1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Copyright (C) 2008 Matt Fleming <matt@console-pimps.org>
4 * Copyright (C) 2008 Paul Mundt <lethal@linux-sh.org>
5 *
6 * Code for replacing ftrace calls with jumps.
7 *
8 * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
9 *
10 * Thanks goes to Ingo Molnar, for suggesting the idea.
11 * Mathieu Desnoyers, for suggesting postponing the modifications.
12 * Arjan van de Ven, for keeping me straight, and explaining to me
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[MCOUNT_INSN_SIZE];
28
29 static unsigned char ftrace_nop[4];
30 /*
31 * If we're trying to nop out a call to a function, we instead
32 * place a call to the address after the memory table.
33 *
34 * 8c011060 <a>:
35 * 8c011060: 02 d1 mov.l 8c01106c <a+0xc>,r1
36 * 8c011062: 22 4f sts.l pr,@-r15
37 * 8c011064: 02 c7 mova 8c011070 <a+0x10>,r0
38 * 8c011066: 2b 41 jmp @r1
39 * 8c011068: 2a 40 lds r0,pr
40 * 8c01106a: 09 00 nop
41 * 8c01106c: 68 24 .word 0x2468 <--- ip
42 * 8c01106e: 1d 8c .word 0x8c1d
43 * 8c011070: 26 4f lds.l @r15+,pr <--- ip + MCOUNT_INSN_SIZE
44 *
45 * We write 0x8c011070 to 0x8c01106c so that on entry to a() we branch
46 * past the _mcount call and continue executing code like normal.
47 */
48 static unsigned char *ftrace_nop_replace(unsigned long ip)
49 {
50 __raw_writel(ip + MCOUNT_INSN_SIZE, ftrace_nop);
51 return ftrace_nop;
52 }
53
54 static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
55 {
56 /* Place the address in the memory table. */
57 __raw_writel(addr, ftrace_replaced_code);
58
59 /*
60 * No locking needed, this must be called via kstop_machine
61 * which in essence is like running on a uniprocessor machine.
62 */
63 return ftrace_replaced_code;
64 }
65
66 /*
67 * Modifying code must take extra care. On an SMP machine, if
68 * the code being modified is also being executed on another CPU
69 * that CPU will have undefined results and possibly take a GPF.
70 * We use kstop_machine to stop other CPUS from executing code.
71 * But this does not stop NMIs from happening. We still need
72 * to protect against that. We separate out the modification of
73 * the code to take care of this.
74 *
75 * Two buffers are added: An IP buffer and a "code" buffer.
76 *
77 * 1) Put the instruction pointer into the IP buffer
78 * and the new code into the "code" buffer.
79 * 2) Wait for any running NMIs to finish and set a flag that says
80 * we are modifying code, it is done in an atomic operation.
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 does is to call
86 * "ftrace_nmi_enter". This will check if the flag is set to write
87 * and if it is, it will write what is in the IP and "code" buffers.
88 *
89 * The trick is, it does not matter if everyone is writing the same
90 * content to the code location. Also, if a CPU is executing code
91 * it is OK to write to that code location if the contents being written
92 * are the same as what exists.
93 */
94 #define MOD_CODE_WRITE_FLAG (1 << 31) /* set when NMI should do the write */
95 static atomic_t nmi_running = ATOMIC_INIT(0);
96 static int mod_code_status; /* holds return value of text write */
97 static void *mod_code_ip; /* holds the IP to write to */
98 static void *mod_code_newcode; /* holds the text to write to the IP */
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_WRITE_FLAG;
106
107 if (old == new)
108 break;
109
110 old = atomic_cmpxchg(&nmi_running, old, new);
111 }
112 }
113
114 static void ftrace_mod_code(void)
115 {
116 /*
117 * Yes, more than one CPU process can be writing to mod_code_status.
118 * (and the code itself)
119 * But if one were to fail, then they all should, and if one were
120 * to succeed, then they all should.
121 */
122 mod_code_status = copy_to_kernel_nofault(mod_code_ip, mod_code_newcode,
123 MCOUNT_INSN_SIZE);
124
125 /* if we fail, then kill any new writers */
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) & MOD_CODE_WRITE_FLAG) {
133 smp_rmb();
134 ftrace_mod_code();
135 }
136 /* Must have previous changes seen before executions */
137 smp_mb();
138 }
139
140 void arch_ftrace_nmi_exit(void)
141 {
142 /* Finish all executions before clearing nmi_running */
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, MOD_CODE_WRITE_FLAG))
150 return;
151
152 do {
153 cpu_relax();
154 } while (atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG));
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_code)
169 {
170 mod_code_ip = (void *)ip;
171 mod_code_newcode = new_code;
172
173 /* The buffers need to be visible before we let NMIs write them */
174 smp_mb();
175
176 wait_for_nmi_and_set_mod_flag();
177
178 /* Make sure all running NMIs have finished before we write the code */
179 smp_mb();
180
181 ftrace_mod_code();
182
183 /* Make sure the write happens before clearing the bit */
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, unsigned char *old_code,
193 unsigned char *new_code)
194 {
195 unsigned char replaced[MCOUNT_INSN_SIZE];
196
197 /*
198 * Note:
199 * We are paranoid about modifying text, as if a bug was to happen, it
200 * could cause us to read or write to someplace that could cause harm.
