arch/i386/kernel/ptrace.c

   1 /* ptrace.c */
   2 /* By Ross Biro 1/23/92 */
   3 /*
   4  * Pentium III FXSR, SSE support
   5  *      Gareth Hughes <gareth@valinux.com>, May 2000
   6  */
   7
   8 #include <linux/kernel.h>
   9 #include <linux/sched.h>
  10 #include <linux/mm.h>
  11 #include <linux/smp.h>
  12 #include <linux/smp_lock.h>
  13 #include <linux/errno.h>
  14 #include <linux/ptrace.h>
  15 #include <linux/user.h>
  16 #include <linux/security.h>
  17 #include <linux/audit.h>
  18 #include <linux/seccomp.h>
  19 #include <linux/signal.h>
  20
  21 #include <asm/uaccess.h>
  22 #include <asm/pgtable.h>
  23 #include <asm/system.h>
  24 #include <asm/processor.h>
  25 #include <asm/i387.h>
  26 #include <asm/debugreg.h>
  27 #include <asm/ldt.h>
  28 #include <asm/desc.h>
  29
  30 /*
  31  * does not yet catch signals sent when the child dies.
  32  * in exit.c or in signal.c.
  33  */
  34
  35 /*
  36  * Determines which flags the user has access to [1 = access, 0 = no access].
  37  * Prohibits changing ID(21), VIP(20), VIF(19), VM(17), NT(14), IOPL(12-13), IF(9).
  38  * Also masks reserved bits (31-22, 15, 5, 3, 1).
  39  */
  40 #define FLAG_MASK 0x00050dd5
  41
  42 /* set's the trap flag. */
  43 #define TRAP_FLAG 0x100
  44
  45 /*
  46  * Offset of eflags on child stack..
  47  */
  48 #define EFL_OFFSET ((EFL-2)*4-sizeof(struct pt_regs))
  49
  50 static inline struct pt_regs *get_child_regs(struct task_struct *task)
  51 {
  52         void *stack_top = (void *)task->thread.esp0;
  53         return stack_top - sizeof(struct pt_regs);
  54 }
  55
  56 /*
  57  * this routine will get a word off of the processes privileged stack.
  58  * the offset is how far from the base addr as stored in the TSS.
  59  * this routine assumes that all the privileged stacks are in our
  60  * data space.
  61  */
  62 static inline int get_stack_long(struct task_struct *task, int offset)
  63 {
  64         unsigned char *stack;
  65
  66         stack = (unsigned char *)task->thread.esp0;
  67         stack += offset;
  68         return (*((int *)stack));
  69 }
  70
  71 /*
  72  * this routine will put a word on the processes privileged stack.
  73  * the offset is how far from the base addr as stored in the TSS.
  74  * this routine assumes that all the privileged stacks are in our
  75  * data space.
