or NULL. */
62 struct task_struct *t;
63 /* Collecting coverage from remote (background) threads. */
64 bool remote;
65 /* Size of remote area (in long's). */
66 unsigned int remote_size;
67 /*
68 * Sequence is incremented each time kcov is reenabled, used by
69 * kcov_remote_stop(), see the comment there.
70 */
71 int sequence;
72 };
73
74 struct kcov_remote_area {
75 struct list_head list;
76 unsigned int size;
77 };
78
79 struct kcov_remote {
80 u64 handle;
81 struct kcov *kcov;
82 struct hlist_node hnode;
83 };
84
85 static DEFINE_SPINLOCK(kcov_remote_lock);
86 static DEFINE_HASHTABLE(kcov_remote_map, 4);
87 static struct list_head kcov_remote_areas = LIST_HEAD_INIT(kcov_remote_areas);
88
89 struct kcov_percpu_data {
90 void *irq_area;
91
92 unsigned int saved_mode;
93 unsigned int saved_size;
94 void *saved_area;
95 struct kcov *saved_kcov;
96 int saved_sequence;
97 };
98
99 static DEFINE_PER_CPU(struct kcov_percpu_data, kcov_percpu_data);
100
101 /* Must be called with kcov_remote_lock locked. */
kcov_remote_find(u64 handle)102 static struct kcov_remote *kcov_remote_find(u64 handle)
103 {
104 struct kcov_remote *remote;
105
106 hash_for_each_possible(kcov_remote_map, remote, hnode, handle) {
107 if (remote->handle == handle)
108 return remote;
109 }
110 return NULL;
111 }
112
113 /* Must be called with kcov_remote_lock locked. */
kcov_remote_add(struct kcov * kcov,u64 handle)114 static struct kcov_remote *kcov_remote_add(struct kcov *kcov, u64 handle)
115 {
116 struct kcov_remote *remote;
117
118 if (kcov_remote_find(handle))
119 return ERR_PTR(-EEXIST);
120 remote = kmalloc(sizeof(*remote), GFP_ATOMIC);
121 if (!remote)
122 return ERR_PTR(-ENOMEM);
123 remote->handle = handle;
124 remote->kcov = kcov;
125 hash_add(kcov_remote_map, &remote->hnode, handle);
126 return remote;
127 }
128
129 /* Must be called with kcov_remote_lock locked. */
kcov_remote_area_get(unsigned int size)130 static struct kcov_remote_area *kcov_remote_area_get(unsigned int size)
131 {
132 struct kcov_remote_area *area;
133 struct list_head *pos;
134
135 list_for_each(pos, &kcov_remote_areas) {
136 area = list_entry(pos, struct kcov_remote_area, list);
137 if (area->size == size) {
138 list_del(&area->list);
139 return area;
140 }
141 }
142 return NULL;
143 }
144
145 /* Must be called with kcov_remote_lock locked. */
kcov_remote_area_put(struct kcov_remote_area * area,unsigned int size)146 static void kcov_remote_area_put(struct kcov_remote_area *area,
147 unsigned int size)
148 {
149 INIT_LIST_HEAD(&area->list);
150 area->size = size;
151 list_add(&area->list, &kcov_remote_areas);
152 }
153
check_kcov_mode(enum kcov_mode needed_mode,struct task_struct * t)154 static notrace bool check_kcov_mode(enum kcov_mode needed_mode, struct task_struct *t)
155 {
156 unsigned int mode;
157
158 /*
159 * We are interested in code coverage as a function of a syscall inputs,
160 * so we ignore code executed in interrupts, unless we are in a remote
161 * coverage collection section in a softirq.
162 */
163 if (!in_task() && !(in_serving_softirq() && t->kcov_softirq))
164 return false;
165 mode = READ_ONCE(t->kcov_mode);
166 /*
167 * There is some code that runs in interrupts but for which
168 * in_interrupt() returns false (e.g. preempt_schedule_irq()).
169 * READ_ONCE()/barrier() effectively provides load-acquire wrt
170 * interrupts, there are paired barrier()/WRITE_ONCE() in
171 * kcov_start().
172 */
173 barrier();
174 return mode == needed_mode;
175 }
176
canonicalize_ip(unsigned long ip)177 static notrace unsigned long canonicalize_ip(unsigned long ip)
178 {
179 #ifdef CONFIG_RANDOMIZE_BASE
180 ip -= kaslr_offset();
181 #endif
182 return ip;
183 }
184
185 /*
186 * Entry point from instrumented code.
187 * This is called once per basic-block/edge.