201 * Carefully read and modify the code with probe_kernel_*(), and make
202 * sure what we read is what we expected it to be before modifying it.
203 */
204
205 /* read the text we want to modify */
206 if (copy_from_kernel_nofault(replaced, (void *)ip, MCOUNT_INSN_SIZE))
207 return -EFAULT;
208
209 /* Make sure it is what we expect it to be */
210 if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
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_INSN_SIZE);
218
219 return 0;
220 }
221
222 int ftrace_update_ftrace_func(ftrace_func_t func)
223 {
224 unsigned long ip = (unsigned long)(&ftrace_call) + MCOUNT_INSN_OFFSET;
225 unsigned char old[MCOUNT_INSN_SIZE], *new;
226
227 memcpy(old, (unsigned char *)ip, MCOUNT_INSN_SIZE);
228 new = ftrace_call_replace(ip, (unsigned long)func);
229
230 return ftrace_modify_code(ip, old, new);
231 }
232
233 int ftrace_make_nop(struct module *mod,
234 struct dyn_ftrace *rec, unsigned long addr)
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, new);
243 }
244
245 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
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, new);
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, unsigned long old_addr,
262 unsigned long new_addr)
263 {
264 unsigned char code[MCOUNT_INSN_SIZE];
265
266 if (copy_from_kernel_nofault(code, (void *)ip, MCOUNT_INSN_SIZE))
267 return -EFAULT;
268
269 if (old_addr != __raw_readl((unsigned long *)code))
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_call) + GRAPH_INSN_OFFSET;
281 old_addr = (unsigned long)(&skip_trace);
282 new_addr = (unsigned long)(&ftrace_graph_caller);
283
284 return ftrace_mod(ip, old_addr, new_addr);
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_call) + GRAPH_INSN_OFFSET;
292 old_addr = (unsigned long)(&ftrace_graph_caller);
293 new_addr = (unsigned long)(&skip_trace);
294
295 return ftrace_mod(ip, old_addr, new_addr);
296 }
297 #endif /* CONFIG_DYNAMIC_FTRACE */
298
299 /*
300 * Hook the return address and push it in the stack of return addrs
301 * in the current thread info.
302 *
303 * This is the main routine for the function graph tracer. The function
304 * graph tracer essentially works like this:
305 *
306 * parent is the stack address containing self_addr's return address.
307 * We pull the real return address out of parent and store it in
308 * current's ret_stack. Then, we replace the return address on the stack
309 * with the address of return_to_handler. self_addr is the function that
310 * called mcount.
311 *
312 * When self_addr returns, it will jump to return_to_handler which calls
313 * ftrace_return_to_handler. ftrace_return_to_handler will pull the real
314 * return address off of current's ret_stack and jump to it.
315 */
316 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
317 {
318 unsigned long old;
319 int faulted;
320 unsigned long return_hooker = (unsigned long)&return_to_handler;
321
322 if (unlikely(ftrace_graph_is_dead()))
323 return;
324
325 if (unlikely(atomic_read(¤t->tracing_graph_pause)))
326 return;
327
328 /*
329 * Protect against fault, even if it shouldn't
330 * happen. This tool is too much intrusive to
331 * ignore such a protection.
332 */
333 __asm__ __volatile__(
334 "1: \n\t"
335 "mov.l @%2, %0 \n\t"
336 "2: \n\t"
337 "mov.l %3, @%2 \n\t"
338 "mov #0, %1 \n\t"
339 "3: \n\t"
340 ".section .fixup, \"ax\" \n\t"
341 "4: \n\t"
342 "mov.l 5f, %0 \n\t"
343 "jmp @%0 \n\t"
344 " mov #1, %1 \n\t"
345 ".balign 4 \n\t"
346 "5: .long 3b \n\t"
347 ".previous \n\t"
348 ".section __ex_table,\"a\" \n\t"
349 ".long 1b, 4b \n\t"
350 ".long 2b, 4b \n\t"
351 ".previous \n\t"
352 : "=&r" (old), "=r" (faulted)
353 : "r" (parent), "r" (return_hooker)
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_addr, 0, NULL))
363 __raw_writel(old, parent);
364 }
365 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
366
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