arch/x86/kernel/kprobes/opt.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  *  Kernel Probes Jump Optimization (Optprobes)
   4  *
   5  * Copyright (C) IBM Corporation, 2002, 2004
   6  * Copyright (C) Hitachi Ltd., 2012
   7  */
   8 #include <linux/kprobes.h>
   9 #include <linux/perf_event.h>
  10 #include <linux/ptrace.h>
  11 #include <linux/string.h>
  12 #include <linux/slab.h>
  13 #include <linux/hardirq.h>
  14 #include <linux/preempt.h>
  15 #include <linux/extable.h>
  16 #include <linux/kdebug.h>
  17 #include <linux/kallsyms.h>
  18 #include <linux/kgdb.h>
  19 #include <linux/ftrace.h>
  20 #include <linux/objtool.h>
  21 #include <linux/pgtable.h>
  22 #include <linux/static_call.h>
  23
  24 #include <asm/text-patching.h>
  25 #include <asm/cacheflush.h>
  26 #include <asm/desc.h>
  27 #include <linux/uaccess.h>
  28 #include <asm/alternative.h>
  29 #include <asm/insn.h>
  30 #include <asm/debugreg.h>
  31 #include <asm/set_memory.h>
  32 #include <asm/sections.h>
  33 #include <asm/nospec-branch.h>
  34
  35 #include "common.h"
  36
  37 unsigned long __recover_optprobed_insn(kprobe_opcode_t *buf, unsigned long addr)
  38 {
  39         struct optimized_kprobe *op;
  40         struct kprobe *kp;
  41         long offs;
  42         int i;
  43
  44         for (i = 0; i < JMP32_INSN_SIZE; i++) {
  45                 kp = get_kprobe((void *)addr - i);
  46                 /* This function only handles jump-optimized kprobe */
  47                 if (kp && kprobe_optimized(kp)) {
  48                         op = container_of(kp, struct optimized_kprobe, kp);
  49                         /* If op is optimized or under unoptimizing */
  50                         if (list_empty(&op->list) || optprobe_queued_unopt(op))
  51                                 goto found;
  52                 }
  53         }
  54
  55         return addr;
  56 found:
  57         /*
  58          * If the kprobe can be optimized, original bytes which can be
  59          * overwritten by jump destination address. In this case, original
  60          * bytes must be recovered from op->optinsn.copied_insn buffer.
  61          */
  62         if (copy_from_kernel_nofault(buf, (void *)addr,
  63                 MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
  64                 return 0UL;
  65
  66         if (addr == (unsigned long)kp->addr) {
  67                 buf[0] = kp->opcode;
  68                 memcpy(buf + 1, op->optinsn.copied_insn, DISP32_SIZE);
  69         } else {
  70                 offs = addr - (unsigned long)kp->addr - 1;
  71                 memcpy(buf, op->optinsn.copied_insn + offs, DISP32_SIZE - offs);
  72         }
  73
  74         return (unsigned long)buf;
  75 }
  76
  77 static void synthesize_clac(kprobe_opcode_t *addr)
  78 {
  79         /*
  80          * Can't be static_cpu_has() due to how objtool treats this feature bit.
  81          * This isn't a fast path anyway.
