arch/arm64/kernel/ftrace.c

   1 /*
   2  * arch/arm64/kernel/ftrace.c
   3  *
   4  * Copyright (C) 2013 Linaro Limited
   5  * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  */
  11
  12 #include <linux/ftrace.h>
  13 #include <linux/module.h>
  14 #include <linux/swab.h>
  15 #include <linux/uaccess.h>
  16
  17 #include <asm/cacheflush.h>
  18 #include <asm/debug-monitors.h>
  19 #include <asm/ftrace.h>
  20 #include <asm/insn.h>
  21
  22 #ifdef CONFIG_DYNAMIC_FTRACE
  23 /*
  24  * Replace a single instruction, which may be a branch or NOP.
  25  * If @validate == true, a replaced instruction is checked against 'old'.
  26  */
  27 static int ftrace_modify_code(unsigned long pc, u32 old, u32 new,
  28                               bool validate)
  29 {
  30         u32 replaced;
  31
  32         /*
  33          * Note:
  34          * We are paranoid about modifying text, as if a bug were to happen, it
  35          * could cause us to read or write to someplace that could cause harm.
  36          * Carefully read and modify the code with aarch64_insn_*() which uses
  37          * probe_kernel_*(), and make sure what we read is what we expected it
  38          * to be before modifying it.
  39          */
  40         if (validate) {
  41                 if (aarch64_insn_read((void *)pc, &replaced))
  42                         return -EFAULT;
  43
  44                 if (replaced != old)
  45                         return -EINVAL;
  46         }
  47         if (aarch64_insn_patch_text_nosync((void *)pc, new))
  48                 return -EPERM;
  49
  50         return 0;
  51 }
  52
  53 /*
  54  * Replace tracer function in ftrace_caller()
  55  */
  56 int ftrace_update_ftrace_func(ftrace_func_t func)
  57 {
  58         unsigned long pc;
  59         u32 new;
  60
  61         pc = (unsigned long)&ftrace_call;
  62         new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func,
  63                                           AARCH64_INSN_BRANCH_LINK);
  64
  65         return ftrace_modify_code(pc, 0, new, false);
  66 }
  67
  68 /*
  69  * Turn on the call to ftrace_caller() in instrumented function
  70  */
  71 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
  72 {
  73         unsigned long pc = rec->ip;
  74         u32 old, new;
  75         long offset = (long)pc - (long)addr;
  76
  77         if (offset < -SZ_128M || offset >= SZ_128M) {
  78 #ifdef CONFIG_ARM64_MODULE_PLTS
  79                 struct plt_entry trampoline;
  80                 struct module *mod;
  81
  82                 /*
  83                  * On kernels that support module PLTs, the offset between the
  84                  * branch instruction and its target may legally exceed the
  85                  * range of an ordinary relative 'bl' opcode. In this case, we
  86                  * need to branch via a trampoline in the module.
  87                  *
  88                  * NOTE: __module_text_address() must be called with preemption
  89                  * disabled, but we can rely on ftrace_lock to ensure that 'mod'
  90                  * retains its validity throughout the remainder of this code.
  91                  */
  92                 preempt_disable();
  93                 mod = __module_text_address(pc);
  94                 preempt_enable();
  95
  96                 if (WARN_ON(!mod))
  97                         return -EINVAL;
  98
  99                 /*
 100                  * There is only one ftrace trampoline per module. For now,
 101                  * this is not a problem since on arm64, all dynamic ftrace
 102                  * invocations are routed via ftrace_caller(). This will need
 103                  * to be revisited if support for multiple ftrace entry points
 104                  * is added in the future, but for now, the pr_err() below
 105                  * deals with a theoretical issue only.
 106                  *
 107                  * Note that PLTs are place relative, and plt_entries_equal()
 108                  * checks whether they point to the same target. Here, we need
 109                  * to check if the actual opcodes are in fact identical,
 110                  * regardless of the offset in memory so use memcmp() instead.
 111                  */
 112                 trampoline = get_plt_entry(addr, mod->arch.ftrace_trampoline);
 113                 if (memcmp(mod->arch.ftrace_trampoline, &trampoline,
 114                            sizeof(trampoline))) {
 115                         if (plt_entry_is_initialized(mod->arch.ftrace_trampoline)) {
 116                                 pr_err("ftrace: far branches to multiple entry points unsupported inside a single module\n");
 117                                 return -EINVAL;
 118                         }
 119
 120                         /* point the trampoline to our ftrace entry point */
 121                         module_disable_ro(mod);
 122                         *mod->arch.ftrace_trampoline = trampoline;
 123                         module_enable_ro(mod, true);
 124
 125                         /* update trampoline before patching in the branch */
 126                         smp_wmb();
 127                 }
 128                 addr = (unsigned long)(void *)mod->arch.ftrace_trampoline;
 129 #else /* CONFIG_ARM64_MODULE_PLTS */
 130                 return -EINVAL;
 131 #endif /* CONFIG_ARM64_MODULE_PLTS */
 132         }
 133
 134         old = aarch64_insn_gen_nop();
 135         new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
 136
 137         return ftrace_modify_code(pc, old, new, true);
 138 }
 139
 140 /*
 141  * Turn off the call to ftrace_caller() in instrumented function
 142  */
 143 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
 144                     unsigned long addr)
 145 {
 146         unsigned long pc = rec->ip;
 147         bool validate = true;
 148         u32 old = 0, new;
 149         long offset = (long)pc - (long)addr;
 150
 151         if (offset < -SZ_128M || offset >= SZ_128M) {
 152 #ifdef CONFIG_ARM64_MODULE_PLTS
 153                 u32 replaced;
 154
 155                 /*
 156                  * 'mod' is only set at module load time, but if we end up
 157                  * dealing with an out-of-range condition, we can assume it
 158                  * is due to a module being loaded far away from the kernel.
 159                  */
 160                 if (!mod) {
 161                         preempt_disable();
 162                         mod = __module_text_address(pc);
 163                         preempt_enable();
 164
 165                         if (WARN_ON(!mod))
 166                                 return -EINVAL;
 167                 }
 168
 169                 /*
 170                  * The instruction we are about to patch may be a branch and
 171                  * link instruction that was redirected via a PLT entry. In
 172                  * this case, the normal validation will fail, but we can at
 173                  * least check that we are dealing with a branch and link
 174                  * instruction that points into the right module.
 175                  */
 176                 if (aarch64_insn_read((void *)pc, &replaced))
 177                         return -EFAULT;
 178
 179                 if (!aarch64_insn_is_bl(replaced) ||
 180                     !within_module(pc + aarch64_get_branch_offset(replaced),
 181                                    mod))
 182                         return -EINVAL;
 183
 184                 validate = false;
 185 #else /* CONFIG_ARM64_MODULE_PLTS */
 186                 return -EINVAL;
 187 #endif /* CONFIG_ARM64_MODULE_PLTS */
 188         } else {
 189                 old = aarch64_insn_gen_branch_imm(pc, addr,
 190                                                   AARCH64_INSN_BRANCH_LINK);
 191         }
 192
 193         new = aarch64_insn_gen_nop();
 194
 195         return ftrace_modify_code(pc, old, new, validate);
 196 }
 197
 198 void arch_ftrace_update_code(int command)
 199 {
 200         command |= FTRACE_MAY_SLEEP;
 201         ftrace_modify_all_code(command);
 202 }
 203
 204 int __init ftrace_dyn_arch_init(void)
 205 {
 206         return 0;
 207 }
 208 #endif /* CONFIG_DYNAMIC_FTRACE */
 209
 210 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 211 /*
 212  * function_graph tracer expects ftrace_return_to_handler() to be called
 213  * on the way back to parent. For this purpose, this function is called
 214  * in _mcount() or ftrace_caller() to replace return address (*parent) on
 215  * the call stack to return_to_handler.
 216  *
 217  * Note that @frame_pointer is used only for sanity check later.
 218  */
 219 void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
 220                            unsigned long frame_pointer)
 221 {
 222         unsigned long return_hooker = (unsigned long)&return_to_handler;
 223         unsigned long old;
 224
 225         if (unlikely(atomic_read(&current->tracing_graph_pause)))
 226                 return;
 227
 228         /*
 229          * Note:
 230          * No protection against faulting at *parent, which may be seen
 231          * on other archs. It's unlikely on AArch64.
 232          */
 233         old = *parent;
 234
 235         if (!function_graph_enter(old, self_addr, frame_pointer, NULL))
 236                 *parent = return_hooker;
 237 }
 238
 239 #ifdef CONFIG_DYNAMIC_FTRACE
 240 /*
 241  * Turn on/off the call to ftrace_graph_caller() in ftrace_caller()
 242  * depending on @enable.
 243  */
 244 static int ftrace_modify_graph_caller(bool enable)
 245 {
 246         unsigned long pc = (unsigned long)&ftrace_graph_call;
 247         u32 branch, nop;
 248
 249         branch = aarch64_insn_gen_branch_imm(pc,
 250                                              (unsigned long)ftrace_graph_caller,
 251                                              AARCH64_INSN_BRANCH_NOLINK);
 252         nop = aarch64_insn_gen_nop();
 253
 254         if (enable)
 255                 return ftrace_modify_code(pc, nop, branch, true);
 256         else
 257                 return ftrace_modify_code(pc, branch, nop, true);
 258 }
 259
 260 int ftrace_enable_ftrace_graph_caller(void)
 261 {
 262         return ftrace_modify_graph_caller(true);
 263 }
 264
 265 int ftrace_disable_ftrace_graph_caller(void)
 266 {
 267         return ftrace_modify_graph_caller(false);
 268 }
 269 #endif /* CONFIG_DYNAMIC_FTRACE */
 270 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */