1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (C) 2018 The FreeBSD Foundation. All rights reserved.
5 * Copyright (C) 2018, 2019 Andrew Turner
6 *
7 * This software was developed by Mitchell Horne under sponsorship of
8 * the FreeBSD Foundation.
9 *
10 * This software was developed by SRI International and the University of
11 * Cambridge Computer Laboratory under DARPA/AFRL contract FA8750-10-C-0237
12 * ("CTSRD"), as part of the DARPA CRASH research programme.
13 *
14 * Redistribution and use in source and binary forms, with or without
15 * modification, are permitted provided that the following conditions
16 * are met:
17 * 1. Redistributions of source code must retain the above copyright
18 * notice, this list of conditions and the following disclaimer.
19 * 2. Redistributions in binary form must reproduce the above copyright
20 * notice, this list of conditions and the following disclaimer in the
21 * documentation and/or other materials provided with the distribution.
22 *
23 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
26 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 * SUCH DAMAGE.
34 */
35
36 /* Interceptors are required for KMSAN. */
37 #if defined(KASAN) || defined(KCSAN)
38 #define SAN_RUNTIME
39 #endif
40
41 #include <sys/param.h>
42 #include <sys/systm.h>
43 #include <sys/conf.h>
44 #include <sys/eventhandler.h>
45 #include <sys/kcov.h>
46 #include <sys/kernel.h>
47 #include <sys/limits.h>
48 #include <sys/lock.h>
49 #include <sys/malloc.h>
50 #include <sys/mman.h>
51 #include <sys/mutex.h>
52 #include <sys/proc.h>
53 #include <sys/rwlock.h>
54 #include <sys/sysctl.h>
55
56 #include <vm/vm.h>
57 #include <vm/pmap.h>
58 #include <vm/vm_extern.h>
59 #include <vm/vm_object.h>
60 #include <vm/vm_page.h>
61 #include <vm/vm_pager.h>
62 #include <vm/vm_param.h>
63
64 MALLOC_DEFINE(M_KCOV_INFO, "kcovinfo", "KCOV info type");
65
66 #define KCOV_ELEMENT_SIZE sizeof(uint64_t)
67
68 /*
69 * To know what the code can safely perform at any point in time we use a
70 * state machine. In the normal case the state transitions are:
71 *
72 * OPEN -> READY -> RUNNING -> DYING
73 * | | ^ | ^ ^
74 * | | +--------+ | |
75 * | +-------------------+ |
76 * +-----------------------------+
77 *
78 * The states are:
79 * OPEN: The kcov fd has been opened, but no buffer is available to store
80 * coverage data.
81 * READY: The buffer to store coverage data has been allocated. Userspace
82 * can set this by using ioctl(fd, KIOSETBUFSIZE, entries);. When
83 * this has been set the buffer can be written to by the kernel,
84 * and mmaped by userspace.
85 * RUNNING: The coverage probes are able to store coverage data in the buffer.
86 * This is entered with ioctl(fd, KIOENABLE, mode);. The READY state
87 * can be exited by ioctl(fd, KIODISABLE); or exiting the thread to
88 * return to the READY state to allow tracing to be reused, or by
89 * closing the kcov fd to enter the DYING state.
90 * DYING: The fd has been closed. All states can enter into this state when
91 * userspace closes the kcov fd.
92 *
93 * We need to be careful when moving into and out of the RUNNING state. As
94 * an interrupt may happen while this is happening the ordering of memory
95 * operations is important so struct kcov_info is valid for the tracing
96 * functions.
97 *
98 * When moving into the RUNNING state prior stores to struct kcov_info need
99 * to be observed before the state is set. This allows for interrupts that
100 * may call into one of the coverage functions to fire at any point while
101 * being enabled and see a consistent struct kcov_info.
102 *
103 * When moving out of the RUNNING state any later stores to struct kcov_info
104 * need to be observed after the state is set. As with entering this is to
105 * present a consistent struct kcov_info to interrupts.