188 */
__sanitizer_cov_trace_pc(void)189 void notrace __sanitizer_cov_trace_pc(void)
190 {
191 struct task_struct *t;
192 unsigned long *area;
193 unsigned long ip = canonicalize_ip(_RET_IP_);
194 unsigned long pos;
195
196 t = current;
197 if (!check_kcov_mode(KCOV_MODE_TRACE_PC, t))
198 return;
199
200 area = t->kcov_area;
201 /* The first 64-bit word is the number of subsequent PCs. */
202 pos = READ_ONCE(area[0]) + 1;
203 if (likely(pos < t->kcov_size)) {
204 area[pos] = ip;
205 WRITE_ONCE(area[0], pos);
206 }
207 }
208 EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
209
210 #ifdef CONFIG_KCOV_ENABLE_COMPARISONS
write_comp_data(u64 type,u64 arg1,u64 arg2,u64 ip)211 static void notrace write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
212 {
213 struct task_struct *t;
214 u64 *area;
215 u64 count, start_index, end_pos, max_pos;
216
217 t = current;
218 if (!check_kcov_mode(KCOV_MODE_TRACE_CMP, t))
219 return;
220
221 ip = canonicalize_ip(ip);
222
223 /*
224 * We write all comparison arguments and types as u64.
225 * The buffer was allocated for t->kcov_size unsigned longs.
226 */
227 area = (u64 *)t->kcov_area;
228 max_pos = t->kcov_size * sizeof(unsigned long);
229
230 count = READ_ONCE(area[0]);
231
232 /* Every record is KCOV_WORDS_PER_CMP 64-bit words. */
233 start_index = 1 + count * KCOV_WORDS_PER_CMP;
234 end_pos = (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64);
235 if (likely(end_pos <= max_pos)) {
236 area[start_index] = type;
237 area[start_index + 1] = arg1;
238 area[start_index + 2] = arg2;
239 area[start_index + 3] = ip;
240 WRITE_ONCE(area[0], count + 1);
241 }
242 }
243
__sanitizer_cov_trace_cmp1(u8 arg1,u8 arg2)244 void notrace __sanitizer_cov_trace_cmp1(u8 arg1, u8 arg2)
245 {
246 write_comp_data(KCOV_CMP_SIZE(0), arg1, arg2, _RET_IP_);
247 }
248 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp1);
249
__sanitizer_cov_trace_cmp2(u16 arg1,u16 arg2)250 void notrace __sanitizer_cov_trace_cmp2(u16 arg1, u16 arg2)
251 {
252 write_comp_data(KCOV_CMP_SIZE(1), arg1, arg2, _RET_IP_);
253 }
254 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp2);
255
__sanitizer_cov_trace_cmp4(u32 arg1,u32 arg2)256 void notrace __sanitizer_cov_trace_cmp4(u32 arg1, u32 arg2)
257 {
258 write_comp_data(KCOV_CMP_SIZE(2), arg1, arg2, _RET_IP_);
259 }
260 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp4);
261
__sanitizer_cov_trace_cmp8(u64 arg1,u64 arg2)262 void notrace __sanitizer_cov_trace_cmp8(u64 arg1, u64 arg2)
263 {
264 write_comp_data(KCOV_CMP_SIZE(3), arg1, arg2, _RET_IP_);
265 }
266 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp8);
267
__sanitizer_cov_trace_const_cmp1(u8 arg1,u8 arg2)268 void notrace __sanitizer_cov_trace_const_cmp1(u8 arg1, u8 arg2)
269 {
270 write_comp_data(KCOV_CMP_SIZE(0) | KCOV_CMP_CONST, arg1, arg2,
271 _RET_IP_);
272 }
273 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp1);
274
__sanitizer_cov_trace_const_cmp2(u16 arg1,u16 arg2)275 void notrace __sanitizer_cov_trace_const_cmp2(u16 arg1, u16 arg2)
276 {
277 write_comp_data(KCOV_CMP_SIZE(1) | KCOV_CMP_CONST, arg1, arg2,
278 _RET_IP_);
279 }
280 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp2);
281
__sanitizer_cov_trace_const_cmp4(u32 arg1,u32 arg2)282 void notrace __sanitizer_cov_trace_const_cmp4(u32 arg1, u32 arg2)
283 {
284 write_comp_data(KCOV_CMP_SIZE(2) | KCOV_CMP_CONST, arg1, arg2,
285 _RET_IP_);
286 }
287 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp4);
288
__sanitizer_cov_trace_const_cmp8(u64 arg1,u64 arg2)289 void notrace __sanitizer_cov_trace_const_cmp8(u64 arg1, u64 arg2)
290 {
291 write_comp_data(KCOV_CMP_SIZE(3) | KCOV_CMP_CONST, arg1, arg2,
292 _RET_IP_);
293 }
294 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp8);
295
