1 /*
2 * Copyright (C) 2008 Matt Fleming <matt@console-pimps.org>
3 * Copyright (C) 2008 Paul Mundt <lethal@linux-sh.org>
4 *
5 * Code for replacing ftrace calls with jumps.
6 *
7 * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
8 *
9 * Thanks goes to Ingo Molnar, for suggesting the idea.
10 * Mathieu Desnoyers, for suggesting postponing the modifications.
11 * Arjan van de Ven, for keeping me straight, and explaining to me
12 * the dangers of modifying code on the run.
13 */
14 #include <linux/uaccess.h>
15 #include <linux/ftrace.h>
16 #include <linux/string.h>
17 #include <linux/init.h>
18 #include <linux/io.h>
19 #include <linux/kernel.h>
20 #include <asm/ftrace.h>
21 #include <asm/cacheflush.h>
22 #include <asm/unistd.h>
23 #include <trace/syscall.h>
24
25 #ifdef CONFIG_DYNAMIC_FTRACE
26 static unsigned char ftrace_replaced_code[MCOUNT_INSN_SIZE];
27
28 static unsigned char ftrace_nop[4];
29 /*
30 * If we're trying to nop out a call to a function, we instead
31 * place a call to the address after the memory table.
32 *
33 * 8c011060 <a>:
34 * 8c011060: 02 d1 mov.l 8c01106c <a+0xc>,r1
35 * 8c011062: 22 4f sts.l pr,@-r15
36 * 8c011064: 02 c7 mova 8c011070 <a+0x10>,r0
37 * 8c011066: 2b 41 jmp @r1
38 * 8c011068: 2a 40 lds r0,pr
39 * 8c01106a: 09 00 nop
40 * 8c01106c: 68 24 .word 0x2468 <--- ip
41 * 8c01106e: 1d 8c .word 0x8c1d
42 * 8c011070: 26 4f lds.l @r15+,pr <--- ip + MCOUNT_INSN_SIZE
43 *
44 * We write 0x8c011070 to 0x8c01106c so that on entry to a() we branch
45 * past the _mcount call and continue executing code like normal.
46 */
ftrace_nop_replace(unsigned long ip)47 static unsigned char *ftrace_nop_replace(unsigned long ip)
48 {
49 __raw_writel(ip + MCOUNT_INSN_SIZE, ftrace_nop);
50 return ftrace_nop;
51 }
52
ftrace_call_replace(unsigned long ip,unsigned long addr)53 static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
54 {
55 /* Place the address in the memory table. */
56 __raw_writel(addr, ftrace_replaced_code);
57
58 /*
59 * No locking needed, this must be called via kstop_machine
60 * which in essence is like running on a uniprocessor machine.
61 */
62 return ftrace_replaced_code;
63 }
64
65 /*
66 * Modifying code must take extra care. On an SMP machine, if
67 * the code being modified is also being executed on another CPU
68 * that CPU will have undefined results and possibly take a GPF.
69 * We use kstop_machine to stop other CPUS from exectuing code.
70 * But this does not stop NMIs from happening. We still need
71 * to protect against that. We separate out the modification of
72 * the code to take care of this.
73 *
74 * Two buffers are added: An IP buffer and a "code" buffer.
75 *
76 * 1) Put the instruction pointer into the IP buffer
77 * and the new code into the "code" buffer.
78 * 2) Wait for any running NMIs to finish and set a flag that says
79 * we are modifying code, it is done in an atomic operation.
80 * 3) Write the code
81 * 4) clear the flag.
82 * 5) Wait for any running NMIs to finish.
83 *
84 * If an NMI is executed, the first thing it does is to call
85 * "ftrace_nmi_enter". This will check if the flag is set to write
86 * and if it is, it will write what is in the IP and "code" buffers.
87 *
88 * The trick is, it does not matter if everyone is writing the same
89 * content to the code location. Also, if a CPU is executing code
90 * it is OK to write to that code location if the contents being written
91 * are the same as what exists.
92 */
93 #define MOD_CODE_WRITE_FLAG (1 << 31) /* set when NMI should do the write */
94 static atomic_t nmi_running = ATOMIC_INIT(0);
95 static int mod_code_status; /* holds return value of text write */
96 static void *mod_code_ip; /* holds the IP to write to */
97 static void *mod_code_newcode; /* holds the text to write to the IP */
98
99 static unsigned nmi_wait_count;
100 static atomic_t nmi_update_count = ATOMIC_INIT(0);
101
ftrace_arch_read_dyn_info(char * buf,int size)102 int ftrace_arch_read_dyn_info(char *buf, int size)
103 {
104 int r;
105
106 r = snprintf(buf, size, "%u %u",
107 nmi_wait_count,
108 atomic_read(&nmi_update_count));
109 return r;
110 }
111
clear_mod_flag(void)112 static void clear_mod_flag(void)
113 {
114 int old = atomic_read(&nmi_running);
115
116 for (;;) {
117 int new = old & ~MOD_CODE_WRITE_FLAG;
118
119 if (old == new)
120 break;
121
122 old = atomic_cmpxchg(&nmi_running, old, new);
123 }
124 }
125
ftrace_mod_code(void)126 static void ftrace_mod_code(void)
127 {
128 /*
129 * Yes, more than one CPU process can be writing to mod_code_status.
