arch/x86/kernel/ftrace.c

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This source file includes following definitions.
ftrace_arch_code_modify_prepare
ftrace_arch_code_modify_post_process
ftrace_calc_offset
ftrace_text_replace
ftrace_call_replace
within
text_ip_addr
ftrace_nop_replace
ftrace_modify_code_direct
ftrace_make_nop
ftrace_make_call
ftrace_modify_call
update_ftrace_func
ftrace_update_ftrace_func
is_ftrace_caller
ftrace_int3_handler
ftrace_write
add_break
add_brk_on_call
add_brk_on_nop
add_breakpoints
remove_breakpoint
add_update_code
add_update_call
add_update_nop
add_update
finish_update_call
finish_update_nop
finish_update
do_sync_core
run_sync
ftrace_replace_code
ftrace_modify_code
arch_ftrace_update_code
ftrace_dyn_arch_init
alloc_tramp
tramp_free
alloc_tramp
tramp_free
create_trampoline
calc_trampoline_call_offset
arch_ftrace_update_trampoline
addr_from_call
static_tramp_func
arch_ftrace_trampoline_func
arch_ftrace_trampoline_free
ftrace_jmp_replace
ftrace_mod_jmp
ftrace_enable_ftrace_graph_caller
ftrace_disable_ftrace_graph_caller
prepare_ftrace_return
   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Dynamic function tracing support.
   4  *
   5  * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
   6  *
   7  * Thanks goes to Ingo Molnar, for suggesting the idea.
   8  * Mathieu Desnoyers, for suggesting postponing the modifications.
   9  * Arjan van de Ven, for keeping me straight, and explaining to me
  10  * the dangers of modifying code on the run.
  11  */
  12 
  13 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  14 
  15 #include <linux/spinlock.h>
  16 #include <linux/hardirq.h>
  17 #include <linux/uaccess.h>
  18 #include <linux/ftrace.h>
  19 #include <linux/percpu.h>
  20 #include <linux/sched.h>
  21 #include <linux/slab.h>
  22 #include <linux/init.h>
  23 #include <linux/list.h>
  24 #include <linux/module.h>
  25 #include <linux/memory.h>
  26 
  27 #include <trace/syscall.h>
  28 
  29 #include <asm/set_memory.h>
  30 #include <asm/kprobes.h>
  31 #include <asm/ftrace.h>
  32 #include <asm/nops.h>
  33 #include <asm/text-patching.h>
  34 
  35 #ifdef CONFIG_DYNAMIC_FTRACE
  36 
  37 int ftrace_arch_code_modify_prepare(void)
  38     __acquires(&text_mutex)
  39 {
  40         /*
  41          * Need to grab text_mutex to prevent a race from module loading
  42          * and live kernel patching from changing the text permissions while
  43          * ftrace has it set to "read/write".
  44          */
  45         mutex_lock(&text_mutex);
  46         set_kernel_text_rw();
  47         set_all_modules_text_rw();
  48         return 0;
  49 }
  50 
  51 int ftrace_arch_code_modify_post_process(void)
  52     __releases(&text_mutex)
  53 {
  54         set_all_modules_text_ro();
  55         set_kernel_text_ro();
  56         mutex_unlock(&text_mutex);
  57         return 0;
  58 }
  59 
  60 union ftrace_code_union {
  61         char code[MCOUNT_INSN_SIZE];
  62         struct {
  63                 unsigned char op;
  64                 int offset;
  65         } __attribute__((packed));
  66 };
  67 
  68 static int ftrace_calc_offset(long ip, long addr)
  69 {
  70         return (int)(addr - ip);
  71 }
  72 
  73 static unsigned char *
  74 ftrace_text_replace(unsigned char op, unsigned long ip, unsigned long addr)
  75 {
  76         static union ftrace_code_union calc;
  77 
  78         calc.op         = op;
  79         calc.offset     = ftrace_calc_offset(ip + MCOUNT_INSN_SIZE, addr);
  80 
  81         return calc.code;
  82 }
  83 
  84 static unsigned char *
  85 ftrace_call_replace(unsigned long ip, unsigned long addr)
  86 {
  87         return ftrace_text_replace(0xe8, ip, addr);
  88 }
  89 
  90 static inline int
  91 within(unsigned long addr, unsigned long start, unsigned long end)
  92 {
  93         return addr >= start && addr < end;
  94 }
  95 
  96 static unsigned long text_ip_addr(unsigned long ip)
  97 {
  98         /*
  99          * On x86_64, kernel text mappings are mapped read-only, so we use
 100          * the kernel identity mapping instead of the kernel text mapping
 101          * to modify the kernel text.
 102          *
 103          * For 32bit kernels, these mappings are same and we can use
 104          * kernel identity mapping to modify code.
