1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
4 *
5 */
6 #include <linux/sched/task_stack.h>
7 #include <linux/stacktrace.h>
8 #include <linux/security.h>
9 #include <linux/kallsyms.h>
10 #include <linux/seq_file.h>
11 #include <linux/spinlock.h>
12 #include <linux/uaccess.h>
13 #include <linux/ftrace.h>
14 #include <linux/module.h>
15 #include <linux/sysctl.h>
16 #include <linux/init.h>
17
18 #include <asm/setup.h>
19
20 #include "trace.h"
21
22 #define STACK_TRACE_ENTRIES 500
23
24 static unsigned long stack_dump_trace[STACK_TRACE_ENTRIES];
25 static unsigned stack_trace_index[STACK_TRACE_ENTRIES];
26
27 static unsigned int stack_trace_nr_entries;
28 static unsigned long stack_trace_max_size;
29 static arch_spinlock_t stack_trace_max_lock =
30 (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
31
32 DEFINE_PER_CPU(int, disable_stack_tracer);
33 static DEFINE_MUTEX(stack_sysctl_mutex);
34
35 int stack_tracer_enabled;
36
print_max_stack(void)37 static void print_max_stack(void)
38 {
39 long i;
40 int size;
41
42 pr_emerg(" Depth Size Location (%d entries)\n"
43 " ----- ---- --------\n",
44 stack_trace_nr_entries);
45
46 for (i = 0; i < stack_trace_nr_entries; i++) {
47 if (i + 1 == stack_trace_nr_entries)
48 size = stack_trace_index[i];
49 else
50 size = stack_trace_index[i] - stack_trace_index[i+1];
51
52 pr_emerg("%3ld) %8d %5d %pS\n", i, stack_trace_index[i],
53 size, (void *)stack_dump_trace[i]);
54 }
55 }
56
57 /*
58 * The stack tracer looks for a maximum stack at each call from a function. It
59 * registers a callback from ftrace, and in that callback it examines the stack
60 * size. It determines the stack size from the variable passed in, which is the
61 * address of a local variable in the stack_trace_call() callback function.
62 * The stack size is calculated by the address of the local variable to the top
63 * of the current stack. If that size is smaller than the currently saved max
64 * stack size, nothing more is done.
65 *
66 * If the size of the stack is greater than the maximum recorded size, then the
67 * following algorithm takes place.
68 *
69 * For architectures (like x86) that store the function's return address before
70 * saving the function's local variables, the stack will look something like
71 * this:
72 *
73 * [ top of stack ]
74 * 0: sys call entry frame
75 * 10: return addr to entry code
76 * 11: start of sys_foo frame
77 * 20: return addr to sys_foo
78 * 21: start of kernel_func_bar frame
79 * 30: return addr to kernel_func_bar
80 * 31: [ do trace stack here ]
81 *
82 * The save_stack_trace() is called returning all the functions it finds in the
83 * current stack. Which would be (from the bottom of the stack to the top):
84 *
85 * return addr to kernel_func_bar
86 * return addr to sys_foo
87 * return addr to entry code
88 *
89 * Now to figure out how much each of these functions' local variable size is,
90 * a search of the stack is made to find these values. When a match is made, it
91 * is added to the stack_dump_trace[] array. The offset into the stack is saved
92 * in the stack_trace_index[] array. The above example would show:
93 *
94 * stack_dump_trace[] | stack_trace_index[]
95 * ------------------ + -------------------
96 * return addr to kernel_func_bar | 30
97 * return addr to sys_foo | 20
98 * return addr to entry | 10
99 *
100 * The print_max_stack() function above, uses these values to print the size of
101 * each function's portion of the stack.
