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
|
/*
* Code for replacing ftrace calls with jumps.
*
* Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
*
* Thanks goes to Ingo Molnar, for suggesting the idea.
* Mathieu Desnoyers, for suggesting postponing the modifications.
* Arjan van de Ven, for keeping me straight, and explaining to me
* the dangers of modifying code on the run.
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/spinlock.h>
#include <linux/hardirq.h>
#include <linux/uaccess.h>
#include <linux/ftrace.h>
#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/module.h>
#include <trace/syscall.h>
#include <asm/cacheflush.h>
#include <asm/ftrace.h>
#include <asm/nops.h>
#include <asm/nmi.h>
#ifdef CONFIG_DYNAMIC_FTRACE
/*
* modifying_code is set to notify NMIs that they need to use
* memory barriers when entering or exiting. But we don't want
* to burden NMIs with unnecessary memory barriers when code
* modification is not being done (which is most of the time).
*
* A mutex is already held when ftrace_arch_code_modify_prepare
* and post_process are called. No locks need to be taken here.
*
* Stop machine will make sure currently running NMIs are done
* and new NMIs will see the updated variable before we need
* to worry about NMIs doing memory barriers.
*/
static int modifying_code __read_mostly;
static DEFINE_PER_CPU(int, save_modifying_code);
int ftrace_arch_code_modify_prepare(void)
{
set_kernel_text_rw();
set_all_modules_text_rw();
modifying_code = 1;
return 0;
}
int ftrace_arch_code_modify_post_process(void)
{
modifying_code = 0;
set_all_modules_text_ro();
set_kernel_text_ro();
return 0;
}
union ftrace_code_union {
char code[MCOUNT_INSN_SIZE];
struct {
char e8;
int offset;
} __attribute__((packed));
};
static int ftrace_calc_offset(long ip, long addr)
{
return (int)(addr - ip);
}
static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
{
static union ftrace_code_union calc;
calc.e8 = 0xe8;
calc.offset = ftrace_calc_offset(ip + MCOUNT_INSN_SIZE, addr);
/*
* No locking needed, this must be called via kstop_machine
* which in essence is like running on a uniprocessor machine.
*/
return calc.code;
}
/*
* Modifying code must take extra care. On an SMP machine, if
* the code being modified is also being executed on another CPU
* that CPU will have undefined results and possibly take a GPF.
* We use kstop_machine to stop other CPUS from exectuing code.
* But this does not stop NMIs from happening. We still need
* to protect against that. We separate out the modification of
* the code to take care of this.
*
* Two buffers are added: An IP buffer and a "code" buffer.
*
* 1) Put the instruction pointer into the IP buffer
* and the new code into the "code" buffer.
* 2) Wait for any running NMIs to finish and set a flag that says
* we are modifying code, it is done in an atomic operation.
* 3) Write the code
* 4) clear the flag.
* 5) Wait for any running NMIs to finish.
*
* If an NMI is executed, the first thing it does is to call
* "ftrace_nmi_enter". This will check if the flag is set to write
* and if it is, it will write what is in the IP and "code" buffers.
*
* The trick is, it does not matter if everyone is writing the same
* content to the code location. Also, if a CPU is executing code
* it is OK to write to that code location if the contents being written
* are the same as what exists.
*/
#define MOD_CODE_WRITE_FLAG (1 << 31) /* set when NMI should do the write */
static atomic_t nmi_running = ATOMIC_INIT(0);
static int mod_code_status; /* holds return value of text write */
static void *mod_code_ip; /* holds the IP to write to */
static void *mod_code_newcode; /* holds the text to write to the IP */
static unsigned nmi_wait_count;
static atomic_t nmi_update_count = ATOMIC_INIT(0);
int ftrace_arch_read_dyn_info(char *buf, int size)
{
int r;
r = snprintf(buf, size, "%u %u",
nmi_wait_count,
atomic_read(&nmi_update_count));
return r;
}
static void clear_mod_flag(void)
{
int old = atomic_read(&nmi_running);
for (;;) {
int new = old & ~MOD_CODE_WRITE_FLAG;
if (old == new)
break;
old = atomic_cmpxchg(&nmi_running, old, new);
}
}
static void ftrace_mod_code(void)
{
/*
* Yes, more than one CPU process can be writing to mod_code_status.
* (and the code itself)
* But if one were to fail, then they all should, and if one were
* to succeed, then they all should.
