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                         "       pushq $" __stringify(__KERNEL_DS) "\n"
 111                         /* Save the 'sp - 8', this will be fixed later. */
 112                         "       pushq %rsp\n"
 113                         "       pushfq\n"
 114                         ".global optprobe_template_clac\n"
 115                         "optprobe_template_clac:\n"
 116                         ASM_NOP3
 117                         SAVE_REGS_STRING
 118                         "       movq %rsp, %rsi\n"
 119                         ".global optprobe_template_val\n"
 120                         "optprobe_template_val:\n"
 121                         ASM_NOP5
 122                         ASM_NOP5
 123                         ".global optprobe_template_call\n"
 124                         "optprobe_template_call:\n"
 125                         ASM_NOP5
 126                         /* Copy 'regs->flags' into 'regs->ss'. */
 127                         "       movq 18*8(%rsp), %rdx\n"
 128                         "       movq %rdx, 20*8(%rsp)\n"
 129                         RESTORE_REGS_STRING
 130                         /* Skip 'regs->flags' and 'regs->sp'. */
 131                         "       addq $16, %rsp\n"
 132                         /* And pop flags register from 'regs->ss'. */
 133                         "       popfq\n"
 134 #else /* CONFIG_X86_32 */
 135                         "       pushl %ss\n"
 136                         /* Save the 'sp - 4', this will be fixed later. */
 137                         "       pushl %esp\n"
 138                         "       pushfl\n"
 139                         ".global optprobe_template_clac\n"
 140                         "optprobe_template_clac:\n"
 141                         ASM_NOP3
 142                         SAVE_REGS_STRING
 143                         "       movl %esp, %edx\n"
 144                         ".global optprobe_template_val\n"
 145                         "optprobe_template_val:\n"
 146                         ASM_NOP5
 147                         ".global optprobe_template_call\n"
 148                         "optprobe_template_call:\n"
 149                         ASM_NOP5
 150                         /* Copy 'regs->flags' into 'regs->ss'. */
 151                         "       movl 14*4(%esp), %edx\n"
 152                         "       movl %edx, 16*4(%esp)\n"
 153                         RESTORE_REGS_STRING
 154                         /* Skip 'regs->flags' and 'regs->sp'. */
 155                         "       addl $8, %esp\n"
 156                         /* And pop flags register from 'regs->ss'. */
 157                         "       popfl\n"
 158 #endif
 159                         ".global optprobe_template_end\n"
 160                         "optprobe_template_end:\n"
 161                         ".popsection\n");
 162
 163 void optprobe_template_func(void);
 164 STACK_FRAME_NON_STANDARD(optprobe_template_func);
 165
 166 #define TMPL_CLAC_IDX \
 167         ((long)optprobe_template_clac - (long)optprobe_template_entry)
 168 #define TMPL_MOVE_IDX \
 169         ((long)optprobe_template_val - (long)optprobe_template_entry)
 170 #define TMPL_CALL_IDX \
 171         ((long)optprobe_template_call - (long)optprobe_template_entry)
 172 #define TMPL_END_IDX \
 173         ((long)optprobe_template_end - (long)optprobe_template_entry)
 174
 175 /* Optimized kprobe call back function: called from optinsn */
 176 static void
 177 optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
 178 {
 179         /* This is possible if op is under delayed unoptimizing */
 180         if (kprobe_disabled(&op->kp))
 181                 return;
 182
 183         preempt_disable();
 184         if (kprobe_running()) {
 185                 kprobes_inc_nmissed_count(&op->kp);
 186         } else {
 187                 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 188                 /* Adjust stack pointer */
 189                 regs->sp += sizeof(long);
 190                 /* Save skipped registers */
 191                 regs->cs = __KERNEL_CS;
 192 #ifdef CONFIG_X86_32
 193                 regs->gs = 0;
 194 #endif
 195                 regs->ip = (unsigned long)op->kp.addr + INT3_INSN_SIZE;
 196                 regs->orig_ax = ~0UL;
 197
 198                 __this_cpu_write(current_kprobe, &op->kp);
 199                 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 200                 opt_pre_handler(&op->kp, regs);
 201                 __this_cpu_write(current_kprobe, NULL);
 202         }
 203         preempt_enable();
 204 }
 205 NOKPROBE_SYMBOL(optimized_callback);
 206
 207 static int copy_optimized_instructions(u8 *dest, u8 *src, u8 *real)
 208 {
 209         struct insn insn;
 210         int len = 0, ret;
 211
 212         while (len < JMP32_INSN_SIZE) {