 105          */
 106         if (within(ip, (unsigned long)_text, (unsigned long)_etext))
 107                 ip = (unsigned long)__va(__pa_symbol(ip));
 108 
 109         return ip;
 110 }
 111 
 112 static const unsigned char *ftrace_nop_replace(void)
 113 {
 114         return ideal_nops[NOP_ATOMIC5];
 115 }
 116 
 117 static int
 118 ftrace_modify_code_direct(unsigned long ip, unsigned const char *old_code,
 119                    unsigned const char *new_code)
 120 {
 121         unsigned char replaced[MCOUNT_INSN_SIZE];
 122 
 123         ftrace_expected = old_code;
 124 
 125         /*
 126          * Note:
 127          * We are paranoid about modifying text, as if a bug was to happen, it
 128          * could cause us to read or write to someplace that could cause harm.
 129          * Carefully read and modify the code with probe_kernel_*(), and make
 130          * sure what we read is what we expected it to be before modifying it.
 131          */
 132 
 133         /* read the text we want to modify */
 134         if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
 135                 return -EFAULT;
 136 
 137         /* Make sure it is what we expect it to be */
 138         if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
 139                 return -EINVAL;
 140 
 141         ip = text_ip_addr(ip);
 142 
 143         /* replace the text with the new text */
 144         if (probe_kernel_write((void *)ip, new_code, MCOUNT_INSN_SIZE))
 145                 return -EPERM;
 146 
 147         sync_core();
 148 
 149         return 0;
 150 }
 151 
 152 int ftrace_make_nop(struct module *mod,
 153                     struct dyn_ftrace *rec, unsigned long addr)
 154 {
 155         unsigned const char *new, *old;
 156         unsigned long ip = rec->ip;
 157 
 158         old = ftrace_call_replace(ip, addr);
 159         new = ftrace_nop_replace();
 160 
 161         /*
 162          * On boot up, and when modules are loaded, the MCOUNT_ADDR
 163          * is converted to a nop, and will never become MCOUNT_ADDR
 164          * again. This code is either running before SMP (on boot up)
 165          * or before the code will ever be executed (module load).
 166          * We do not want to use the breakpoint version in this case,
 167          * just modify the code directly.
 168          */
 169         if (addr == MCOUNT_ADDR)
 170                 return ftrace_modify_code_direct(rec->ip, old, new);
 171 
 172         ftrace_expected = NULL;
 173 
 174         /* Normal cases use add_brk_on_nop */
 175         WARN_ONCE(1, "invalid use of ftrace_make_nop");
 176         return -EINVAL;
 177 }
 178 
 179 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 180 {
 181         unsigned const char *new, *old;
 182         unsigned long ip = rec->ip;
 183 
 184         old = ftrace_nop_replace();
 185         new = ftrace_call_replace(ip, addr);
 186 
 187         /* Should only be called when module is loaded */
 188         return ftrace_modify_code_direct(rec->ip, old, new);
 189 }
 190 
 191 /*
 192  * The modifying_ftrace_code is used to tell the breakpoint
 193  * handler to call ftrace_int3_handler(). If it fails to
 194  * call this handler for a breakpoint added by ftrace, then
 195  * the kernel may crash.
 196  *
 197  * As atomic_writes on x86 do not need a barrier, we do not
 198  * need to add smp_mb()s for this to work. It is also considered
 199  * that we can not read the modifying_ftrace_code before
 200  * executing the breakpoint. That would be quite remarkable if
 201  * it could do that. Here's the flow that is required:
 202  *
 203  *   CPU-0                          CPU-1
 204  *
 205  * atomic_inc(mfc);
 206  * write int3s
 207  *                              <trap-int3> // implicit (r)mb
 208  *                              if (atomic_read(mfc))
 209  *                                      call ftrace_int3_handler()
 210  *
 211  * Then when we are finished:
 212  *
 213  * atomic_dec(mfc);
 214  *
 215  * If we hit a breakpoint that was not set by ftrace, it does not
 216  * matter if ftrace_int3_handler() is called or not. It will
 217  * simply be ignored. But it is crucial that a ftrace nop/caller
 218  * breakpoint is handled. No other user should ever place a
 219  * breakpoint on an ftrace nop/caller location. It must only
 220  * be done by this code.
 221  */
 222 atomic_t modifying_ftrace_code __read_mostly;
 223 
 224 static int
 225 ftrace_modify_code(unsigned long ip, unsigned const char *old_code,
 226                    unsigned const char *new_code);
 227 
 228 /*
 229  * Should never be called:
 230  *  As it is only called by __ftrace_replace_code() which is called by
 231  *  ftrace_replace_code() that x86 overrides, and by ftrace_update_code()
 232  *  which is called to turn mcount into nops or nops into function calls
 233  *  but not to convert a function from not using regs to one that uses
 234  *  regs, which ftrace_modify_call() is for.