__sanitizer_cov_trace_switch(u64 val,u64 * cases)296 void notrace __sanitizer_cov_trace_switch(u64 val, u64 *cases)
297 {
298 u64 i;
299 u64 count = cases[0];
300 u64 size = cases[1];
301 u64 type = KCOV_CMP_CONST;
302
303 switch (size) {
304 case 8:
305 type |= KCOV_CMP_SIZE(0);
306 break;
307 case 16:
308 type |= KCOV_CMP_SIZE(1);
309 break;
310 case 32:
311 type |= KCOV_CMP_SIZE(2);
312 break;
313 case 64:
314 type |= KCOV_CMP_SIZE(3);
315 break;
316 default:
317 return;
318 }
319 for (i = 0; i < count; i++)
320 write_comp_data(type, cases[i + 2], val, _RET_IP_);
321 }
322 EXPORT_SYMBOL(__sanitizer_cov_trace_switch);
323 #endif /* ifdef CONFIG_KCOV_ENABLE_COMPARISONS */
324
kcov_start(struct task_struct * t,struct kcov * kcov,unsigned int size,void * area,enum kcov_mode mode,int sequence)325 static void kcov_start(struct task_struct *t, struct kcov *kcov,
326 unsigned int size, void *area, enum kcov_mode mode,
327 int sequence)
328 {
329 kcov_debug("t = %px, size = %u, area = %px\n", t, size, area);
330 t->kcov = kcov;
331 /* Cache in task struct for performance. */
332 t->kcov_size = size;
333 t->kcov_area = area;
334 t->kcov_sequence = sequence;
335 /* See comment in check_kcov_mode(). */
336 barrier();
337 WRITE_ONCE(t->kcov_mode, mode);
338 }
339
kcov_stop(struct task_struct * t)340 static void kcov_stop(struct task_struct *t)
341 {
342 WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED);
343 barrier();
344 t->kcov = NULL;
345 t->kcov_size = 0;
346 t->kcov_area = NULL;
347 }
348
kcov_task_reset(struct task_struct * t)349 static void kcov_task_reset(struct task_struct *t)
350 {
351 kcov_stop(t);
352 t->kcov_sequence = 0;
353 t->kcov_handle = 0;
354 }
355
kcov_task_init(struct task_struct * t)356 void kcov_task_init(struct task_struct *t)
357 {
358 kcov_task_reset(t);
359 t->kcov_handle = current->kcov_handle;
360 }
361
kcov_reset(struct kcov * kcov)362 static void kcov_reset(struct kcov *kcov)
363 {
364 kcov->t = NULL;
365 kcov->mode = KCOV_MODE_INIT;
366 kcov->remote = false;
367 kcov->remote_size = 0;
368 kcov->sequence++;
369 }
370
kcov_remote_reset(struct kcov * kcov)371 static void kcov_remote_reset(struct kcov *kcov)
372 {
373 int bkt;
374 struct kcov_remote *remote;
375 struct hlist_node *tmp;
376 unsigned long flags;
377
378 spin_lock_irqsave(&kcov_remote_lock, flags);
379 hash_for_each_safe(kcov_remote_map, bkt, tmp, remote, hnode) {
380 if (remote->kcov != kcov)
381 continue;
382 hash_del(&remote->hnode);
383 kfree(remote);
384 }
385 /* Do reset before unlock to prevent races with kcov_remote_start(). */
386 kcov_reset(kcov);
387 spin_unlock_irqrestore(&kcov_remote_lock, flags);
388 }
389
kcov_disable(struct task_struct * t,struct kcov * kcov)390 static void kcov_disable(struct task_struct *t, struct kcov *kcov)
391 {
392 kcov_task_reset(t);
393 if (kcov->remote)
394 kcov_remote_reset(kcov);
395 else
396 kcov_reset(kcov);
397 }
398
kcov_get(struct kcov * kcov)399 static void kcov_get(struct kcov *kcov)
400 {
401 refcount_inc(&kcov->refcount);
402 }
403
kcov_put(struct kcov * kcov)404 static void kcov_put(struct kcov *kcov)
405 {
406 if (refcount_dec_and_test(&kcov->refcount)) {
407 kcov_remote_reset(kcov);
408 vfree(kcov->area);
409 kfree(kcov);
410 }
411 }
412
kcov_task_exit(struct task_struct * t)413 void kcov_task_exit(struct task_struct *t)
414 {
415 struct kcov *kcov;
416 unsigned long flags;
417
418 kcov = t->kcov;
419 if (kcov == NULL)
420 return;
421
422 spin_lock_irqsave(&kcov->lock, flags);
423 kcov_debug("t = %px, kcov->t = %px\n", t, kcov->t);
424 /*
425 * For KCOV_ENABLE devices we want to make sure that t->kcov->t == t,
426 * which comes down to:
427 * WARN_ON(!kcov->remote && kcov->t != t);
428 *
429 * For KCOV_REMOTE_ENABLE devices, the exiting task is either:
430 *
431 * 1. A remote task between kcov_remote_start() and kcov_remote_stop().
