Commit | Line | Data |
---|---|---|
3d083395 SR |
1 | /* |
2 | * Code for replacing ftrace calls with jumps. | |
3 | * | |
4 | * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com> | |
5 | * | |
6 | * Thanks goes to Ingo Molnar, for suggesting the idea. | |
7 | * Mathieu Desnoyers, for suggesting postponing the modifications. | |
8 | * Arjan van de Ven, for keeping me straight, and explaining to me | |
9 | * the dangers of modifying code on the run. | |
10 | */ | |
11 | ||
3bb258bf JP |
12 | #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt |
13 | ||
3d083395 SR |
14 | #include <linux/spinlock.h> |
15 | #include <linux/hardirq.h> | |
6f93fc07 | 16 | #include <linux/uaccess.h> |
3d083395 SR |
17 | #include <linux/ftrace.h> |
18 | #include <linux/percpu.h> | |
19b3e967 | 19 | #include <linux/sched.h> |
3d083395 SR |
20 | #include <linux/init.h> |
21 | #include <linux/list.h> | |
84e1c6bb | 22 | #include <linux/module.h> |
3d083395 | 23 | |
47788c58 FW |
24 | #include <trace/syscall.h> |
25 | ||
16239630 | 26 | #include <asm/cacheflush.h> |
395a59d0 | 27 | #include <asm/ftrace.h> |
732f3ca7 | 28 | #include <asm/nops.h> |
caf4b323 | 29 | #include <asm/nmi.h> |
3d083395 | 30 | |
3d083395 | 31 | |
caf4b323 | 32 | #ifdef CONFIG_DYNAMIC_FTRACE |
3d083395 | 33 | |
0c54dd34 SR |
34 | /* |
35 | * modifying_code is set to notify NMIs that they need to use | |
36 | * memory barriers when entering or exiting. But we don't want | |
37 | * to burden NMIs with unnecessary memory barriers when code | |
38 | * modification is not being done (which is most of the time). | |
39 | * | |
40 | * A mutex is already held when ftrace_arch_code_modify_prepare | |
41 | * and post_process are called. No locks need to be taken here. | |
42 | * | |
43 | * Stop machine will make sure currently running NMIs are done | |
44 | * and new NMIs will see the updated variable before we need | |
45 | * to worry about NMIs doing memory barriers. | |
46 | */ | |
47 | static int modifying_code __read_mostly; | |
48 | static DEFINE_PER_CPU(int, save_modifying_code); | |
49 | ||
16239630 SR |
50 | int ftrace_arch_code_modify_prepare(void) |
51 | { | |
52 | set_kernel_text_rw(); | |
84e1c6bb | 53 | set_all_modules_text_rw(); |
0c54dd34 | 54 | modifying_code = 1; |
16239630 SR |
55 | return 0; |
56 | } | |
57 | ||
58 | int ftrace_arch_code_modify_post_process(void) | |
59 | { | |
0c54dd34 | 60 | modifying_code = 0; |
84e1c6bb | 61 | set_all_modules_text_ro(); |
16239630 SR |
62 | set_kernel_text_ro(); |
63 | return 0; | |
64 | } | |
65 | ||
3d083395 | 66 | union ftrace_code_union { |
395a59d0 | 67 | char code[MCOUNT_INSN_SIZE]; |
3d083395 SR |
68 | struct { |
69 | char e8; | |
70 | int offset; | |
71 | } __attribute__((packed)); | |
72 | }; | |
73 | ||
15adc048 | 74 | static int ftrace_calc_offset(long ip, long addr) |
3c1720f0 SR |
75 | { |
76 | return (int)(addr - ip); | |
77 | } | |
3d083395 | 78 | |
31e88909 | 79 | static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr) |
3c1720f0 SR |
80 | { |
81 | static union ftrace_code_union calc; | |
3d083395 | 82 | |
3c1720f0 | 83 | calc.e8 = 0xe8; |
395a59d0 | 84 | calc.offset = ftrace_calc_offset(ip + MCOUNT_INSN_SIZE, addr); |
3c1720f0 SR |
85 | |
86 | /* | |
87 | * No locking needed, this must be called via kstop_machine | |
88 | * which in essence is like running on a uniprocessor machine. | |