106 */
107 typedef enum {
108 KCOV_STATE_INVALID,
109 KCOV_STATE_OPEN, /* The device is open, but with no buffer */
110 KCOV_STATE_READY, /* The buffer has been allocated */
111 KCOV_STATE_RUNNING, /* Recording trace data */
112 KCOV_STATE_DYING, /* The fd was closed */
113 } kcov_state_t;
114
115 /*
116 * (l) Set while holding the kcov_lock mutex and not in the RUNNING state.
117 * (o) Only set once while in the OPEN state. Cleaned up while in the DYING
118 * state, and with no thread associated with the struct kcov_info.
119 * (s) Set atomically to enter or exit the RUNNING state, non-atomically
120 * otherwise. See above for a description of the other constraints while
121 * moving into or out of the RUNNING state.
122 */
123 struct kcov_info {
124 struct thread *thread; /* (l) */
125 vm_object_t bufobj; /* (o) */
126 vm_offset_t kvaddr; /* (o) */
127 size_t entries; /* (o) */
128 size_t bufsize; /* (o) */
129 kcov_state_t state; /* (s) */
130 int mode; /* (l) */
131 };
132
133 /* Prototypes */
134 static d_open_t kcov_open;
135 static d_close_t kcov_close;
136 static d_mmap_single_t kcov_mmap_single;
137 static d_ioctl_t kcov_ioctl;
138
139 static int kcov_alloc(struct kcov_info *info, size_t entries);
140 static void kcov_free(struct kcov_info *info);
141 static void kcov_init(const void *unused);
142
143 static struct cdevsw kcov_cdevsw = {
144 .d_version = D_VERSION,
145 .d_open = kcov_open,
146 .d_close = kcov_close,
147 .d_mmap_single = kcov_mmap_single,
148 .d_ioctl = kcov_ioctl,
149 .d_name = "kcov",
150 };
151
152 SYSCTL_NODE(_kern, OID_AUTO, kcov, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
153 "Kernel coverage");
154
155 static u_int kcov_max_entries = KCOV_MAXENTRIES;
156 SYSCTL_UINT(_kern_kcov, OID_AUTO, max_entries, CTLFLAG_RW,
157 &kcov_max_entries, 0,
158 "Maximum number of entries in the kcov buffer");
159
160 static struct mtx kcov_lock;
161 static int active_count;
162
163 static struct kcov_info * __nosanitizeaddress __nosanitizememory
get_kinfo(struct thread * td)164 get_kinfo(struct thread *td)
165 {
166 struct kcov_info *info;
167
168 /* We might have a NULL thread when releasing the secondary CPUs */
169 if (td == NULL)
170 return (NULL);
171
172 /*
173 * We are in an interrupt, stop tracing as it is not explicitly
174 * part of a syscall.
175 */
176 if (td->td_intr_nesting_level > 0 || td->td_intr_frame != NULL)
177 return (NULL);
178
179 /*
180 * If info is NULL or the state is not running we are not tracing.
181 */
182 info = td->td_kcov_info;
183 if (info == NULL ||
184 atomic_load_acq_int(&info->state) != KCOV_STATE_RUNNING)
185 return (NULL);
186
187 return (info);
188 }
189
190 static void __nosanitizeaddress __nosanitizememory
trace_pc(uintptr_t ret)191 trace_pc(uintptr_t ret)
192 {
193 struct thread *td;
194 struct kcov_info *info;
195 uint64_t *buf, index;
196
197 td = curthread;
198 info = get_kinfo(td);
199 if (info == NULL)
200 return;
201
202 /*
203 * Check we are in the PC-trace mode.
204 */
205 if (info->mode != KCOV_MODE_TRACE_PC)
206 return;
207
208 KASSERT(info->kvaddr != 0, ("%s: NULL buf while running", __func__));
209
210 buf = (uint64_t *)info->kvaddr;
211
212 /* The first entry of the buffer holds the index */
213 index = buf[0];
214 if (index + 2 > info->entries)
215 return;
216
217 buf[index + 1] = ret;
218 buf[0] = index + 1;
219 }
220
221 static bool __nosanitizeaddress __nosanitizememory
trace_cmp(uint64_t type,uint64_t arg1,uint64_t arg2,uint64_t ret)222 trace_cmp(uint64_t type, uint64_t arg1, uint64_t arg2, uint64_t ret)
223 {
224 struct thread *td;
225 struct kcov_info *info;
226 uint64_t *buf, index;
227
228 td = curthread;
229 info = get_kinfo(td);
230 if (info == NULL)
231 return (false);
232
233 /*
234 * Check we are in the comparison-trace mode.
