arch/x86_64/kernel/kprobes.c

   1 /*
   2  *  Kernel Probes (KProbes)
   3  *  arch/x86_64/kernel/kprobes.c
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program; if not, write to the Free Software
  17  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  18  *
  19  * Copyright (C) IBM Corporation, 2002, 2004
  20  *
  21  * 2002-Oct     Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
  22  *              Probes initial implementation ( includes contributions from
  23  *              Rusty Russell).
  24  * 2004-July    Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
  25  *              interface to access function arguments.
  26  * 2004-Oct     Jim Keniston <kenistoj@us.ibm.com> and Prasanna S Panchamukhi
  27  *              <prasanna@in.ibm.com> adapted for x86_64
  28  * 2005-Mar     Roland McGrath <roland@redhat.com>
  29  *              Fixed to handle %rip-relative addressing mode correctly.
  30  */
  31
  32 #include <linux/config.h>
  33 #include <linux/kprobes.h>
  34 #include <linux/ptrace.h>
  35 #include <linux/spinlock.h>
  36 #include <linux/string.h>
  37 #include <linux/slab.h>
  38 #include <linux/preempt.h>
  39 #include <linux/moduleloader.h>
  40
  41 #include <asm/pgtable.h>
  42 #include <asm/kdebug.h>
  43
  44 static DECLARE_MUTEX(kprobe_mutex);
  45
  46 /* kprobe_status settings */
  47 #define KPROBE_HIT_ACTIVE       0x00000001
  48 #define KPROBE_HIT_SS           0x00000002
  49
  50 static struct kprobe *current_kprobe;
  51 static unsigned long kprobe_status, kprobe_old_rflags, kprobe_saved_rflags;
  52 static struct pt_regs jprobe_saved_regs;
  53 static long *jprobe_saved_rsp;
  54 static kprobe_opcode_t *get_insn_slot(void);
  55 static void free_insn_slot(kprobe_opcode_t *slot);
  56 void jprobe_return_end(void);
  57
  58 /* copy of the kernel stack at the probe fire time */
  59 static kprobe_opcode_t jprobes_stack[MAX_STACK_SIZE];
  60
  61 /*
  62  * returns non-zero if opcode modifies the interrupt flag.
  63  */
  64 static inline int is_IF_modifier(kprobe_opcode_t *insn)
  65 {
  66         switch (*insn) {
  67         case 0xfa:              /* cli */
  68         case 0xfb:              /* sti */
  69         case 0xcf:              /* iret/iretd */
  70         case 0x9d:              /* popf/popfd */
  71                 return 1;
  72         }
  73
  74         if (*insn  >= 0x40 && *insn <= 0x4f && *++insn == 0xcf)
  75                 return 1;
  76         return 0;
  77 }
  78
  79 int arch_prepare_kprobe(struct kprobe *p)
  80 {
  81         /* insn: must be on special executable page on x86_64. */
  82         up(&kprobe_mutex);
  83         p->ainsn.insn = get_insn_slot();
  84         down(&kprobe_mutex);
  85         if (!p->ainsn.insn) {
  86                 return -ENOMEM;
  87         }
  88         return 0;
  89 }
  90
  91 /*
  92  * Determine if the instruction uses the %rip-relative addressing mode.
  93  * If it does, return the address of the 32-bit displacement word.
  94  * If not, return null.
