summaryrefslogtreecommitdiffstats
path: root/arch/sh/kernel/ftrace.c
blob: d18724d186f3cf59022e4c5246b882bfed6f9d3f (plain)
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
/*
 * Copyright (C) 2008 Matt Fleming <matt@console-pimps.org>
 * Copyright (C) 2008 Paul Mundt <lethal@linux-sh.org>
 *
 * 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.
 */
#include <linux/uaccess.h>
#include <linux/ftrace.h>
#include <linux/string.h>
#include <linux/init.h>
#include <linux/io.h>
#include <linux/kernel.h>
#include <asm/ftrace.h>
#include <asm/cacheflush.h>
#include <asm/unistd.h>
#include <trace/syscall.h>

#ifdef CONFIG_DYNAMIC_FTRACE
static unsigned char ftrace_replaced_code[MCOUNT_INSN_SIZE];

static unsigned char ftrace_nop[4];
/*
 * If we're trying to nop out a call to a function, we instead
 * place a call to the address after the memory table.
 *
 * 8c011060 <a>:
 * 8c011060:       02 d1           mov.l   8c01106c <a+0xc>,r1
 * 8c011062:       22 4f           sts.l   pr,@-r15
 * 8c011064:       02 c7           mova    8c011070 <a+0x10>,r0
 * 8c011066:       2b 41           jmp     @r1
 * 8c011068:       2a 40           lds     r0,pr
 * 8c01106a:       09 00           nop
 * 8c01106c:       68 24           .word 0x2468     <--- ip
 * 8c01106e:       1d 8c           .word 0x8c1d
 * 8c011070:       26 4f           lds.l   @r15+,pr <--- ip + MCOUNT_INSN_SIZE
 *
 * We write 0x8c011070 to 0x8c01106c so that on entry to a() we branch
 * past the _mcount call and continue executing code like normal.
 */
static unsigned char *ftrace_nop_replace(unsigned long ip)
{
	__raw_writel(ip + MCOUNT_INSN_SIZE, ftrace_nop);
	return ftrace_nop;
}

static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
{
	/* Place the address in the memory table. */
	__raw_writel(addr, ftrace_replaced_code);

	/*
	 * No locking needed, this must be called via kstop_machine
	 * which in essence is like running on a uniprocessor machine.
	 */
	return ftrace_replaced_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 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 arch_ftrace_nmi_enter(void)
{
	if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) {
		smp_rmb();
		ftrace_mod_code();
	}
	/* Must have previous changes seen before executions */
	smp_mb();
}

void arch_ftrace_nmi_exit(void)
{
	/* 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));
}

static void wait_for_nmi(void)
{
	if (!atomic_read(&nmi_running))
		return;

	do {
		cpu_relax();
	} while (atomic_read(&nmi_running));
}

static int
do_ftrace_mod_code(unsigned long ip, void *new_code)
{
	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 int ftrace_modify_code(unsigned long ip, unsigned char *old_code,
		       unsigned char *new_code)
{
	unsigned char replaced[MCOUNT_INSN_SIZE];

	/*
	 * Note:
	 * We are paranoid about modifying text, as if a bug was to happen, it
	 * could cause us to read or write to someplace that could cause harm.
	 * Carefully read and modify the code with probe_kernel_*(), and make
	 * sure what we read is what we expected it to be before modifying it.
	 */

	/* 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;

	flush_icache_range(ip, ip + MCOUNT_INSN_SIZE);

	return 0;
}

int ftrace_update_ftrace_func(ftrace_func_t func)
{
	unsigned long ip = (unsigned long)(&ftrace_call) + MCOUNT_INSN_OFFSET;
	unsigned char old[MCOUNT_INSN_SIZE], *new;

	memcpy(old, (unsigned char *)ip, MCOUNT_INSN_SIZE);
	new = ftrace_call_replace(ip, (unsigned long)func);

	return ftrace_modify_code(ip, old, new);
}

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(ip);