130 * (and the code itself)
131 * But if one were to fail, then they all should, and if one were
132 * to succeed, then they all should.
133 */
134 mod_code_status = probe_kernel_write(mod_code_ip, mod_code_newcode,
135 MCOUNT_INSN_SIZE);
136
137 /* if we fail, then kill any new writers */
138 if (mod_code_status)
139 clear_mod_flag();
140 }
141
ftrace_nmi_enter(void)142 void ftrace_nmi_enter(void)
143 {
144 if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) {
145 smp_rmb();
146 ftrace_mod_code();
147 atomic_inc(&nmi_update_count);
148 }
149 /* Must have previous changes seen before executions */
150 smp_mb();
151 }
152
ftrace_nmi_exit(void)153 void ftrace_nmi_exit(void)
154 {
155 /* Finish all executions before clearing nmi_running */
156 smp_mb();
157 atomic_dec(&nmi_running);
158 }
159
wait_for_nmi_and_set_mod_flag(void)160 static void wait_for_nmi_and_set_mod_flag(void)
161 {
162 if (!atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG))
163 return;
164
165 do {
166 cpu_relax();
167 } while (atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG));
168
169 nmi_wait_count++;
170 }
171
wait_for_nmi(void)172 static void wait_for_nmi(void)
173 {
174 if (!atomic_read(&nmi_running))
175 return;
176
177 do {
178 cpu_relax();
179 } while (atomic_read(&nmi_running));
180
181 nmi_wait_count++;
182 }
183
184 static int
do_ftrace_mod_code(unsigned long ip,void * new_code)185 do_ftrace_mod_code(unsigned long ip, void *new_code)
186 {
187 mod_code_ip = (void *)ip;
188 mod_code_newcode = new_code;
189
190 /* The buffers need to be visible before we let NMIs write them */
191 smp_mb();
192
193 wait_for_nmi_and_set_mod_flag();
194
195 /* Make sure all running NMIs have finished before we write the code */
196 smp_mb();
197
198 ftrace_mod_code();
199
200 /* Make sure the write happens before clearing the bit */
201 smp_mb();
202
203 clear_mod_flag();
204 wait_for_nmi();
205
206 return mod_code_status;
207 }
208
ftrace_modify_code(unsigned long ip,unsigned char * old_code,unsigned char * new_code)209 static int ftrace_modify_code(unsigned long ip, unsigned char *old_code,
210 unsigned char *new_code)
211 {
212 unsigned char replaced[MCOUNT_INSN_SIZE];
213
214 /*
215 * Note: Due to modules and __init, code can
216 * disappear and change, we need to protect against faulting
217 * as well as code changing. We do this by using the
218 * probe_kernel_* functions.
219 *
220 * No real locking needed, this code is run through
221 * kstop_machine, or before SMP starts.
222 */
223
224 /* read the text we want to modify */
225 if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
226 return -EFAULT;
227
228 /* Make sure it is what we expect it to be */
229 if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
230 return -EINVAL;
231
232 /* replace the text with the new text */
233 if (do_ftrace_mod_code(ip, new_code))
234 return -EPERM;
235
236 flush_icache_range(ip, ip + MCOUNT_INSN_SIZE);
237
238 return 0;
239 }
240
ftrace_update_ftrace_func(ftrace_func_t func)241 int ftrace_update_ftrace_func(ftrace_func_t func)
242 {
243 unsigned long ip = (unsigned long)(&ftrace_call) + MCOUNT_INSN_OFFSET;
244 unsigned char old[MCOUNT_INSN_SIZE], *new;
245
246 memcpy(old, (unsigned char *)ip, MCOUNT_INSN_SIZE);
247 new = ftrace_call_replace(ip, (unsigned long)func);
248
249 return ftrace_modify_code(ip, old, new);
250 }
251
ftrace_make_nop(struct module * mod,struct dyn_ftrace * rec,unsigned long addr)252 int ftrace_make_nop(struct module *mod,
253 struct dyn_ftrace *rec, unsigned long addr)
254 {
255 unsigned char *new, *old;
256 unsigned long ip = rec->ip;
257
258 old = ftrace_call_replace(ip, addr);
259 new = ftrace_nop_replace(ip);
260
261 return ftrace_modify_code(rec->ip, old, new);
262 }
263
ftrace_make_call(struct dyn_ftrace * rec,unsigned long addr)264 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
265 {
266 unsigned char *new, *old;
267 unsigned long ip = rec->ip;
268
269 old = ftrace_nop_replace(ip);