235 */
236 if (info->mode != KCOV_MODE_TRACE_CMP)
237 return (false);
238
239 KASSERT(info->kvaddr != 0, ("%s: NULL buf while running", __func__));
240
241 buf = (uint64_t *)info->kvaddr;
242
243 /* The first entry of the buffer holds the index */
244 index = buf[0];
245
246 /* Check we have space to store all elements */
247 if (index * 4 + 4 + 1 > info->entries)
248 return (false);
249
250 while (1) {
251 buf[index * 4 + 1] = type;
252 buf[index * 4 + 2] = arg1;
253 buf[index * 4 + 3] = arg2;
254 buf[index * 4 + 4] = ret;
255
256 if (atomic_cmpset_64(&buf[0], index, index + 1))
257 break;
258 buf[0] = index;
259 }
260
261 return (true);
262 }
263
264 /*
265 * The fd is being closed, cleanup everything we can.
266 */
267 static void
kcov_mmap_cleanup(void * arg)268 kcov_mmap_cleanup(void *arg)
269 {
270 struct kcov_info *info = arg;
271 struct thread *thread;
272
273 mtx_lock_spin(&kcov_lock);
274 /*
275 * Move to KCOV_STATE_DYING to stop adding new entries.
276 *
277 * If the thread is running we need to wait until thread exit to
278 * clean up as it may currently be adding a new entry. If this is
279 * the case being in KCOV_STATE_DYING will signal that the buffer
280 * needs to be cleaned up.
281 */
282 atomic_store_int(&info->state, KCOV_STATE_DYING);
283 atomic_thread_fence_seq_cst();
284 thread = info->thread;
285 mtx_unlock_spin(&kcov_lock);
286
287 if (thread != NULL)
288 return;
289
290 /*
291 * We can safely clean up the info struct as it is in the
292 * KCOV_STATE_DYING state with no thread associated.
293 *
294 * The KCOV_STATE_DYING stops new threads from using it.
295 * The lack of a thread means nothing is currently using the buffers.
296 */
297 kcov_free(info);
298 }
299
300 static int
kcov_open(struct cdev * dev,int oflags,int devtype,struct thread * td)301 kcov_open(struct cdev *dev, int oflags, int devtype, struct thread *td)
302 {
303 struct kcov_info *info;
304 int error;
305
306 info = malloc(sizeof(struct kcov_info), M_KCOV_INFO, M_ZERO | M_WAITOK);
307 info->state = KCOV_STATE_OPEN;
308 info->thread = NULL;
309 info->mode = -1;
310
311 if ((error = devfs_set_cdevpriv(info, kcov_mmap_cleanup)) != 0)
312 kcov_mmap_cleanup(info);
313
314 return (error);
315 }
316
317 static int
kcov_close(struct cdev * dev,int fflag,int devtype,struct thread * td)318 kcov_close(struct cdev *dev, int fflag, int devtype, struct thread *td)
319 {
320 struct kcov_info *info;
321 int error;
322
323 if ((error = devfs_get_cdevpriv((void **)&info)) != 0)
324 return (error);
325
326 KASSERT(info != NULL, ("kcov_close with no kcov_info structure"));
327
328 /* Trying to close, but haven't disabled */
329 if (info->state == KCOV_STATE_RUNNING)
330 return (EBUSY);
331
332 return (0);
333 }
334
335 static int
kcov_mmap_single(struct cdev * dev,vm_ooffset_t * offset,vm_size_t size,struct vm_object ** object,int nprot)336 kcov_mmap_single(struct cdev *dev, vm_ooffset_t *offset, vm_size_t size,
