arch/um/os-Linux/skas/process.c

   1 /*
   2  * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
   3  * Copyright (C) 2002- 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   4  * Licensed under the GPL
   5  */
   6
   7 #include <stdlib.h>
   8 #include <unistd.h>
   9 #include <sched.h>
  10 #include <errno.h>
  11 #include <string.h>
  12 #include <sys/mman.h>
  13 #include <sys/wait.h>
  14 #include <asm/unistd.h>
  15 #include <as-layout.h>
  16 #include <init.h>
  17 #include <kern_util.h>
  18 #include <mem.h>
  19 #include <os.h>
  20 #include <ptrace_user.h>
  21 #include <registers.h>
  22 #include <skas.h>
  23 #include <sysdep/stub.h>
  24 #include <linux/threads.h>
  25
  26 int is_skas_winch(int pid, int fd, void *data)
  27 {
  28         return pid == getpgrp();
  29 }
  30
  31 static int ptrace_dump_regs(int pid)
  32 {
  33         unsigned long regs[MAX_REG_NR];
  34         int i;
  35
  36         if (ptrace(PTRACE_GETREGS, pid, 0, regs) < 0)
  37                 return -errno;
  38
  39         printk(UM_KERN_ERR "Stub registers -\n");
  40         for (i = 0; i < ARRAY_SIZE(regs); i++)
  41                 printk(UM_KERN_ERR "\t%d - %lx\n", i, regs[i]);
  42
  43         return 0;
  44 }
  45
  46 /*
  47  * Signals that are OK to receive in the stub - we'll just continue it.
  48  * SIGWINCH will happen when UML is inside a detached screen.
  49  */
  50 #define STUB_SIG_MASK ((1 << SIGALRM) | (1 << SIGWINCH))
  51
  52 /* Signals that the stub will finish with - anything else is an error */
  53 #define STUB_DONE_MASK (1 << SIGTRAP)
  54
  55 void wait_stub_done(int pid)
  56 {
  57         int n, status, err;
  58
  59         while (1) {
  60                 CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
  61                 if ((n < 0) || !WIFSTOPPED(status))
  62                         goto bad_wait;
  63
  64                 if (((1 << WSTOPSIG(status)) & STUB_SIG_MASK) == 0)
  65                         break;
  66
  67                 err = ptrace(PTRACE_CONT, pid, 0, 0);
  68                 if (err) {
  69                         printk(UM_KERN_ERR "wait_stub_done : continue failed, "
  70                                "errno = %d\n", errno);
  71                         fatal_sigsegv();
  72                 }
  73         }
  74
  75         if (((1 << WSTOPSIG(status)) & STUB_DONE_MASK) != 0)
  76                 return;
  77
  78 bad_wait:
  79         err = ptrace_dump_regs(pid);
  80         if (err)
  81                 printk(UM_KERN_ERR "Failed to get registers from stub, "
  82                        "errno = %d\n", -err);
  83         printk(UM_KERN_ERR "wait_stub_done : failed to wait for SIGTRAP, "
  84                "pid = %d, n = %d, errno = %d, status = 0x%x\n", pid, n, errno,
  85                status);
  86         fatal_sigsegv();
  87 }
  88
  89 extern unsigned long current_stub_stack(void);
  90
  91 static void get_skas_faultinfo(int pid, struct faultinfo *fi, unsigned long *aux_fp_regs)
  92 {
  93         int err;
  94
  95         err = get_fp_registers(pid, aux_fp_regs);
  96         if (err < 0) {
  97                 printk(UM_KERN_ERR "save_fp_registers returned %d\n",
  98                        err);
  99                 fatal_sigsegv();
 100         }
 101         err = ptrace(PTRACE_CONT, pid, 0, SIGSEGV);
 102         if (err) {
 103                 printk(UM_KERN_ERR "Failed to continue stub, pid = %d, "
 104                        "errno = %d\n", pid, errno);
 105                 fatal_sigsegv();
 106         }
 107         wait_stub_done(pid);
 108
 109         /*
 110          * faultinfo is prepared by the stub_segv_handler at start of
 111          * the stub stack page. We just have to copy it.