  95  */
  96 static inline s32 *is_riprel(u8 *insn)
  97 {
  98 #define W(row,b0,b1,b2,b3,b4,b5,b6,b7,b8,b9,ba,bb,bc,bd,be,bf)                \
  99         (((b0##UL << 0x0)|(b1##UL << 0x1)|(b2##UL << 0x2)|(b3##UL << 0x3) |   \
 100           (b4##UL << 0x4)|(b5##UL << 0x5)|(b6##UL << 0x6)|(b7##UL << 0x7) |   \
 101           (b8##UL << 0x8)|(b9##UL << 0x9)|(ba##UL << 0xa)|(bb##UL << 0xb) |   \
 102           (bc##UL << 0xc)|(bd##UL << 0xd)|(be##UL << 0xe)|(bf##UL << 0xf))    \
 103          << (row % 64))
 104         static const u64 onebyte_has_modrm[256 / 64] = {
 105                 /*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
 106                 /*      -------------------------------         */
 107                 W(0x00, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0)| /* 00 */
 108                 W(0x10, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0)| /* 10 */
 109                 W(0x20, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0)| /* 20 */
 110                 W(0x30, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0), /* 30 */
 111                 W(0x40, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 40 */
 112                 W(0x50, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 50 */
 113                 W(0x60, 0,0,1,1,0,0,0,0,0,1,0,1,0,0,0,0)| /* 60 */
 114                 W(0x70, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 70 */
 115                 W(0x80, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 80 */
 116                 W(0x90, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 90 */
 117                 W(0xa0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* a0 */
 118                 W(0xb0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* b0 */
 119                 W(0xc0, 1,1,0,0,1,1,1,1,0,0,0,0,0,0,0,0)| /* c0 */
 120                 W(0xd0, 1,1,1,1,0,0,0,0,1,1,1,1,1,1,1,1)| /* d0 */
 121                 W(0xe0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* e0 */
 122                 W(0xf0, 0,0,0,0,0,0,1,1,0,0,0,0,0,0,1,1)  /* f0 */
 123                 /*      -------------------------------         */
 124                 /*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
 125         };
 126         static const u64 twobyte_has_modrm[256 / 64] = {
 127                 /*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
 128                 /*      -------------------------------         */
 129                 W(0x00, 1,1,1,1,0,0,0,0,0,0,0,0,0,1,0,1)| /* 0f */
 130                 W(0x10, 1,1,1,1,1,1,1,1,1,0,0,0,0,0,0,0)| /* 1f */
 131                 W(0x20, 1,1,1,1,1,0,1,0,1,1,1,1,1,1,1,1)| /* 2f */
 132                 W(0x30, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 3f */
 133                 W(0x40, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 4f */
 134                 W(0x50, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 5f */
 135                 W(0x60, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 6f */
 136                 W(0x70, 1,1,1,1,1,1,1,0,0,0,0,0,1,1,1,1), /* 7f */
 137                 W(0x80, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 8f */
 138                 W(0x90, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 9f */
 139                 W(0xa0, 0,0,0,1,1,1,1,1,0,0,0,1,1,1,1,1)| /* af */
 140                 W(0xb0, 1,1,1,1,1,1,1,1,0,0,1,1,1,1,1,1), /* bf */
 141                 W(0xc0, 1,1,1,1,1,1,1,1,0,0,0,0,0,0,0,0)| /* cf */
 142                 W(0xd0, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* df */
 143                 W(0xe0, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* ef */
 144                 W(0xf0, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0)  /* ff */
 145                 /*      -------------------------------         */
 146                 /*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
 147         };
 148 #undef  W
 149         int need_modrm;
 150
 151         /* Skip legacy instruction prefixes.  */
 152         while (1) {
 153                 switch (*insn) {
 154                 case 0x66:
 155                 case 0x67:
 156                 case 0x2e:
 157                 case 0x3e:
 158                 case 0x26:
 159                 case 0x64:
 160                 case 0x65:
 161                 case 0x36:
 162                 case 0xf0:
 163                 case 0xf3:
 164                 case 0xf2:
 165                         ++insn;
 166                         continue;
 167                 }
 168                 break;
 169         }
 170
 171         /* Skip REX instruction prefix.  */
 172         if ((*insn & 0xf0) == 0x40)
 173                 ++insn;
 174
 175         if (*insn == 0x0f) {    /* Two-byte opcode.  */
 176                 ++insn;
 177                 need_modrm = test_bit(*insn, twobyte_has_modrm);
 178         } else {                /* One-byte opcode.  */
 179                 need_modrm = test_bit(*insn, onebyte_has_modrm);
 180         }
 181
 182         if (need_modrm) {
 183                 u8 modrm = *++insn;
 184                 if ((modrm & 0xc7) == 0x05) { /* %rip+disp32 addressing mode */
 185                         /* Displacement follows ModRM byte.  */
 186                         return (s32 *) ++insn;
 187                 }
 188         }
 189
 190         /* No %rip-relative addressing mode here.  */
 191         return NULL;
 192 }
 193
 194 void arch_copy_kprobe(struct kprobe *p)
 195 {
 196         s32 *ripdisp;
 197         memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE);
 198         ripdisp = is_riprel(p->ainsn.insn);
 199         if (ripdisp) {
 200                 /*
 201                  * The copied instruction uses the %rip-relative
 202                  * addressing mode.  Adjust the displacement for the
 203                  * difference between the original location of this
 204                  * instruction and the location of the copy that will
 205                  * actually be run.  The tricky bit here is making sure
 206                  * that the sign extension happens correctly in this
 207                  * calculation, since we need a signed 32-bit result to
 208                  * be sign-extended to 64 bits when it's added to the
 209                  * %rip value and yield the same 64-bit result that the
 210                  * sign-extension of the original signed 32-bit
 211                  * displacement would have given.