	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(ip);
	new = ftrace_call_replace(ip, addr);

	return ftrace_modify_code(rec->ip, old, new);
}

int __init ftrace_dyn_arch_init(void)
{
	return 0;
}
#endif /* CONFIG_DYNAMIC_FTRACE */

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
#ifdef CONFIG_DYNAMIC_FTRACE
extern void ftrace_graph_call(void);

static int ftrace_mod(unsigned long ip, unsigned long old_addr,
		      unsigned long new_addr)
{
	unsigned char code[MCOUNT_INSN_SIZE];

	if (probe_kernel_read(code, (void *)ip, MCOUNT_INSN_SIZE))
		return -EFAULT;

	if (old_addr != __raw_readl((unsigned long *)code))
		return -EINVAL;

	__raw_writel(new_addr, ip);
	return 0;
}

int ftrace_enable_ftrace_graph_caller(void)
{
	unsigned long ip, old_addr, new_addr;

	ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
	old_addr = (unsigned long)(&skip_trace);
	new_addr = (unsigned long)(&ftrace_graph_caller);

	return ftrace_mod(ip, old_addr, new_addr);
}

int ftrace_disable_ftrace_graph_caller(void)
{
	unsigned long ip, old_addr, new_addr;

	ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
	old_addr = (unsigned long)(&ftrace_graph_caller);
	new_addr = (unsigned long)(&skip_trace);

	return ftrace_mod(ip, old_addr, new_addr);
}
#endif /* CONFIG_DYNAMIC_FTRACE */

/*
 * Hook the return address and push it in the stack of return addrs
 * in the current thread info.
 *
 * This is the main routine for the function graph tracer. The function
 * graph tracer essentially works like this:
 *
 * parent is the stack address containing self_addr's return address.
 * We pull the real return address out of parent and store it in
 * current's ret_stack. Then, we replace the return address on the stack
 * with the address of return_to_handler. self_addr is the function that
 * called mcount.
 *
 * When self_addr returns, it will jump to return_to_handler which calls
 * ftrace_return_to_handler. ftrace_return_to_handler will pull the real
 * return address off of current's ret_stack and jump to it.
 */
void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
{
	unsigned long old;
	int faulted, err;
	struct ftrace_graph_ent trace;
	unsigned long return_hooker = (unsigned long)&return_to_handler;

	if (unlikely(ftrace_graph_is_dead()))
		return;

	if (unlikely(atomic_read(&current->tracing_graph_pause)))
		return;

	/*
	 * Protect against fault, even if it shouldn't
	 * happen. This tool is too much intrusive to
	 * ignore such a protection.
	 */
	__asm__ __volatile__(
		"1:						\n\t"
		"mov.l		@%2, %0				\n\t"
		"2:						\n\t"
		"mov.l		%3, @%2				\n\t"
		"mov		#0, %1				\n\t"
		"3:						\n\t"
		".section .fixup, \"ax\"			\n\t"
		"4:						\n\t"
		"mov.l		5f, %0				\n\t"
		"jmp		@%0				\n\t"
		" mov		#1, %1				\n\t"
		".balign 4					\n\t"
		"5:	.long 3b				\n\t"
		".previous					\n\t"
		".section __ex_table,\"a\"			\n\t"
		".long 1b, 4b					\n\t"
		".long 2b, 4b					\n\t"
		".previous					\n\t"
		: "=&r" (old), "=r" (faulted)
		: "r" (parent), "r" (return_hooker)
	);

	if (unlikely(faulted)) {
		ftrace_graph_stop();
		WARN_ON(1);
		return;
	}

	err = ftrace_push_return_trace(old, self_addr, &trace.depth, 0, NULL);
	if (err == -EBUSY) {
		__raw_writel(old, parent);
		return;
	}

	trace.func = self_addr;

	/* Only trace if the calling function expects to */
	if (!ftrace_graph_entry(&trace)) {
		current->curr_ret_stack--;
		__raw_writel(old, parent);
	}
}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */