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Linux/arch/sh/kernel/ftrace.c

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  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 exectuing 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 = probe_kernel_write(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 (probe_kernel_read(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 
256 int __init ftrace_dyn_arch_init(void)
257 {
258         return 0;
259 }
260 #endif /* CONFIG_DYNAMIC_FTRACE */
261 
262 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
263 #ifdef CONFIG_DYNAMIC_FTRACE
264 extern void ftrace_graph_call(void);
265 
266 static int ftrace_mod(unsigned long ip, unsigned long old_addr,
267                       unsigned long new_addr)
268 {
269         unsigned char code[MCOUNT_INSN_SIZE];
270 
271         if (probe_kernel_read(code, (void *)ip, MCOUNT_INSN_SIZE))
272                 return -EFAULT;
273 
274         if (old_addr != __raw_readl((unsigned long *)code))
275                 return -EINVAL;
276 
277         __raw_writel(new_addr, ip);
278         return 0;
279 }
280 
281 int ftrace_enable_ftrace_graph_caller(void)
282 {
283         unsigned long ip, old_addr, new_addr;
284 
285         ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
286         old_addr = (unsigned long)(&skip_trace);
287         new_addr = (unsigned long)(&ftrace_graph_caller);
288 
289         return ftrace_mod(ip, old_addr, new_addr);
290 }
291 
292 int ftrace_disable_ftrace_graph_caller(void)
293 {
294         unsigned long ip, old_addr, new_addr;
295 
296         ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
297         old_addr = (unsigned long)(&ftrace_graph_caller);
298         new_addr = (unsigned long)(&skip_trace);
299 
300         return ftrace_mod(ip, old_addr, new_addr);
301 }
302 #endif /* CONFIG_DYNAMIC_FTRACE */
303 
304 /*
305  * Hook the return address and push it in the stack of return addrs
306  * in the current thread info.
307  *
308  * This is the main routine for the function graph tracer. The function
309  * graph tracer essentially works like this:
310  *
311  * parent is the stack address containing self_addr's return address.
312  * We pull the real return address out of parent and store it in
313  * current's ret_stack. Then, we replace the return address on the stack
314  * with the address of return_to_handler. self_addr is the function that
315  * called mcount.
316  *
317  * When self_addr returns, it will jump to return_to_handler which calls
318  * ftrace_return_to_handler. ftrace_return_to_handler will pull the real
319  * return address off of current's ret_stack and jump to it.
320  */
321 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
322 {
323         unsigned long old;
324         int faulted;
325         unsigned long return_hooker = (unsigned long)&return_to_handler;
326 
327         if (unlikely(ftrace_graph_is_dead()))
328                 return;
329 
330         if (unlikely(atomic_read(&current->tracing_graph_pause)))
331                 return;
332 
333         /*
334          * Protect against fault, even if it shouldn't
335          * happen. This tool is too much intrusive to
336          * ignore such a protection.
337          */
338         __asm__ __volatile__(
339                 "1:                                             \n\t"
340                 "mov.l          @%2, %0                         \n\t"
341                 "2:                                             \n\t"
342                 "mov.l          %3, @%2                         \n\t"
343                 "mov            #0, %1                          \n\t"
344                 "3:                                             \n\t"
345                 ".section .fixup, \"ax\"                        \n\t"
346                 "4:                                             \n\t"
347                 "mov.l          5f, %0                          \n\t"
348                 "jmp            @%0                             \n\t"
349                 " mov           #1, %1                          \n\t"
350                 ".balign 4                                      \n\t"
351                 "5:     .long 3b                                \n\t"
352                 ".previous                                      \n\t"
353                 ".section __ex_table,\"a\"                      \n\t"
354                 ".long 1b, 4b                                   \n\t"
355                 ".long 2b, 4b                                   \n\t"
356                 ".previous                                      \n\t"
357                 : "=&r" (old), "=r" (faulted)
358                 : "r" (parent), "r" (return_hooker)
359         );
360 
361         if (unlikely(faulted)) {
362                 ftrace_graph_stop();
363                 WARN_ON(1);
364                 return;
365         }
366 
367         if (function_graph_enter(old, self_addr, 0, NULL))
368                 __raw_writel(old, parent);
369 }
370 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
371 

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