 112          */
 113         memcpy(fi, (void *)current_stub_stack(), sizeof(*fi));
 114
 115         err = put_fp_registers(pid, aux_fp_regs);
 116         if (err < 0) {
 117                 printk(UM_KERN_ERR "put_fp_registers returned %d\n",
 118                        err);
 119                 fatal_sigsegv();
 120         }
 121 }
 122
 123 static void handle_segv(int pid, struct uml_pt_regs *regs, unsigned long *aux_fp_regs)
 124 {
 125         get_skas_faultinfo(pid, &regs->faultinfo, aux_fp_regs);
 126         segv(regs->faultinfo, 0, 1, NULL);
 127 }
 128
 129 /*
 130  * To use the same value of using_sysemu as the caller, ask it that value
 131  * (in local_using_sysemu
 132  */
 133 static void handle_trap(int pid, struct uml_pt_regs *regs,
 134                         int local_using_sysemu)
 135 {
 136         int err, status;
 137
 138         if ((UPT_IP(regs) >= STUB_START) && (UPT_IP(regs) < STUB_END))
 139                 fatal_sigsegv();
 140
 141         if (!local_using_sysemu)
 142         {
 143                 err = ptrace(PTRACE_POKEUSER, pid, PT_SYSCALL_NR_OFFSET,
 144                              __NR_getpid);
 145                 if (err < 0) {
 146                         printk(UM_KERN_ERR "handle_trap - nullifying syscall "
 147                                "failed, errno = %d\n", errno);
 148                         fatal_sigsegv();
 149                 }
 150
 151                 err = ptrace(PTRACE_SYSCALL, pid, 0, 0);
 152                 if (err < 0) {
 153                         printk(UM_KERN_ERR "handle_trap - continuing to end of "
 154                                "syscall failed, errno = %d\n", errno);
 155                         fatal_sigsegv();
 156                 }
 157
 158                 CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
 159                 if ((err < 0) || !WIFSTOPPED(status) ||
 160                     (WSTOPSIG(status) != SIGTRAP + 0x80)) {
 161                         err = ptrace_dump_regs(pid);
 162                         if (err)
 163                                 printk(UM_KERN_ERR "Failed to get registers "
 164                                        "from process, errno = %d\n", -err);
 165                         printk(UM_KERN_ERR "handle_trap - failed to wait at "
 166                                "end of syscall, errno = %d, status = %d\n",
 167                                errno, status);
 168                         fatal_sigsegv();
 169                 }
 170         }
 171
 172         handle_syscall(regs);
 173 }
 174
 175 extern char __syscall_stub_start[];
 176
 177 /**
 178  * userspace_tramp() - userspace trampoline
 179  * @stack:      pointer to the new userspace stack page, can be NULL, if? FIXME:
 180  *
 181  * The userspace trampoline is used to setup a new userspace process in start_userspace() after it was clone()'ed.
 182  * This function will run on a temporary stack page.
 183  * It ptrace()'es itself, then
 184  * Two pages are mapped into the userspace address space:
 185  * - STUB_CODE (with EXEC), which contains the skas stub code
 186  * - STUB_DATA (with R/W), which contains a data page that is used to transfer certain data between the UML userspace process and the UML kernel.
 187  * Also for the userspace process a SIGSEGV handler is installed to catch pagefaults in the userspace process.
 188  * And last the process stops itself to give control to the UML kernel for this userspace process.
