linux/arch/sh/kernel/ftrace.c
<<
>>
Prefs
   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
  27static unsigned char ftrace_replaced_code[MCOUNT_INSN_SIZE];
  28
  29static 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 */
  48static unsigned char *ftrace_nop_replace(unsigned long ip)
  49{
  50        __raw_writel(ip + MCOUNT_INSN_SIZE, ftrace_nop);
  51        return ftrace_nop;
  52}
  53
  54static 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 */
  95static atomic_t nmi_running = ATOMIC_INIT(0);
  96static int mod_code_status;             /* holds return value of text write */
  97static void *mod_code_ip;               /* holds the IP to write to */
  98static void *mod_code_newcode;          /* holds the text to write to the IP */
  99
 100static 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
 114static 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
 130void 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
 140void arch_ftrace_nmi_exit(void)
 141{
 142        /* Finish all executions before clearing nmi_running */
 143        smp_mb();
 144        atomic_dec(&nmi_running);
 145}
 146
 147static 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
 157static 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
 167static int
 168do_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
 192static 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
 222int 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
 233int 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
 245int 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
 259extern void ftrace_graph_call(void);
 260
 261static 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
 276int 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
 287int 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 */
 316void 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(&current->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