432 * In this case we should print a warning right away, since a task
433 * shouldn't be exiting when it's in a kcov coverage collection
434 * section. Here t points to the task that is collecting remote
435 * coverage, and t->kcov->t points to the thread that created the
436 * kcov device. Which means that to detect this case we need to
437 * check that t != t->kcov->t, and this gives us the following:
438 * WARN_ON(kcov->remote && kcov->t != t);
439 *
440 * 2. The task that created kcov exiting without calling KCOV_DISABLE,
441 * and then again we make sure that t->kcov->t == t:
442 * WARN_ON(kcov->remote && kcov->t != t);
443 *
444 * By combining all three checks into one we get:
445 */
446 if (WARN_ON(kcov->t != t)) {
447 spin_unlock_irqrestore(&kcov->lock, flags);
448 return;
449 }
450 /* Just to not leave dangling references behind. */
451 kcov_disable(t, kcov);
452 spin_unlock_irqrestore(&kcov->lock, flags);
453 kcov_put(kcov);
454 }
455
kcov_mmap(struct file * filep,struct vm_area_struct * vma)456 static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
457 {
458 int res = 0;
459 void *area;
460 struct kcov *kcov = vma->vm_file->private_data;
461 unsigned long size, off;
462 struct page *page;
463 unsigned long flags;
464
465 area = vmalloc_user(vma->vm_end - vma->vm_start);
466 if (!area)
467 return -ENOMEM;
468
469 spin_lock_irqsave(&kcov->lock, flags);
470 size = kcov->size * sizeof(unsigned long);
471 if (kcov->mode != KCOV_MODE_INIT || vma->vm_pgoff != 0 ||
472 vma->vm_end - vma->vm_start != size) {
473 res = -EINVAL;
474 goto exit;
475 }
476 if (!kcov->area) {
477 kcov->area = area;
478 vma->vm_flags |= VM_DONTEXPAND;
479 spin_unlock_irqrestore(&kcov->lock, flags);
480 for (off = 0; off < size; off += PAGE_SIZE) {
481 page = vmalloc_to_page(kcov->area + off);
482 if (vm_insert_page(vma, vma->vm_start + off, page))
483 WARN_ONCE(1, "vm_insert_page() failed");
484 }
485 return 0;
486 }
487 exit:
488 spin_unlock_irqrestore(&kcov->lock, flags);
489 vfree(area);
490 return res;
491 }
492
kcov_open(struct inode * inode,struct file * filep)493 static int kcov_open(struct inode *inode, struct file *filep)
494 {
495 struct kcov *kcov;
496
497 kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
498 if (!kcov)
499 return -ENOMEM;
500 kcov->mode = KCOV_MODE_DISABLED;
501 kcov->sequence = 1;
502 refcount_set(&kcov->refcount, 1);
503 spin_lock_init(&kcov->lock);
504 filep->private_data = kcov;
505 return nonseekable_open(inode, filep);
506 }
507
kcov_close(struct inode * inode,struct file * filep)508 static int kcov_close(struct inode *inode, struct file *filep)
509 {
510 kcov_put(filep->private_data);
511 return 0;
512 }
513
kcov_get_mode(unsigned long arg)514 static int kcov_get_mode(unsigned long arg)
515 {
516 if (arg == KCOV_TRACE_PC)
517 return KCOV_MODE_TRACE_PC;
518 else if (arg == KCOV_TRACE_CMP)
519 #ifdef CONFIG_KCOV_ENABLE_COMPARISONS
520 return KCOV_MODE_TRACE_CMP;
521 #else
522 return -ENOTSUPP;
523 #endif
524 else
525 return -EINVAL;
526 }
527
528 /*
529 * Fault in a lazily-faulted vmalloc area before it can be used by
530 * __santizer_cov_trace_pc(), to avoid recursion issues if any code on the
531 * vmalloc fault handling path is instrumented.
532 */
kcov_fault_in_area(struct kcov * kcov)533 static void kcov_fault_in_area(struct kcov *kcov)
534 {
535 unsigned long stride = PAGE_SIZE / sizeof(unsigned long);
536 unsigned long *area = kcov->area;
537 unsigned long offset;
538
539 for (offset = 0; offset < kcov->size; offset += stride)
540 READ_ONCE(area[offset]);
541 }
542
kcov_check_handle(u64 handle,bool common_valid,bool uncommon_valid,bool zero_valid)543 static inline bool kcov_check_handle(u64 handle, bool common_valid,
544 bool uncommon_valid, bool zero_valid)
545 {
546 if (handle & ~(KCOV_SUBSYSTEM_MASK | KCOV_INSTANCE_MASK))
547 return false;
548 switch (handle & KCOV_SUBSYSTEM_MASK) {
549 case KCOV_SUBSYSTEM_COMMON:
550 return (handle & KCOV_INSTANCE_MASK) ?