 213                 ret = __copy_instruction(dest + len, src + len, real + len, &insn);
 214                 if (!ret || !can_boost(&insn, src + len))
 215                         return -EINVAL;
 216                 len += ret;
 217         }
 218         /* Check whether the address range is reserved */
 219         if (ftrace_text_reserved(src, src + len - 1) ||
 220             alternatives_text_reserved(src, src + len - 1) ||
 221             jump_label_text_reserved(src, src + len - 1) ||
 222             static_call_text_reserved(src, src + len - 1))
 223                 return -EBUSY;
 224
 225         return len;
 226 }
 227
 228 /* Check whether insn is indirect jump */
 229 static int insn_is_indirect_jump(struct insn *insn)
 230 {
 231         return ((insn->opcode.bytes[0] == 0xff &&
 232                 (X86_MODRM_REG(insn->modrm.value) & 6) == 4) || /* Jump */
 233                 insn->opcode.bytes[0] == 0xea); /* Segment based jump */
 234 }
 235
 236 /* Check whether insn jumps into specified address range */
 237 static int insn_jump_into_range(struct insn *insn, unsigned long start, int len)
 238 {
 239         unsigned long target = 0;
 240
 241         switch (insn->opcode.bytes[0]) {
 242         case 0xe0:      /* loopne */
 243         case 0xe1:      /* loope */
 244         case 0xe2:      /* loop */
 245         case 0xe3:      /* jcxz */
 246         case 0xe9:      /* near relative jump */
 247         case 0xeb:      /* short relative jump */
 248                 break;
 249         case 0x0f:
 250                 if ((insn->opcode.bytes[1] & 0xf0) == 0x80) /* jcc near */
 251                         break;
 252                 return 0;
 253         default:
 254                 if ((insn->opcode.bytes[0] & 0xf0) == 0x70) /* jcc short */
 255                         break;
 256                 return 0;
 257         }
 258         target = (unsigned long)insn->next_byte + insn->immediate.value;
 259
 260         return (start <= target && target <= start + len);
 261 }
 262
 263 /* Decode whole function to ensure any instructions don't jump into target */
 264 static int can_optimize(unsigned long paddr)
 265 {
 266         unsigned long addr, size = 0, offset = 0;
 267         struct insn insn;
 268         kprobe_opcode_t buf[MAX_INSN_SIZE];
 269
 270         /* Lookup symbol including addr */
 271         if (!kallsyms_lookup_size_offset(paddr, &size, &offset))
 272                 return 0;
 273
 274         /*
 275          * Do not optimize in the entry code due to the unstable
 276          * stack handling and registers setup.
 277          */
 278         if (((paddr >= (unsigned long)__entry_text_start) &&
 279              (paddr <  (unsigned long)__entry_text_end)))
 280                 return 0;
 281
 282         /* Check there is enough space for a relative jump. */
 283         if (size - offset < JMP32_INSN_SIZE)
 284                 return 0;
 285
 286         /* Decode instructions */
 287         addr = paddr - offset;
 288         while (addr < paddr - offset + size) { /* Decode until function end */
 289                 unsigned long recovered_insn;
 290                 int ret;
 291
 292                 if (search_exception_tables(addr))
 293                         /*
 294                          * Since some fixup code will jumps into this function,
 295                          * we can't optimize kprobe in this function.
 296                          */
 297                         return 0;
 298                 recovered_insn = recover_probed_instruction(buf, addr);
 299                 if (!recovered_insn)
 300                         return 0;
 301
 302                 ret = insn_decode_kernel(&insn, (void *)recovered_insn);
 303                 if (ret < 0)
 304                         return 0;
 305 #ifdef CONFIG_KGDB
 306                 /*
 307                  * If there is a dynamically installed kgdb sw breakpoint,
 308                  * this function should not be probed.
 309                  */
 310                 if (insn.opcode.bytes[0] == INT3_INSN_OPCODE &&
 311                     kgdb_has_hit_break(addr))
 312                         return 0;
 313 #endif
 314                 /* Recover address */
 315                 insn.kaddr = (void *)addr;
 316                 insn.next_byte = (void *)(addr + insn.length);
 317                 /*
 318                  * Check any instructions don't jump into target, indirectly or
 319                  * directly.
 320                  *
 321                  * The indirect case is present to handle a code with jump
 322                  * tables. When the kernel uses retpolines, the check should in
 323                  * theory additionally look for jumps to indirect thunks.
 324                  * However, the kernel built with retpolines or IBT has jump
 325                  * tables disabled so the check can be skipped altogether.