  82          */
  83         if (!boot_cpu_has(X86_FEATURE_SMAP))
  84                 return;
  85
  86         /* Replace the NOP3 with CLAC */
  87         addr[0] = 0x0f;
  88         addr[1] = 0x01;
  89         addr[2] = 0xca;
  90 }
  91
  92 /* Insert a move instruction which sets a pointer to eax/rdi (1st arg). */
  93 static void synthesize_set_arg1(kprobe_opcode_t *addr, unsigned long val)
  94 {
  95 #ifdef CONFIG_X86_64
  96         *addr++ = 0x48;
  97         *addr++ = 0xbf;
  98 #else
  99         *addr++ = 0xb8;
 100 #endif
 101         *(unsigned long *)addr = val;
 102 }
 103
 104 asm (
 105                         ".pushsection .rodata\n"
 106                         "optprobe_template_func:\n"
 107                         ".global optprobe_template_entry\n"
 108                         "optprobe_template_entry:\n"
 109 #ifdef CONFIG_X86_64
 110                         /* We don't bother saving the ss register */
 111                         "       pushq %rsp\n"
 112                         "       pushfq\n"
 113                         ".global optprobe_template_clac\n"
 114                         "optprobe_template_clac:\n"
 115                         ASM_NOP3
 116                         SAVE_REGS_STRING
 117                         "       movq %rsp, %rsi\n"
 118                         ".global optprobe_template_val\n"
 119                         "optprobe_template_val:\n"
 120                         ASM_NOP5
 121                         ASM_NOP5
 122                         ".global optprobe_template_call\n"
 123                         "optprobe_template_call:\n"
 124                         ASM_NOP5
 125                         /* Move flags to rsp */
 126                         "       movq 18*8(%rsp), %rdx\n"
 127                         "       movq %rdx, 19*8(%rsp)\n"
 128                         RESTORE_REGS_STRING
 129                         /* Skip flags entry */
 130                         "       addq $8, %rsp\n"
 131                         "       popfq\n"
 132 #else /* CONFIG_X86_32 */
 133                         "       pushl %esp\n"
 134                         "       pushfl\n"
 135                         ".global optprobe_template_clac\n"
 136                         "optprobe_template_clac:\n"
 137                         ASM_NOP3
 138                         SAVE_REGS_STRING
 139                         "       movl %esp, %edx\n"
 140                         ".global optprobe_template_val\n"
 141                         "optprobe_template_val:\n"
 142                         ASM_NOP5
 143                         ".global optprobe_template_call\n"
 144                         "optprobe_template_call:\n"
 145                         ASM_NOP5
 146                         /* Move flags into esp */
 147                         "       movl 14*4(%esp), %edx\n"
 148                         "       movl %edx, 15*4(%esp)\n"
 149                         RESTORE_REGS_STRING
 150                         /* Skip flags entry */
 151                         "       addl $4, %esp\n"
 152                         "       popfl\n"
 153 #endif
 154                         ".global optprobe_template_end\n"
 155                         "optprobe_template_end:\n"
 156                         ".popsection\n");
 157
 158 void optprobe_template_func(void);
 159 STACK_FRAME_NON_STANDARD(optprobe_template_func);
 160
 161 #define TMPL_CLAC_IDX \
 162         ((long)optprobe_template_clac - (long)optprobe_template_entry)
 163 #define TMPL_MOVE_IDX \
 164         ((long)optprobe_template_val - (long)optprobe_template_entry)
 165 #define TMPL_CALL_IDX \
 166         ((long)optprobe_template_call - (long)optprobe_template_entry)
 167 #define TMPL_END_IDX \
 168         ((long)optprobe_template_end - (long)optprobe_template_entry)
 169
 170 /* Optimized kprobe call back function: called from optinsn */
 171 static void
 172 optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
 173 {
 174         /* This is possible if op is under delayed unoptimizing */
 175         if (kprobe_disabled(&op->kp))
 176                 return;
 177
 178         preempt_disable();
 179         if (kprobe_running()) {
 180                 kprobes_inc_nmissed_count(&op->kp);
 181         } else {
 182                 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 183                 /* Save skipped registers */
 184                 regs->cs = __KERNEL_CS;
 185 #ifdef CONFIG_X86_32
 186                 regs->gs = 0;
 187 #endif
 188                 regs->ip = (unsigned long)op->kp.addr + INT3_INSN_SIZE;
 189                 regs->orig_ax = ~0UL;
 190
 191                 __this_cpu_write(current_kprobe, &op->kp);
 192                 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 193                 opt_pre_handler(&op->kp, regs);
 194                 __this_cpu_write(current_kprobe, NULL);
 195         }
 196         preempt_enable();
 197 }
 198 NOKPROBE_SYMBOL(optimized_callback);
 199