  76  */
  77 static inline int put_stack_long(struct task_struct *task, int offset,
  78         unsigned long data)
  79 {
  80         unsigned char * stack;
  81
  82         stack = (unsigned char *) task->thread.esp0;
  83         stack += offset;
  84         *(unsigned long *) stack = data;
  85         return 0;
  86 }
  87
  88 static int putreg(struct task_struct *child,
  89         unsigned long regno, unsigned long value)
  90 {
  91         switch (regno >> 2) {
  92                 case FS:
  93                         if (value && (value & 3) != 3)
  94                                 return -EIO;
  95                         child->thread.fs = value;
  96                         return 0;
  97                 case GS:
  98                         if (value && (value & 3) != 3)
  99                                 return -EIO;
 100                         child->thread.gs = value;
 101                         return 0;
 102                 case DS:
 103                 case ES:
 104                         if (value && (value & 3) != 3)
 105                                 return -EIO;
 106                         value &= 0xffff;
 107                         break;
 108                 case SS:
 109                 case CS:
 110                         if ((value & 3) != 3)
 111                                 return -EIO;
 112                         value &= 0xffff;
 113                         break;
 114                 case EFL:
 115                         value &= FLAG_MASK;
 116                         value |= get_stack_long(child, EFL_OFFSET) & ~FLAG_MASK;
 117                         break;
 118         }
 119         if (regno > GS*4)
 120                 regno -= 2*4;
 121         put_stack_long(child, regno - sizeof(struct pt_regs), value);
 122         return 0;
 123 }
 124
 125 static unsigned long getreg(struct task_struct *child,
 126         unsigned long regno)
 127 {
 128         unsigned long retval = ~0UL;
 129
 130         switch (regno >> 2) {
 131                 case FS:
 132                         retval = child->thread.fs;
 133                         break;
 134                 case GS:
 135                         retval = child->thread.gs;
 136                         break;
 137                 case DS:
 138                 case ES:
 139                 case SS:
 140                 case CS:
 141                         retval = 0xffff;
 142                         /* fall through */
 143                 default:
 144                         if (regno > GS*4)
 145                                 regno -= 2*4;
 146                         regno = regno - sizeof(struct pt_regs);
 147                         retval &= get_stack_long(child, regno);
 148         }
 149         return retval;
 150 }
 151
 152 #define LDT_SEGMENT 4
 153
 154 static unsigned long convert_eip_to_linear(struct task_struct *child, struct pt_regs *regs)
 155 {
 156         unsigned long addr, seg;
 157
 158         addr = regs->eip;
 159         seg = regs->xcs & 0xffff;
 160         if (regs->eflags & VM_MASK) {
 161                 addr = (addr & 0xffff) + (seg << 4);
 162                 return addr;
 163         }
 164
 165         /*
 166          * We'll assume that the code segments in the GDT
 167          * are all zero-based. That is largely true: the
 168          * TLS segments are used for data, and the PNPBIOS
 169          * and APM bios ones we just ignore here.
 170          */
 171         if (seg & LDT_SEGMENT) {
 172                 u32 *desc;
 173                 unsigned long base;
 174
 175                 down(&child->mm->context.sem);
 176                 desc = child->mm->context.ldt + (seg & ~7);
 177                 base = (desc[0] >> 16) | ((desc[1] & 0xff) << 16) | (desc[1] & 0xff000000);
 178
 179                 /* 16-bit code segment? */
 180                 if (!((desc[1] >> 22) & 1))
 181                         addr &= 0xffff;
 182                 addr += base;
 183                 up(&child->mm->context.sem);
 184         }
 185         return addr;
 186 }
 187
 188 static inline int is_at_popf(struct task_struct *child, struct pt_regs *regs)
 189 {
 190         int i, copied;
 191         unsigned char opcode[16];
 192         unsigned long addr = convert_eip_to_linear(child, regs);
 193
 194         copied = access_process_vm(child, addr, opcode, sizeof(opcode), 0);
 195         for (i = 0; i < copied; i++) {
 196                 switch (opcode[i]) {
 197                 /* popf */
 198                 case 0x9d:
 199                         return 1;
 200                 /* opcode and address size prefixes */
 201                 case 0x66: case 0x67:
 202                         continue;
 203                 /* irrelevant prefixes (segment overrides and repeats) */
 204                 case 0x26: case 0x2e:
 205                 case 0x36: case 0x3e:
 206                 case 0x64: case 0x65:
 207                 case 0xf0: case 0xf2: case 0xf3:
 208                         continue;
 209
 210                 /*
 211                  * pushf: NOTE! We should probably not let
 212                  * the user see the TF bit being set. But
 213                  * it's more pain than it's worth to avoid
 214                  * it, and a debugger could emulate this
 215                  * all in user space if it _really_ cares.
 216                  */
 217                 case 0x9c:
 218                 default:
 219                         return 0;
 220                 }
 221         }
 222         return 0;
 223 }
 224
 225 static void set_singlestep(struct task_struct *child)
 226 {
 227         struct pt_regs *regs = get_child_regs(child);
 228
 229         /*
 230          * Always set TIF_SINGLESTEP - this guarantees that
 231          * we single-step system calls etc..  This will also
 232          * cause us to set TF when returning to user mode.