102 *
103 * for (i = 0; i < nr_entries; i++) {
104 * size = i == nr_entries - 1 ? stack_trace_index[i] :
105 * stack_trace_index[i] - stack_trace_index[i+1]
106 * print "%d %d %d %s\n", i, stack_trace_index[i], size, stack_dump_trace[i]);
107 * }
108 *
109 * The above shows
110 *
111 * depth size location
112 * ----- ---- --------
113 * 0 30 10 kernel_func_bar
114 * 1 20 10 sys_foo
115 * 2 10 10 entry code
116 *
117 * Now for architectures that might save the return address after the functions
118 * local variables (saving the link register before calling nested functions),
119 * this will cause the stack to look a little different:
120 *
121 * [ top of stack ]
122 * 0: sys call entry frame
123 * 10: start of sys_foo_frame
124 * 19: return addr to entry code << lr saved before calling kernel_func_bar
125 * 20: start of kernel_func_bar frame
126 * 29: return addr to sys_foo_frame << lr saved before calling next function
127 * 30: [ do trace stack here ]
128 *
129 * Although the functions returned by save_stack_trace() may be the same, the
130 * placement in the stack will be different. Using the same algorithm as above
131 * would yield:
132 *
133 * stack_dump_trace[] | stack_trace_index[]
134 * ------------------ + -------------------
135 * return addr to kernel_func_bar | 30
136 * return addr to sys_foo | 29
137 * return addr to entry | 19
138 *
139 * Where the mapping is off by one:
140 *
141 * kernel_func_bar stack frame size is 29 - 19 not 30 - 29!
142 *
143 * To fix this, if the architecture sets ARCH_RET_ADDR_AFTER_LOCAL_VARS the
144 * values in stack_trace_index[] are shifted by one to and the number of
145 * stack trace entries is decremented by one.
146 *
147 * stack_dump_trace[] | stack_trace_index[]
148 * ------------------ + -------------------
149 * return addr to kernel_func_bar | 29
150 * return addr to sys_foo | 19
151 *
152 * Although the entry function is not displayed, the first function (sys_foo)
153 * will still include the stack size of it.
154 */
check_stack(unsigned long ip,unsigned long * stack)155 static void check_stack(unsigned long ip, unsigned long *stack)
156 {
157 unsigned long this_size, flags; unsigned long *p, *top, *start;
158 static int tracer_frame;
159 int frame_size = READ_ONCE(tracer_frame);
160 int i, x;
161
162 this_size = ((unsigned long)stack) & (THREAD_SIZE-1);
163 this_size = THREAD_SIZE - this_size;
164 /* Remove the frame of the tracer */
165 this_size -= frame_size;
166
167 if (this_size <= stack_trace_max_size)
168 return;
169
170 /* we do not handle interrupt stacks yet */
171 if (!object_is_on_stack(stack))
172 return;
173
174 /* Can't do this from NMI context (can cause deadlocks) */
175 if (in_nmi())
176 return;
177
178 local_irq_save(flags);
179 arch_spin_lock(&stack_trace_max_lock);
180
181 /* In case another CPU set the tracer_frame on us */
182 if (unlikely(!frame_size))
183 this_size -= tracer_frame;
184
185 /* a race could have already updated it */
186 if (this_size <= stack_trace_max_size)
187 goto out;
188
189 stack_trace_max_size = this_size;
190
191 stack_trace_nr_entries = stack_trace_save(stack_dump_trace,
192 ARRAY_SIZE(stack_dump_trace) - 1,
193 0);
194
195 /* Skip over the overhead of the stack tracer itself */
196 for (i = 0; i < stack_trace_nr_entries; i++) {
197 if (stack_dump_trace[i] == ip)
198 break;
199 }
200
201 /*
202 * Some archs may not have the passed in ip in the dump.
203 * If that happens, we need to show everything.
204 */
205 if (i == stack_trace_nr_entries)
206 i = 0;
207
208 /*
209 * Now find where in the stack these are.
210 */
211 x = 0;
212 start = stack;
213 top = (unsigned long *)
214 (((unsigned long)start & ~(THREAD_SIZE-1)) + THREAD_SIZE);
215
216 /*
217 * Loop through all the entries. One of the entries may
218 * for some reason be missed on the stack, so we may
219 * have to account for them. If they are all there, this
220 * loop will only happen once. This code only takes place
221 * on a new max, so it is far from a fast path.
