Free Electrons

Embedded Linux Experts

  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
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
/*
 * Copyright 2010 Tilera Corporation. All Rights Reserved.
 *
 *   This program is free software; you can redistribute it and/or
 *   modify it under the terms of the GNU General Public License
 *   as published by the Free Software Foundation, version 2.
 *
 *   This program is distributed in the hope that it will be useful, but
 *   WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
 *   NON INFRINGEMENT.  See the GNU General Public License for
 *   more details.
 */

#include <linux/sched.h>
#include <linux/sched/debug.h>
#include <linux/sched/task_stack.h>
#include <linux/kernel.h>
#include <linux/kprobes.h>
#include <linux/module.h>
#include <linux/pfn.h>
#include <linux/kallsyms.h>
#include <linux/stacktrace.h>
#include <linux/uaccess.h>
#include <linux/mmzone.h>
#include <linux/dcache.h>
#include <linux/fs.h>
#include <linux/hardirq.h>
#include <linux/string.h>
#include <asm/backtrace.h>
#include <asm/page.h>
#include <asm/ucontext.h>
#include <asm/switch_to.h>
#include <asm/sigframe.h>
#include <asm/stack.h>
#include <asm/vdso.h>
#include <arch/abi.h>
#include <arch/interrupts.h>

#define KBT_ONGOING	0  /* Backtrace still ongoing */
#define KBT_DONE	1  /* Backtrace cleanly completed */
#define KBT_RUNNING	2  /* Can't run backtrace on a running task */
#define KBT_LOOP	3  /* Backtrace entered a loop */

/* Is address on the specified kernel stack? */
static int in_kernel_stack(struct KBacktraceIterator *kbt, unsigned long sp)
{
	ulong kstack_base = (ulong) kbt->task->stack;
	if (kstack_base == 0)  /* corrupt task pointer; just follow stack... */
		return sp >= PAGE_OFFSET && sp < (unsigned long)high_memory;
	return sp >= kstack_base && sp < kstack_base + THREAD_SIZE;
}

/* Callback for backtracer; basically a glorified memcpy */
static bool read_memory_func(void *result, unsigned long address,
			     unsigned int size, void *vkbt)
{
	int retval;
	struct KBacktraceIterator *kbt = (struct KBacktraceIterator *)vkbt;

	if (address == 0)
		return 0;
	if (__kernel_text_address(address)) {
		/* OK to read kernel code. */
	} else if (address >= PAGE_OFFSET) {
		/* We only tolerate kernel-space reads of this task's stack */
		if (!in_kernel_stack(kbt, address))
			return 0;
	} else if (!kbt->is_current) {
		return 0;	/* can't read from other user address spaces */
	}
	pagefault_disable();
	retval = __copy_from_user_inatomic(result,
					   (void __user __force *)address,
					   size);
	pagefault_enable();
	return (retval == 0);
}

/* Return a pt_regs pointer for a valid fault handler frame */
static struct pt_regs *valid_fault_handler(struct KBacktraceIterator* kbt)
{
	char fault[64];
	unsigned long sp = kbt->it.sp;
	struct pt_regs *p;

	if (sp % sizeof(long) != 0)
		return NULL;
	if (!in_kernel_stack(kbt, sp))
		return NULL;
	if (!in_kernel_stack(kbt, sp + C_ABI_SAVE_AREA_SIZE + PTREGS_SIZE-1))
		return NULL;
	p = (struct pt_regs *)(sp + C_ABI_SAVE_AREA_SIZE);
	if (kbt->verbose) {     /* else we aren't going to use it */
		if (p->faultnum == INT_SWINT_1 ||
		    p->faultnum == INT_SWINT_1_SIGRETURN)
			snprintf(fault, sizeof(fault),
				 "syscall %ld", p->regs[TREG_SYSCALL_NR]);
		else
			snprintf(fault, sizeof(fault),
				 "interrupt %ld", p->faultnum);
	}
	if (EX1_PL(p->ex1) == KERNEL_PL &&
	    __kernel_text_address(p->pc) &&
	    in_kernel_stack(kbt, p->sp) &&
	    p->sp >= sp) {
		if (kbt->verbose)
			pr_err("  <%s while in kernel mode>\n", fault);
	} else if (user_mode(p) &&
		   p->sp < PAGE_OFFSET && p->sp != 0) {
		if (kbt->verbose)
			pr_err("  <%s while in user mode>\n", fault);
	} else {
		if (kbt->verbose && (p->pc != 0 || p->sp != 0 || p->ex1 != 0))
			pr_err("  (odd fault: pc %#lx, sp %#lx, ex1 %#lx?)\n",
			       p->pc, p->sp, p->ex1);
		return NULL;
	}
	if (kbt->profile && ((1ULL << p->faultnum) & QUEUED_INTERRUPTS) != 0)
		return NULL;
	return p;
}