 200 static int copy_optimized_instructions(u8 *dest, u8 *src, u8 *real)
 201 {
 202         struct insn insn;
 203         int len = 0, ret;
 204
 205         while (len < JMP32_INSN_SIZE) {
 206                 ret = __copy_instruction(dest + len, src + len, real + len, &insn);
 207                 if (!ret || !can_boost(&insn, src + len))
 208                         return -EINVAL;
 209                 len += ret;
 210         }
 211         /* Check whether the address range is reserved */
 212         if (ftrace_text_reserved(src, src + len - 1) ||
 213             alternatives_text_reserved(src, src + len - 1) ||
 214             jump_label_text_reserved(src, src + len - 1) ||
 215             static_call_text_reserved(src, src + len - 1))
 216                 return -EBUSY;
 217
 218         return len;
 219 }
 220
 221 /* Check whether insn is indirect jump */
 222 static int __insn_is_indirect_jump(struct insn *insn)
 223 {
 224         return ((insn->opcode.bytes[0] == 0xff &&
 225                 (X86_MODRM_REG(insn->modrm.value) & 6) == 4) || /* Jump */
 226                 insn->opcode.bytes[0] == 0xea); /* Segment based jump */
 227 }
 228
 229 /* Check whether insn jumps into specified address range */
 230 static int insn_jump_into_range(struct insn *insn, unsigned long start, int len)
 231 {
 232         unsigned long target = 0;
 233
 234         switch (insn->opcode.bytes[0]) {
 235         case 0xe0:      /* loopne */
 236         case 0xe1:      /* loope */
 237         case 0xe2:      /* loop */
 238         case 0xe3:      /* jcxz */
 239         case 0xe9:      /* near relative jump */
 240         case 0xeb:      /* short relative jump */
 241                 break;
 242         case 0x0f:
 243                 if ((insn->opcode.bytes[1] & 0xf0) == 0x80) /* jcc near */
 244                         break;
 245                 return 0;
 246         default:
 247                 if ((insn->opcode.bytes[0] & 0xf0) == 0x70) /* jcc short */
 248                         break;
 249                 return 0;
 250         }
 251         target = (unsigned long)insn->next_byte + insn->immediate.value;
 252
 253         return (start <= target && target <= start + len);
 254 }
 255
 256 static int insn_is_indirect_jump(struct insn *insn)
 257 {
 258         int ret = __insn_is_indirect_jump(insn);
 259
 260 #ifdef CONFIG_RETPOLINE
 261         /*
 262          * Jump to x86_indirect_thunk_* is treated as an indirect jump.
 263          * Note that even with CONFIG_RETPOLINE=y, the kernel compiled with
 264          * older gcc may use indirect jump. So we add this check instead of
 265          * replace indirect-jump check.
 266          */
 267         if (!ret)
 268                 ret = insn_jump_into_range(insn,
 269                                 (unsigned long)__indirect_thunk_start,
 270                                 (unsigned long)__indirect_thunk_end -
 271                                 (unsigned long)__indirect_thunk_start);
 272 #endif
 273         return ret;
 274 }
 275
 276 /* Decode whole function to ensure any instructions don't jump into target */
 277 static int can_optimize(unsigned long paddr)
 278 {
 279         unsigned long addr, size = 0, offset = 0;
 280         struct insn insn;
 281         kprobe_opcode_t buf[MAX_INSN_SIZE];
 282
 283         /* Lookup symbol including addr */
 284         if (!kallsyms_lookup_size_offset(paddr, &size, &offset))
 285                 return 0;
 286
 287         /*
 288          * Do not optimize in the entry code due to the unstable
 289          * stack handling and registers setup.
 290          */
 291         if (((paddr >= (unsigned long)__entry_text_start) &&
 292              (paddr <  (unsigned long)__entry_text_end)))
 293                 return 0;
 294
 295         /* Check there is enough space for a relative jump. */
 296         if (size - offset < JMP32_INSN_SIZE)
 297                 return 0;
 298
 299         /* Decode instructions */
 300         addr = paddr - offset;
 301         while (addr < paddr - offset + size) { /* Decode until function end */
 302                 unsigned long recovered_insn;
 303                 int ret;
 304
 305                 if (search_exception_tables(addr))
 306                         /*
 307                          * Since some fixup code will jumps into this function,
 308                          * we can't optimize kprobe in this function.
 309                          */
 310                         return 0;
 311                 recovered_insn = recover_probed_instruction(buf, addr);
 312                 if (!recovered_insn)
 313                         return 0;
 314
 315                 ret = insn_decode_kernel(&insn, (void *)recovered_insn);
 316                 if (ret < 0)
 317                         return 0;
 318 #ifdef CONFIG_KGDB
 319                 /*
 320                  * If there is a dynamically installed kgdb sw breakpoint,
 321                  * this function should not be probed.