222 */
223 while (i < stack_trace_nr_entries) {
224 int found = 0;
225
226 stack_trace_index[x] = this_size;
227 p = start;
228
229 for (; p < top && i < stack_trace_nr_entries; p++) {
230 /*
231 * The READ_ONCE_NOCHECK is used to let KASAN know that
232 * this is not a stack-out-of-bounds error.
233 */
234 if ((READ_ONCE_NOCHECK(*p)) == stack_dump_trace[i]) {
235 stack_dump_trace[x] = stack_dump_trace[i++];
236 this_size = stack_trace_index[x++] =
237 (top - p) * sizeof(unsigned long);
238 found = 1;
239 /* Start the search from here */
240 start = p + 1;
241 /*
242 * We do not want to show the overhead
243 * of the stack tracer stack in the
244 * max stack. If we haven't figured
245 * out what that is, then figure it out
246 * now.
247 */
248 if (unlikely(!tracer_frame)) {
249 tracer_frame = (p - stack) *
250 sizeof(unsigned long);
251 stack_trace_max_size -= tracer_frame;
252 }
253 }
254 }
255
256 if (!found)
257 i++;
258 }
259
260 #ifdef ARCH_FTRACE_SHIFT_STACK_TRACER
261 /*
262 * Some archs will store the link register before calling
263 * nested functions. This means the saved return address
264 * comes after the local storage, and we need to shift
265 * for that.
266 */
267 if (x > 1) {
268 memmove(&stack_trace_index[0], &stack_trace_index[1],
269 sizeof(stack_trace_index[0]) * (x - 1));
270 x--;
271 }
272 #endif
273
274 stack_trace_nr_entries = x;
275
276 if (task_stack_end_corrupted(current)) {
277 print_max_stack();
278 BUG();
279 }
280
281 out:
282 arch_spin_unlock(&stack_trace_max_lock);
283 local_irq_restore(flags);
284 }
285
286 /* Some archs may not define MCOUNT_INSN_SIZE */
287 #ifndef MCOUNT_INSN_SIZE
288 # define MCOUNT_INSN_SIZE 0
289 #endif
290
291 static void
stack_trace_call(unsigned long ip,unsigned long parent_ip,struct ftrace_ops * op,struct ftrace_regs * fregs)292 stack_trace_call(unsigned long ip, unsigned long parent_ip,
293 struct ftrace_ops *op, struct ftrace_regs *fregs)
294 {
295 unsigned long stack;
296
297 preempt_disable_notrace();
298
299 /* no atomic needed, we only modify this variable by this cpu */
300 __this_cpu_inc(disable_stack_tracer);
301 if (__this_cpu_read(disable_stack_tracer) != 1)
302 goto out;
303
304 /* If rcu is not watching, then save stack trace can fail */
305 if (!rcu_is_watching())
306 goto out;
307
308 ip += MCOUNT_INSN_SIZE;
309
310 check_stack(ip, &stack);
311
312 out:
313 __this_cpu_dec(disable_stack_tracer);
314 /* prevent recursion in schedule */
315 preempt_enable_notrace();
316 }
317
318 static struct ftrace_ops trace_ops __read_mostly =
319 {
320 .func = stack_trace_call,
321 };
322
323 static ssize_t
stack_max_size_read(struct file * filp,char __user * ubuf,size_t count,loff_t * ppos)324 stack_max_size_read(struct file *filp, char __user *ubuf,
325 size_t count, loff_t *ppos)
326 {
327 unsigned long *ptr = filp->private_data;
328 char buf[64];
329 int r;
330
331 r = snprintf(buf, sizeof(buf), "%ld\n", *ptr);
332 if (r > sizeof(buf))
333 r = sizeof(buf);
334 return simple_read_from_buffer(ubuf, count, ppos, buf, r);
335 }
336
337 static ssize_t
stack_max_size_write(struct file * filp,const char __user * ubuf,size_t count,loff_t * ppos)338 stack_max_size_write(struct file *filp, const char __user *ubuf,
339 size_t count, loff_t *ppos)
340 {
341 long *ptr = filp->private_data;
342 unsigned long val, flags;
343 int ret;
344
345 ret = kstrtoul_from_user(ubuf, count, 10, &val);
346 if (ret)
347 return ret;
348
349 local_irq_save(flags);
350
351 /*
352 * In case we trace inside arch_spin_lock() or after (NMI),
353 * we will cause circular lock, so we also need to increase
354 * the percpu disable_stack_tracer here.