/* Is the iterator pointing to a sigreturn trampoline? */
static int is_sigreturn(struct KBacktraceIterator *kbt)
{
	return kbt->task->mm &&
		(kbt->it.pc == ((ulong)kbt->task->mm->context.vdso_base +
				(ulong)&__vdso_rt_sigreturn));
}

/* Return a pt_regs pointer for a valid signal handler frame */
static struct pt_regs *valid_sigframe(struct KBacktraceIterator* kbt,
				      struct rt_sigframe* kframe)
{
	BacktraceIterator *b = &kbt->it;

	if (is_sigreturn(kbt) && b->sp < PAGE_OFFSET &&
	    b->sp % sizeof(long) == 0) {
		int retval;
		pagefault_disable();
		retval = __copy_from_user_inatomic(
			kframe, (void __user __force *)b->sp,
			sizeof(*kframe));
		pagefault_enable();
		if (retval != 0 ||
		    (unsigned int)(kframe->info.si_signo) >= _NSIG)
			return NULL;
		if (kbt->verbose) {
			pr_err("  <received signal %d>\n",
			       kframe->info.si_signo);
		}
		return (struct pt_regs *)&kframe->uc.uc_mcontext;
	}
	return NULL;
}

static int KBacktraceIterator_restart(struct KBacktraceIterator *kbt)
{
	struct pt_regs *p;
	struct rt_sigframe kframe;

	p = valid_fault_handler(kbt);
	if (p == NULL)
		p = valid_sigframe(kbt, &kframe);
	if (p == NULL)
		return 0;
	backtrace_init(&kbt->it, read_memory_func, kbt,
		       p->pc, p->lr, p->sp, p->regs[52]);
	kbt->new_context = 1;
	return 1;
}

/* Find a frame that isn't a sigreturn, if there is one. */
static int KBacktraceIterator_next_item_inclusive(
	struct KBacktraceIterator *kbt)
{
	for (;;) {
		do {
			if (!is_sigreturn(kbt))
				return KBT_ONGOING;
		} while (backtrace_next(&kbt->it));

		if (!KBacktraceIterator_restart(kbt))
			return KBT_DONE;
	}
}

/*
 * If the current sp is on a page different than what we recorded
 * as the top-of-kernel-stack last time we context switched, we have
 * probably blown the stack, and nothing is going to work out well.
 * If we can at least get out a warning, that may help the debug,
 * though we probably won't be able to backtrace into the code that
 * actually did the recursive damage.
 */
static void validate_stack(struct pt_regs *regs)
{
	int cpu = raw_smp_processor_id();
	unsigned long ksp0 = get_current_ksp0();
	unsigned long ksp0_base = ksp0 & -THREAD_SIZE;
	unsigned long sp = stack_pointer;

	if (EX1_PL(regs->ex1) == KERNEL_PL && regs->sp >= ksp0) {
		pr_err("WARNING: cpu %d: kernel stack %#lx..%#lx underrun!\n"
		       "  sp %#lx (%#lx in caller), caller pc %#lx, lr %#lx\n",
		       cpu, ksp0_base, ksp0, sp, regs->sp, regs->pc, regs->lr);
	}

	else if (sp < ksp0_base + sizeof(struct thread_info)) {
		pr_err("WARNING: cpu %d: kernel stack %#lx..%#lx overrun!\n"
		       "  sp %#lx (%#lx in caller), caller pc %#lx, lr %#lx\n",
		       cpu, ksp0_base, ksp0, sp, regs->sp, regs->pc, regs->lr);
	}
}

void KBacktraceIterator_init(struct KBacktraceIterator *kbt,
			     struct task_struct *t, struct pt_regs *regs)
{
	unsigned long pc, lr, sp, r52;
	int is_current;

	/*
	 * Set up callback information.  We grab the kernel stack base
	 * so we will allow reads of that address range.
	 */
	is_current = (t == NULL || t == current);
	kbt->is_current = is_current;
	if (is_current)
		t = validate_current();
	kbt->task = t;
	kbt->verbose = 0;   /* override in caller if desired */
	kbt->profile = 0;   /* override in caller if desired */
	kbt->end = KBT_ONGOING;
	kbt->new_context = 1;
	if (is_current)
		validate_stack(regs);

	if (regs == NULL) {
		if (is_current || t->state == TASK_RUNNING) {
			/* Can't do this; we need registers */
			kbt->end = KBT_RUNNING;
			return;
		}
		pc = get_switch_to_pc();
		lr = t->thread.pc;
		sp = t->thread.ksp;
		r52 = 0;
	} else {
		pc = regs->pc;
		lr = regs->lr;
		sp = regs->sp;
		r52 = regs->regs[52];
	}