270 new = ftrace_call_replace(ip, addr);
271
272 return ftrace_modify_code(rec->ip, old, new);
273 }
274
ftrace_dyn_arch_init(void)275 int __init ftrace_dyn_arch_init(void)
276 {
277 return 0;
278 }
279 #endif /* CONFIG_DYNAMIC_FTRACE */
280
281 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
282 #ifdef CONFIG_DYNAMIC_FTRACE
283 extern void ftrace_graph_call(void);
284
ftrace_mod(unsigned long ip,unsigned long old_addr,unsigned long new_addr)285 static int ftrace_mod(unsigned long ip, unsigned long old_addr,
286 unsigned long new_addr)
287 {
288 unsigned char code[MCOUNT_INSN_SIZE];
289
290 if (probe_kernel_read(code, (void *)ip, MCOUNT_INSN_SIZE))
291 return -EFAULT;
292
293 if (old_addr != __raw_readl((unsigned long *)code))
294 return -EINVAL;
295
296 __raw_writel(new_addr, ip);
297 return 0;
298 }
299
ftrace_enable_ftrace_graph_caller(void)300 int ftrace_enable_ftrace_graph_caller(void)
301 {
302 unsigned long ip, old_addr, new_addr;
303
304 ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
305 old_addr = (unsigned long)(&skip_trace);
306 new_addr = (unsigned long)(&ftrace_graph_caller);
307
308 return ftrace_mod(ip, old_addr, new_addr);
309 }
310
ftrace_disable_ftrace_graph_caller(void)311 int ftrace_disable_ftrace_graph_caller(void)
312 {
313 unsigned long ip, old_addr, new_addr;
314
315 ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
316 old_addr = (unsigned long)(&ftrace_graph_caller);
317 new_addr = (unsigned long)(&skip_trace);
318
319 return ftrace_mod(ip, old_addr, new_addr);
320 }
321 #endif /* CONFIG_DYNAMIC_FTRACE */
322
323 /*
324 * Hook the return address and push it in the stack of return addrs
325 * in the current thread info.
326 *
327 * This is the main routine for the function graph tracer. The function
328 * graph tracer essentially works like this:
329 *
330 * parent is the stack address containing self_addr's return address.
331 * We pull the real return address out of parent and store it in
332 * current's ret_stack. Then, we replace the return address on the stack
333 * with the address of return_to_handler. self_addr is the function that
334 * called mcount.
335 *
336 * When self_addr returns, it will jump to return_to_handler which calls
337 * ftrace_return_to_handler. ftrace_return_to_handler will pull the real
338 * return address off of current's ret_stack and jump to it.
339 */
prepare_ftrace_return(unsigned long * parent,unsigned long self_addr)340 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
341 {
342 unsigned long old;
343 int faulted, err;
344 struct ftrace_graph_ent trace;
345 unsigned long return_hooker = (unsigned long)&return_to_handler;
346
347 if (unlikely(ftrace_graph_is_dead()))
348 return;
349
350 if (unlikely(atomic_read(¤t->tracing_graph_pause)))
351 return;
352
353 /*
354 * Protect against fault, even if it shouldn't
355 * happen. This tool is too much intrusive to
356 * ignore such a protection.
357 */
358 __asm__ __volatile__(
359 "1: \n\t"
360 "mov.l @%2, %0 \n\t"
361 "2: \n\t"
362 "mov.l %3, @%2 \n\t"
363 "mov #0, %1 \n\t"
364 "3: \n\t"
365 ".section .fixup, \"ax\" \n\t"
366 "4: \n\t"
367 "mov.l 5f, %0 \n\t"
368 "jmp @%0 \n\t"
369 " mov #1, %1 \n\t"
370 ".balign 4 \n\t"
371 "5: .long 3b \n\t"
372 ".previous \n\t"
373 ".section __ex_table,\"a\" \n\t"
374 ".long 1b, 4b \n\t"
375 ".long 2b, 4b \n\t"
376 ".previous \n\t"
377 : "=&r" (old), "=r" (faulted)
378 : "r" (parent), "r" (return_hooker)
379 );
380
381 if (unlikely(faulted)) {
382 ftrace_graph_stop();
383 WARN_ON(1);
384 return;
385 }
386
387 err = ftrace_push_return_trace(old, self_addr, &trace.depth, 0);
388 if (err == -EBUSY) {
389 __raw_writel(old, parent);
390 return;
391 }
392
393 trace.func = self_addr;
394
395 /* Only trace if the calling function expects to */
396 if (!ftrace_graph_entry(&trace)) {
397 current->curr_ret_stack--;
398 __raw_writel(old, parent);
399 }
400 }
401 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
402