89 | */ | |
90 | return calc.code; | |
3d083395 SR |
91 | } |
92 | ||
17666f02 SR |
93 | /* |
94 | * Modifying code must take extra care. On an SMP machine, if | |
95 | * the code being modified is also being executed on another CPU | |
96 | * that CPU will have undefined results and possibly take a GPF. | |
97 | * We use kstop_machine to stop other CPUS from exectuing code. | |
98 | * But this does not stop NMIs from happening. We still need | |
99 | * to protect against that. We separate out the modification of | |
100 | * the code to take care of this. | |
101 | * | |
102 | * Two buffers are added: An IP buffer and a "code" buffer. | |
103 | * | |
a26a2a27 | 104 | * 1) Put the instruction pointer into the IP buffer |
17666f02 | 105 | * and the new code into the "code" buffer. |
e9d9df44 LJ |
106 | * 2) Wait for any running NMIs to finish and set a flag that says |
107 | * we are modifying code, it is done in an atomic operation. | |
108 | * 3) Write the code | |
109 | * 4) clear the flag. | |
110 | * 5) Wait for any running NMIs to finish. | |
17666f02 SR |
111 | * |
112 | * If an NMI is executed, the first thing it does is to call | |
113 | * "ftrace_nmi_enter". This will check if the flag is set to write | |
114 | * and if it is, it will write what is in the IP and "code" buffers. | |
115 | * | |
116 | * The trick is, it does not matter if everyone is writing the same | |
117 | * content to the code location. Also, if a CPU is executing code | |
118 | * it is OK to write to that code location if the contents being written | |
119 | * are the same as what exists. | |
120 | */ | |
121 | ||
e9d9df44 | 122 | #define MOD_CODE_WRITE_FLAG (1 << 31) /* set when NMI should do the write */ |
4e6ea144 | 123 | static atomic_t nmi_running = ATOMIC_INIT(0); |
a26a2a27 | 124 | static int mod_code_status; /* holds return value of text write */ |
a26a2a27 SR |
125 | static void *mod_code_ip; /* holds the IP to write to */ |
126 | static void *mod_code_newcode; /* holds the text to write to the IP */ | |
17666f02 | 127 | |
a26a2a27 SR |
128 | static unsigned nmi_wait_count; |
129 | static atomic_t nmi_update_count = ATOMIC_INIT(0); | |
b807c3d0 SR |
130 | |
131 | int ftrace_arch_read_dyn_info(char *buf, int size) | |
132 | { | |
133 | int r; | |
134 | ||
135 | r = snprintf(buf, size, "%u %u", | |
136 | nmi_wait_count, | |
137 | atomic_read(&nmi_update_count)); | |
138 | return r; | |
139 | } | |
140 | ||
e9d9df44 LJ |
141 | static void clear_mod_flag(void) |
142 | { | |
143 | int old = atomic_read(&nmi_running); | |
144 | ||
145 | for (;;) { | |
146 | int new = old & ~MOD_CODE_WRITE_FLAG; | |
147 | ||
148 | if (old == new) | |
149 | break; | |
150 | ||
151 | old = atomic_cmpxchg(&nmi_running, old, new); | |
152 | } | |
153 | } | |
154 | ||
17666f02 SR |
155 | static void ftrace_mod_code(void) |
156 | { | |
157 | /* | |
158 | * Yes, more than one CPU process can be writing to mod_code_status. | |
159 | * (and the code itself) | |
160 | * But if one were to fail, then they all should, and if one were | |
161 | * to succeed, then they all should. | |
162 | */ | |
163 | mod_code_status = probe_kernel_write(mod_code_ip, mod_code_newcode, | |
164 | MCOUNT_INSN_SIZE); | |
90c7ac49 SR |
165 | |
166 | /* if we fail, then kill any new writers */ | |
167 | if (mod_code_status) | |
e9d9df44 | 168 | clear_mod_flag(); |
17666f02 SR |