 189  *
 190  * Return: Always zero, otherwise the current userspace process is ended with non null exit() call
 191  */
 192 static int userspace_tramp(void *stack)
 193 {
 194         void *addr;
 195         int fd;
 196         unsigned long long offset;
 197
 198         ptrace(PTRACE_TRACEME, 0, 0, 0);
 199
 200         signal(SIGTERM, SIG_DFL);
 201         signal(SIGWINCH, SIG_IGN);
 202
 203         /*
 204          * This has a pte, but it can't be mapped in with the usual
 205          * tlb_flush mechanism because this is part of that mechanism
 206          */
 207         fd = phys_mapping(to_phys(__syscall_stub_start), &offset);
 208         addr = mmap64((void *) STUB_CODE, UM_KERN_PAGE_SIZE,
 209                       PROT_EXEC, MAP_FIXED | MAP_PRIVATE, fd, offset);
 210         if (addr == MAP_FAILED) {
 211                 printk(UM_KERN_ERR "mapping mmap stub at 0x%lx failed, "
 212                        "errno = %d\n", STUB_CODE, errno);
 213                 exit(1);
 214         }
 215
 216         if (stack != NULL) {
 217                 fd = phys_mapping(to_phys(stack), &offset);
 218                 addr = mmap((void *) STUB_DATA,
 219                             UM_KERN_PAGE_SIZE, PROT_READ | PROT_WRITE,
 220                             MAP_FIXED | MAP_SHARED, fd, offset);
 221                 if (addr == MAP_FAILED) {
 222                         printk(UM_KERN_ERR "mapping segfault stack "
 223                                "at 0x%lx failed, errno = %d\n",
 224                                STUB_DATA, errno);
 225                         exit(1);
 226                 }
 227         }
 228         if (stack != NULL) {
 229                 struct sigaction sa;
 230
 231                 unsigned long v = STUB_CODE +
 232                                   (unsigned long) stub_segv_handler -
 233                                   (unsigned long) __syscall_stub_start;
 234
 235                 set_sigstack((void *) STUB_DATA, UM_KERN_PAGE_SIZE);
 236                 sigemptyset(&sa.sa_mask);
 237                 sa.sa_flags = SA_ONSTACK | SA_NODEFER | SA_SIGINFO;
 238                 sa.sa_sigaction = (void *) v;
 239                 sa.sa_restorer = NULL;
 240                 if (sigaction(SIGSEGV, &sa, NULL) < 0) {
 241                         printk(UM_KERN_ERR "userspace_tramp - setting SIGSEGV "
 242                                "handler failed - errno = %d\n", errno);
 243                         exit(1);
 244                 }
 245         }
 246
 247         kill(os_getpid(), SIGSTOP);
 248         return 0;
 249 }
 250
 251 int userspace_pid[NR_CPUS];
 252
 253 /**
 254  * start_userspace() - prepare a new userspace process
 255  * @stub_stack: pointer to the stub stack. Can be NULL, if? FIXME:
 256  *
 257  * Setups a new temporary stack page that is used while userspace_tramp() runs
 258  * Clones the kernel process into a new userspace process, with FDs only.
 259  *
 260  * Return: When positive: the process id of the new userspace process,
 261  *         when negative: an error number.
 262  * FIXME: can PIDs become negative?!
 263  */
 264 int start_userspace(unsigned long stub_stack)
 265 {
 266         void *stack;
 267         unsigned long sp;
 268         int pid, status, n, flags, err;
 269
 270         /* setup a temporary stack page */
 271         stack = mmap(NULL, UM_KERN_PAGE_SIZE,
 272                      PROT_READ | PROT_WRITE | PROT_EXEC,
 273                      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 274         if (stack == MAP_FAILED) {
 275                 err = -errno;
 276                 printk(UM_KERN_ERR "start_userspace : mmap failed, "
 277                        "errno = %d\n", errno);
 278                 return err;
 279         }
 280
 281         /* set stack pointer to the end of the stack page, so it can grow downwards */
 282         sp = (unsigned long) stack + UM_KERN_PAGE_SIZE - sizeof(void *);
 283
 284         flags = CLONE_FILES | SIGCHLD;
 285
 286         /* clone into new userspace process */
 287         pid = clone(userspace_tramp, (void *) sp, flags, (void *) stub_stack);
 288         if (pid < 0) {
 289                 err = -errno;
 290                 printk(UM_KERN_ERR "start_userspace : clone failed, "
 291                        "errno = %d\n", errno);
 292                 return err;
 293         }
 294
 295         do {
 296                 CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
 297                 if (n < 0) {
 298                         err = -errno;
 299                         printk(UM_KERN_ERR "start_userspace : wait failed, "
 300                                "errno = %d\n", errno);
 301                         goto out_kill;
 302                 }
 303         } while (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGALRM));
 304
 305         if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP)) {
 306                 err = -EINVAL;
 307                 printk(UM_KERN_ERR "start_userspace : expected SIGSTOP, got "
 308                        "status = %d\n", status);
 309                 goto out_kill;
 310         }
 311
 312         if (ptrace(PTRACE_OLDSETOPTIONS, pid, NULL,
 313                    (void *) PTRACE_O_TRACESYSGOOD) < 0) {
 314                 err = -errno;
 315                 printk(UM_KERN_ERR "start_userspace : PTRACE_OLDSETOPTIONS "
 316                        "failed, errno = %d\n", errno);
 317                 goto out_kill;
 318         }
 319
 320         if (munmap(stack, UM_KERN_PAGE_SIZE) < 0) {
 321                 err = -errno;
 322                 printk(UM_KERN_ERR "start_userspace : munmap failed, "
 323                        "errno = %d\n", errno);
 324                 goto out_kill;
 325         }
 326
 327         return pid;
 328
 329  out_kill:
 330         os_kill_ptraced_process(pid, 1);
 331         return err;
 332 }
 333
 334 void userspace(struct uml_pt_regs *regs, unsigned long *aux_fp_regs)
 335 {
 336         int err, status, op, pid = userspace_pid[0];
 337         /* To prevent races if using_sysemu changes under us.*/
 338         int local_using_sysemu;
 339         siginfo_t si;
 340
 341         /* Handle any immediate reschedules or signals */
 342         interrupt_end();
 343
 344         while (1) {
 345
 346                 /*
 347                  * This can legitimately fail if the process loads a
 348                  * bogus value into a segment register.  It will
 349                  * segfault and PTRACE_GETREGS will read that value
 350                  * out of the process.  However, PTRACE_SETREGS will
 351                  * fail.  In this case, there is nothing to do but
 352                  * just kill the process.
 353                  */
 354                 if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp)) {
 355                         printk(UM_KERN_ERR "userspace - ptrace set regs "
 356                                "failed, errno = %d\n", errno);
 357                         fatal_sigsegv();
 358                 }
 359
 360                 if (put_fp_registers(pid, regs->fp)) {
 361                         printk(UM_KERN_ERR "userspace - ptrace set fp regs "
 362                                "failed, errno = %d\n", errno);
 363                         fatal_sigsegv();
 364                 }
 365
 366                 /* Now we set local_using_sysemu to be used for one loop */
 367                 local_using_sysemu = get_using_sysemu();
 368
 369                 op = SELECT_PTRACE_OPERATION(local_using_sysemu,
 370                                              singlestepping(NULL));
 371
 372                 if (ptrace(op, pid, 0, 0)) {
 373                         printk(UM_KERN_ERR "userspace - ptrace continue "
 374                                "failed, op = %d, errno = %d\n", op, errno);
 375                         fatal_sigsegv();
 376                 }
 377
 378                 CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
 379                 if (err < 0) {
 380                         printk(UM_KERN_ERR "userspace - wait failed, "
 381                                "errno = %d\n", errno);
 382                         fatal_sigsegv();
 383                 }
 384
 385                 regs->is_user = 1;
 386                 if (ptrace(PTRACE_GETREGS, pid, 0, regs->gp)) {
 387                         printk(UM_KERN_ERR "userspace - PTRACE_GETREGS failed, "
 388                                "errno = %d\n", errno);
 389                         fatal_sigsegv();
 390                 }
 391
 392                 if (get_fp_registers(pid, regs->fp)) {
 393                         printk(UM_KERN_ERR "userspace -  get_fp_registers failed, "
 394                                "errno = %d\n", errno);
 395                         fatal_sigsegv();
 396                 }
 397
 398                 UPT_SYSCALL_NR(regs) = -1; /* Assume: It's not a syscall */
 399
 400                 if (WIFSTOPPED(status)) {
 401                         int sig = WSTOPSIG(status);
 402
 403                         ptrace(PTRACE_GETSIGINFO, pid, 0, (struct siginfo *)&si);
 404
 405                         switch (sig) {
 406                         case SIGSEGV:
 407                                 if (PTRACE_FULL_FAULTINFO) {
 408                                         get_skas_faultinfo(pid,
 409                                                            &regs->faultinfo, aux_fp_regs);
 410                                         (*sig_info[SIGSEGV])(SIGSEGV, (struct siginfo *)&si,
 411                                                              regs);
 412                                 }
 413                                 else handle_segv(pid, regs, aux_fp_regs);
 414                                 break;
 415                         case SIGTRAP + 0x80:
 416                                 handle_trap(pid, regs, local_using_sysemu);
 417                                 break;
 418                         case SIGTRAP:
 419                                 relay_signal(SIGTRAP, (struct siginfo *)&si, regs);
 420                                 break;
 421                         case SIGALRM:
 422                                 break;
 423                         case SIGIO:
 424                         case SIGILL:
 425                         case SIGBUS:
 426                         case SIGFPE:
 427                         case SIGWINCH:
 428                                 block_signals();
 429                                 (*sig_info[sig])(sig, (struct siginfo *)&si, regs);
 430                                 unblock_signals();
 431                                 break;
 432                         default:
 433                                 printk(UM_KERN_ERR "userspace - child stopped "
 434                                        "with signal %d\n", sig);
