arch/x86/kernel/kprobes/opt.c

   1 /*
   2  *  Kernel Probes Jump Optimization (Optprobes)
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  17  *
  18  * Copyright (C) IBM Corporation, 2002, 2004
  19  * Copyright (C) Hitachi Ltd., 2012
  20  */
  21 #include <linux/kprobes.h>
  22 #include <linux/ptrace.h>
  23 #include <linux/string.h>
  24 #include <linux/slab.h>
  25 #include <linux/hardirq.h>
  26 #include <linux/preempt.h>
  27 #include <linux/extable.h>
  28 #include <linux/kdebug.h>
  29 #include <linux/kallsyms.h>
  30 #include <linux/ftrace.h>
  31 #include <linux/frame.h>
  32
  33 #include <asm/text-patching.h>
  34 #include <asm/cacheflush.h>
  35 #include <asm/desc.h>
  36 #include <asm/pgtable.h>
  37 #include <linux/uaccess.h>
  38 #include <asm/alternative.h>
  39 #include <asm/insn.h>
  40 #include <asm/debugreg.h>
  41 #include <asm/set_memory.h>
  42 #include <asm/sections.h>
  43 #include <asm/nospec-branch.h>
  44
  45 #include "common.h"
  46
  47 unsigned long __recover_optprobed_insn(kprobe_opcode_t *buf, unsigned long addr)
  48 {
  49         struct optimized_kprobe *op;
  50         struct kprobe *kp;
  51         long offs;
  52         int i;
  53
  54         for (i = 0; i < RELATIVEJUMP_SIZE; i++) {
  55                 kp = get_kprobe((void *)addr - i);
  56                 /* This function only handles jump-optimized kprobe */
  57                 if (kp && kprobe_optimized(kp)) {
  58                         op = container_of(kp, struct optimized_kprobe, kp);
  59                         /* If op->list is not empty, op is under optimizing */
  60                         if (list_empty(&op->list))
  61                                 goto found;
  62                 }
  63         }
  64
  65         return addr;
  66 found:
  67         /*
  68          * If the kprobe can be optimized, original bytes which can be
  69          * overwritten by jump destination address. In this case, original
  70          * bytes must be recovered from op->optinsn.copied_insn buffer.
  71          */
  72         if (probe_kernel_read(buf, (void *)addr,
  73                 MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
  74                 return 0UL;
  75
  76         if (addr == (unsigned long)kp->addr) {
  77                 buf[0] = kp->opcode;
  78                 memcpy(buf + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE);
  79         } else {
  80                 offs = addr - (unsigned long)kp->addr - 1;
  81                 memcpy(buf, op->optinsn.copied_insn + offs, RELATIVE_ADDR_SIZE - offs);
  82         }
  83
  84         return (unsigned long)buf;
  85 }
  86
  87 /* Insert a move instruction which sets a pointer to eax/rdi (1st arg). */
  88 static void synthesize_set_arg1(kprobe_opcode_t *addr, unsigned long val)
  89 {
  90 #ifdef CONFIG_X86_64
  91         *addr++ = 0x48;
  92         *addr++ = 0xbf;
  93 #else
  94         *addr++ = 0xb8;
  95 #endif
  96         *(unsigned long *)addr = val;
  97 }
  98
  99 asm (
 100                         "optprobe_template_func:\n"
 101                         ".global optprobe_template_entry\n"
 102                         "optprobe_template_entry:\n"
 103 #ifdef CONFIG_X86_64
 104                         /* We don't bother saving the ss register */
 105                         "       pushq %rsp\n"
 106                         "       pushfq\n"
 107                         SAVE_REGS_STRING
 108                         "       movq %rsp, %rsi\n"
 109                         ".global optprobe_template_val\n"
 110                         "optprobe_template_val:\n"
 111                         ASM_NOP5
 112                         ASM_NOP5
 113                         ".global optprobe_template_call\n"
 114                         "optprobe_template_call:\n"
 115                         ASM_NOP5
 116                         /* Move flags to rsp */
 117                         "       movq 144(%rsp), %rdx\n"
 118                         "       movq %rdx, 152(%rsp)\n"
 119                         RESTORE_REGS_STRING
 120                         /* Skip flags entry */
 121                         "       addq $8, %rsp\n"
 122                         "       popfq\n"
 123 #else /* CONFIG_X86_32 */
 124                         "       pushf\n"
 125                         SAVE_REGS_STRING
 126                         "       movl %esp, %edx\n"
 127                         ".global optprobe_template_val\n"
 128                         "optprobe_template_val:\n"
 129                         ASM_NOP5
 130                         ".global optprobe_template_call\n"
 131                         "optprobe_template_call:\n"
 132                         ASM_NOP5
 133                         RESTORE_REGS_STRING