169 | } |
170 | ||
a81bd80a | 171 | void ftrace_nmi_enter(void) |
17666f02 | 172 | { |
0a3aee0d | 173 | __this_cpu_write(save_modifying_code, modifying_code); |
0c54dd34 | 174 | |
0a3aee0d | 175 | if (!__this_cpu_read(save_modifying_code)) |
0c54dd34 SR |
176 | return; |
177 | ||
e9d9df44 LJ |
178 | if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) { |
179 | smp_rmb(); | |
17666f02 | 180 | ftrace_mod_code(); |
b807c3d0 SR |
181 | atomic_inc(&nmi_update_count); |
182 | } | |
e9d9df44 LJ |
183 | /* Must have previous changes seen before executions */ |
184 | smp_mb(); | |
17666f02 SR |
185 | } |
186 | ||
a81bd80a | 187 | void ftrace_nmi_exit(void) |
17666f02 | 188 | { |
0a3aee0d | 189 | if (!__this_cpu_read(save_modifying_code)) |
0c54dd34 SR |
190 | return; |
191 | ||
4e6ea144 | 192 | /* Finish all executions before clearing nmi_running */ |
e9d9df44 | 193 | smp_mb(); |
4e6ea144 | 194 | atomic_dec(&nmi_running); |
17666f02 SR |
195 | } |
196 | ||
e9d9df44 LJ |
197 | static void wait_for_nmi_and_set_mod_flag(void) |
198 | { | |
199 | if (!atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG)) | |
200 | return; | |
201 | ||
202 | do { | |
203 | cpu_relax(); | |
204 | } while (atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG)); | |
205 | ||
206 | nmi_wait_count++; | |
207 | } | |
208 | ||
17666f02 SR |
209 | static void wait_for_nmi(void) |
210 | { | |
4e6ea144 | 211 | if (!atomic_read(&nmi_running)) |
89025282 | 212 | return; |
b807c3d0 | 213 | |
89025282 | 214 | do { |
17666f02 | 215 | cpu_relax(); |
4e6ea144 | 216 | } while (atomic_read(&nmi_running)); |
b807c3d0 | 217 | |
89025282 | 218 | nmi_wait_count++; |
17666f02 SR |
219 | } |
220 | ||
55ca3cc1 SS |
221 | static inline int |
222 | within(unsigned long addr, unsigned long start, unsigned long end) | |
223 | { | |
224 | return addr >= start && addr < end; | |
225 | } | |
226 | ||
17666f02 SR |
227 | static int |
228 | do_ftrace_mod_code(unsigned long ip, void *new_code) | |
229 | { | |
55ca3cc1 SS |
230 | /* |
231 | * On x86_64, kernel text mappings are mapped read-only with | |
232 | * CONFIG_DEBUG_RODATA. So we use the kernel identity mapping instead | |
233 | * of the kernel text mapping to modify the kernel text. | |
234 | * | |
235 | * For 32bit kernels, these mappings are same and we can use | |
236 | * kernel identity mapping to modify code. | |
237 | */ | |
238 | if (within(ip, (unsigned long)_text, (unsigned long)_etext)) | |
239 | ip = (unsigned long)__va(__pa(ip)); | |
240 | ||
17666f02 SR |
241 | mod_code_ip = (void *)ip; |
242 | mod_code_newcode = new_code; | |
243 | ||
244 | /* The buffers need to be visible before we let NMIs write them */ | |
17666f02 SR |
245 | smp_mb(); |
246 | ||
e9d9df44 | 247 | wait_for_nmi_and_set_mod_flag(); |
17666f02 SR |
248 | |
249 | /* Make sure all running NMIs have finished before we write the code */ | |
250 | smp_mb(); | |
251 | ||
252 | ftrace_mod_code(); | |
253 | ||
254 | /* Make sure the write happens before clearing the bit */ | |
17666f02 SR |
255 | smp_mb(); |
256 | ||
e9d9df44 | 257 | clear_mod_flag(); |
17666f02 SR |
258 | wait_for_nmi(); |
259 | ||
260 | return mod_code_status; | |
261 | } | |
262 | ||
31e88909 | 263 | static unsigned char *ftrace_nop_replace(void) |
caf4b323 | 264 | { |
f49aa448 | 265 | return ideal_nop5; |
caf4b323 FW |
266 | } |
267 | ||
31e88909 | 268 | static int |