*/
mod_code_status = probe_kernel_write(mod_code_ip, mod_code_newcode,
MCOUNT_INSN_SIZE);
/* if we fail, then kill any new writers */
if (mod_code_status)
clear_mod_flag();
}
void ftrace_nmi_enter(void)
{
__get_cpu_var(save_modifying_code) = modifying_code;
if (!__get_cpu_var(save_modifying_code))
return;
if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) {
smp_rmb();
ftrace_mod_code();
atomic_inc(&nmi_update_count);
}
/* Must have previous changes seen before executions */
smp_mb();
}
void ftrace_nmi_exit(void)
{
if (!__get_cpu_var(save_modifying_code))
return;
/* Finish all executions before clearing nmi_running */
smp_mb();
atomic_dec(&nmi_running);
}
static void wait_for_nmi_and_set_mod_flag(void)
{
if (!atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG))
return;
do {
cpu_relax();
} while (atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG));
nmi_wait_count++;
}
static void wait_for_nmi(void)
{
if (!atomic_read(&nmi_running))
return;
do {
cpu_relax();
} while (atomic_read(&nmi_running));
nmi_wait_count++;
}
static inline int
within(unsigned long addr, unsigned long start, unsigned long end)
{
return addr >= start && addr < end;
}
static int
do_ftrace_mod_code(unsigned long ip, void *new_code)
{
/*
* On x86_64, kernel text mappings are mapped read-only with
* CONFIG_DEBUG_RODATA. So we use the kernel identity mapping instead
* of the kernel text mapping to modify the kernel text.
*
* For 32bit kernels, these mappings are same and we can use
* kernel identity mapping to modify code.
*/
if (within(ip, (unsigned long)_text, (unsigned long)_etext))
ip = (unsigned long)__va(__pa(ip));
mod_code_ip = (void *)ip;
mod_code_newcode = new_code;
/* The buffers need to be visible before we let NMIs write them */
smp_mb();
wait_for_nmi_and_set_mod_flag();
/* Make sure all running NMIs have finished before we write the code */
smp_mb();
ftrace_mod_code();
/* Make sure the write happens before clearing the bit */
smp_mb();
clear_mod_flag();
wait_for_nmi();
return mod_code_status;
}
static unsigned char *ftrace_nop_replace(void)
{
return ideal_nop5;
}
static int
ftrace_modify_code(unsigned long ip, unsigned char *old_code,
unsigned char *new_code)
{
unsigned char replaced[MCOUNT_INSN_SIZE];
/*
* Note: Due to modules and __init, code can
* disappear and change, we need to protect against faulting
* as well as code changing. We do this by using the
* probe_kernel_* functions.
*
* No real locking needed, this code is run through
* kstop_machine, or before SMP starts.
*/
/* read the text we want to modify */
if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
return -EFAULT;
/* Make sure it is what we expect it to be */
if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
return -EINVAL;
/* replace the text with the new text */
if (do_ftrace_mod_code(ip, new_code))
return -EPERM;
sync_core();
return 0;
}
int ftrace_make_nop(struct module *mod,
struct dyn_ftrace *rec, unsigned long addr)
{
unsigned char *new, *old;
unsigned long ip = rec->ip;
old = ftrace_call_replace(ip, addr);
new = ftrace_nop_replace();
return ftrace_modify_code(rec->ip, old, new);
}
int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
unsigned char *new, *old;
unsigned long ip = rec->ip;
old = ftrace_nop_replace();
new = ftrace_call_replace(ip, addr);
return ftrace_modify_code(rec->ip, old, new);
}
int ftrace_update_ftrace_func(ftrace_func_t func)
{
unsigned long ip = (unsigned long)(&ftrace_call);
unsigned char old[MCOUNT_INSN_SIZE], *new;
int ret;
memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE);
new = ftrace_call_replace(ip, (unsigned long)func);
ret = ftrace_modify_code(ip, old, new);
return ret;
}
int __init ftrace_dyn_arch_init(void *data)
{
/* The return code is retured via data */
*(unsigned long *)data = 0;
return 0;
}
#endif
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
#ifdef CONFIG_DYNAMIC_FTRACE
extern void ftrace_graph_call(void);
static int ftrace_mod_jmp(unsigned long ip,
int old_offset, int new_offset)
{
unsigned char code[MCOUNT_INSN_SIZE];
if (probe_kernel_read(code, (void *)ip, MCOUNT_INSN_SIZE))
return -EFAULT;
if
|