 134                         "       addl $4, %esp\n"        /* skip cs */
 135                         "       popf\n"
 136 #endif
 137                         ".global optprobe_template_end\n"
 138                         "optprobe_template_end:\n"
 139                         ".type optprobe_template_func, @function\n"
 140                         ".size optprobe_template_func, .-optprobe_template_func\n");
 141
 142 void optprobe_template_func(void);
 143 STACK_FRAME_NON_STANDARD(optprobe_template_func);
 144
 145 #define TMPL_MOVE_IDX \
 146         ((long)optprobe_template_val - (long)optprobe_template_entry)
 147 #define TMPL_CALL_IDX \
 148         ((long)optprobe_template_call - (long)optprobe_template_entry)
 149 #define TMPL_END_IDX \
 150         ((long)optprobe_template_end - (long)optprobe_template_entry)
 151
 152 #define INT3_SIZE sizeof(kprobe_opcode_t)
 153
 154 /* Optimized kprobe call back function: called from optinsn */
 155 static void
 156 optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
 157 {
 158         /* This is possible if op is under delayed unoptimizing */
 159         if (kprobe_disabled(&op->kp))
 160                 return;
 161
 162         preempt_disable();
 163         if (kprobe_running()) {
 164                 kprobes_inc_nmissed_count(&op->kp);
 165         } else {
 166                 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 167                 /* Save skipped registers */
 168 #ifdef CONFIG_X86_64
 169                 regs->cs = __KERNEL_CS;
 170 #else
 171                 regs->cs = __KERNEL_CS | get_kernel_rpl();
 172                 regs->gs = 0;
 173 #endif
 174                 regs->ip = (unsigned long)op->kp.addr + INT3_SIZE;
 175                 regs->orig_ax = ~0UL;
 176
 177                 __this_cpu_write(current_kprobe, &op->kp);
 178                 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 179                 opt_pre_handler(&op->kp, regs);
 180                 __this_cpu_write(current_kprobe, NULL);
 181         }
 182         preempt_enable();
 183 }
 184 NOKPROBE_SYMBOL(optimized_callback);
 185
 186 static int copy_optimized_instructions(u8 *dest, u8 *src, u8 *real)
 187 {
 188         struct insn insn;
 189         int len = 0, ret;
 190
 191         while (len < RELATIVEJUMP_SIZE) {
 192                 ret = __copy_instruction(dest + len, src + len, real, &insn);
 193                 if (!ret || !can_boost(&insn, src + len))
 194                         return -EINVAL;
 195                 len += ret;
 196         }
 197         /* Check whether the address range is reserved */
 198         if (ftrace_text_reserved(src, src + len - 1) ||
 199             alternatives_text_reserved(src, src + len - 1) ||
 200             jump_label_text_reserved(src, src + len - 1))
 201                 return -EBUSY;
 202
 203         return len;
 204 }
 205
 206 /* Check whether insn is indirect jump */
 207 static int __insn_is_indirect_jump(struct insn *insn)
 208 {
 209         return ((insn->opcode.bytes[0] == 0xff &&
 210                 (X86_MODRM_REG(insn->modrm.value) & 6) == 4) || /* Jump */
 211                 insn->opcode.bytes[0] == 0xea); /* Segment based jump */
 212 }
 213
 214 /* Check whether insn jumps into specified address range */
 215 static int insn_jump_into_range(struct insn *insn, unsigned long start, int len)
 216 {
 217         unsigned long target = 0;
 218
 219         switch (insn->opcode.bytes[0]) {
 220         case 0xe0:      /* loopne */
 221         case 0xe1:      /* loope */
 222         case 0xe2:      /* loop */
 223         case 0xe3:      /* jcxz */
 224         case 0xe9:      /* near relative jump */
 225         case 0xeb:      /* short relative jump */
 226                 break;
 227         case 0x0f:
 228                 if ((insn->opcode.bytes[1] & 0xf0) == 0x80) /* jcc near */
 229                         break;
 230                 return 0;
 231         default:
 232                 if ((insn->opcode.bytes[0] & 0xf0) == 0x70) /* jcc short */
 233                         break;
 234                 return 0;
 235         }
 236         target = (unsigned long)insn->next_byte + insn->immediate.value;
 237
 238         return (start <= target && target <= start + len);
 239 }
 240
 241 static int insn_is_indirect_jump(struct insn *insn)
 242 {
 243         int ret = __insn_is_indirect_jump(insn);
 244
 245 #ifdef CONFIG_RETPOLINE
 246         /*
 247          * Jump to x86_indirect_thunk_* is treated as an indirect jump.
 248          * Note that even with CONFIG_RETPOLINE=y, the kernel compiled with
 249          * older gcc may use indirect jump. So we add this check instead of
 250          * replace indirect-jump check.
 251          */
 252         if (!ret)
 253                 ret = insn_jump_into_range(insn,
 254                                 (unsigned long)__indirect_thunk_start,
 255                                 (unsigned long)__indirect_thunk_end -
 256                                 (unsigned long)__indirect_thunk_start);
 257 #endif
 258         return ret;
 259 }
 260
 261 /* Decode whole function to ensure any instructions don't jump into target */
 262 static int can_optimize(unsigned long paddr)
 263 {
 264         unsigned long addr, size = 0, offset = 0;
 265         struct insn insn;
 266         kprobe_opcode_t buf[MAX_INSN_SIZE];
 267
 268         /* Lookup symbol including addr */
 269         if (!kallsyms_lookup_size_offset(paddr, &size, &offset))
 270                 return 0;
 271
 272         /*
 273          * Do not optimize in the entry code due to the unstable
 274          * stack handling and registers setup.
 275          */
 276         if (((paddr >= (unsigned long)__entry_text_start) &&
 277              (paddr <  (unsigned long)__entry_text_end)) ||
 278             ((paddr >= (unsigned long)__irqentry_text_start) &&
 279              (paddr <  (unsigned long)__irqentry_text_end)))
 280                 return 0;
 281
 282         /* Check there is enough space for a relative jump. */
 283         if (size - offset < RELATIVEJUMP_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                 if (search_exception_tables(addr))
 291                         /*
 292                          * Since some fixup code will jumps into this function,
 293                          * we can't optimize kprobe in this function.
 294                          */
 295                         return 0;
 296                 recovered_insn = recover_probed_instruction(buf, addr);
 297                 if (!recovered_insn)
 298                         return 0;
 299                 kernel_insn_init(&insn, (void *)recovered_insn, MAX_INSN_SIZE);
 300                 insn_get_length(&insn);
 301                 /* Another subsystem puts a breakpoint */
 302                 if (insn.opcode.bytes[0] == BREAKPOINT_INSTRUCTION)
 303                         return 0;
 304                 /* Recover address */
 305                 insn.kaddr = (void *)addr;
 306                 insn.next_byte = (void *)(addr + insn.length);
 307                 /* Check any instructions don't jump into target */
 308                 if (insn_is_indirect_jump(&insn) ||
 309                     insn_jump_into_range(&insn, paddr + INT3_SIZE,
 310                                          RELATIVE_ADDR_SIZE))
 311                         return 0;
 312                 addr += insn.length;
 313         }
 314
 315         return 1;
 316 }
 317
 318 /* Check optimized_kprobe can actually be optimized. */
 319 int arch_check_optimized_kprobe(struct optimized_kprobe *op)
 320 {
 321         int i;
 322         struct kprobe *p;
 323
 324         for (i = 1; i < op->optinsn.size; i++) {
 325                 p = get_kprobe(op->kp.addr + i);
 326                 if (p && !kprobe_disabled(p))
 327                         return -EEXIST;
 328         }
 329
 330         return 0;
 331 }
 332
 333 /* Check the addr is within the optimized instructions. */
 334 int arch_within_optimized_kprobe(struct optimized_kprobe *op,
 335                                  unsigned long addr)
 336 {
 337         return ((unsigned long)op->kp.addr <= addr &&
 338                 (unsigned long)op->kp.addr + op->optinsn.size > addr);
 339 }
 340
 341 /* Free optimized instruction slot */
 342 static
 343 void __arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
 344 {
 345         if (op->optinsn.insn) {
 346                 free_optinsn_slot(op->optinsn.insn, dirty);
 347                 op->optinsn.insn = NULL;
 348                 op->optinsn.size = 0;
 349         }
 350 }
 351
 352 void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
 353 {
 354         __arch_remove_optimized_kprobe(op, 1);
 355 }
 356
 357 /*
 358  * Copy replacing target instructions
 359  * Target instructions MUST be relocatable (checked inside)
 360  * This is called when new aggr(opt)probe is allocated or reused.
 361  */
 362 int arch_prepare_optimized_kprobe(struct optimized_kprobe *op,
 363                                   struct kprobe *__unused)
 364 {
 365         u8 *buf = NULL, *slot;
 366         int ret, len;
 367         long rel;
 368
 369         if (!can_optimize((unsigned long)op->kp.addr))
 370                 return -EILSEQ;
 371
 372         buf = kzalloc(MAX_OPTINSN_SIZE, GFP_KERNEL);
 373         if (!buf)
 374                 return -ENOMEM;
 375
 376         op->optinsn.insn = slot = get_optinsn_slot();
 377         if (!slot) {
 378                 ret = -ENOMEM;
 379                 goto out;
 380         }
 381
 382         /*
 383          * Verify if the address gap is in 2GB range, because this uses
 384          * a relative jump.