551 common_valid : zero_valid;
552 case KCOV_SUBSYSTEM_USB:
553 return uncommon_valid;
554 default:
555 return false;
556 }
557 return false;
558 }
559
kcov_ioctl_locked(struct kcov * kcov,unsigned int cmd,unsigned long arg)560 static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
561 unsigned long arg)
562 {
563 struct task_struct *t;
564 unsigned long size, unused;
565 int mode, i;
566 struct kcov_remote_arg *remote_arg;
567 struct kcov_remote *remote;
568 unsigned long flags;
569
570 switch (cmd) {
571 case KCOV_INIT_TRACE:
572 /*
573 * Enable kcov in trace mode and setup buffer size.
574 * Must happen before anything else.
575 */
576 if (kcov->mode != KCOV_MODE_DISABLED)
577 return -EBUSY;
578 /*
579 * Size must be at least 2 to hold current position and one PC.
580 * Later we allocate size * sizeof(unsigned long) memory,
581 * that must not overflow.
582 */
583 size = arg;
584 if (size < 2 || size > INT_MAX / sizeof(unsigned long))
585 return -EINVAL;
586 kcov->size = size;
587 kcov->mode = KCOV_MODE_INIT;
588 return 0;
589 case KCOV_ENABLE:
590 /*
591 * Enable coverage for the current task.
592 * At this point user must have been enabled trace mode,
593 * and mmapped the file. Coverage collection is disabled only
594 * at task exit or voluntary by KCOV_DISABLE. After that it can
595 * be enabled for another task.
596 */
597 if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
598 return -EINVAL;
599 t = current;
600 if (kcov->t != NULL || t->kcov != NULL)
601 return -EBUSY;
602 mode = kcov_get_mode(arg);
603 if (mode < 0)
604 return mode;
605 kcov_fault_in_area(kcov);
606 kcov->mode = mode;
607 kcov_start(t, kcov, kcov->size, kcov->area, kcov->mode,
608 kcov->sequence);
609 kcov->t = t;
610 /* Put either in kcov_task_exit() or in KCOV_DISABLE. */
611 kcov_get(kcov);
612 return 0;
613 case KCOV_DISABLE:
614 /* Disable coverage for the current task. */
615 unused = arg;
616 if (unused != 0 || current->kcov != kcov)
617 return -EINVAL;
618 t = current;
619 if (WARN_ON(kcov->t != t))
620 return -EINVAL;
621 kcov_disable(t, kcov);
622 kcov_put(kcov);
623 return 0;
624 case KCOV_REMOTE_ENABLE:
625 if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
626 return -EINVAL;
627 t = current;
628 if (kcov->t != NULL || t->kcov != NULL)
629 return -EBUSY;
630 remote_arg = (struct kcov_remote_arg *)arg;
631 mode = kcov_get_mode(remote_arg->trace_mode);
632 if (mode < 0)
633 return mode;
634 if (remote_arg->area_size > LONG_MAX / sizeof(unsigned long))
635 return -EINVAL;
636 kcov->mode = mode;
637 t->kcov = kcov;
638 kcov->t = t;
639 kcov->remote = true;
640 kcov->remote_size = remote_arg->area_size;
641 spin_lock_irqsave(&kcov_remote_lock, flags);
642 for (i = 0; i < remote_arg->num_handles; i++) {
643 if (!kcov_check_handle(remote_arg->handles[i],
644 false, true, false)) {
645 spin_unlock_irqrestore(&kcov_remote_lock,
646 flags);
647 kcov_disable(t, kcov);
648 return -EINVAL;
649 }
650 remote = kcov_remote_add(kcov, remote_arg->handles[i]);
651 if (IS_ERR(remote)) {
652 spin_unlock_irqrestore(&kcov_remote_lock,
653 flags);
654 kcov_disable(t, kcov);
655 return PTR_ERR(remote);
656 }
657 }
658 if (remote_arg->common_handle) {
659 if (!kcov_check_handle(remote_arg->common_handle,
660 true, false, false)) {
661 spin_unlock_irqrestore(&kcov_remote_lock,
662 flags);
663 kcov_disable(t, kcov);
664 return -EINVAL;
665 }
666 remote = kcov_remote_add(kcov,
667 remote_arg->common_handle);
668 if (IS_ERR(remote)) {
669 spin_unlock_irqrestore(&kcov_remote_lock,
670 flags);
671 kcov_disable(t, kcov);
672 return PTR_ERR(remote);
673 }
674 t->kcov_handle = remote_arg->common_handle;
675 }
676 spin_unlock_irqrestore(&kcov_remote_lock, flags);
677 /* Put either in kcov_task_exit() or in KCOV_DISABLE. */
678 kcov_get(kcov);
679 return 0;
680 default:
681 return -ENOTTY;
682 }
683 }
684
