1 // SPDX-License-Identifier: GPL-2.0 1
2 /*
3 * Copyright (C) 2008 Matt Fleming <matt@conso
4 * Copyright (C) 2008 Paul Mundt <lethal@linux
5 *
6 * Code for replacing ftrace calls with jumps.
7 *
8 * Copyright (C) 2007-2008 Steven Rostedt <sro
9 *
10 * Thanks goes to Ingo Molnar, for suggesting
11 * Mathieu Desnoyers, for suggesting postponin
12 * Arjan van de Ven, for keeping me straight,
13 * the dangers of modifying code on the run.
14 */
15 #include <linux/uaccess.h>
16 #include <linux/ftrace.h>
17 #include <linux/string.h>
18 #include <linux/init.h>
19 #include <linux/io.h>
20 #include <linux/kernel.h>
21 #include <asm/ftrace.h>
22 #include <asm/cacheflush.h>
23 #include <asm/unistd.h>
24 #include <trace/syscall.h>
25
26 #ifdef CONFIG_DYNAMIC_FTRACE
27 static unsigned char ftrace_replaced_code[MCOU
28
29 static unsigned char ftrace_nop[4];
30 /*
31 * If we're trying to nop out a call to a func
32 * place a call to the address after the memor
33 *
34 * 8c011060 <a>:
35 * 8c011060: 02 d1 mov.l 8c0
36 * 8c011062: 22 4f sts.l pr,
37 * 8c011064: 02 c7 mova 8c0
38 * 8c011066: 2b 41 jmp @r1
39 * 8c011068: 2a 40 lds r0,
40 * 8c01106a: 09 00 nop
41 * 8c01106c: 68 24 .word 0x246
42 * 8c01106e: 1d 8c .word 0x8c1
43 * 8c011070: 26 4f lds.l @r1
44 *
45 * We write 0x8c011070 to 0x8c01106c so that o
46 * past the _mcount call and continue executin
47 */
48 static unsigned char *ftrace_nop_replace(unsig
49 {
50 __raw_writel(ip + MCOUNT_INSN_SIZE, ft
51 return ftrace_nop;
52 }
53
54 static unsigned char *ftrace_call_replace(unsi
55 {
56 /* Place the address in the memory tab
57 __raw_writel(addr, ftrace_replaced_cod
58
59 /*
60 * No locking needed, this must be cal
61 * which in essence is like running on
62 */
63 return ftrace_replaced_code;
64 }
65
66 /*
67 * Modifying code must take extra care. On an
68 * the code being modified is also being execu
69 * that CPU will have undefined results and po
70 * We use kstop_machine to stop other CPUS fro
71 * But this does not stop NMIs from happening.
72 * to protect against that. We separate out th
73 * the code to take care of this.
74 *
75 * Two buffers are added: An IP buffer and a "
76 *
77 * 1) Put the instruction pointer into the IP
78 * and the new code into the "code" buffer.
79 * 2) Wait for any running NMIs to finish and
80 * we are modifying code, it is done in an
81 * 3) Write the code
82 * 4) clear the flag.
83 * 5) Wait for any running NMIs to finish.
84 *
85 * If an NMI is executed, the first thing it d
86 * "ftrace_nmi_enter". This will check if the
87 * and if it is, it will write what is in the
88 *
89 * The trick is, it does not matter if everyon
90 * content to the code location. Also, if a CP
91 * it is OK to write to that code location if
92 * are the same as what exists.
93 */
94 #define MOD_CODE_WRITE_FLAG (1 << 31) /* set
95 static atomic_t nmi_running = ATOMIC_INIT(0);
96 static int mod_code_status; /* hol
97 static void *mod_code_ip; /* hol
98 static void *mod_code_newcode; /* hol
99
100 static void clear_mod_flag(void)
101 {
102 int old = atomic_read(&nmi_running);
103
104 for (;;) {
105 int new = old & ~MOD_CODE_WRIT
106
107 if (old == new)
108 break;
109
110 old = atomic_cmpxchg(&nmi_runn
111 }
112 }
113
114 static void ftrace_mod_code(void)
115 {
116 /*
117 * Yes, more than one CPU process can
118 * (and the code itself)
119 * But if one were to fail, then they
120 * to succeed, then they all should.