 233          */
 234         set_tsk_thread_flag(child, TIF_SINGLESTEP);
 235
 236         /*
 237          * If TF was already set, don't do anything else
 238          */
 239         if (regs->eflags & TRAP_FLAG)
 240                 return;
 241
 242         /* Set TF on the kernel stack.. */
 243         regs->eflags |= TRAP_FLAG;
 244
 245         /*
 246          * ..but if TF is changed by the instruction we will trace,
 247          * don't mark it as being "us" that set it, so that we
 248          * won't clear it by hand later.
 249          */
 250         if (is_at_popf(child, regs))
 251                 return;
 252
 253         child->ptrace |= PT_DTRACE;
 254 }
 255
 256 static void clear_singlestep(struct task_struct *child)
 257 {
 258         /* Always clear TIF_SINGLESTEP... */
 259         clear_tsk_thread_flag(child, TIF_SINGLESTEP);
 260
 261         /* But touch TF only if it was set by us.. */
 262         if (child->ptrace & PT_DTRACE) {
 263                 struct pt_regs *regs = get_child_regs(child);
 264                 regs->eflags &= ~TRAP_FLAG;
 265                 child->ptrace &= ~PT_DTRACE;
 266         }
 267 }
 268
 269 /*
 270  * Called by kernel/ptrace.c when detaching..
 271  *
 272  * Make sure the single step bit is not set.
 273  */
 274 void ptrace_disable(struct task_struct *child)
 275 {
 276         clear_singlestep(child);
 277         clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 278         clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
 279 }
 280
 281 /*
 282  * Perform get_thread_area on behalf of the traced child.
 283  */
 284 static int
 285 ptrace_get_thread_area(struct task_struct *child,
 286                        int idx, struct user_desc __user *user_desc)
 287 {
 288         struct user_desc info;
 289         struct desc_struct *desc;
 290
 291 /*
 292  * Get the current Thread-Local Storage area:
 293  */
 294
 295 #define GET_BASE(desc) ( \
 296         (((desc)->a >> 16) & 0x0000ffff) | \
 297         (((desc)->b << 16) & 0x00ff0000) | \
 298         ( (desc)->b        & 0xff000000)   )
 299
 300 #define GET_LIMIT(desc) ( \
 301         ((desc)->a & 0x0ffff) | \
 302          ((desc)->b & 0xf0000) )
 303
 304 #define GET_32BIT(desc)         (((desc)->b >> 22) & 1)
 305 #define GET_CONTENTS(desc)      (((desc)->b >> 10) & 3)
 306 #define GET_WRITABLE(desc)      (((desc)->b >>  9) & 1)
 307 #define GET_LIMIT_PAGES(desc)   (((desc)->b >> 23) & 1)
 308 #define GET_PRESENT(desc)       (((desc)->b >> 15) & 1)
 309 #define GET_USEABLE(desc)       (((desc)->b >> 20) & 1)
 310
 311         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 312                 return -EINVAL;
 313
 314         desc = child->thread.tls_array + idx - GDT_ENTRY_TLS_MIN;
 315
 316         info.entry_number = idx;
 317         info.base_addr = GET_BASE(desc);
 318         info.limit = GET_LIMIT(desc);
 319         info.seg_32bit = GET_32BIT(desc);
 320         info.contents = GET_CONTENTS(desc);
 321         info.read_exec_only = !GET_WRITABLE(desc);
 322         info.limit_in_pages = GET_LIMIT_PAGES(desc);
 323         info.seg_not_present = !GET_PRESENT(desc);
 324         info.useable = GET_USEABLE(desc);
 325
 326         if (copy_to_user(user_desc, &info, sizeof(info)))
 327                 return -EFAULT;
 328
 329         return 0;
 330 }
 331
 332 /*
 333  * Perform set_thread_area on behalf of the traced child.
 334  */
 335 static int
 336 ptrace_set_thread_area(struct task_struct *child,
 337                        int idx, struct user_desc __user *user_desc)
 338 {
 339         struct user_desc info;
 340         struct desc_struct *desc;
 341
 342         if (copy_from_user(&info, user_desc, sizeof(info)))
 343                 return -EFAULT;
 344
 345         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 346                 return -EINVAL;
 347
 348         desc = child->thread.tls_array + idx - GDT_ENTRY_TLS_MIN;
 349         if (LDT_empty(&info)) {
 350                 desc->a = 0;
 351                 desc->b = 0;
 352         } else {
 353                 desc->a = LDT_entry_a(&info);
 354                 desc->b = LDT_entry_b(&info);
 355         }
 356
 357         return 0;
 358 }
 359
 360 long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 361 {
 362         struct user * dummy = NULL;
 363         int i, ret;
 364         unsigned long __user *datap = (unsigned long __user *)data;
 365
 366         switch (request) {
 367         /* when I and D space are separate, these will need to be fixed. */
 368         case PTRACE_PEEKTEXT: /* read word at location addr. */
 369         case PTRACE_PEEKDATA: {
 370                 unsigned long tmp;
 371                 int copied;
 372
 373                 copied = access_process_vm(child, addr, &tmp, sizeof(tmp), 0);
 374                 ret = -EIO;
 375                 if (copied != sizeof(tmp))
 376                         break;
 377                 ret = put_user(tmp, datap);
 378                 break;
 379         }
 380
 381         /* read the word at location addr in the USER area. */
 382         case PTRACE_PEEKUSR: {
 383                 unsigned long tmp;
 384
 385                 ret = -EIO;
 386                 if ((addr & 3) || addr < 0 ||
 387                     addr > sizeof(struct user) - 3)
 388                         break;
 389
 390                 tmp = 0;  /* Default return condition */
 391                 if(addr < FRAME_SIZE*sizeof(long))
 392                         tmp = getreg(child, addr);
 393                 if(addr >= (long) &dummy->u_debugreg[0] &&
 394                    addr <= (long) &dummy->u_debugreg[7]){
 395                         addr -= (long) &dummy->u_debugreg[0];
 396                         addr = addr >> 2;
 397                         tmp = child->thread.debugreg[addr];
 398                 }
 399                 ret = put_user(tmp, datap);
 400                 break;
 401         }
 402
 403         /* when I and D space are separate, this will have to be fixed. */
 404         case PTRACE_POKETEXT: /* write the word at location addr. */
 405         case PTRACE_POKEDATA:
 406                 ret = 0;
 407                 if (access_process_vm(child, addr, &data, sizeof(data), 1) == sizeof(data))
 408                         break;
 409                 ret = -EIO;
 410                 break;
 411
 412         case PTRACE_POKEUSR: /* write the word at location addr in the USER area */
 413                 ret = -EIO;
 414                 if ((addr & 3) || addr < 0 ||
 415                     addr > sizeof(struct user) - 3)
 416                         break;
 417
 418                 if (addr < FRAME_SIZE*sizeof(long)) {
 419                         ret = putreg(child, addr, data);
 420                         break;
 421                 }
 422                 /* We need to be very careful here.  We implicitly
 423                    want to modify a portion of the task_struct, and we
 424                    have to be selective about what portions we allow someone
 425                    to modify. */
 426
 427                   ret = -EIO;
 428                   if(addr >= (long) &dummy->u_debugreg[0] &&
 429                      addr <= (long) &dummy->u_debugreg[7]){
 430
 431                           if(addr == (long) &dummy->u_debugreg[4]) break;
 432                           if(addr == (long) &dummy->u_debugreg[5]) break;
 433                           if(addr < (long) &dummy->u_debugreg[4] &&
 434                              ((unsigned long) data) >= TASK_SIZE-3) break;
 435
 436                           /* Sanity-check data. Take one half-byte at once with
 437                            * check = (val >> (16 + 4*i)) & 0xf. It contains the
 438                            * R/Wi and LENi bits; bits 0 and 1 are R/Wi, and bits
 439                            * 2 and 3 are LENi. Given a list of invalid values,
 440                            * we do mask |= 1 << invalid_value, so that
 441                            * (mask >> check) & 1 is a correct test for invalid
 442                            * values.
 443                            *
 444                            * R/Wi contains the type of the breakpoint /
 445                            * watchpoint, LENi contains the length of the watched
 446                            * data in the watchpoint case.
 447                            *
 448                            * The invalid values are:
 449                            * - LENi == 0x10 (undefined), so mask |= 0x0f00.
 450                            * - R/Wi == 0x10 (break on I/O reads or writes), so
 451                            *   mask |= 0x4444.
 452                            * - R/Wi == 0x00 && LENi != 0x00, so we have mask |=
 453                            *   0x1110.
 454                            *
 455                            * Finally, mask = 0x0f00 | 0x4444 | 0x1110 == 0x5f54.
 456                            *
 457                            * See the Intel Manual "System Programming Guide",
 458                            * 15.2.4
 459                            *
 460                            * Note that LENi == 0x10 is defined on x86_64 in long
 461                            * mode (i.e. even for 32-bit userspace software, but
 462                            * 64-bit kernel), so the x86_64 mask value is 0x5454.
 463                            * See the AMD manual no. 24593 (AMD64 System
 464                            * Programming)*/
 465
 466                           if(addr == (long) &dummy->u_debugreg[7]) {
 467                                   data &= ~DR_CONTROL_RESERVED;
 468                                   for(i=0; i<4; i++)
 469                                           if ((0x5f54 >> ((data >> (16 + 4*i)) & 0xf)) & 1)
 470                                                   goto out_tsk;
 471                           }
 472
 473                           addr -= (long) &dummy->u_debugreg;
 474                           addr = addr >> 2;
 475                           child->thread.debugreg[addr] = data;
 476                           ret = 0;
 477                   }
 478                   break;
 479
 480         case PTRACE_SYSEMU: /* continue and stop at next syscall, which will not be executed */
 481         case PTRACE_SYSCALL:    /* continue and stop at next (return from) syscall */
 482         case PTRACE_CONT:       /* restart after signal. */
 483                 ret = -EIO;
 484                 if (!valid_signal(data))
 485                         break;
 486                 if (request == PTRACE_SYSEMU) {
 487                         set_tsk_thread_flag(child, TIF_SYSCALL_EMU);
 488                         clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 489                 } else if (request == PTRACE_SYSCALL) {
 490                         set_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 491                         clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
 492                 } else {
 493                         clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
 494                         clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 495                 }
 496                 child->exit_code = data;
 497                 /* make sure the single step bit is not set. */
 498                 clear_singlestep(child);
 499                 wake_up_process(child);
 500                 ret = 0;
 501                 break;
 502
 503 /*
 504  * make the child exit.  Best I can do is send it a sigkill.
 505  * perhaps it should be put in the status that it wants to
 506  * exit.
 507  */
 508         case PTRACE_KILL:
 509                 ret = 0;
 510                 if (child->exit_state == EXIT_ZOMBIE)   /* already dead */
 511                         break;
 512                 child->exit_code = SIGKILL;
 513                 /* make sure the single step bit is not set. */
 514                 clear_singlestep(child);
 515                 wake_up_process(child);
 516                 break;
 517
 518         case PTRACE_SYSEMU_SINGLESTEP: /* Same as SYSEMU, but singlestep if not syscall */
 519         case PTRACE_SINGLESTEP: /* set the trap flag. */
 520                 ret = -EIO;
 521                 if (!valid_signal(data))
 522                         break;
 523
 524                 if (request == PTRACE_SYSEMU_SINGLESTEP)
 525                         set_tsk_thread_flag(child, TIF_SYSCALL_EMU);
 526                 else
 527                         clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
 528
 529                 clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 530                 set_singlestep(child);
 531                 child->exit_code = data;
 532                 /* give it a chance to run. */
 533                 wake_up_process(child);
 534                 ret = 0;
 535                 break;
 536
 537         case PTRACE_DETACH:
 538                 /* detach a process that was attached. */
 539                 ret = ptrace_detach(child, data);
 540                 break;
 541
 542         case PTRACE_GETREGS: { /* Get all gp regs from the child. */
 543                 if (!access_ok(VERIFY_WRITE, datap, FRAME_SIZE*sizeof(long))) {
 544                         ret = -EIO;
 545                         break;
 546                 }
 547                 for ( i = 0; i < FRAME_SIZE*sizeof(long); i += sizeof(long) ) {
 548                         __put_user(getreg(child, i), datap);
 549                         datap++;
 550                 }
 551                 ret = 0;
 552                 break;
 553         }
 554
 555         case PTRACE_SETREGS: { /* Set all gp regs in the child. */
 556                 unsigned long tmp;
 557                 if (!access_ok(VERIFY_READ, datap, FRAME_SIZE*sizeof(long))) {
 558                         ret = -EIO;
 559                         break;
 560                 }
 561                 for ( i = 0; i < FRAME_SIZE*sizeof(long); i += sizeof(long) ) {
 562                         __get_user(tmp, datap);
 563                         putreg(child, i, tmp);
 564                         datap++;
 565                 }
 566                 ret = 0;
 567                 break;
 568         }
 569
 570         case PTRACE_GETFPREGS: { /* Get the child FPU state. */
 571                 if (!access_ok(VERIFY_WRITE, datap,
 572                                sizeof(struct user_i387_struct))) {
 573                         ret = -EIO;
 574                         break;
 575                 }
 576                 ret = 0;
 577                 if (!tsk_used_math(child))
 578                         init_fpu(child);
 579                 get_fpregs((struct user_i387_struct __user *)data, child);
 580                 break;
 581         }
 582
 583         case PTRACE_SETFPREGS: { /* Set the child FPU state. */
 584                 if (!access_ok(VERIFY_READ, datap,
 585                                sizeof(struct user_i387_struct))) {
 586                         ret = -EIO;
 587                         break;
 588                 }
 589                 set_stopped_child_used_math(child);
 590                 set_fpregs(child, (struct user_i387_struct __user *)data);
 591                 ret = 0;
 592                 break;
 593         }
 594
 595         case PTRACE_GETFPXREGS: { /* Get the child extended FPU state. */
 596                 if (!access_ok(VERIFY_WRITE, datap,
 597                                sizeof(struct user_fxsr_struct))) {
 598                         ret = -EIO;
 599                         break;
 600                 }
 601                 if (!tsk_used_math(child))
 602                         init_fpu(child);
 603                 ret = get_fpxregs((struct user_fxsr_struct __user *)data, child);
 604                 break;
 605         }
 606
 607         case PTRACE_SETFPXREGS: { /* Set the child extended FPU state. */
 608                 if (!access_ok(VERIFY_READ, datap,
 609                                sizeof(struct user_fxsr_struct))) {
 610                         ret = -EIO;
 611                         break;
 612                 }
 613                 set_stopped_child_used_math(child);
 614                 ret = set_fpxregs(child, (struct user_fxsr_struct __user *)data);
 615                 break;
 616         }
 617
 618         case PTRACE_GET_THREAD_AREA:
 619                 ret = ptrace_get_thread_area(child, addr,
 620                                         (struct user_desc __user *) data);
 621                 break;
 622
 623         case PTRACE_SET_THREAD_AREA:
 624                 ret = ptrace_set_thread_area(child, addr,
 625                                         (struct user_desc __user *) data);
 626                 break;
 627
 628         default:
 629                 ret = ptrace_request(child, request, addr, data);
 630                 break;
 631         }
 632  out_tsk:
 633         return ret;
 634 }
 635
 636 void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs, int error_code)
 637 {
 638         struct siginfo info;
 639
 640         tsk->thread.trap_no = 1;
 641         tsk->thread.error_code = error_code;
 642
 643         memset(&info, 0, sizeof(info));
 644         info.si_signo = SIGTRAP;
 645         info.si_code = TRAP_BRKPT;
 646
 647         /* User-mode eip? */
 648         info.si_addr = user_mode_vm(regs) ? (void __user *) regs->eip : NULL;
 649
 650         /* Send us the fakey SIGTRAP */
 651         force_sig_info(SIGTRAP, &info, tsk);
 652 }
 653
 654 /* notification of system call entry/exit
 655  * - triggered by current->work.syscall_trace
 656  */
 657 __attribute__((regparm(3)))
 658 int do_syscall_trace(struct pt_regs *regs, int entryexit)
 659 {
 660         int is_sysemu = test_thread_flag(TIF_SYSCALL_EMU);
 661         /*
 662          * With TIF_SYSCALL_EMU set we want to ignore TIF_SINGLESTEP for syscall
 663          * interception
 664          */
 665         int is_singlestep = !is_sysemu && test_thread_flag(TIF_SINGLESTEP);
 666         int ret = 0;
 667
 668         /* do the secure computing check first */
 669         if (!entryexit)
 670                 secure_computing(regs->orig_eax);
 671
 672         if (unlikely(current->audit_context)) {
 673                 if (entryexit)
 674                         audit_syscall_exit(AUDITSC_RESULT(regs->eax),
 675                                                 regs->eax);
 676                 /* Debug traps, when using PTRACE_SINGLESTEP, must be sent only
 677                  * on the syscall exit path. Normally, when TIF_SYSCALL_AUDIT is
 678                  * not used, entry.S will call us only on syscall exit, not
 679                  * entry; so when TIF_SYSCALL_AUDIT is used we must avoid
 680                  * calling send_sigtrap() on syscall entry.
 681                  *
 682                  * Note that when PTRACE_SYSEMU_SINGLESTEP is used,
 683                  * is_singlestep is false, despite his name, so we will still do
 684                  * the correct thing.
 685                  */
 686                 else if (is_singlestep)
 687                         goto out;
 688         }
 689
 690         if (!(current->ptrace & PT_PTRACED))
 691                 goto out;
 692
 693         /* If a process stops on the 1st tracepoint with SYSCALL_TRACE
 694          * and then is resumed with SYSEMU_SINGLESTEP, it will come in
 695          * here. We have to check this and return */
 696         if (is_sysemu && entryexit)
 697                 return 0;
 698
 699         /* Fake a debug trap */
 700         if (is_singlestep)
 701                 send_sigtrap(current, regs, 0);
 702
 703         if (!test_thread_flag(TIF_SYSCALL_TRACE) && !is_sysemu)
 704                 goto out;
 705
 706         /* the 0x80 provides a way for the tracing parent to distinguish
 707            between a syscall stop and SIGTRAP delivery */
 708         /* Note that the debugger could change the result of test_thread_flag!*/
 709         ptrace_notify(SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD) ? 0x80:0));
 710
 711         /*
 712          * this isn't the same as continuing with a signal, but it will do
 713          * for normal use.  strace only continues with a signal if the
 714          * stopping signal is not SIGTRAP.  -brl
 715          */
 716         if (current->exit_code) {
 717                 send_sig(current->exit_code, current, 1);
 718                 current->exit_code = 0;
 719         }
 720         ret = is_sysemu;
 721 out:
 722         if (unlikely(current->audit_context) && !entryexit)
 723                 audit_syscall_entry(AUDIT_ARCH_I386, regs->orig_eax,
 724                                     regs->ebx, regs->ecx, regs->edx, regs->esi);
 725         if (ret == 0)
 726                 return 0;
 727
 728         regs->orig_eax = -1; /* force skip of syscall restarting */
 729         if (unlikely(current->audit_context))
 730                 audit_syscall_exit(AUDITSC_RESULT(regs->eax), regs->eax);
 731         return 1;
 732 }