 235  */
 236 int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 237                                  unsigned long addr)
 238 {
 239         WARN_ON(1);
 240         ftrace_expected = NULL;
 241         return -EINVAL;
 242 }
 243 
 244 static unsigned long ftrace_update_func;
 245 static unsigned long ftrace_update_func_call;
 246 
 247 static int update_ftrace_func(unsigned long ip, void *new)
 248 {
 249         unsigned char old[MCOUNT_INSN_SIZE];
 250         int ret;
 251 
 252         memcpy(old, (void *)ip, MCOUNT_INSN_SIZE);
 253 
 254         ftrace_update_func = ip;
 255         /* Make sure the breakpoints see the ftrace_update_func update */
 256         smp_wmb();
 257 
 258         /* See comment above by declaration of modifying_ftrace_code */
 259         atomic_inc(&modifying_ftrace_code);
 260 
 261         ret = ftrace_modify_code(ip, old, new);
 262 
 263         atomic_dec(&modifying_ftrace_code);
 264 
 265         return ret;
 266 }
 267 
 268 int ftrace_update_ftrace_func(ftrace_func_t func)
 269 {
 270         unsigned long ip = (unsigned long)(&ftrace_call);
 271         unsigned char *new;
 272         int ret;
 273 
 274         ftrace_update_func_call = (unsigned long)func;
 275 
 276         new = ftrace_call_replace(ip, (unsigned long)func);
 277         ret = update_ftrace_func(ip, new);
 278 
 279         /* Also update the regs callback function */
 280         if (!ret) {
 281                 ip = (unsigned long)(&ftrace_regs_call);
 282                 new = ftrace_call_replace(ip, (unsigned long)func);
 283                 ret = update_ftrace_func(ip, new);
 284         }
 285 
 286         return ret;
 287 }
 288 
 289 static nokprobe_inline int is_ftrace_caller(unsigned long ip)
 290 {
 291         if (ip == ftrace_update_func)
 292                 return 1;
 293 
 294         return 0;
 295 }
 296 
 297 /*
 298  * A breakpoint was added to the code address we are about to
 299  * modify, and this is the handle that will just skip over it.
 300  * We are either changing a nop into a trace call, or a trace
 301  * call to a nop. While the change is taking place, we treat
 302  * it just like it was a nop.
 303  */
 304 int ftrace_int3_handler(struct pt_regs *regs)
 305 {
 306         unsigned long ip;
 307 
 308         if (WARN_ON_ONCE(!regs))
 309                 return 0;
 310 
 311         ip = regs->ip - INT3_INSN_SIZE;
 312 
 313         if (ftrace_location(ip)) {
 314                 int3_emulate_call(regs, (unsigned long)ftrace_regs_caller);
 315                 return 1;
 316         } else if (is_ftrace_caller(ip)) {
 317                 if (!ftrace_update_func_call) {
 318                         int3_emulate_jmp(regs, ip + CALL_INSN_SIZE);
 319                         return 1;
 320                 }
 321                 int3_emulate_call(regs, ftrace_update_func_call);
 322                 return 1;
 323         }
 324 
 325         return 0;
 326 }
 327 NOKPROBE_SYMBOL(ftrace_int3_handler);
 328 
 329 static int ftrace_write(unsigned long ip, const char *val, int size)
 330 {
 331         ip = text_ip_addr(ip);
 332 
 333         if (probe_kernel_write((void *)ip, val, size))
 334                 return -EPERM;
 335 
 336         return 0;
 337 }
 338 
 339 static int add_break(unsigned long ip, const char *old)
 340 {
 341         unsigned char replaced[MCOUNT_INSN_SIZE];
 342         unsigned char brk = BREAKPOINT_INSTRUCTION;
 343 
 344         if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
 345                 return -EFAULT;
 346 
 347         ftrace_expected = old;
 348 
 349         /* Make sure it is what we expect it to be */
 350         if (memcmp(replaced, old, MCOUNT_INSN_SIZE) != 0)
 351                 return -EINVAL;
 352 
 353         return ftrace_write(ip, &brk, 1);
 354 }
 355 
 356 static int add_brk_on_call(struct dyn_ftrace *rec, unsigned long addr)
 357 {
 358         unsigned const char *old;
 359         unsigned long ip = rec->ip;
 360 
 361         old = ftrace_call_replace(ip, addr);
 362 
 363         return add_break(rec->ip, old);
 364 }
 365 
 366 
 367 static int add_brk_on_nop(struct dyn_ftrace *rec)
 368 {
 369         unsigned const char *old;
 370 
 371         old = ftrace_nop_replace();
 372 
 373         return add_break(rec->ip, old);
 374 }
 375 
 376 static int add_breakpoints(struct dyn_ftrace *rec, bool enable)
 377 {
 378         unsigned long ftrace_addr;
 379         int ret;
 380 
 381         ftrace_addr = ftrace_get_addr_curr(rec);
 382 
 383         ret = ftrace_test_record(rec, enable);
 384 
 385         switch (ret) {
 386         case FTRACE_UPDATE_IGNORE:
 387                 return 0;
 388 
 389         case FTRACE_UPDATE_MAKE_CALL:
 390                 /* converting nop to call */
 391                 return add_brk_on_nop(rec);
 392 
 393         case FTRACE_UPDATE_MODIFY_CALL:
 394         case FTRACE_UPDATE_MAKE_NOP:
 395                 /* converting a call to a nop */
 396                 return add_brk_on_call(rec, ftrace_addr);
 397         }
 398         return 0;
 399 }
 400 
 401 /*
 402  * On error, we need to remove breakpoints. This needs to
 403  * be done caefully. If the address does not currently have a
 404  * breakpoint, we know we are done. Otherwise, we look at the
 405  * remaining 4 bytes of the instruction. If it matches a nop
 406  * we replace the breakpoint with the nop. Otherwise we replace
 407  * it with the call instruction.