kcov_ioctl(struct file * filep,unsigned int cmd,unsigned long arg)685 static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
686 {
687 struct kcov *kcov;
688 int res;
689 struct kcov_remote_arg *remote_arg = NULL;
690 unsigned int remote_num_handles;
691 unsigned long remote_arg_size;
692 unsigned long flags;
693
694 if (cmd == KCOV_REMOTE_ENABLE) {
695 if (get_user(remote_num_handles, (unsigned __user *)(arg +
696 offsetof(struct kcov_remote_arg, num_handles))))
697 return -EFAULT;
698 if (remote_num_handles > KCOV_REMOTE_MAX_HANDLES)
699 return -EINVAL;
700 remote_arg_size = struct_size(remote_arg, handles,
701 remote_num_handles);
702 remote_arg = memdup_user((void __user *)arg, remote_arg_size);
703 if (IS_ERR(remote_arg))
704 return PTR_ERR(remote_arg);
705 if (remote_arg->num_handles != remote_num_handles) {
706 kfree(remote_arg);
707 return -EINVAL;
708 }
709 arg = (unsigned long)remote_arg;
710 }
711
712 kcov = filep->private_data;
713 spin_lock_irqsave(&kcov->lock, flags);
714 res = kcov_ioctl_locked(kcov, cmd, arg);
715 spin_unlock_irqrestore(&kcov->lock, flags);
716
717 kfree(remote_arg);
718
719 return res;
720 }
721
722 static const struct file_operations kcov_fops = {
723 .open = kcov_open,
724 .unlocked_ioctl = kcov_ioctl,
725 .compat_ioctl = kcov_ioctl,
726 .mmap = kcov_mmap,
727 .release = kcov_close,
728 };
729
730 /*
731 * kcov_remote_start() and kcov_remote_stop() can be used to annotate a section
732 * of code in a kernel background thread or in a softirq to allow kcov to be
733 * used to collect coverage from that part of code.
734 *
735 * The handle argument of kcov_remote_start() identifies a code section that is
736 * used for coverage collection. A userspace process passes this handle to
737 * KCOV_REMOTE_ENABLE ioctl to make the used kcov device start collecting
738 * coverage for the code section identified by this handle.
739 *
740 * The usage of these annotations in the kernel code is different depending on
741 * the type of the kernel thread whose code is being annotated.
742 *
743 * For global kernel threads that are spawned in a limited number of instances
744 * (e.g. one USB hub_event() worker thread is spawned per USB HCD) and for
745 * softirqs, each instance must be assigned a unique 4-byte instance id. The
746 * instance id is then combined with a 1-byte subsystem id to get a handle via
747 * kcov_remote_handle(subsystem_id, instance_id).
748 *
749 * For local kernel threads that are spawned from system calls handler when a
750 * user interacts with some kernel interface (e.g. vhost workers), a handle is
751 * passed from a userspace process as the common_handle field of the
752 * kcov_remote_arg struct (note, that the user must generate a handle by using
753 * kcov_remote_handle() with KCOV_SUBSYSTEM_COMMON as the subsystem id and an
754 * arbitrary 4-byte non-zero number as the instance id). This common handle
755 * then gets saved into the task_struct of the process that issued the
756 * KCOV_REMOTE_ENABLE ioctl. When this process issues system calls that spawn
757 * kernel threads, the common handle must be retrieved via kcov_common_handle()
758 * and passed to the spawned threads via custom annotations. Those kernel
759 * threads must in turn be annotated with kcov_remote_start(common_handle) and
760 * kcov_remote_stop(). All of the threads that are spawned by the same process
761 * obtain the same handle, hence the name "common".
762 *
763 * See Documentation/dev-tools/kcov.rst for more details.
764 *
765 * Internally, kcov_remote_start() looks up the kcov device associated with the
766 * provided handle, allocates an area for coverage collection, and saves the
767 * pointers to kcov and area into the current task_struct to allow coverage to
768 * be collected via __sanitizer_cov_trace_pc().
769 * In turns kcov_remote_stop() clears those pointers from task_struct to stop
770 * collecting coverage and copies all collected coverage into the kcov area.
771 */
772
kcov_mode_enabled(unsigned int mode)773 static inline bool kcov_mode_enabled(unsigned int mode)
774 {
775 return (mode & ~KCOV_IN_CTXSW) != KCOV_MODE_DISABLED;
776 }
777
kcov_remote_softirq_start(struct task_struct * t)778 static void kcov_remote_softirq_start(struct task_struct *t)
779 {
780 struct kcov_percpu_data *data = this_cpu_ptr(&kcov_percpu_data);
781 unsigned int mode;
782
783 mode = READ_ONCE(t->kcov_mode);
784 barrier();
785 if (kcov_mode_enabled(mode)) {
786 data->saved_mode = mode;
787 data->saved_size = t->kcov_size;
788 data->saved_area = t->kcov_area;
789 data->saved_sequence = t->kcov_sequence;
790 data->saved_kcov = t->kcov;
791 kcov_stop(t);
792 }
793 }
794
kcov_remote_softirq_stop(struct task_struct * t)795 static void kcov_remote_softirq_stop(struct task_struct *t)
796 {
797 struct kcov_percpu_data *data = this_cpu_ptr(&kcov_percpu_data);
798
799 if (data->saved_kcov) {
800 kcov_start(t, data->saved_kcov, data->saved_size,
801 data->saved_area, data->saved_mode,
802 data->saved_sequence);
803 data->saved_mode = 0;
804 data->saved_size = 0;
805 data->saved_area = NULL;
806 data->saved_sequence = 0;
807 data->saved_kcov = NULL;
808 }
809 }
810
kcov_remote_start(u64 handle)811 void kcov_remote_start(u64 handle)
812 {
813 struct task_struct *t = current;
814 struct kcov_remote *remote;
815 struct kcov *kcov;
816 unsigned int mode;
817 void *area;
818 unsigned int size;
819 int sequence;
820 unsigned long flags;
821
822 if (WARN_ON(!kcov_check_handle(handle, true, true, true)))
823 return;
824 if (!in_task() && !in_serving_softirq())
825 return;
826
827 local_irq_save(flags);
828
829 /*
830 * Check that kcov_remote_start() is not called twice in background
831 * threads nor called by user tasks (with enabled kcov).
832 */
833 mode = READ_ONCE(t->kcov_mode);
834 if (WARN_ON(in_task() && kcov_mode_enabled(mode))) {
835 local_irq_restore(flags);
836 return;
837 }
838 /*
839 * Check that kcov_remote_start() is not called twice in softirqs.
840 * Note, that kcov_remote_start() can be called from a softirq that
841 * happened while collecting coverage from a background thread.
842 */
843 if (WARN_ON(in_serving_softirq() && t->kcov_softirq)) {
844 local_irq_restore(flags);
845 return;
846 }
847
848 spin_lock(&kcov_remote_lock);
849 remote = kcov_remote_find(handle);
850 if (!remote) {
851 spin_unlock_irqrestore(&kcov_remote_lock, flags);
852 return;
853 }
854 kcov_debug("handle = %llx, context: %s\n", handle,
855 in_task() ? "task" : "softirq");
856 kcov = remote->kcov;
857 /* Put in kcov_remote_stop(). */
858 kcov_get(kcov);
859 /*
860 * Read kcov fields before unlock to prevent races with
861 * KCOV_DISABLE / kcov_remote_reset().
862 */
863 mode = kcov->mode;
864 sequence = kcov->sequence;
865 if (in_task()) {
866 size = kcov->remote_size;
867 area = kcov_remote_area_get(size);
868 } else {
869 size = CONFIG_KCOV_IRQ_AREA_SIZE;
870 area = this_cpu_ptr(&kcov_percpu_data)->irq_area;
871 }
872 spin_unlock_irqrestore(&kcov_remote_lock, flags);
873
874 /* Can only happen when in_task(). */
875 if (!area) {
876 area = vmalloc(size * sizeof(unsigned long));
877 if (!area) {
878 kcov_put(kcov);
879 return;
880 }
881 }
882
883 local_irq_save(flags);
884
885 /* Reset coverage size. */
886 *(u64 *)area = 0;
887
888 if (in_serving_softirq()) {
889 kcov_remote_softirq_start(t);
890 t->kcov_softirq = 1;
891 }
892 kcov_start(t, kcov, size, area, mode, sequence);
893
894 local_irq_restore(flags);
895
896 }
897 EXPORT_SYMBOL(kcov_remote_start);
898
kcov_move_area(enum kcov_mode mode,void * dst_area,unsigned int dst_area_size,void * src_area)899 static void kcov_move_area(enum kcov_mode mode, void *dst_area,
900 unsigned int dst_area_size, void *src_area)
901 {
902 u64 word_size = sizeof(unsigned long);
903 u64 count_size, entry_size_log;
904 u64 dst_len, src_len;
905 void *dst_entries, *src_entries;
906 u64 dst_occupied, dst_free, bytes_to_move, entries_moved;
907
908 kcov_debug("%px %u <= %px %lu\n",
909 dst_area, dst_area_size, src_area, *(unsigned long *)src_area);
910