 326                  */
 327                 if (!IS_ENABLED(CONFIG_MITIGATION_RETPOLINE) &&
 328                     !IS_ENABLED(CONFIG_X86_KERNEL_IBT) &&
 329                     insn_is_indirect_jump(&insn))
 330                         return 0;
 331                 if (insn_jump_into_range(&insn, paddr + INT3_INSN_SIZE,
 332                                          DISP32_SIZE))
 333                         return 0;
 334                 addr += insn.length;
 335         }
 336
 337         return 1;
 338 }
 339
 340 /* Check optimized_kprobe can actually be optimized. */
 341 int arch_check_optimized_kprobe(struct optimized_kprobe *op)
 342 {
 343         int i;
 344         struct kprobe *p;
 345
 346         for (i = 1; i < op->optinsn.size; i++) {
 347                 p = get_kprobe(op->kp.addr + i);
 348                 if (p && !kprobe_disarmed(p))
 349                         return -EEXIST;
 350         }
 351
 352         return 0;
 353 }
 354
 355 /* Check the addr is within the optimized instructions. */
 356 int arch_within_optimized_kprobe(struct optimized_kprobe *op,
 357                                  kprobe_opcode_t *addr)
 358 {
 359         return (op->kp.addr <= addr &&
 360                 op->kp.addr + op->optinsn.size > addr);
 361 }
 362
 363 /* Free optimized instruction slot */
 364 static
 365 void __arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
 366 {
 367         u8 *slot = op->optinsn.insn;
 368         if (slot) {
 369                 int len = TMPL_END_IDX + op->optinsn.size + JMP32_INSN_SIZE;
 370
 371                 /* Record the perf event before freeing the slot */
 372                 if (dirty)
 373                         perf_event_text_poke(slot, slot, len, NULL, 0);
 374
 375                 free_optinsn_slot(slot, dirty);
 376                 op->optinsn.insn = NULL;
 377                 op->optinsn.size = 0;
 378         }
 379 }
 380
 381 void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
 382 {
 383         __arch_remove_optimized_kprobe(op, 1);
 384 }
 385
 386 /*
 387  * Copy replacing target instructions
 388  * Target instructions MUST be relocatable (checked inside)
 389  * This is called when new aggr(opt)probe is allocated or reused.
 390  */
 391 int arch_prepare_optimized_kprobe(struct optimized_kprobe *op,
 392                                   struct kprobe *__unused)
 393 {
 394         u8 *buf = NULL, *slot;
 395         int ret, len;
 396         long rel;
 397
 398         if (!can_optimize((unsigned long)op->kp.addr))
 399                 return -EILSEQ;
 400
 401         buf = kzalloc(MAX_OPTINSN_SIZE, GFP_KERNEL);
 402         if (!buf)
 403                 return -ENOMEM;
 404
 405         op->optinsn.insn = slot = get_optinsn_slot();
 406         if (!slot) {
 407                 ret = -ENOMEM;
 408                 goto out;
 409         }
 410
 411         /*
 412          * Verify if the address gap is in 2GB range, because this uses
 413          * a relative jump.
 414          */
 415         rel = (long)slot - (long)op->kp.addr + JMP32_INSN_SIZE;
 416         if (abs(rel) > 0x7fffffff) {
 417                 ret = -ERANGE;
 418                 goto err;
 419         }
 420
 421         /* Copy arch-dep-instance from template */
 422         memcpy(buf, optprobe_template_entry, TMPL_END_IDX);
 423
 424         /* Copy instructions into the out-of-line buffer */
 425         ret = copy_optimized_instructions(buf + TMPL_END_IDX, op->kp.addr,
 426                                           slot + TMPL_END_IDX);
 427         if (ret < 0)
 428                 goto err;
 429         op->optinsn.size = ret;
 430         len = TMPL_END_IDX + op->optinsn.size;
 431
 432         synthesize_clac(buf + TMPL_CLAC_IDX);
 433
 434         /* Set probe information */
 435         synthesize_set_arg1(buf + TMPL_MOVE_IDX, (unsigned long)op);
 436
 437         /* Set probe function call */
 438         synthesize_relcall(buf + TMPL_CALL_IDX,
 439                            slot + TMPL_CALL_IDX, optimized_callback);
 440
 441         /* Set returning jmp instruction at the tail of out-of-line buffer */
 442         synthesize_reljump(buf + len, slot + len,
 443                            (u8 *)op->kp.addr + op->optinsn.size);
 444         len += JMP32_INSN_SIZE;
 445
 446         /*
 447          * Note len = TMPL_END_IDX + op->optinsn.size + JMP32_INSN_SIZE is also
 448          * used in __arch_remove_optimized_kprobe().
 449          */
 450
 451         /* We have to use text_poke() for instruction buffer because it is RO */
 452         perf_event_text_poke(slot, NULL, 0, buf, len);
 453         text_poke(slot, buf, len);
 454
 455         ret = 0;
 456 out:
 457         kfree(buf);
 458         return ret;
 459
 460 err:
 461         __arch_remove_optimized_kprobe(op, 0);
 462         goto out;
 463 }
 464
 465 /*
 466  * Replace breakpoints (INT3) with relative jumps (JMP.d32).
 467  * Caller must call with locking kprobe_mutex and text_mutex.
 468  *
 469  * The caller will have installed a regular kprobe and after that issued
 470  * syncrhonize_rcu_tasks(), this ensures that the instruction(s) that live in
 471  * the 4 bytes after the INT3 are unused and can now be overwritten.
 472  */
 473 void arch_optimize_kprobes(struct list_head *oplist)
 474 {
 475         struct optimized_kprobe *op, *tmp;
 476         u8 insn_buff[JMP32_INSN_SIZE];
 477
 478         list_for_each_entry_safe(op, tmp, oplist, list) {
 479                 s32 rel = (s32)((long)op->optinsn.insn -
 480                         ((long)op->kp.addr + JMP32_INSN_SIZE));
 481
 482                 WARN_ON(kprobe_disabled(&op->kp));
 483
 484                 /* Backup instructions which will be replaced by jump address */
 485                 memcpy(op->optinsn.copied_insn, op->kp.addr + INT3_INSN_SIZE,
 486                        DISP32_SIZE);
 487
 488                 insn_buff[0] = JMP32_INSN_OPCODE;
 489                 *(s32 *)(&insn_buff[1]) = rel;
 490
 491                 text_poke_bp(op->kp.addr, insn_buff, JMP32_INSN_SIZE, NULL);
 492
 493                 list_del_init(&op->list);
 494         }
 495 }
 496
 497 /*
 498  * Replace a relative jump (JMP.d32) with a breakpoint (INT3).
 499  *
 500  * After that, we can restore the 4 bytes after the INT3 to undo what
 501  * arch_optimize_kprobes() scribbled. This is safe since those bytes will be
 502  * unused once the INT3 lands.
 503  */
 504 void arch_unoptimize_kprobe(struct optimized_kprobe *op)
 505 {
 506         u8 new[JMP32_INSN_SIZE] = { INT3_INSN_OPCODE, };
 507         u8 old[JMP32_INSN_SIZE];
 508         u8 *addr = op->kp.addr;
 509
 510         memcpy(old, op->kp.addr, JMP32_INSN_SIZE);
 511         memcpy(new + INT3_INSN_SIZE,
 512                op->optinsn.copied_insn,
 513                JMP32_INSN_SIZE - INT3_INSN_SIZE);
 514
 515         text_poke(addr, new, INT3_INSN_SIZE);
 516         text_poke_sync();
 517         text_poke(addr + INT3_INSN_SIZE,
 518                   new + INT3_INSN_SIZE,
 519                   JMP32_INSN_SIZE - INT3_INSN_SIZE);
 520         text_poke_sync();
 521
 522         perf_event_text_poke(op->kp.addr, old, JMP32_INSN_SIZE, new, JMP32_INSN_SIZE);
 523 }
 524
 525 /*
 526  * Recover original instructions and breakpoints from relative jumps.
 527  * Caller must call with locking kprobe_mutex.
 528  */
 529 extern void arch_unoptimize_kprobes(struct list_head *oplist,
 530                                     struct list_head *done_list)
 531 {
 532         struct optimized_kprobe *op, *tmp;
 533
 534         list_for_each_entry_safe(op, tmp, oplist, list) {
 535                 arch_unoptimize_kprobe(op);
 536                 list_move(&op->list, done_list);
 537         }
 538 }
 539
 540 int setup_detour_execution(struct kprobe *p, struct pt_regs *regs, int reenter)
 541 {
 542         struct optimized_kprobe *op;
 543
 544         if (p->flags & KPROBE_FLAG_OPTIMIZED) {
 545                 /* This kprobe is really able to run optimized path. */
 546                 op = container_of(p, struct optimized_kprobe, kp);
 547                 /* Detour through copied instructions */
 548                 regs->ip = (unsigned long)op->optinsn.insn + TMPL_END_IDX;
 549                 if (!reenter)
 550                         reset_current_kprobe();
 551                 return 1;
 552         }
 553         return 0;
 554 }
 555 NOKPROBE_SYMBOL(setup_detour_execution);