 212                  */
 213                 s64 disp = (u8 *) p->addr + *ripdisp - (u8 *) p->ainsn.insn;
 214                 BUG_ON((s64) (s32) disp != disp); /* Sanity check.  */
 215                 *ripdisp = disp;
 216         }
 217 }
 218
 219 void arch_remove_kprobe(struct kprobe *p)
 220 {
 221         up(&kprobe_mutex);
 222         free_insn_slot(p->ainsn.insn);
 223         down(&kprobe_mutex);
 224 }
 225
 226 static inline void disarm_kprobe(struct kprobe *p, struct pt_regs *regs)
 227 {
 228         *p->addr = p->opcode;
 229         regs->rip = (unsigned long)p->addr;
 230 }
 231
 232 static void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 233 {
 234         regs->eflags |= TF_MASK;
 235         regs->eflags &= ~IF_MASK;
 236         /*single step inline if the instruction is an int3*/
 237         if (p->opcode == BREAKPOINT_INSTRUCTION)
 238                 regs->rip = (unsigned long)p->addr;
 239         else
 240                 regs->rip = (unsigned long)p->ainsn.insn;
 241 }
 242
 243 /*
 244  * Interrupts are disabled on entry as trap3 is an interrupt gate and they
 245  * remain disabled thorough out this function.
 246  */
 247 int kprobe_handler(struct pt_regs *regs)
 248 {
 249         struct kprobe *p;
 250         int ret = 0;
 251         kprobe_opcode_t *addr = (kprobe_opcode_t *)(regs->rip - sizeof(kprobe_opcode_t));
 252
 253         /* We're in an interrupt, but this is clear and BUG()-safe. */
 254         preempt_disable();
 255
 256         /* Check we're not actually recursing */
 257         if (kprobe_running()) {
 258                 /* We *are* holding lock here, so this is safe.
 259                    Disarm the probe we just hit, and ignore it. */
 260                 p = get_kprobe(addr);
 261                 if (p) {
 262                         if (kprobe_status == KPROBE_HIT_SS) {
 263                                 regs->eflags &= ~TF_MASK;
 264                                 regs->eflags |= kprobe_saved_rflags;
 265                                 unlock_kprobes();
 266                                 goto no_kprobe;
 267                         }
 268                         disarm_kprobe(p, regs);
 269                         ret = 1;
 270                 } else {
 271                         p = current_kprobe;
 272                         if (p->break_handler && p->break_handler(p, regs)) {
 273                                 goto ss_probe;
 274                         }
 275                 }
 276                 /* If it's not ours, can't be delete race, (we hold lock). */
 277                 goto no_kprobe;
 278         }
 279
 280         lock_kprobes();
 281         p = get_kprobe(addr);
 282         if (!p) {
 283                 unlock_kprobes();
 284                 if (*addr != BREAKPOINT_INSTRUCTION) {
 285                         /*
 286                          * The breakpoint instruction was removed right
 287                          * after we hit it.  Another cpu has removed
 288                          * either a probepoint or a debugger breakpoint
 289                          * at this address.  In either case, no further
 290                          * handling of this interrupt is appropriate.
 291                          */
 292                         ret = 1;
 293                 }
 294                 /* Not one of ours: let kernel handle it */
 295                 goto no_kprobe;
 296         }
 297
 298         kprobe_status = KPROBE_HIT_ACTIVE;
 299         current_kprobe = p;
 300         kprobe_saved_rflags = kprobe_old_rflags
 301             = (regs->eflags & (TF_MASK | IF_MASK));
 302         if (is_IF_modifier(p->ainsn.insn))
 303                 kprobe_saved_rflags &= ~IF_MASK;
 304
 305         if (p->pre_handler && p->pre_handler(p, regs))
 306                 /* handler has already set things up, so skip ss setup */
 307                 return 1;
 308
 309 ss_probe:
 310         prepare_singlestep(p, regs);
 311         kprobe_status = KPROBE_HIT_SS;
 312         return 1;
 313
 314 no_kprobe:
 315         preempt_enable_no_resched();
 316         return ret;
 317 }
 318
 319 /*
 320  * Called after single-stepping.  p->addr is the address of the
 321  * instruction whose first byte has been replaced by the "int 3"
 322  * instruction.  To avoid the SMP problems that can occur when we
 323  * temporarily put back the original opcode to single-step, we
 324  * single-stepped a copy of the instruction.  The address of this
 325  * copy is p->ainsn.insn.