3d083395 SR |
269 | ftrace_modify_code(unsigned long ip, unsigned char *old_code, |
270 | unsigned char *new_code) | |
271 | { | |
6f93fc07 | 272 | unsigned char replaced[MCOUNT_INSN_SIZE]; |
3d083395 SR |
273 | |
274 | /* | |
275 | * Note: Due to modules and __init, code can | |
276 | * disappear and change, we need to protect against faulting | |
76aefee5 | 277 | * as well as code changing. We do this by using the |
ab9a0918 | 278 | * probe_kernel_* functions. |
3d083395 SR |
279 | * |
280 | * No real locking needed, this code is run through | |
6f93fc07 | 281 | * kstop_machine, or before SMP starts. |
3d083395 | 282 | */ |
76aefee5 SR |
283 | |
284 | /* read the text we want to modify */ | |
ab9a0918 | 285 | if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE)) |
593eb8a2 | 286 | return -EFAULT; |
6f93fc07 | 287 | |
76aefee5 | 288 | /* Make sure it is what we expect it to be */ |
6f93fc07 | 289 | if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0) |
593eb8a2 | 290 | return -EINVAL; |
3d083395 | 291 | |
76aefee5 | 292 | /* replace the text with the new text */ |
17666f02 | 293 | if (do_ftrace_mod_code(ip, new_code)) |
593eb8a2 | 294 | return -EPERM; |
6f93fc07 SR |
295 | |
296 | sync_core(); | |
3d083395 | 297 | |
6f93fc07 | 298 | return 0; |
3d083395 SR |
299 | } |
300 | ||
31e88909 SR |
301 | int ftrace_make_nop(struct module *mod, |
302 | struct dyn_ftrace *rec, unsigned long addr) | |
303 | { | |
304 | unsigned char *new, *old; | |
305 | unsigned long ip = rec->ip; | |
306 | ||
307 | old = ftrace_call_replace(ip, addr); | |
308 | new = ftrace_nop_replace(); | |
309 | ||
310 | return ftrace_modify_code(rec->ip, old, new); | |
311 | } | |
312 | ||
313 | int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) | |
314 | { | |
315 | unsigned char *new, *old; | |
316 | unsigned long ip = rec->ip; | |
317 | ||
318 | old = ftrace_nop_replace(); | |
319 | new = ftrace_call_replace(ip, addr); | |
320 | ||
321 | return ftrace_modify_code(rec->ip, old, new); | |
322 | } | |
323 | ||
15adc048 | 324 | int ftrace_update_ftrace_func(ftrace_func_t func) |
d61f82d0 SR |
325 | { |
326 | unsigned long ip = (unsigned long)(&ftrace_call); | |
395a59d0 | 327 | unsigned char old[MCOUNT_INSN_SIZE], *new; |
d61f82d0 SR |
328 | int ret; |
329 | ||
395a59d0 | 330 | memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE); |
d61f82d0 SR |
331 | new = ftrace_call_replace(ip, (unsigned long)func); |
332 | ret = ftrace_modify_code(ip, old, new); | |
333 | ||
334 | return ret; | |
335 | } | |
336 | ||
d61f82d0 | 337 | int __init ftrace_dyn_arch_init(void *data) |
3d083395 | 338 | { |
732f3ca7 SR |
339 | /* The return code is retured via data */ |
340 | *(unsigned long *)data = 0; | |
dfa60aba | 341 | |
3d083395 SR |
342 | return 0; |
343 | } | |
caf4b323 | 344 | #endif |
e7d3737e | 345 | |
fb52607a | 346 | #ifdef CONFIG_FUNCTION_GRAPH_TRACER |
e7d3737e | 347 | |
5a45cfe1 SR |
348 | #ifdef CONFIG_DYNAMIC_FTRACE |
349 | extern void ftrace_graph_call(void); | |
350 | ||
351 | static int ftrace_mod_jmp(unsigned long ip, | |
352 | int old_offset, int new_offset) | |
353 | { | |
354 | unsigned char code[MCOUNT_INSN_SIZE]; | |
355 | ||
356 | if (probe_kernel_read(code, (void *)ip, MCOUNT_INSN_SIZE)) | |
357 | return -EFAULT; | |
358 | ||
359 | if (code[0] != 0xe9 || old_offset != *(int *)(&code[1])) | |