	backtrace_init(&kbt->it, read_memory_func, kbt, pc, lr, sp, r52);
	kbt->end = KBacktraceIterator_next_item_inclusive(kbt);
}
EXPORT_SYMBOL(KBacktraceIterator_init);

int KBacktraceIterator_end(struct KBacktraceIterator *kbt)
{
	return kbt->end != KBT_ONGOING;
}
EXPORT_SYMBOL(KBacktraceIterator_end);

void KBacktraceIterator_next(struct KBacktraceIterator *kbt)
{
	unsigned long old_pc = kbt->it.pc, old_sp = kbt->it.sp;
	kbt->new_context = 0;
	if (!backtrace_next(&kbt->it) && !KBacktraceIterator_restart(kbt)) {
		kbt->end = KBT_DONE;
		return;
	}
	kbt->end = KBacktraceIterator_next_item_inclusive(kbt);
	if (old_pc == kbt->it.pc && old_sp == kbt->it.sp) {
		/* Trapped in a loop; give up. */
		kbt->end = KBT_LOOP;
	}
}
EXPORT_SYMBOL(KBacktraceIterator_next);

static void describe_addr(struct KBacktraceIterator *kbt,
			  unsigned long address,
			  int have_mmap_sem, char *buf, size_t bufsize)
{
	struct vm_area_struct *vma;
	size_t namelen, remaining;
	unsigned long size, offset, adjust;
	char *p, *modname;
	const char *name;
	int rc;

	/*
	 * Look one byte back for every caller frame (i.e. those that
	 * aren't a new context) so we look up symbol data for the
	 * call itself, not the following instruction, which may be on
	 * a different line (or in a different function).
	 */
	adjust = !kbt->new_context;
	address -= adjust;

	if (address >= PAGE_OFFSET) {
		/* Handle kernel symbols. */
		BUG_ON(bufsize < KSYM_NAME_LEN);
		name = kallsyms_lookup(address, &size, &offset,
				       &modname, buf);
		if (name == NULL) {
			buf[0] = '\0';
			return;
		}
		namelen = strlen(buf);
		remaining = (bufsize - 1) - namelen;
		p = buf + namelen;
		rc = snprintf(p, remaining, "+%#lx/%#lx ",
			      offset + adjust, size);
		if (modname && rc < remaining)
			snprintf(p + rc, remaining - rc, "[%s] ", modname);
		buf[bufsize-1] = '\0';
		return;
	}

	/* If we don't have the mmap_sem, we can't show any more info. */
	buf[0] = '\0';
	if (!have_mmap_sem)
		return;

	/* Find vma info. */
	vma = find_vma(kbt->task->mm, address);
	if (vma == NULL || address < vma->vm_start) {
		snprintf(buf, bufsize, "[unmapped address] ");
		return;
	}

	if (vma->vm_file) {
		p = file_path(vma->vm_file, buf, bufsize);
		if (IS_ERR(p))
			p = "?";
		name = kbasename(p);
	} else {
		name = "anon";
	}

	/* Generate a string description of the vma info. */
	namelen = strlen(name);
	remaining = (bufsize - 1) - namelen;
	memmove(buf, name, namelen);
	snprintf(buf + namelen, remaining, "[%lx+%lx] ",
		 vma->vm_start, vma->vm_end - vma->vm_start);
}

/*
 * Avoid possible crash recursion during backtrace.  If it happens, it
 * makes it easy to lose the actual root cause of the failure, so we
 * put a simple guard on all the backtrace loops.
 */
static bool start_backtrace(void)
{
	if (current_thread_info()->in_backtrace) {
		pr_err("Backtrace requested while in backtrace!\n");
		return false;
	}
	current_thread_info()->in_backtrace = true;
	return true;
}

static void end_backtrace(void)
{
	current_thread_info()->in_backtrace = false;
}

/*
 * This method wraps the backtracer's more generic support.
 * It is only invoked from the architecture-specific code; show_stack()
 * and dump_stack() are architecture-independent entry points.
 */
void tile_show_stack(struct KBacktraceIterator *kbt)
{
	int i;
	int have_mmap_sem = 0;

	if (!start_backtrace())
		return;
	kbt->verbose = 1;
	i = 0;
	for (; !KBacktraceIterator_end(kbt); KBacktraceIterator_next(kbt)) {
		char namebuf[KSYM_NAME_LEN+100];
		unsigned long address = kbt->it.pc;