 326  *
 327  * This function prepares to return from the post-single-step
 328  * interrupt.  We have to fix up the stack as follows:
 329  *
 330  * 0) Except in the case of absolute or indirect jump or call instructions,
 331  * the new rip is relative to the copied instruction.  We need to make
 332  * it relative to the original instruction.
 333  *
 334  * 1) If the single-stepped instruction was pushfl, then the TF and IF
 335  * flags are set in the just-pushed eflags, and may need to be cleared.
 336  *
 337  * 2) If the single-stepped instruction was a call, the return address
 338  * that is atop the stack is the address following the copied instruction.
 339  * We need to make it the address following the original instruction.
 340  */
 341 static void resume_execution(struct kprobe *p, struct pt_regs *regs)
 342 {
 343         unsigned long *tos = (unsigned long *)regs->rsp;
 344         unsigned long next_rip = 0;
 345         unsigned long copy_rip = (unsigned long)p->ainsn.insn;
 346         unsigned long orig_rip = (unsigned long)p->addr;
 347         kprobe_opcode_t *insn = p->ainsn.insn;
 348
 349         /*skip the REX prefix*/
 350         if (*insn >= 0x40 && *insn <= 0x4f)
 351                 insn++;
 352
 353         switch (*insn) {
 354         case 0x9c:              /* pushfl */
 355                 *tos &= ~(TF_MASK | IF_MASK);
 356                 *tos |= kprobe_old_rflags;
 357                 break;
 358         case 0xc3:              /* ret/lret */
 359         case 0xcb:
 360         case 0xc2:
 361         case 0xca:
 362                 regs->eflags &= ~TF_MASK;
 363                 /* rip is already adjusted, no more changes required*/
 364                 return;
 365         case 0xe8:              /* call relative - Fix return addr */
 366                 *tos = orig_rip + (*tos - copy_rip);
 367                 break;
 368         case 0xff:
 369                 if ((*insn & 0x30) == 0x10) {
 370                         /* call absolute, indirect */
 371                         /* Fix return addr; rip is correct. */
 372                         next_rip = regs->rip;
 373                         *tos = orig_rip + (*tos - copy_rip);
 374                 } else if (((*insn & 0x31) == 0x20) ||  /* jmp near, absolute indirect */
 375                            ((*insn & 0x31) == 0x21)) {  /* jmp far, absolute indirect */
 376                         /* rip is correct. */
 377                         next_rip = regs->rip;
 378                 }
 379                 break;
 380         case 0xea:              /* jmp absolute -- rip is correct */
 381                 next_rip = regs->rip;
 382                 break;
 383         default:
 384                 break;
 385         }
 386
 387         regs->eflags &= ~TF_MASK;
 388         if (next_rip) {
 389                 regs->rip = next_rip;
 390         } else {
 391                 regs->rip = orig_rip + (regs->rip - copy_rip);
 392         }
 393 }
 394
 395 /*
 396  * Interrupts are disabled on entry as trap1 is an interrupt gate and they
 397  * remain disabled thoroughout this function.  And we hold kprobe lock.
 398  */
 399 int post_kprobe_handler(struct pt_regs *regs)
 400 {
 401         if (!kprobe_running())
 402                 return 0;
 403
 404         if (current_kprobe->post_handler)
 405                 current_kprobe->post_handler(current_kprobe, regs, 0);
 406
 407         resume_execution(current_kprobe, regs);
 408         regs->eflags |= kprobe_saved_rflags;
 409
 410         unlock_kprobes();
 411         preempt_enable_no_resched();
 412
 413         /*
 414          * if somebody else is singlestepping across a probe point, eflags
 415          * will have TF set, in which case, continue the remaining processing
 416          * of do_debug, as if this is not a probe hit.