 408  */
 409 static int remove_breakpoint(struct dyn_ftrace *rec)
 410 {
 411         unsigned char ins[MCOUNT_INSN_SIZE];
 412         unsigned char brk = BREAKPOINT_INSTRUCTION;
 413         const unsigned char *nop;
 414         unsigned long ftrace_addr;
 415         unsigned long ip = rec->ip;
 416 
 417         /* If we fail the read, just give up */
 418         if (probe_kernel_read(ins, (void *)ip, MCOUNT_INSN_SIZE))
 419                 return -EFAULT;
 420 
 421         /* If this does not have a breakpoint, we are done */
 422         if (ins[0] != brk)
 423                 return 0;
 424 
 425         nop = ftrace_nop_replace();
 426 
 427         /*
 428          * If the last 4 bytes of the instruction do not match
 429          * a nop, then we assume that this is a call to ftrace_addr.
 430          */
 431         if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) != 0) {
 432                 /*
 433                  * For extra paranoidism, we check if the breakpoint is on
 434                  * a call that would actually jump to the ftrace_addr.
 435                  * If not, don't touch the breakpoint, we make just create
 436                  * a disaster.
 437                  */
 438                 ftrace_addr = ftrace_get_addr_new(rec);
 439                 nop = ftrace_call_replace(ip, ftrace_addr);
 440 
 441                 if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) == 0)
 442                         goto update;
 443 
 444                 /* Check both ftrace_addr and ftrace_old_addr */
 445                 ftrace_addr = ftrace_get_addr_curr(rec);
 446                 nop = ftrace_call_replace(ip, ftrace_addr);
 447 
 448                 ftrace_expected = nop;
 449 
 450                 if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) != 0)
 451                         return -EINVAL;
 452         }
 453 
 454  update:
 455         return ftrace_write(ip, nop, 1);
 456 }
 457 
 458 static int add_update_code(unsigned long ip, unsigned const char *new)
 459 {
 460         /* skip breakpoint */
 461         ip++;
 462         new++;
 463         return ftrace_write(ip, new, MCOUNT_INSN_SIZE - 1);
 464 }
 465 
 466 static int add_update_call(struct dyn_ftrace *rec, unsigned long addr)
 467 {
 468         unsigned long ip = rec->ip;
 469         unsigned const char *new;
 470 
 471         new = ftrace_call_replace(ip, addr);
 472         return add_update_code(ip, new);
 473 }
 474 
 475 static int add_update_nop(struct dyn_ftrace *rec)
 476 {
 477         unsigned long ip = rec->ip;
 478         unsigned const char *new;
 479 
 480         new = ftrace_nop_replace();
 481         return add_update_code(ip, new);
 482 }
 483 
 484 static int add_update(struct dyn_ftrace *rec, bool enable)
 485 {
 486         unsigned long ftrace_addr;
 487         int ret;
 488 
 489         ret = ftrace_test_record(rec, enable);
 490 
 491         ftrace_addr  = ftrace_get_addr_new(rec);
 492 
 493         switch (ret) {
 494         case FTRACE_UPDATE_IGNORE:
 495                 return 0;
 496 
 497         case FTRACE_UPDATE_MODIFY_CALL:
 498         case FTRACE_UPDATE_MAKE_CALL:
 499                 /* converting nop to call */
 500                 return add_update_call(rec, ftrace_addr);
 501 
 502         case FTRACE_UPDATE_MAKE_NOP:
 503                 /* converting a call to a nop */
 504                 return add_update_nop(rec);
 505         }
 506 
 507         return 0;
 508 }
 509 
 510 static int finish_update_call(struct dyn_ftrace *rec, unsigned long addr)
 511 {
 512         unsigned long ip = rec->ip;
 513         unsigned const char *new;
 514 
 515         new = ftrace_call_replace(ip, addr);
 516 
 517         return ftrace_write(ip, new, 1);
 518 }
 519 
 520 static int finish_update_nop(struct dyn_ftrace *rec)
 521 {
 522         unsigned long ip = rec->ip;
 523         unsigned const char *new;
 524 
 525         new = ftrace_nop_replace();
 526 
 527         return ftrace_write(ip, new, 1);
 528 }