355 */
356 __this_cpu_inc(disable_stack_tracer);
357
358 arch_spin_lock(&stack_trace_max_lock);
359 *ptr = val;
360 arch_spin_unlock(&stack_trace_max_lock);
361
362 __this_cpu_dec(disable_stack_tracer);
363 local_irq_restore(flags);
364
365 return count;
366 }
367
368 static const struct file_operations stack_max_size_fops = {
369 .open = tracing_open_generic,
370 .read = stack_max_size_read,
371 .write = stack_max_size_write,
372 .llseek = default_llseek,
373 };
374
375 static void *
__next(struct seq_file * m,loff_t * pos)376 __next(struct seq_file *m, loff_t *pos)
377 {
378 long n = *pos - 1;
379
380 if (n >= stack_trace_nr_entries)
381 return NULL;
382
383 m->private = (void *)n;
384 return &m->private;
385 }
386
387 static void *
t_next(struct seq_file * m,void * v,loff_t * pos)388 t_next(struct seq_file *m, void *v, loff_t *pos)
389 {
390 (*pos)++;
391 return __next(m, pos);
392 }
393
t_start(struct seq_file * m,loff_t * pos)394 static void *t_start(struct seq_file *m, loff_t *pos)
395 {
396 local_irq_disable();
397
398 __this_cpu_inc(disable_stack_tracer);
399
400 arch_spin_lock(&stack_trace_max_lock);
401
402 if (*pos == 0)
403 return SEQ_START_TOKEN;
404
405 return __next(m, pos);
406 }
407
t_stop(struct seq_file * m,void * p)408 static void t_stop(struct seq_file *m, void *p)
409 {
410 arch_spin_unlock(&stack_trace_max_lock);
411
412 __this_cpu_dec(disable_stack_tracer);
413
414 local_irq_enable();
415 }
416
trace_lookup_stack(struct seq_file * m,long i)417 static void trace_lookup_stack(struct seq_file *m, long i)
418 {
419 unsigned long addr = stack_dump_trace[i];
420
421 seq_printf(m, "%pS\n", (void *)addr);
422 }
423
print_disabled(struct seq_file * m)424 static void print_disabled(struct seq_file *m)
425 {
426 seq_puts(m, "#\n"
427 "# Stack tracer disabled\n"
428 "#\n"
429 "# To enable the stack tracer, either add 'stacktrace' to the\n"
430 "# kernel command line\n"
431 "# or 'echo 1 > /proc/sys/kernel/stack_tracer_enabled'\n"
432 "#\n");
433 }
434
t_show(struct seq_file * m,void * v)435 static int t_show(struct seq_file *m, void *v)
436 {
437 long i;
438 int size;
439
440 if (v == SEQ_START_TOKEN) {
441 seq_printf(m, " Depth Size Location"
442 " (%d entries)\n"
443 " ----- ---- --------\n",
444 stack_trace_nr_entries);
445
446 if (!stack_tracer_enabled && !stack_trace_max_size)
447 print_disabled(m);
448
449 return 0;
450 }
451
452 i = *(long *)v;
453
454 if (i >= stack_trace_nr_entries)
455 return 0;
456
457 if (i + 1 == stack_trace_nr_entries)
458 size = stack_trace_index[i];
459 else
460 size = stack_trace_index[i] - stack_trace_index[i+1];
461
462 seq_printf(m, "%3ld) %8d %5d ", i, stack_trace_index[i], size);
463
464 trace_lookup_stack(m, i);
465
466 return 0;
467 }
468
469 static const struct seq_operations stack_trace_seq_ops = {
470 .start = t_start,
471 .next = t_next,
472 .stop = t_stop,
473 .show = t_show,
474 };
475