		/*
		 * Try to acquire the mmap_sem as we pass into userspace.
		 * If we're in an interrupt context, don't even try, since
		 * it's not safe to call e.g. d_path() from an interrupt,
		 * since it uses spin locks without disabling interrupts.
		 * Note we test "kbt->task == current", not "kbt->is_current",
		 * since we're checking that "current" will work in d_path().
		 */
		if (kbt->task == current && address < PAGE_OFFSET &&
		    !have_mmap_sem && kbt->task->mm && !in_interrupt()) {
			have_mmap_sem =
				down_read_trylock(&kbt->task->mm->mmap_sem);
		}

		describe_addr(kbt, address, have_mmap_sem,
			      namebuf, sizeof(namebuf));

		pr_err("  frame %d: 0x%lx %s(sp 0x%lx)\n",
		       i++, address, namebuf, (unsigned long)(kbt->it.sp));

		if (i >= 100) {
			pr_err("Stack dump truncated (%d frames)\n", i);
			break;
		}
	}
	if (kbt->end == KBT_LOOP)
		pr_err("Stack dump stopped; next frame identical to this one\n");
	if (have_mmap_sem)
		up_read(&kbt->task->mm->mmap_sem);
	end_backtrace();
}
EXPORT_SYMBOL(tile_show_stack);

static struct pt_regs *regs_to_pt_regs(struct pt_regs *regs,
				       ulong pc, ulong lr, ulong sp, ulong r52)
{
	memset(regs, 0, sizeof(struct pt_regs));
	regs->pc = pc;
	regs->lr = lr;
	regs->sp = sp;
	regs->regs[52] = r52;
	return regs;
}

/* Deprecated function currently only used by kernel_double_fault(). */
void _dump_stack(int dummy, ulong pc, ulong lr, ulong sp, ulong r52)
{
	struct KBacktraceIterator kbt;
	struct pt_regs regs;

	regs_to_pt_regs(&regs, pc, lr, sp, r52);
	KBacktraceIterator_init(&kbt, NULL, &regs);
	tile_show_stack(&kbt);
}

/* This is called from KBacktraceIterator_init_current() */
void _KBacktraceIterator_init_current(struct KBacktraceIterator *kbt, ulong pc,
				      ulong lr, ulong sp, ulong r52)
{
	struct pt_regs regs;
	KBacktraceIterator_init(kbt, NULL,
				regs_to_pt_regs(&regs, pc, lr, sp, r52));
}

/*
 * Called from sched_show_task() with task != NULL, or dump_stack()
 * with task == NULL.  The esp argument is always NULL.
 */
void show_stack(struct task_struct *task, unsigned long *esp)
{
	struct KBacktraceIterator kbt;
	if (task == NULL || task == current) {
		KBacktraceIterator_init_current(&kbt);
		KBacktraceIterator_next(&kbt);  /* don't show first frame */
	} else {
		KBacktraceIterator_init(&kbt, task, NULL);
	}
	tile_show_stack(&kbt);
}

#ifdef CONFIG_STACKTRACE

/* Support generic Linux stack API too */

static void save_stack_trace_common(struct task_struct *task,
				    struct pt_regs *regs,
				    bool user,
				    struct stack_trace *trace)
{
	struct KBacktraceIterator kbt;
	int skip = trace->skip;
	int i = 0;

	if (!start_backtrace())
		goto done;
	if (regs != NULL) {
		KBacktraceIterator_init(&kbt, NULL, regs);
	} else if (task == NULL || task == current) {
		KBacktraceIterator_init_current(&kbt);
		skip++;  /* don't show KBacktraceIterator_init_current */
	} else {
		KBacktraceIterator_init(&kbt, task, NULL);
	}
	for (; !KBacktraceIterator_end(&kbt); KBacktraceIterator_next(&kbt)) {
		if (skip) {
			--skip;
			continue;
		}
		if (i >= trace->max_entries ||
		    (!user && kbt.it.pc < PAGE_OFFSET))
			break;
		trace->entries[i++] = kbt.it.pc;
	}
	end_backtrace();
done:
	if (i < trace->max_entries)
		trace->entries[i++] = ULONG_MAX;
	trace->nr_entries = i;
}

void save_stack_trace_tsk(struct task_struct *task, struct stack_trace *trace)
{
	save_stack_trace_common(task, NULL, false, trace);
}
EXPORT_SYMBOL(save_stack_trace_tsk);

void save_stack_trace(struct stack_trace *trace)
{
	save_stack_trace_common(NULL, NULL, false, trace);
}
EXPORT_SYMBOL_GPL(save_stack_trace);

void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
{
	save_stack_trace_common(NULL, regs, false, trace);
}

void save_stack_trace_user(struct stack_trace *trace)
{
	/* Trace user stack if we are not a kernel thread. */
	if (current->mm)
		save_stack_trace_common(NULL, task_pt_regs(current),
					true, trace);
	else if (trace->nr_entries < trace->max_entries)
		trace->entries[trace->nr_entries++] = ULONG_MAX;
}
#endif

/* In entry.S */
EXPORT_SYMBOL(KBacktraceIterator_init_current);