121 */
122 mod_code_status = copy_to_kernel_nofau
123 M
124
125 /* if we fail, then kill any new write
126 if (mod_code_status)
127 clear_mod_flag();
128 }
129
130 void arch_ftrace_nmi_enter(void)
131 {
132 if (atomic_inc_return(&nmi_running) &
133 smp_rmb();
134 ftrace_mod_code();
135 }
136 /* Must have previous changes seen bef
137 smp_mb();
138 }
139
140 void arch_ftrace_nmi_exit(void)
141 {
142 /* Finish all executions before cleari
143 smp_mb();
144 atomic_dec(&nmi_running);
145 }
146
147 static void wait_for_nmi_and_set_mod_flag(void
148 {
149 if (!atomic_cmpxchg(&nmi_running, 0, M
150 return;
151
152 do {
153 cpu_relax();
154 } while (atomic_cmpxchg(&nmi_running,
155 }
156
157 static void wait_for_nmi(void)
158 {
159 if (!atomic_read(&nmi_running))
160 return;
161
162 do {
163 cpu_relax();
164 } while (atomic_read(&nmi_running));
165 }
166
167 static int
168 do_ftrace_mod_code(unsigned long ip, void *new
169 {
170 mod_code_ip = (void *)ip;
171 mod_code_newcode = new_code;
172
173 /* The buffers need to be visible befo
174 smp_mb();
175
176 wait_for_nmi_and_set_mod_flag();
177
178 /* Make sure all running NMIs have fin
179 smp_mb();
180
181 ftrace_mod_code();
182
183 /* Make sure the write happens before
184 smp_mb();
185
186 clear_mod_flag();
187 wait_for_nmi();
188
189 return mod_code_status;
190 }
191
192 static int ftrace_modify_code(unsigned long ip
193 unsigned char *new_code
194 {
195 unsigned char replaced[MCOUNT_INSN_SIZ
196
197 /*
198 * Note:
199 * We are paranoid about modifying tex
200 * could cause us to read or write to
201 * Carefully read and modify the code
202 * sure what we read is what we expect
203 */
204
205 /* read the text we want to modify */
206 if (copy_from_kernel_nofault(replaced,
207 return -EFAULT;
208
209 /* Make sure it is what we expect it t
210 if (memcmp(replaced, old_code, MCOUNT_
211 return -EINVAL;
212
213 /* replace the text with the new text
214 if (do_ftrace_mod_code(ip, new_code))
215 return -EPERM;
216
217 flush_icache_range(ip, ip + MCOUNT_INS
218
219 return 0;
220 }
221
222 int ftrace_update_ftrace_func(ftrace_func_t fu
223 {
224 unsigned long ip = (unsigned long)(&ft
225 unsigned char old[MCOUNT_INSN_SIZE], *
226
227 memcpy(old, (unsigned char *)ip, MCOUN
228 new = ftrace_call_replace(ip, (unsigne
229
230 return ftrace_modify_code(ip, old, new
231 }
232
233 int ftrace_make_nop(struct module *mod,
234 struct dyn_ftrace *rec, un
235 {
236 unsigned char *new, *old;
237 unsigned long ip = rec->ip;
238
239 old = ftrace_call_replace(ip, addr);
240 new = ftrace_nop_replace(ip);
241
242 return ftrace_modify_code(rec->ip, old
243 }
244
245 int ftrace_make_call(struct dyn_ftrace *rec, u
246 {
247 unsigned char *new, *old;
248 unsigned long ip = rec->ip;
249
250 old = ftrace_nop_replace(ip);
251 new = ftrace_call_replace(ip, addr);
252
253 return ftrace_modify_code(rec->ip, old
254 }
255 #endif /* CONFIG_DYNAMIC_FTRACE */
256
257 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
258 #ifdef CONFIG_DYNAMIC_FTRACE
259 extern void ftrace_graph_call(void);
260
261 static int ftrace_mod(unsigned long ip, unsign
262 unsigned long new_addr)
263 {
264 unsigned char code[MCOUNT_INSN_SIZE];
265
266 if (copy_from_kernel_nofault(code, (vo
267 return -EFAULT;
268
269 if (old_addr != __raw_readl((unsigned
270 return -EINVAL;
271
272 __raw_writel(new_addr, ip);
273 return 0;
274 }
275
276 int ftrace_enable_ftrace_graph_caller(void)
277 {
278 unsigned long ip, old_addr, new_addr;
279
280 ip = (unsigned long)(&ftrace_graph_cal
281 old_addr = (unsigned long)(&skip_trace
282 new_addr = (unsigned long)(&ftrace_gra
283
284 return ftrace_mod(ip, old_addr, new_ad
285 }
286
287 int ftrace_disable_ftrace_graph_caller(void)
288 {
289 unsigned long ip, old_addr, new_addr;
290
291 ip = (unsigned long)(&ftrace_graph_cal
292 old_addr = (unsigned long)(&ftrace_gra
293 new_addr = (unsigned long)(&skip_trace
294
295 return ftrace_mod(ip, old_addr, new_ad
296 }
297 #endif /* CONFIG_DYNAMIC_FTRACE */
298
299 /*
300 * Hook the return address and push it in the
301 * in the current thread info.
302 *
303 * This is the main routine for the function g
304 * graph tracer essentially works like this:
305 *
306 * parent is the stack address containing self
307 * We pull the real return address out of pare
308 * current's ret_stack. Then, we replace the r
309 * with the address of return_to_handler. self
310 * called mcount.
311 *
312 * When self_addr returns, it will jump to ret
313 * ftrace_return_to_handler. ftrace_return_to_
314 * return address off of current's ret_stack a
315 */
316 void prepare_ftrace_return(unsigned long *pare
317 {
318 unsigned long old;
319 int faulted;
320 unsigned long return_hooker = (unsigne
321
322 if (unlikely(ftrace_graph_is_dead()))
323 return;
324
325 if (unlikely(atomic_read(¤t->tra
326 return;
327
328 /*
329 * Protect against fault, even if it s
330 * happen. This tool is too much intru
331 * ignore such a protection.
332 */
333 __asm__ __volatile__(
334 "1:
335 "mov.l @%2, %0
336 "2:
337 "mov.l %3, @%2
338 "mov #0, %1
339 "3:
340 ".section .fixup, \"ax\"
341 "4:
342 "mov.l 5f, %0
343 "jmp @%0
344 " mov #1, %1
345 ".balign 4
346 "5: .long 3b
347 ".previous
348 ".section __ex_table,\"a\"
349 ".long 1b, 4b
350 ".long 2b, 4b
351 ".previous
352 : "=&r" (old), "=r" (faulted)
353 : "r" (parent), "r" (return_ho
354 );
355
356 if (unlikely(faulted)) {
357 ftrace_graph_stop();
358 WARN_ON(1);
359 return;
360 }
361
362 if (function_graph_enter(old, self_add
363 __raw_writel(old, parent);
364 }
365 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
366
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