360 | return -EINVAL; | |
361 | ||
362 | *(int *)(&code[1]) = new_offset; | |
363 | ||
364 | if (do_ftrace_mod_code(ip, &code)) | |
365 | return -EPERM; | |
366 | ||
367 | return 0; | |
368 | } | |
369 | ||
370 | int ftrace_enable_ftrace_graph_caller(void) | |
371 | { | |
372 | unsigned long ip = (unsigned long)(&ftrace_graph_call); | |
373 | int old_offset, new_offset; | |
374 | ||
375 | old_offset = (unsigned long)(&ftrace_stub) - (ip + MCOUNT_INSN_SIZE); | |
376 | new_offset = (unsigned long)(&ftrace_graph_caller) - (ip + MCOUNT_INSN_SIZE); | |
377 | ||
378 | return ftrace_mod_jmp(ip, old_offset, new_offset); | |
379 | } | |
380 | ||
381 | int ftrace_disable_ftrace_graph_caller(void) | |
382 | { | |
383 | unsigned long ip = (unsigned long)(&ftrace_graph_call); | |
384 | int old_offset, new_offset; | |
385 | ||
386 | old_offset = (unsigned long)(&ftrace_graph_caller) - (ip + MCOUNT_INSN_SIZE); | |
387 | new_offset = (unsigned long)(&ftrace_stub) - (ip + MCOUNT_INSN_SIZE); | |
388 | ||
389 | return ftrace_mod_jmp(ip, old_offset, new_offset); | |
390 | } | |
391 | ||
e7d3737e FW |
392 | #endif /* !CONFIG_DYNAMIC_FTRACE */ |
393 | ||
e7d3737e FW |
394 | /* |
395 | * Hook the return address and push it in the stack of return addrs | |
396 | * in current thread info. | |
397 | */ | |
71e308a2 SR |
398 | void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr, |
399 | unsigned long frame_pointer) | |
e7d3737e FW |
400 | { |
401 | unsigned long old; | |
e7d3737e | 402 | int faulted; |
287b6e68 | 403 | struct ftrace_graph_ent trace; |
e7d3737e FW |
404 | unsigned long return_hooker = (unsigned long) |
405 | &return_to_handler; | |
406 | ||
380c4b14 | 407 | if (unlikely(atomic_read(¤t->tracing_graph_pause))) |
e7d3737e FW |
408 | return; |
409 | ||
410 | /* | |
411 | * Protect against fault, even if it shouldn't | |
412 | * happen. This tool is too much intrusive to | |
413 | * ignore such a protection. | |
414 | */ | |
415 | asm volatile( | |
96665788 SR |
416 | "1: " _ASM_MOV " (%[parent]), %[old]\n" |
417 | "2: " _ASM_MOV " %[return_hooker], (%[parent])\n" | |
e7d3737e | 418 | " movl $0, %[faulted]\n" |
e3944bfa | 419 | "3:\n" |
e7d3737e FW |
420 | |
421 | ".section .fixup, \"ax\"\n" | |
e3944bfa SR |
422 | "4: movl $1, %[faulted]\n" |
423 | " jmp 3b\n" | |
e7d3737e FW |
424 | ".previous\n" |
425 | ||
e3944bfa SR |
426 | _ASM_EXTABLE(1b, 4b) |
427 | _ASM_EXTABLE(2b, 4b) | |
e7d3737e | 428 | |
aa512a27 | 429 | : [old] "=&r" (old), [faulted] "=r" (faulted) |
96665788 | 430 | : [parent] "r" (parent), [return_hooker] "r" (return_hooker) |
e7d3737e FW |
431 | : "memory" |
432 | ); | |
433 | ||
14a866c5 SR |
434 | if (unlikely(faulted)) { |
435 | ftrace_graph_stop(); | |
436 | WARN_ON(1); | |
e7d3737e FW |
437 | return; |
438 | } | |
439 | ||
287b6e68 | 440 | trace.func = self_addr; |
722b3c74 | 441 | trace.depth = current->curr_ret_stack + 1; |
287b6e68 | 442 | |
e49dc19c SR |
443 | /* Only trace if the calling function expects to */ |
444 | if (!ftrace_graph_entry(&trace)) { | |
e49dc19c | 445 | *parent = old; |
722b3c74 SR |
446 | return; |
447 | } | |
448 | ||
449 | if (ftrace_push_return_trace(old, self_addr, &trace.depth, | |
450 | frame_pointer) == -EBUSY) { | |
451 | *parent = old; | |
452 | return; | |
e49dc19c | 453 | } |
e7d3737e | 454 | } |
fb52607a | 455 | #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ |