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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 | // SPDX-License-Identifier: GPL-2.0 /* * Copyright (C) 2008 Matt Fleming <matt@console-pimps.org> * Copyright (C) 2008 Paul Mundt <lethal@linux-sh.org> * * Code for replacing ftrace calls with jumps. * * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com> * * Thanks goes to Ingo Molnar, for suggesting the idea. * Mathieu Desnoyers, for suggesting postponing the modifications. * Arjan van de Ven, for keeping me straight, and explaining to me * the dangers of modifying code on the run. */ #include <linux/uaccess.h> #include <linux/ftrace.h> #include <linux/string.h> #include <linux/init.h> #include <linux/io.h> #include <linux/kernel.h> #include <asm/ftrace.h> #include <asm/cacheflush.h> #include <asm/unistd.h> #include <trace/syscall.h> #ifdef CONFIG_DYNAMIC_FTRACE static unsigned char ftrace_replaced_code[MCOUNT_INSN_SIZE]; static unsigned char ftrace_nop[4]; /* * If we're trying to nop out a call to a function, we instead * place a call to the address after the memory table. * * 8c011060 <a>: * 8c011060: 02 d1 mov.l 8c01106c <a+0xc>,r1 * 8c011062: 22 4f sts.l pr,@-r15 * 8c011064: 02 c7 mova 8c011070 <a+0x10>,r0 * 8c011066: 2b 41 jmp @r1 * 8c011068: 2a 40 lds r0,pr * 8c01106a: 09 00 nop * 8c01106c: 68 24 .word 0x2468 <--- ip * 8c01106e: 1d 8c .word 0x8c1d * 8c011070: 26 4f lds.l @r15+,pr <--- ip + MCOUNT_INSN_SIZE * * We write 0x8c011070 to 0x8c01106c so that on entry to a() we branch * past the _mcount call and continue executing code like normal. */ static unsigned char *ftrace_nop_replace(unsigned long ip) { __raw_writel(ip + MCOUNT_INSN_SIZE, ftrace_nop); return ftrace_nop; } static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr) { /* Place the address in the memory table. */ __raw_writel(addr, ftrace_replaced_code); /* * No locking needed, this must be called via kstop_machine * which in essence is like running on a uniprocessor machine. */ return ftrace_replaced_code; } /* * Modifying code must take extra care. On an SMP machine, if * the code being modified is also being executed on another CPU * that CPU will have undefined results and possibly take a GPF. * We use kstop_machine to stop other CPUS from executing code. * But this does not stop NMIs from happening. We still need * to protect against that. We separate out the modification of * the code to take care of this. * * Two buffers are added: An IP buffer and a "code" buffer. * * 1) Put the instruction pointer into the IP buffer * and the new code into the "code" buffer. * 2) Wait for any running NMIs to finish and set a flag that says * we are modifying code, it is done in an atomic operation. * 3) Write the code * 4) clear the flag. * 5) Wait for any running NMIs to finish. * * If an NMI is executed, the first thing it does is to call * "ftrace_nmi_enter". This will check if the flag is set to write * and if it is, it will write what is in the IP and "code" buffers. * * The trick is, it does not matter if everyone is writing the same * content to the code location. Also, if a CPU is executing code * it is OK to write to that code location if the contents being written * are the same as what exists. */ #define MOD_CODE_WRITE_FLAG (1 << 31) /* set when NMI should do the write */ static atomic_t nmi_running = ATOMIC_INIT(0); static int mod_code_status; /* holds return value of text write */ static void *mod_code_ip; /* holds the IP to write to */ static void *mod_code_newcode; /* holds the text to write to the IP */ static void clear_mod_flag(void) { int old = atomic_read(&nmi_running); for (;;) { int new = old & ~MOD_CODE_WRITE_FLAG; if (old == new) break; old = atomic_cmpxchg(&nmi_running, old, new); } } static void ftrace_mod_code(void) { /* * Yes, more than one CPU process can be writing to mod_code_status. * (and the code itself) * But if one were to fail, then they all should, and if one were * to succeed, then they all should. */ mod_code_status = copy_to_kernel_nofault(mod_code_ip, mod_code_newcode, MCOUNT_INSN_SIZE); /* if we fail, then kill any new writers */ if (mod_code_status) clear_mod_flag(); } void arch_ftrace_nmi_enter(void) { if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) { smp_rmb(); ftrace_mod_code(); } /* Must have previous changes seen before executions */ smp_mb(); } void arch_ftrace_nmi_exit(void) { /* Finish all executions before clearing nmi_running */ smp_mb(); atomic_dec(&nmi_running); } static void wait_for_nmi_and_set_mod_flag(void) { if (!atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG)) return; do { cpu_relax(); } while (atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG)); } static void wait_for_nmi(void) { if (!atomic_read(&nmi_running)) return; do { cpu_relax(); } while (atomic_read(&nmi_running)); } static