 529 
 530 static int finish_update(struct dyn_ftrace *rec, bool enable)
 531 {
 532         unsigned long ftrace_addr;
 533         int ret;
 534 
 535         ret = ftrace_update_record(rec, enable);
 536 
 537         ftrace_addr = ftrace_get_addr_new(rec);
 538 
 539         switch (ret) {
 540         case FTRACE_UPDATE_IGNORE:
 541                 return 0;
 542 
 543         case FTRACE_UPDATE_MODIFY_CALL:
 544         case FTRACE_UPDATE_MAKE_CALL:
 545                 /* converting nop to call */
 546                 return finish_update_call(rec, ftrace_addr);
 547 
 548         case FTRACE_UPDATE_MAKE_NOP:
 549                 /* converting a call to a nop */
 550                 return finish_update_nop(rec);
 551         }
 552 
 553         return 0;
 554 }
 555 
 556 static void do_sync_core(void *data)
 557 {
 558         sync_core();
 559 }
 560 
 561 static void run_sync(void)
 562 {
 563         int enable_irqs;
 564 
 565         /* No need to sync if there's only one CPU */
 566         if (num_online_cpus() == 1)
 567                 return;
 568 
 569         enable_irqs = irqs_disabled();
 570 
 571         /* We may be called with interrupts disabled (on bootup). */
 572         if (enable_irqs)
 573                 local_irq_enable();
 574         on_each_cpu(do_sync_core, NULL, 1);
 575         if (enable_irqs)
 576                 local_irq_disable();
 577 }
 578 
 579 void ftrace_replace_code(int enable)
 580 {
 581         struct ftrace_rec_iter *iter;
 582         struct dyn_ftrace *rec;
 583         const char *report = "adding breakpoints";
 584         int count = 0;
 585         int ret;
 586 
 587         for_ftrace_rec_iter(iter) {
 588                 rec = ftrace_rec_iter_record(iter);
 589 
 590                 ret = add_breakpoints(rec, enable);
 591                 if (ret)
 592                         goto remove_breakpoints;
 593                 count++;
 594         }
 595 
 596         run_sync();
 597 
 598         report = "updating code";
 599         count = 0;
 600 
 601         for_ftrace_rec_iter(iter) {
 602                 rec = ftrace_rec_iter_record(iter);
 603 
 604                 ret = add_update(rec, enable);
 605                 if (ret)
 606                         goto remove_breakpoints;
 607                 count++;
 608         }
 609 
 610         run_sync();
 611 
 612         report = "removing breakpoints";
 613         count = 0;
 614 
 615         for_ftrace_rec_iter(iter) {
 616                 rec = ftrace_rec_iter_record(iter);
 617 
 618                 ret = finish_update(rec, enable);
 619                 if (ret)
 620                         goto remove_breakpoints;
 621                 count++;
 622         }
 623 
 624         run_sync();
 625 
 626         return;
 627 
 628  remove_breakpoints:
 629         pr_warn("Failed on %s (%d):\n", report, count);
 630         ftrace_bug(ret, rec);
 631         for_ftrace_rec_iter(iter) {
 632                 rec = ftrace_rec_iter_record(iter);
 633                 /*
 634                  * Breakpoints are handled only when this function is in
 635                  * progress. The system could not work with them.
 636                  */
 637                 if (remove_breakpoint(rec))
 638                         BUG();
 639         }
 640         run_sync();
 641 }
 642 
 643 static int
 644 ftrace_modify_code(unsigned long ip, unsigned const char *old_code,
 645                    unsigned const char *new_code)
 646 {
 647         int ret;
 648 
 649         ret = add_break(ip, old_code);
 650         if (ret)
 651                 goto out;
 652 
 653         run_sync();
 654 
 655         ret = add_update_code(ip, new_code);
 656         if (ret)
 657                 goto fail_update;
 658 
 659         run_sync();
 660 
 661         ret = ftrace_write(ip, new_code, 1);
 662         /*
 663          * The breakpoint is handled only when this function is in progress.
 664          * The system could not work if we could not remove it.