 385          */
 386         rel = (long)slot - (long)op->kp.addr + RELATIVEJUMP_SIZE;
 387         if (abs(rel) > 0x7fffffff) {
 388                 ret = -ERANGE;
 389                 goto err;
 390         }
 391
 392         /* Copy arch-dep-instance from template */
 393         memcpy(buf, optprobe_template_entry, TMPL_END_IDX);
 394
 395         /* Copy instructions into the out-of-line buffer */
 396         ret = copy_optimized_instructions(buf + TMPL_END_IDX, op->kp.addr,
 397                                           slot + TMPL_END_IDX);
 398         if (ret < 0)
 399                 goto err;
 400         op->optinsn.size = ret;
 401         len = TMPL_END_IDX + op->optinsn.size;
 402
 403         /* Set probe information */
 404         synthesize_set_arg1(buf + TMPL_MOVE_IDX, (unsigned long)op);
 405
 406         /* Set probe function call */
 407         synthesize_relcall(buf + TMPL_CALL_IDX,
 408                            slot + TMPL_CALL_IDX, optimized_callback);
 409
 410         /* Set returning jmp instruction at the tail of out-of-line buffer */
 411         synthesize_reljump(buf + len, slot + len,
 412                            (u8 *)op->kp.addr + op->optinsn.size);
 413         len += RELATIVEJUMP_SIZE;
 414
 415         /* We have to use text_poke for instuction buffer because it is RO */
 416         text_poke(slot, buf, len);
 417         ret = 0;
 418 out:
 419         kfree(buf);
 420         return ret;
 421
 422 err:
 423         __arch_remove_optimized_kprobe(op, 0);
 424         goto out;
 425 }
 426
 427 /*
 428  * Replace breakpoints (int3) with relative jumps.
 429  * Caller must call with locking kprobe_mutex and text_mutex.
 430  */
 431 void arch_optimize_kprobes(struct list_head *oplist)
 432 {
 433         struct optimized_kprobe *op, *tmp;
 434         u8 insn_buf[RELATIVEJUMP_SIZE];
 435
 436         list_for_each_entry_safe(op, tmp, oplist, list) {
 437                 s32 rel = (s32)((long)op->optinsn.insn -
 438                         ((long)op->kp.addr + RELATIVEJUMP_SIZE));
 439
 440                 WARN_ON(kprobe_disabled(&op->kp));
 441
 442                 /* Backup instructions which will be replaced by jump address */
 443                 memcpy(op->optinsn.copied_insn, op->kp.addr + INT3_SIZE,
 444                        RELATIVE_ADDR_SIZE);
 445
 446                 insn_buf[0] = RELATIVEJUMP_OPCODE;
 447                 *(s32 *)(&insn_buf[1]) = rel;
 448
 449                 text_poke_bp(op->kp.addr, insn_buf, RELATIVEJUMP_SIZE,
 450                              op->optinsn.insn);
 451
 452                 list_del_init(&op->list);
 453         }
 454 }
 455
 456 /* Replace a relative jump with a breakpoint (int3).  */
 457 void arch_unoptimize_kprobe(struct optimized_kprobe *op)
 458 {
 459         u8 insn_buf[RELATIVEJUMP_SIZE];
 460
 461         /* Set int3 to first byte for kprobes */
 462         insn_buf[0] = BREAKPOINT_INSTRUCTION;
 463         memcpy(insn_buf + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE);
 464         text_poke_bp(op->kp.addr, insn_buf, RELATIVEJUMP_SIZE,
 465                      op->optinsn.insn);
 466 }
 467
 468 /*
 469  * Recover original instructions and breakpoints from relative jumps.
 470  * Caller must call with locking kprobe_mutex.
 471  */
 472 extern void arch_unoptimize_kprobes(struct list_head *oplist,
 473                                     struct list_head *done_list)
 474 {
 475         struct optimized_kprobe *op, *tmp;
 476
 477         list_for_each_entry_safe(op, tmp, oplist, list) {
 478                 arch_unoptimize_kprobe(op);
 479                 list_move(&op->list, done_list);
 480         }
 481 }
 482
 483 int setup_detour_execution(struct kprobe *p, struct pt_regs *regs, int reenter)
 484 {
 485         struct optimized_kprobe *op;
 486
 487         if (p->flags & KPROBE_FLAG_OPTIMIZED) {
 488                 /* This kprobe is really able to run optimized path. */
 489                 op = container_of(p, struct optimized_kprobe, kp);
 490                 /* Detour through copied instructions */
 491                 regs->ip = (unsigned long)op->optinsn.insn + TMPL_END_IDX;
 492                 if (!reenter)
 493                         reset_current_kprobe();
 494                 return 1;
 495         }
 496         return 0;
 497 }
 498 NOKPROBE_SYMBOL(setup_detour_execution);