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