 665          */
 666         BUG_ON(ret);
 667  out:
 668         run_sync();
 669         return ret;
 670 
 671  fail_update:
 672         /* Also here the system could not work with the breakpoint */
 673         if (ftrace_write(ip, old_code, 1))
 674                 BUG();
 675         goto out;
 676 }
 677 
 678 void arch_ftrace_update_code(int command)
 679 {
 680         /* See comment above by declaration of modifying_ftrace_code */
 681         atomic_inc(&modifying_ftrace_code);
 682 
 683         ftrace_modify_all_code(command);
 684 
 685         atomic_dec(&modifying_ftrace_code);
 686 }
 687 
 688 int __init ftrace_dyn_arch_init(void)
 689 {
 690         return 0;
 691 }
 692 
 693 /* Currently only x86_64 supports dynamic trampolines */
 694 #ifdef CONFIG_X86_64
 695 
 696 #ifdef CONFIG_MODULES
 697 #include <linux/moduleloader.h>
 698 /* Module allocation simplifies allocating memory for code */
 699 static inline void *alloc_tramp(unsigned long size)
 700 {
 701         return module_alloc(size);
 702 }
 703 static inline void tramp_free(void *tramp)
 704 {
 705         module_memfree(tramp);
 706 }
 707 #else
 708 /* Trampolines can only be created if modules are supported */
 709 static inline void *alloc_tramp(unsigned long size)
 710 {
 711         return NULL;
 712 }
 713 static inline void tramp_free(void *tramp) { }
 714 #endif
 715 
 716 /* Defined as markers to the end of the ftrace default trampolines */
 717 extern void ftrace_regs_caller_end(void);
 718 extern void ftrace_epilogue(void);
 719 extern void ftrace_caller_op_ptr(void);
 720 extern void ftrace_regs_caller_op_ptr(void);
 721 
 722 /* movq function_trace_op(%rip), %rdx */
 723 /* 0x48 0x8b 0x15 <offset-to-ftrace_trace_op (4 bytes)> */
 724 #define OP_REF_SIZE     7
 725 
 726 /*
 727  * The ftrace_ops is passed to the function callback. Since the
 728  * trampoline only services a single ftrace_ops, we can pass in
 729  * that ops directly.
 730  *
 731  * The ftrace_op_code_union is used to create a pointer to the
 732  * ftrace_ops that will be passed to the callback function.
 733  */
 734 union ftrace_op_code_union {
 735         char code[OP_REF_SIZE];
 736         struct {
 737                 char op[3];
 738                 int offset;
 739         } __attribute__((packed));
 740 };
 741 
 742 #define RET_SIZE                1
 743 
 744 static unsigned long
 745 create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
 746 {
 747         unsigned long start_offset;
 748         unsigned long end_offset;
 749         unsigned long op_offset;
 750         unsigned long offset;
 751         unsigned long npages;
 752         unsigned long size;
 753         unsigned long retq;
 754         unsigned long *ptr;
 755         void *trampoline;
 756         void *ip;
 757         /* 48 8b 15 <offset> is movq <offset>(%rip), %rdx */
 758         unsigned const char op_ref[] = { 0x48, 0x8b, 0x15 };
 759         union ftrace_op_code_union op_ptr;
 760         int ret;
 761 
 762         if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {
 763                 start_offset = (unsigned long)ftrace_regs_caller;
 764                 end_offset = (unsigned long)ftrace_regs_caller_end;
 765                 op_offset = (unsigned long)ftrace_regs_caller_op_ptr;
 766         } else {
 767                 start_offset = (unsigned long)ftrace_caller;
 768                 end_offset = (unsigned long)ftrace_epilogue;
 769                 op_offset = (unsigned long)ftrace_caller_op_ptr;
 770         }
 771 
 772         size = end_offset - start_offset;
 773 
 774         /*
 775          * Allocate enough size to store the ftrace_caller code,
 776          * the iret , as well as the address of the ftrace_ops this
 777          * trampoline is used for.
 778          */
 779         trampoline = alloc_tramp(size + RET_SIZE + sizeof(void *));
 780         if (!trampoline)
 781                 return 0;
 782 
 783         *tramp_size = size + RET_SIZE + sizeof(void *);
 784         npages = DIV_ROUND_UP(*tramp_size, PAGE_SIZE);
 785 
 786         /* Copy ftrace_caller onto the trampoline memory */
 787         ret = probe_kernel_read(trampoline, (void *)start_offset, size);
 788         if (WARN_ON(ret < 0))
 789                 goto fail;
 790 
 791         ip = trampoline + size;
 792 
 793         /* The trampoline ends with ret(q) */
 794         retq = (unsigned long)ftrace_stub;
 795         ret = probe_kernel_read(ip, (void *)retq, RET_SIZE);
 796         if (WARN_ON(ret < 0))
 797                 goto fail;
 798 
 799         /*
 800          * The address of the ftrace_ops that is used for this trampoline
 801          * is stored at the end of the trampoline. This will be used to
 802          * load the third parameter for the callback. Basically, that
 803          * location at the end of the trampoline takes the place of
 804          * the global function_trace_op variable.
 805          */
 806 
 807         ptr = (unsigned long *)(trampoline + size + RET_SIZE);
 808         *ptr = (unsigned long)ops;
 809 
 810         op_offset -= start_offset;
 811         memcpy(&op_ptr, trampoline + op_offset, OP_REF_SIZE);
 812 
 813         /* Are we pointing to the reference? */
 814         if (WARN_ON(memcmp(op_ptr.op, op_ref, 3) != 0))
 815                 goto fail;
 816 
 817         /* Load the contents of ptr into the callback parameter */
 818         offset = (unsigned long)ptr;
 819         offset -= (unsigned long)trampoline + op_offset + OP_REF_SIZE;
 820 
 821         op_ptr.offset = offset;
 822 
 823         /* put in the new offset to the ftrace_ops */
 824         memcpy(trampoline + op_offset, &op_ptr, OP_REF_SIZE);
 825 
 826         /* ALLOC_TRAMP flags lets us know we created it */
 827         ops->flags |= FTRACE_OPS_FL_ALLOC_TRAMP;
 828 
 829         set_vm_flush_reset_perms(trampoline);
 830 
 831         /*
 832          * Module allocation needs to be completed by making the page
 833          * executable. The page is still writable, which is a security hazard,
 834          * but anyhow ftrace breaks W^X completely.
 835          */
 836         set_memory_x((unsigned long)trampoline, npages);
 837         return (unsigned long)trampoline;
 838 fail:
 839         tramp_free(trampoline);
 840         return 0;
 841 }
 842 
 843 static unsigned long calc_trampoline_call_offset(bool save_regs)
 844 {
 845         unsigned long start_offset;
 846         unsigned long call_offset;
 847 
 848         if (save_regs) {
 849                 start_offset = (unsigned long)ftrace_regs_caller;
 850                 call_offset = (unsigned long)ftrace_regs_call;
 851         } else {
 852                 start_offset = (unsigned long)ftrace_caller;
 853                 call_offset = (unsigned long)ftrace_call;
 854         }
 855 
 856         return call_offset - start_offset;
 857 }
 858 
 859 void arch_ftrace_update_trampoline(struct ftrace_ops *ops)
 860 {
 861         ftrace_func_t func;
 862         unsigned char *new;
 863         unsigned long offset;
 864         unsigned long ip;
 865         unsigned int size;
 866         int ret, npages;
 867 
 868         if (ops->trampoline) {
 869                 /*
 870                  * The ftrace_ops caller may set up its own trampoline.
 871                  * In such a case, this code must not modify it.
 872                  */
 873                 if (!(ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP))
 874                         return;
 875                 npages = PAGE_ALIGN(ops->trampoline_size) >> PAGE_SHIFT;
 876                 set_memory_rw(ops->trampoline, npages);
 877         } else {
 878                 ops->trampoline = create_trampoline(ops, &size);
 879                 if (!ops->trampoline)
 880                         return;
 881                 ops->trampoline_size = size;
 882                 npages = PAGE_ALIGN(size) >> PAGE_SHIFT;
 883         }
 884 
 885         offset = calc_trampoline_call_offset(ops->flags & FTRACE_OPS_FL_SAVE_REGS);
 886         ip = ops->trampoline + offset;
 887 
 888         func = ftrace_ops_get_func(ops);
 889 
 890         ftrace_update_func_call = (unsigned long)func;
 891 
 892         /* Do a safe modify in case the trampoline is executing */
 893         new = ftrace_call_replace(ip, (unsigned long)func);
 894         ret = update_ftrace_func(ip, new);
 895         set_memory_ro(ops->trampoline, npages);
 896 
 897         /* The update should never fail */
 898         WARN_ON(ret);
 899 }
 900 
 901 /* Return the address of the function the trampoline calls */
 902 static void *addr_from_call(void *ptr)
 903 {
 904         union ftrace_code_union calc;
 905         int ret;
 906 
 907         ret = probe_kernel_read(&calc, ptr, MCOUNT_INSN_SIZE);
 908         if (WARN_ON_ONCE(ret < 0))
 909                 return NULL;
 910 
 911         /* Make sure this is a call */
 912         if (WARN_ON_ONCE(calc.op != 0xe8)) {
 913                 pr_warn("Expected e8, got %x\n", calc.op);
 914                 return NULL;
 915         }
 916 
 917         return ptr + MCOUNT_INSN_SIZE + calc.offset;
 918 }
 919 
 920 void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
 921                            unsigned long frame_pointer);
 922 
 923 /*
 924  * If the ops->trampoline was not allocated, then it probably
 925  * has a static trampoline func, or is the ftrace caller itself.
 926  */
 927 static void *static_tramp_func(struct ftrace_ops *ops, struct dyn_ftrace *rec)
 928 {
 929         unsigned long offset;
 930         bool save_regs = rec->flags & FTRACE_FL_REGS_EN;
 931         void *ptr;
 932 
 933         if (ops && ops->trampoline) {
 934 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 935                 /*
 936                  * We only know about function graph tracer setting as static
 937                  * trampoline.