 322                  */
 323                 if (insn.opcode.bytes[0] == INT3_INSN_OPCODE &&
 324                     kgdb_has_hit_break(addr))
 325                         return 0;
 326 #endif
 327                 /* Recover address */
 328                 insn.kaddr = (void *)addr;
 329                 insn.next_byte = (void *)(addr + insn.length);
 330                 /* Check any instructions don't jump into target */
 331                 if (insn_is_indirect_jump(&insn) ||
 332                     insn_jump_into_range(&insn, paddr + INT3_INSN_SIZE,
 333                                          DISP32_SIZE))
 334                         return 0;
 335                 addr += insn.length;
 336         }
 337
 338         return 1;
 339 }
 340
 341 /* Check optimized_kprobe can actually be optimized. */
 342 int arch_check_optimized_kprobe(struct optimized_kprobe *op)
 343 {
 344         int i;
 345         struct kprobe *p;
 346
 347         for (i = 1; i < op->optinsn.size; i++) {
 348                 p = get_kprobe(op->kp.addr + i);
 349                 if (p && !kprobe_disarmed(p))
 350                         return -EEXIST;
 351         }
 352
 353         return 0;
 354 }
 355
 356 /* Check the addr is within the optimized instructions. */
 357 int arch_within_optimized_kprobe(struct optimized_kprobe *op,
 358                                  unsigned long addr)
 359 {
 360         return ((unsigned long)op->kp.addr <= addr &&
 361                 (unsigned long)op->kp.addr + op->optinsn.size > addr);
 362 }
 363
 364 /* Free optimized instruction slot */
 365 static
 366 void __arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
 367 {
 368         u8 *slot = op->optinsn.insn;
 369         if (slot) {
 370                 int len = TMPL_END_IDX + op->optinsn.size + JMP32_INSN_SIZE;
 371
 372                 /* Record the perf event before freeing the slot */
 373                 if (dirty)
 374                         perf_event_text_poke(slot, slot, len, NULL, 0);
 375
 376                 free_optinsn_slot(slot, dirty);
 377                 op->optinsn.insn = NULL;
 378                 op->optinsn.size = 0;
 379         }
 380 }
 381
 382 void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
 383 {
 384         __arch_remove_optimized_kprobe(op, 1);
 385 }
 386
 387 /*
 388  * Copy replacing target instructions
 389  * Target instructions MUST be relocatable (checked inside)
 390  * This is called when new aggr(opt)probe is allocated or reused.
 391  */
 392 int arch_prepare_optimized_kprobe(struct optimized_kprobe *op,
 393                                   struct kprobe *__unused)
 394 {
 395         u8 *buf = NULL, *slot;
 396         int ret, len;
 397         long rel;
 398
 399         if (!can_optimize((unsigned long)op->kp.addr))
 400                 return -EILSEQ;
 401
 402         buf = kzalloc(MAX_OPTINSN_SIZE, GFP_KERNEL);
 403         if (!buf)
 404                 return -ENOMEM;
 405
 406         op->optinsn.insn = slot = get_optinsn_slot();
 407         if (!slot) {
 408                 ret = -ENOMEM;
 409                 goto out;
 410         }
 411
 412         /*
 413          * Verify if the address gap is in 2GB range, because this uses
 414          * a relative jump.
 415          */
 416         rel = (long)slot - (long)op->kp.addr + JMP32_INSN_SIZE;
 417         if (abs(rel) > 0x7fffffff) {
 418                 ret = -ERANGE;
 419                 goto err;
 420         }
 421
 422         /* Copy arch-dep-instance from template */
 423         memcpy(buf, optprobe_template_entry, TMPL_END_IDX);
 424
 425         /* Copy instructions into the out-of-line buffer */
 426         ret = copy_optimized_instructions(buf + TMPL_END_IDX, op->kp.addr,
 427                                           slot + TMPL_END_IDX);
 428         if (ret < 0)
 429                 goto err;
 430         op->optinsn.size = ret;
 431         len = TMPL_END_IDX + op->optinsn.size;
 432
 433         synthesize_clac(buf + TMPL_CLAC_IDX);
 434
 435         /* Set probe information */
 436         synthesize_set_arg1(buf + TMPL_MOVE_IDX, (unsigned long)op);
 437
 438         /* Set probe function call */
 439         synthesize_relcall(buf + TMPL_CALL_IDX,
 440                            slot + TMPL_CALL_IDX, optimized_callback);
 441
 442         /* Set returning jmp instruction at the tail of out-of-line buffer */
 443         synthesize_reljump(buf + len, slot + len,
 444                            (u8 *)op->kp.addr + op->optinsn.size);
 445         len += JMP32_INSN_SIZE;
 446
 447         /*
 448          * Note len = TMPL_END_IDX + op->optinsn.size + JMP32_INSN_SIZE is also
 449          * used in __arch_remove_optimized_kprobe().
