arch/sh/kernel/ftrace.c

   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 */