337 struct vm_object **object, int nprot)
338 {
339 struct kcov_info *info;
340 int error;
341
342 if ((nprot & (PROT_EXEC | PROT_READ | PROT_WRITE)) !=
343 (PROT_READ | PROT_WRITE))
344 return (EINVAL);
345
346 if ((error = devfs_get_cdevpriv((void **)&info)) != 0)
347 return (error);
348
349 if (info->kvaddr == 0 || size / KCOV_ELEMENT_SIZE != info->entries)
350 return (EINVAL);
351
352 vm_object_reference(info->bufobj);
353 *offset = 0;
354 *object = info->bufobj;
355 return (0);
356 }
357
358 static int
kcov_alloc(struct kcov_info * info,size_t entries)359 kcov_alloc(struct kcov_info *info, size_t entries)
360 {
361 size_t n, pages;
362 vm_page_t m;
363
364 KASSERT(info->kvaddr == 0, ("kcov_alloc: Already have a buffer"));
365 KASSERT(info->state == KCOV_STATE_OPEN,
366 ("kcov_alloc: Not in open state (%x)", info->state));
367
368 if (entries < 2 || entries > kcov_max_entries)
369 return (EINVAL);
370
371 /* Align to page size so mmap can't access other kernel memory */
372 info->bufsize = roundup2(entries * KCOV_ELEMENT_SIZE, PAGE_SIZE);
373 pages = info->bufsize / PAGE_SIZE;
374
375 if ((info->kvaddr = kva_alloc(info->bufsize)) == 0)
376 return (ENOMEM);
377
378 info->bufobj = vm_pager_allocate(OBJT_PHYS, 0, info->bufsize,
379 PROT_READ | PROT_WRITE, 0, curthread->td_ucred);
380
381 VM_OBJECT_WLOCK(info->bufobj);
382 for (n = 0; n < pages; n++) {
383 m = vm_page_grab(info->bufobj, n,
384 VM_ALLOC_ZERO | VM_ALLOC_WIRED);
385 vm_page_valid(m);
386 vm_page_xunbusy(m);
387 pmap_qenter(info->kvaddr + n * PAGE_SIZE, &m, 1);
388 }
389 VM_OBJECT_WUNLOCK(info->bufobj);
390
391 info->entries = entries;
392
393 return (0);
394 }
395
396 static void
kcov_free(struct kcov_info * info)397 kcov_free(struct kcov_info *info)
398 {
399 vm_page_t m;
400 size_t i;
401
402 if (info->kvaddr != 0) {
403 pmap_qremove(info->kvaddr, info->bufsize / PAGE_SIZE);
404 kva_free(info->kvaddr, info->bufsize);
405 }
406 if (info->bufobj != NULL) {
407 VM_OBJECT_WLOCK(info->bufobj);
408 m = vm_page_lookup(info->bufobj, 0);
409 for (i = 0; i < info->bufsize / PAGE_SIZE; i++) {
410 vm_page_unwire_noq(m);
411 m = vm_page_next(m);
412 }
413 VM_OBJECT_WUNLOCK(info->bufobj);
414 vm_object_deallocate(info->bufobj);
415 }
416 free(info, M_KCOV_INFO);
417 }
418
419 static int
kcov_ioctl(struct cdev * dev,u_long cmd,caddr_t data,int fflag __unused,struct thread * td)420 kcov_ioctl(struct cdev *dev, u_long cmd, caddr_t data, int fflag __unused,
421 struct thread *td)
422 {
423 struct kcov_info *info;
424 int mode, error;
425
426 if ((error = devfs_get_cdevpriv((void **)&info)) != 0)
427 return (error);
428
429 if (cmd == KIOSETBUFSIZE) {
430 /*
431 * Set the size of the coverage buffer. Should be called
432 * before enabling coverage collection for that thread.