911 switch (mode) {
912 case KCOV_MODE_TRACE_PC:
913 dst_len = READ_ONCE(*(unsigned long *)dst_area);
914 src_len = *(unsigned long *)src_area;
915 count_size = sizeof(unsigned long);
916 entry_size_log = __ilog2_u64(sizeof(unsigned long));
917 break;
918 case KCOV_MODE_TRACE_CMP:
919 dst_len = READ_ONCE(*(u64 *)dst_area);
920 src_len = *(u64 *)src_area;
921 count_size = sizeof(u64);
922 BUILD_BUG_ON(!is_power_of_2(KCOV_WORDS_PER_CMP));
923 entry_size_log = __ilog2_u64(sizeof(u64) * KCOV_WORDS_PER_CMP);
924 break;
925 default:
926 WARN_ON(1);
927 return;
928 }
929
930 /* As arm can't divide u64 integers use log of entry size. */
931 if (dst_len > ((dst_area_size * word_size - count_size) >>
932 entry_size_log))
933 return;
934 dst_occupied = count_size + (dst_len << entry_size_log);
935 dst_free = dst_area_size * word_size - dst_occupied;
936 bytes_to_move = min(dst_free, src_len << entry_size_log);
937 dst_entries = dst_area + dst_occupied;
938 src_entries = src_area + count_size;
939 memcpy(dst_entries, src_entries, bytes_to_move);
940 entries_moved = bytes_to_move >> entry_size_log;
941
942 switch (mode) {
943 case KCOV_MODE_TRACE_PC:
944 WRITE_ONCE(*(unsigned long *)dst_area, dst_len + entries_moved);
945 break;
946 case KCOV_MODE_TRACE_CMP:
947 WRITE_ONCE(*(u64 *)dst_area, dst_len + entries_moved);
948 break;
949 default:
950 break;
951 }
952 }
953
954 /* See the comment before kcov_remote_start() for usage details. */
kcov_remote_stop(void)955 void kcov_remote_stop(void)
956 {
957 struct task_struct *t = current;
958 struct kcov *kcov;
959 unsigned int mode;
960 void *area;
961 unsigned int size;
962 int sequence;
963 unsigned long flags;
964
965 if (!in_task() && !in_serving_softirq())
966 return;
967
968 local_irq_save(flags);
969
970 mode = READ_ONCE(t->kcov_mode);
971 barrier();
972 if (!kcov_mode_enabled(mode)) {
973 local_irq_restore(flags);
974 return;
975 }
976 /*
977 * When in softirq, check if the corresponding kcov_remote_start()
978 * actually found the remote handle and started collecting coverage.
979 */
980 if (in_serving_softirq() && !t->kcov_softirq) {
981 local_irq_restore(flags);
982 return;
983 }
984 /* Make sure that kcov_softirq is only set when in softirq. */
985 if (WARN_ON(!in_serving_softirq() && t->kcov_softirq)) {
986 local_irq_restore(flags);
987 return;
988 }
989
990 kcov = t->kcov;
991 area = t->kcov_area;
992 size = t->kcov_size;
993 sequence = t->kcov_sequence;
994
995 kcov_stop(t);
996 if (in_serving_softirq()) {
997 t->kcov_softirq = 0;
998 kcov_remote_softirq_stop(t);
999 }
1000
1001 spin_lock(&kcov->lock);
1002 /*
1003 * KCOV_DISABLE could have been called between kcov_remote_start()
1004 * and kcov_remote_stop(), hence the sequence check.
1005 */
1006 if (sequence == kcov->sequence && kcov->remote)
1007 kcov_move_area(kcov->mode, kcov->area, kcov->size, area);
1008 spin_unlock(&kcov->lock);
1009
1010 if (in_task()) {
1011 spin_lock(&kcov_remote_lock);
1012 kcov_remote_area_put(area, size);
1013 spin_unlock(&kcov_remote_lock);
1014 }
1015
1016 local_irq_restore(flags);
1017
1018 /* Get in kcov_remote_start(). */
1019 kcov_put(kcov);
1020 }
1021 EXPORT_SYMBOL(kcov_remote_stop);
1022
1023 /* See the comment before kcov_remote_start() for usage details. */
kcov_common_handle(void)1024 u64 kcov_common_handle(void)
1025 {
1026 return current->kcov_handle;
1027 }
1028 EXPORT_SYMBOL(kcov_common_handle);
1029
kcov_init(void)1030 static int __init kcov_init(void)
1031 {
1032 int cpu;
1033
1034 for_each_possible_cpu(cpu) {
1035 void *area = vmalloc(CONFIG_KCOV_IRQ_AREA_SIZE *
1036 sizeof(unsigned long));
1037 if (!area)
1038 return -ENOMEM;
1039 per_cpu_ptr(&kcov_percpu_data, cpu)->irq_area = area;
1040 }
1041
1042 /*
1043 * The kcov debugfs file won't ever get removed and thus,
1044 * there is no need to protect it against removal races. The
1045 * use of debugfs_create_file_unsafe() is actually safe here.
1046 */
1047 debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops);
1048
1049 return 0;
1050 }
1051
1052 device_initcall(kcov_init);
1053