 417          */
 418         if (regs->eflags & TF_MASK)
 419                 return 0;
 420
 421         return 1;
 422 }
 423
 424 /* Interrupts disabled, kprobe_lock held. */
 425 int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 426 {
 427         if (current_kprobe->fault_handler
 428             && current_kprobe->fault_handler(current_kprobe, regs, trapnr))
 429                 return 1;
 430
 431         if (kprobe_status & KPROBE_HIT_SS) {
 432                 resume_execution(current_kprobe, regs);
 433                 regs->eflags |= kprobe_old_rflags;
 434
 435                 unlock_kprobes();
 436                 preempt_enable_no_resched();
 437         }
 438         return 0;
 439 }
 440
 441 /*
 442  * Wrapper routine for handling exceptions.
 443  */
 444 int kprobe_exceptions_notify(struct notifier_block *self, unsigned long val,
 445                              void *data)
 446 {
 447         struct die_args *args = (struct die_args *)data;
 448         switch (val) {
 449         case DIE_INT3:
 450                 if (kprobe_handler(args->regs))
 451                         return NOTIFY_STOP;
 452                 break;
 453         case DIE_DEBUG:
 454                 if (post_kprobe_handler(args->regs))
 455                         return NOTIFY_STOP;
 456                 break;
 457         case DIE_GPF:
 458                 if (kprobe_running() &&
 459                     kprobe_fault_handler(args->regs, args->trapnr))
 460                         return NOTIFY_STOP;
 461                 break;
 462         case DIE_PAGE_FAULT:
 463                 if (kprobe_running() &&
 464                     kprobe_fault_handler(args->regs, args->trapnr))
 465                         return NOTIFY_STOP;
 466                 break;
 467         default:
 468                 break;
 469         }
 470         return NOTIFY_DONE;
 471 }
 472
 473 int setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 474 {
 475         struct jprobe *jp = container_of(p, struct jprobe, kp);
 476         unsigned long addr;
 477
 478         jprobe_saved_regs = *regs;
 479         jprobe_saved_rsp = (long *) regs->rsp;
 480         addr = (unsigned long)jprobe_saved_rsp;
 481         /*
 482          * As Linus pointed out, gcc assumes that the callee
 483          * owns the argument space and could overwrite it, e.g.
 484          * tailcall optimization. So, to be absolutely safe
 485          * we also save and restore enough stack bytes to cover
 486          * the argument area.
 487          */
 488         memcpy(jprobes_stack, (kprobe_opcode_t *) addr, MIN_STACK_SIZE(addr));
 489         regs->eflags &= ~IF_MASK;
 490         regs->rip = (unsigned long)(jp->entry);
 491         return 1;
 492 }
 493
 494 void jprobe_return(void)
 495 {
 496         preempt_enable_no_resched();
 497         asm volatile ("       xchg   %%rbx,%%rsp     \n"
 498                       "       int3                      \n"
 499                       "       .globl jprobe_return_end  \n"
 500                       "       jprobe_return_end:        \n"
 501                       "       nop                       \n"::"b"
 502                       (jprobe_saved_rsp):"memory");
 503 }
 504
 505 int longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 506 {
 507         u8 *addr = (u8 *) (regs->rip - 1);
 508         unsigned long stack_addr = (unsigned long)jprobe_saved_rsp;
 509         struct jprobe *jp = container_of(p, struct jprobe, kp);
 510
 511         if ((addr > (u8 *) jprobe_return) && (addr < (u8 *) jprobe_return_end)) {
 512                 if ((long *)regs->rsp != jprobe_saved_rsp) {
 513                         struct pt_regs *saved_regs =
 514                             container_of(jprobe_saved_rsp, struct pt_regs, rsp);
 515                         printk("current rsp %p does not match saved rsp %p\n",
 516                                (long *)regs->rsp, jprobe_saved_rsp);
 517                         printk("Saved registers for jprobe %p\n", jp);
 518                         show_registers(saved_regs);
 519                         printk("Current registers\n");
 520                         show_registers(regs);
 521                         BUG();
 522                 }
 523                 *regs = jprobe_saved_regs;
 524                 memcpy((kprobe_opcode_t *) stack_addr, jprobes_stack,
 525                        MIN_STACK_SIZE(stack_addr));
 526                 return 1;
 527         }
 528         return 0;
 529 }
 530
 531 /*
 532  * kprobe->ainsn.insn points to the copy of the instruction to be single-stepped.
 533  * By default on x86_64, pages we get from kmalloc or vmalloc are not
 534  * executable.  Single-stepping an instruction on such a page yields an
 535  * oops.  So instead of storing the instruction copies in their respective
 536  * kprobe objects, we allocate a page, map it executable, and store all the
 537  * instruction copies there.  (We can allocate additional pages if somebody
 538  * inserts a huge number of probes.)  Each page can hold up to INSNS_PER_PAGE
 539  * instruction slots, each of which is MAX_INSN_SIZE*sizeof(kprobe_opcode_t)
 540  * bytes.
 541  */
 542 #define INSNS_PER_PAGE (PAGE_SIZE/(MAX_INSN_SIZE*sizeof(kprobe_opcode_t)))
 543 struct kprobe_insn_page {
 544         struct hlist_node hlist;
 545         kprobe_opcode_t *insns;         /* page of instruction slots */
 546         char slot_used[INSNS_PER_PAGE];
 547         int nused;
 548 };
 549
 550 static struct hlist_head kprobe_insn_pages;
 551
 552 /**
 553  * get_insn_slot() - Find a slot on an executable page for an instruction.
 554  * We allocate an executable page if there's no room on existing ones.
 555  */
 556 static kprobe_opcode_t *get_insn_slot(void)
 557 {
 558         struct kprobe_insn_page *kip;
 559         struct hlist_node *pos;
 560
 561         hlist_for_each(pos, &kprobe_insn_pages) {
 562                 kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
 563                 if (kip->nused < INSNS_PER_PAGE) {
 564                         int i;
 565                         for (i = 0; i < INSNS_PER_PAGE; i++) {
 566                                 if (!kip->slot_used[i]) {
 567                                         kip->slot_used[i] = 1;
 568                                         kip->nused++;
 569                                         return kip->insns + (i*MAX_INSN_SIZE);
 570                                 }
 571                         }
 572                         /* Surprise!  No unused slots.  Fix kip->nused. */
 573                         kip->nused = INSNS_PER_PAGE;
 574                 }
 575         }
 576
 577         /* All out of space.  Need to allocate a new page. Use slot 0.*/
 578         kip = kmalloc(sizeof(struct kprobe_insn_page), GFP_KERNEL);
 579         if (!kip) {
 580                 return NULL;
 581         }
 582
 583         /*
 584          * For the %rip-relative displacement fixups to be doable, we
 585          * need our instruction copy to be within +/- 2GB of any data it
 586          * might access via %rip.  That is, within 2GB of where the
 587          * kernel image and loaded module images reside.  So we allocate
 588          * a page in the module loading area.
 589          */
 590         kip->insns = module_alloc(PAGE_SIZE);
 591         if (!kip->insns) {
 592                 kfree(kip);
 593                 return NULL;
 594         }
 595         INIT_HLIST_NODE(&kip->hlist);
 596         hlist_add_head(&kip->hlist, &kprobe_insn_pages);
 597         memset(kip->slot_used, 0, INSNS_PER_PAGE);
 598         kip->slot_used[0] = 1;
 599         kip->nused = 1;
 600         return kip->insns;
 601 }
 602
 603 /**
 604  * free_insn_slot() - Free instruction slot obtained from get_insn_slot().
 605  */
 606 static void free_insn_slot(kprobe_opcode_t *slot)
 607 {
 608         struct kprobe_insn_page *kip;
 609         struct hlist_node *pos;
 610
 611         hlist_for_each(pos, &kprobe_insn_pages) {
 612                 kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
 613                 if (kip->insns <= slot
 614                     && slot < kip->insns+(INSNS_PER_PAGE*MAX_INSN_SIZE)) {
 615                         int i = (slot - kip->insns) / MAX_INSN_SIZE;
 616                         kip->slot_used[i] = 0;
 617                         kip->nused--;
 618                         if (kip->nused == 0) {
 619                                 /*
 620                                  * Page is no longer in use.  Free it unless
 621                                  * it's the last one.  We keep the last one
 622                                  * so as not to have to set it up again the
 623                                  * next time somebody inserts a probe.
 624                                  */
 625                                 hlist_del(&kip->hlist);
 626                                 if (hlist_empty(&kprobe_insn_pages)) {
 627                                         INIT_HLIST_NODE(&kip->hlist);
 628                                         hlist_add_head(&kip->hlist,
 629                                                 &kprobe_insn_pages);
 630                                 } else {
 631                                         module_free(NULL, kip->insns);
 632                                         kfree(kip);
 633                                 }
 634                         }
 635                         return;
 636                 }
 637         }
 638 }