 938                  */
 939                 if (ops->trampoline == FTRACE_GRAPH_ADDR)
 940                         return (void *)prepare_ftrace_return;
 941 #endif
 942                 return NULL;
 943         }
 944 
 945         offset = calc_trampoline_call_offset(save_regs);
 946 
 947         if (save_regs)
 948                 ptr = (void *)FTRACE_REGS_ADDR + offset;
 949         else
 950                 ptr = (void *)FTRACE_ADDR + offset;
 951 
 952         return addr_from_call(ptr);
 953 }
 954 
 955 void *arch_ftrace_trampoline_func(struct ftrace_ops *ops, struct dyn_ftrace *rec)
 956 {
 957         unsigned long offset;
 958 
 959         /* If we didn't allocate this trampoline, consider it static */
 960         if (!ops || !(ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP))
 961                 return static_tramp_func(ops, rec);
 962 
 963         offset = calc_trampoline_call_offset(ops->flags & FTRACE_OPS_FL_SAVE_REGS);
 964         return addr_from_call((void *)ops->trampoline + offset);
 965 }
 966 
 967 void arch_ftrace_trampoline_free(struct ftrace_ops *ops)
 968 {
 969         if (!ops || !(ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP))
 970                 return;
 971 
 972         tramp_free((void *)ops->trampoline);
 973         ops->trampoline = 0;
 974 }
 975 
 976 #endif /* CONFIG_X86_64 */
 977 #endif /* CONFIG_DYNAMIC_FTRACE */
 978 
 979 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 980 
 981 #ifdef CONFIG_DYNAMIC_FTRACE
 982 extern void ftrace_graph_call(void);
 983 
 984 static unsigned char *ftrace_jmp_replace(unsigned long ip, unsigned long addr)
 985 {
 986         return ftrace_text_replace(0xe9, ip, addr);
 987 }
 988 
 989 static int ftrace_mod_jmp(unsigned long ip, void *func)
 990 {
 991         unsigned char *new;
 992 
 993         ftrace_update_func_call = 0UL;
 994         new = ftrace_jmp_replace(ip, (unsigned long)func);
 995 
 996         return update_ftrace_func(ip, new);
 997 }
 998 
 999 int ftrace_enable_ftrace_graph_caller(void)
1000 {
1001         unsigned long ip = (unsigned long)(&ftrace_graph_call);
1002 
1003         return ftrace_mod_jmp(ip, &ftrace_graph_caller);
1004 }
1005 
1006 int ftrace_disable_ftrace_graph_caller(void)
1007 {
1008         unsigned long ip = (unsigned long)(&ftrace_graph_call);
1009 
1010         return ftrace_mod_jmp(ip, &ftrace_stub);
1011 }
1012 
1013 #endif /* !CONFIG_DYNAMIC_FTRACE */
1014 
1015 /*
1016  * Hook the return address and push it in the stack of return addrs
1017  * in current thread info.
1018  */
1019 void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
1020                            unsigned long frame_pointer)
1021 {
1022         unsigned long old;
1023         int faulted;
1024         unsigned long return_hooker = (unsigned long)
1025                                 &return_to_handler;
1026 
1027         /*
1028          * When resuming from suspend-to-ram, this function can be indirectly
1029          * called from early CPU startup code while the CPU is in real mode,
1030          * which would fail miserably.  Make sure the stack pointer is a
1031          * virtual address.
1032          *
1033          * This check isn't as accurate as virt_addr_valid(), but it should be
1034          * good enough for this purpose, and it's fast.
1035          */
1036         if (unlikely((long)__builtin_frame_address(0) >= 0))
1037                 return;
1038 
1039         if (unlikely(ftrace_graph_is_dead()))
1040                 return;
1041 
1042         if (unlikely(atomic_read(&current->tracing_graph_pause)))
1043                 return;
1044 
1045         /*
1046          * Protect against fault, even if it shouldn't
1047          * happen. This tool is too much intrusive to
1048          * ignore such a protection.
1049          */
1050         asm volatile(
1051                 "1: " _ASM_MOV " (%[parent]), %[old]\n"
1052                 "2: " _ASM_MOV " %[return_hooker], (%[parent])\n"
1053                 "   movl $0, %[faulted]\n"
1054                 "3:\n"
1055 
1056                 ".section .fixup, \"ax\"\n"
1057                 "4: movl $1, %[faulted]\n"
1058                 "   jmp 3b\n"
1059                 ".previous\n"
1060 
1061                 _ASM_EXTABLE(1b, 4b)
1062                 _ASM_EXTABLE(2b, 4b)
1063 
1064                 : [old] "=&r" (old), [faulted] "=r" (faulted)
1065                 : [parent] "r" (parent), [return_hooker] "r" (return_hooker)
1066                 : "memory"
1067         );
1068 
1069         if (unlikely(faulted)) {
1070                 ftrace_graph_stop();
1071                 WARN_ON(1);
1072                 return;
1073         }
1074 
1075         if (function_graph_enter(old, self_addr, frame_pointer, parent))
1076                 *parent = old;
1077 }
1078 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
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root/arch/x86/kernel/ftrace.c

DEFINITIONS