 450          */
 451
 452         /* We have to use text_poke() for instruction buffer because it is RO */
 453         perf_event_text_poke(slot, NULL, 0, buf, len);
 454         text_poke(slot, buf, len);
 455
 456         ret = 0;
 457 out:
 458         kfree(buf);
 459         return ret;
 460
 461 err:
 462         __arch_remove_optimized_kprobe(op, 0);
 463         goto out;
 464 }
 465
 466 /*
 467  * Replace breakpoints (INT3) with relative jumps (JMP.d32).
 468  * Caller must call with locking kprobe_mutex and text_mutex.
 469  *
 470  * The caller will have installed a regular kprobe and after that issued
 471  * syncrhonize_rcu_tasks(), this ensures that the instruction(s) that live in
 472  * the 4 bytes after the INT3 are unused and can now be overwritten.
 473  */
 474 void arch_optimize_kprobes(struct list_head *oplist)
 475 {
 476         struct optimized_kprobe *op, *tmp;
 477         u8 insn_buff[JMP32_INSN_SIZE];
 478
 479         list_for_each_entry_safe(op, tmp, oplist, list) {
 480                 s32 rel = (s32)((long)op->optinsn.insn -
 481                         ((long)op->kp.addr + JMP32_INSN_SIZE));
 482
 483                 WARN_ON(kprobe_disabled(&op->kp));
 484
 485                 /* Backup instructions which will be replaced by jump address */
 486                 memcpy(op->optinsn.copied_insn, op->kp.addr + INT3_INSN_SIZE,
 487                        DISP32_SIZE);
 488
 489                 insn_buff[0] = JMP32_INSN_OPCODE;
 490                 *(s32 *)(&insn_buff[1]) = rel;
 491
 492                 text_poke_bp(op->kp.addr, insn_buff, JMP32_INSN_SIZE, NULL);
 493
 494                 list_del_init(&op->list);
 495         }
 496 }
 497
 498 /*
 499  * Replace a relative jump (JMP.d32) with a breakpoint (INT3).
 500  *
 501  * After that, we can restore the 4 bytes after the INT3 to undo what
 502  * arch_optimize_kprobes() scribbled. This is safe since those bytes will be
 503  * unused once the INT3 lands.
 504  */
 505 void arch_unoptimize_kprobe(struct optimized_kprobe *op)
 506 {
 507         u8 new[JMP32_INSN_SIZE] = { INT3_INSN_OPCODE, };
 508         u8 old[JMP32_INSN_SIZE];
 509         u8 *addr = op->kp.addr;
 510
 511         memcpy(old, op->kp.addr, JMP32_INSN_SIZE);
 512         memcpy(new + INT3_INSN_SIZE,
 513                op->optinsn.copied_insn,
 514                JMP32_INSN_SIZE - INT3_INSN_SIZE);
 515
 516         text_poke(addr, new, INT3_INSN_SIZE);
 517         text_poke_sync();
 518         text_poke(addr + INT3_INSN_SIZE,
 519                   new + INT3_INSN_SIZE,
 520                   JMP32_INSN_SIZE - INT3_INSN_SIZE);
 521         text_poke_sync();
 522
 523         perf_event_text_poke(op->kp.addr, old, JMP32_INSN_SIZE, new, JMP32_INSN_SIZE);
 524 }
 525
 526 /*
 527  * Recover original instructions and breakpoints from relative jumps.
 528  * Caller must call with locking kprobe_mutex.
 529  */
 530 extern void arch_unoptimize_kprobes(struct list_head *oplist,
 531                                     struct list_head *done_list)
 532 {
 533         struct optimized_kprobe *op, *tmp;
 534
 535         list_for_each_entry_safe(op, tmp, oplist, list) {
 536                 arch_unoptimize_kprobe(op);
 537                 list_move(&op->list, done_list);
 538         }
 539 }
 540
 541 int setup_detour_execution(struct kprobe *p, struct pt_regs *regs, int reenter)
 542 {
 543         struct optimized_kprobe *op;
 544
 545         if (p->flags & KPROBE_FLAG_OPTIMIZED) {
 546                 /* This kprobe is really able to run optimized path. */
 547                 op = container_of(p, struct optimized_kprobe, kp);
 548                 /* Detour through copied instructions */
 549                 regs->ip = (unsigned long)op->optinsn.insn + TMPL_END_IDX;
 550                 if (!reenter)
 551                         reset_current_kprobe();
 552                 return 1;
 553         }
 554         return 0;
 555 }
 556 NOKPROBE_SYMBOL(setup_detour_execution);