433 */
434 if (info->state != KCOV_STATE_OPEN) {
435 return (EBUSY);
436 }
437 error = kcov_alloc(info, *(u_int *)data);
438 if (error == 0)
439 info->state = KCOV_STATE_READY;
440 return (error);
441 }
442
443 mtx_lock_spin(&kcov_lock);
444 switch (cmd) {
445 case KIOENABLE:
446 if (info->state != KCOV_STATE_READY) {
447 error = EBUSY;
448 break;
449 }
450 if (td->td_kcov_info != NULL) {
451 error = EINVAL;
452 break;
453 }
454 mode = *(int *)data;
455 if (mode != KCOV_MODE_TRACE_PC && mode != KCOV_MODE_TRACE_CMP) {
456 error = EINVAL;
457 break;
458 }
459
460 /* Lets hope nobody opens this 2 billion times */
461 KASSERT(active_count < INT_MAX,
462 ("%s: Open too many times", __func__));
463 active_count++;
464 if (active_count == 1) {
465 cov_register_pc(&trace_pc);
466 cov_register_cmp(&trace_cmp);
467 }
468
469 KASSERT(info->thread == NULL,
470 ("Enabling kcov when already enabled"));
471 info->thread = td;
472 info->mode = mode;
473 /*
474 * Ensure the mode has been set before starting coverage
475 * tracing.
476 */
477 atomic_store_rel_int(&info->state, KCOV_STATE_RUNNING);
478 td->td_kcov_info = info;
479 break;
480 case KIODISABLE:
481 /* Only the currently enabled thread may disable itself */
482 if (info->state != KCOV_STATE_RUNNING ||
483 info != td->td_kcov_info) {
484 error = EINVAL;
485 break;
486 }
487 KASSERT(active_count > 0, ("%s: Open count is zero", __func__));
488 active_count--;
489 if (active_count == 0) {
490 cov_unregister_pc();
491 cov_unregister_cmp();
492 }
493
494 td->td_kcov_info = NULL;
495 atomic_store_int(&info->state, KCOV_STATE_READY);
496 /*
497 * Ensure we have exited the READY state before clearing the
498 * rest of the info struct.
499 */
500 atomic_thread_fence_rel();
501 info->mode = -1;
502 info->thread = NULL;
503 break;
504 default:
505 error = EINVAL;
506 break;
507 }
508 mtx_unlock_spin(&kcov_lock);
509
510 return (error);
511 }
512
513 static void
kcov_thread_dtor(void * arg __unused,struct thread * td)514 kcov_thread_dtor(void *arg __unused, struct thread *td)
515 {
516 struct kcov_info *info;
517
518 info = td->td_kcov_info;
519 if (info == NULL)
520 return;
521
522 mtx_lock_spin(&kcov_lock);
523 KASSERT(active_count > 0, ("%s: Open count is zero", __func__));
524 active_count--;
525 if (active_count == 0) {
526 cov_unregister_pc();
527 cov_unregister_cmp();
528 }
529 td->td_kcov_info = NULL;
530 if (info->state != KCOV_STATE_DYING) {
531 /*
532 * The kcov file is still open. Mark it as unused and
533 * wait for it to be closed before cleaning up.
534 */
535 atomic_store_int(&info->state, KCOV_STATE_READY);
536 atomic_thread_fence_seq_cst();
537 /* This info struct is unused */
538 info->thread = NULL;
539 mtx_unlock_spin(&kcov_lock);
540 return;
541 }
542 mtx_unlock_spin(&kcov_lock);
543
544 /*
545 * We can safely clean up the info struct as it is in the
546 * KCOV_STATE_DYING state where the info struct is associated with
547 * the current thread that's about to exit.
548 *
549 * The KCOV_STATE_DYING stops new threads from using it.
550 * It also stops the current thread from trying to use the info struct.
551 */
552 kcov_free(info);
553 }
554
555 static void
kcov_init(const void * unused)556 kcov_init(const void *unused)
557 {
558 struct make_dev_args args;
559 struct cdev *dev;
560
561 mtx_init(&kcov_lock, "kcov lock", NULL, MTX_SPIN);
562
563 make_dev_args_init(&args);
564 args.mda_devsw = &kcov_cdevsw;
565 args.mda_uid = UID_ROOT;
566 args.mda_gid = GID_WHEEL;
567 args.mda_mode = 0600;
568 if (make_dev_s(&args, &dev, "kcov") != 0) {
569 printf("%s", "Failed to create kcov device");
570 return;
571 }
572
573 EVENTHANDLER_REGISTER(thread_dtor, kcov_thread_dtor, NULL,
574 EVENTHANDLER_PRI_ANY);
575 }
576
577 SYSINIT(kcovdev, SI_SUB_LAST, SI_ORDER_ANY, kcov_init, NULL);
578