int do_ftrace_mod_code(unsigned long ip, void *new_code) { mod_code_ip = (void *)ip; mod_code_newcode = new_code; /* The buffers need to be visible before we let NMIs write them */ smp_mb(); wait_for_nmi_and_set_mod_flag(); /* Make sure all running NMIs have finished before we write the code */ smp_mb(); ftrace_mod_code(); /* Make sure the write happens before clearing the bit */ smp_mb(); clear_mod_flag(); wait_for_nmi(); return mod_code_status; } static int ftrace_modify_code(unsigned long ip, unsigned char *old_code, unsigned char *new_code) { unsigned char replaced[MCOUNT_INSN_SIZE]; /* * Note: * We are paranoid about modifying text, as if a bug was to happen, it * could cause us to read or write to someplace that could cause harm. * Carefully read and modify the code with probe_kernel_*(), and make * sure what we read is what we expected it to be before modifying it. */ /* read the text we want to modify */ if (copy_from_kernel_nofault(replaced, (void *)ip, MCOUNT_INSN_SIZE)) return -EFAULT; /* Make sure it is what we expect it to be */ if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0) return -EINVAL; /* replace the text with the new text */ if (do_ftrace_mod_code(ip, new_code)) return -EPERM; flush_icache_range(ip, ip + MCOUNT_INSN_SIZE); return 0; } int ftrace_update_ftrace_func(ftrace_func_t func) { unsigned long ip = (unsigned long)(&ftrace_call) + MCOUNT_INSN_OFFSET; unsigned char old[MCOUNT_INSN_SIZE], *new; memcpy(old, (unsigned char *)ip, MCOUNT_INSN_SIZE); new = ftrace_call_replace(ip, (unsigned long)func); return ftrace_modify_code(ip, old, new); } int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr) { unsigned char *new, *old; unsigned long ip = rec->ip; old = ftrace_call_replace(ip, addr); new = ftrace_nop_replace(ip); return ftrace_modify_code(rec->ip, old, new); } int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) { unsigned char *new, *old; unsigned long ip = rec->ip; old = ftrace_nop_replace(ip); new = ftrace_call_replace(ip, addr); return ftrace_modify_code(rec->ip, old, new); } #endif /* CONFIG_DYNAMIC_FTRACE */ #ifdef CONFIG_FUNCTION_GRAPH_TRACER #ifdef CONFIG_DYNAMIC_FTRACE extern void ftrace_graph_call(void); static int ftrace_mod(unsigned long ip, unsigned long old_addr, unsigned long new_addr) { unsigned char code[MCOUNT_INSN_SIZE]; if (copy_from_kernel_nofault(code, (void *)ip, MCOUNT_INSN_SIZE)) return -EFAULT; if (old_addr != __raw_readl((unsigned long *)code)) return -EINVAL; __raw_writel(new_addr, ip); return 0; } int ftrace_enable_ftrace_graph_caller(void) { unsigned long ip, old_addr, new_addr; ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET; old_addr = (unsigned long)(&skip_trace); new_addr = (unsigned long)(&ftrace_graph_caller); return ftrace_mod(ip, old_addr, new_addr); } int ftrace_disable_ftrace_graph_caller(void) { unsigned long ip, old_addr, new_addr; ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET; old_addr = (unsigned long)(&ftrace_graph_caller); new_addr = (unsigned long)(&skip_trace); return ftrace_mod(ip, old_addr, new_addr); } #endif /* CONFIG_DYNAMIC_FTRACE */ /* * Hook the return address and push it in the stack of return addrs * in the current thread info. * * This is the main routine for the function graph tracer. The function * graph tracer essentially works like this: * * parent is the stack address containing self_addr's return address. * We pull the real return address out of parent and store it in * current's ret_stack. Then, we replace the return address on the stack * with the address of return_to_handler. self_addr is the function that * called mcount. * * When self_addr returns, it will jump to return_to_handler which calls * ftrace_return_to_handler. ftrace_return_to_handler will pull the real * return address off of current's ret_stack and jump to it. */ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr) { unsigned long old; int faulted; unsigned long return_hooker = (unsigned long)&return_to_handler; if (unlikely(ftrace_graph_is_dead())) return; if (unlikely(atomic_read(¤t->tracing_graph_pause))) return; /* * Protect against fault, even if it shouldn't * happen. This tool is too much intrusive to * ignore such a protection. */ __asm__ __volatile__( "1: \n\t" "mov.l @%2, %0 \n\t" "2: \n\t" "mov.l %3, @%2 \n\t" "mov #0, %1 \n\t" "3: \n\t" ".section .fixup, \"ax\" \n\t" "4: \n\t" "mov.l 5f, %0 \n\t" "jmp @%0 \n\t" " mov #1, %1 \n\t" ".balign 4 \n\t" "5: .long 3b \n\t" ".previous \n\t" ".section __ex_table,\"a\" \n\t" ".long 1b, 4b \n\t" ".long 2b, 4b \n\t" ".previous \n\t" : "=&r" (old), "=r" (faulted) : "r" (parent), "r" (return_hooker) ); if (unlikely(faulted)) { ftrace_graph_stop(); WARN_ON(1); return; } if (function_graph_enter(old, self_addr, 0, NULL)) __raw_writel(old, parent); } #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ |