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