stack_trace_open(struct inode * inode,struct file * file)476 static int stack_trace_open(struct inode *inode, struct file *file)
477 {
478 int ret;
479
480 ret = security_locked_down(LOCKDOWN_TRACEFS);
481 if (ret)
482 return ret;
483
484 return seq_open(file, &stack_trace_seq_ops);
485 }
486
487 static const struct file_operations stack_trace_fops = {
488 .open = stack_trace_open,
489 .read = seq_read,
490 .llseek = seq_lseek,
491 .release = seq_release,
492 };
493
494 #ifdef CONFIG_DYNAMIC_FTRACE
495
496 static int
stack_trace_filter_open(struct inode * inode,struct file * file)497 stack_trace_filter_open(struct inode *inode, struct file *file)
498 {
499 struct ftrace_ops *ops = inode->i_private;
500
501 /* Checks for tracefs lockdown */
502 return ftrace_regex_open(ops, FTRACE_ITER_FILTER,
503 inode, file);
504 }
505
506 static const struct file_operations stack_trace_filter_fops = {
507 .open = stack_trace_filter_open,
508 .read = seq_read,
509 .write = ftrace_filter_write,
510 .llseek = tracing_lseek,
511 .release = ftrace_regex_release,
512 };
513
514 #endif /* CONFIG_DYNAMIC_FTRACE */
515
516 int
stack_trace_sysctl(struct ctl_table * table,int write,void * buffer,size_t * lenp,loff_t * ppos)517 stack_trace_sysctl(struct ctl_table *table, int write, void *buffer,
518 size_t *lenp, loff_t *ppos)
519 {
520 int was_enabled;
521 int ret;
522
523 mutex_lock(&stack_sysctl_mutex);
524 was_enabled = !!stack_tracer_enabled;
525
526 ret = proc_dointvec(table, write, buffer, lenp, ppos);
527
528 if (ret || !write || (was_enabled == !!stack_tracer_enabled))
529 goto out;
530
531 if (stack_tracer_enabled)
532 register_ftrace_function(&trace_ops);
533 else
534 unregister_ftrace_function(&trace_ops);
535 out:
536 mutex_unlock(&stack_sysctl_mutex);
537 return ret;
538 }
539
540 static char stack_trace_filter_buf[COMMAND_LINE_SIZE+1] __initdata;
541
enable_stacktrace(char * str)542 static __init int enable_stacktrace(char *str)
543 {
544 int len;
545
546 if ((len = str_has_prefix(str, "_filter=")))
547 strncpy(stack_trace_filter_buf, str + len, COMMAND_LINE_SIZE);
548
549 stack_tracer_enabled = 1;
550 return 1;
551 }
552 __setup("stacktrace", enable_stacktrace);
553
stack_trace_init(void)554 static __init int stack_trace_init(void)
555 {
556 int ret;
557
558 ret = tracing_init_dentry();
559 if (ret)
560 return 0;
561
562 trace_create_file("stack_max_size", TRACE_MODE_WRITE, NULL,
563 &stack_trace_max_size, &stack_max_size_fops);
564
565 trace_create_file("stack_trace", TRACE_MODE_READ, NULL,
566 NULL, &stack_trace_fops);
567
568 #ifdef CONFIG_DYNAMIC_FTRACE
569 trace_create_file("stack_trace_filter", TRACE_MODE_WRITE, NULL,
570 &trace_ops, &stack_trace_filter_fops);
571 #endif
572
573 if (stack_trace_filter_buf[0])
574 ftrace_set_early_filter(&trace_ops, stack_trace_filter_buf, 1);
575
576 if (stack_tracer_enabled)
577 register_ftrace_function(&trace_ops);
578
579 return 0;
580 }
581
582 device_initcall(stack_trace_init);
583