 435                                 fatal_sigsegv();
 436                         }
 437                         pid = userspace_pid[0];
 438                         interrupt_end();
 439
 440                         /* Avoid -ERESTARTSYS handling in host */
 441                         if (PT_SYSCALL_NR_OFFSET != PT_SYSCALL_RET_OFFSET)
 442                                 PT_SYSCALL_NR(regs->gp) = -1;
 443                 }
 444         }
 445 }
 446
 447 static unsigned long thread_regs[MAX_REG_NR];
 448 static unsigned long thread_fp_regs[FP_SIZE];
 449
 450 static int __init init_thread_regs(void)
 451 {
 452         get_safe_registers(thread_regs, thread_fp_regs);
 453         /* Set parent's instruction pointer to start of clone-stub */
 454         thread_regs[REGS_IP_INDEX] = STUB_CODE +
 455                                 (unsigned long) stub_clone_handler -
 456                                 (unsigned long) __syscall_stub_start;
 457         thread_regs[REGS_SP_INDEX] = STUB_DATA + UM_KERN_PAGE_SIZE -
 458                 sizeof(void *);
 459 #ifdef __SIGNAL_FRAMESIZE
 460         thread_regs[REGS_SP_INDEX] -= __SIGNAL_FRAMESIZE;
 461 #endif
 462         return 0;
 463 }
 464
 465 __initcall(init_thread_regs);
 466
 467 int copy_context_skas0(unsigned long new_stack, int pid)
 468 {
 469         int err;
 470         unsigned long current_stack = current_stub_stack();
 471         struct stub_data *data = (struct stub_data *) current_stack;
 472         struct stub_data *child_data = (struct stub_data *) new_stack;
 473         unsigned long long new_offset;
 474         int new_fd = phys_mapping(to_phys((void *)new_stack), &new_offset);
 475
 476         /*
 477          * prepare offset and fd of child's stack as argument for parent's
 478          * and child's mmap2 calls
 479          */
 480         *data = ((struct stub_data) {
 481                         .offset = MMAP_OFFSET(new_offset),
 482                         .fd     = new_fd
 483         });
 484
 485         err = ptrace_setregs(pid, thread_regs);
 486         if (err < 0) {
 487                 err = -errno;
 488                 printk(UM_KERN_ERR "copy_context_skas0 : PTRACE_SETREGS "
 489                        "failed, pid = %d, errno = %d\n", pid, -err);
 490                 return err;
 491         }
 492
 493         err = put_fp_registers(pid, thread_fp_regs);
 494         if (err < 0) {
 495                 printk(UM_KERN_ERR "copy_context_skas0 : put_fp_registers "
 496                        "failed, pid = %d, err = %d\n", pid, err);
 497                 return err;
 498         }
 499
 500         /* set a well known return code for detection of child write failure */
 501         child_data->err = 12345678;
 502
 503         /*
 504          * Wait, until parent has finished its work: read child's pid from
 505          * parent's stack, and check, if bad result.
 506          */
 507         err = ptrace(PTRACE_CONT, pid, 0, 0);
 508         if (err) {
 509                 err = -errno;
 510                 printk(UM_KERN_ERR "Failed to continue new process, pid = %d, "
 511                        "errno = %d\n", pid, errno);
 512                 return err;
 513         }
 514
 515         wait_stub_done(pid);
 516
 517         pid = data->err;
 518         if (pid < 0) {
 519                 printk(UM_KERN_ERR "copy_context_skas0 - stub-parent reports "
 520                        "error %d\n", -pid);
 521                 return pid;
 522         }
 523
 524         /*
 525          * Wait, until child has finished too: read child's result from
 526          * child's stack and check it.
 527          */
 528         wait_stub_done(pid);
 529         if (child_data->err != STUB_DATA) {
 530                 printk(UM_KERN_ERR "copy_context_skas0 - stub-child reports "
 531                        "error %ld\n", child_data->err);
 532                 err = child_data->err;
 533                 goto out_kill;
 534         }
 535
 536         if (ptrace(PTRACE_OLDSETOPTIONS, pid, NULL,
 537                    (void *)PTRACE_O_TRACESYSGOOD) < 0) {
 538                 err = -errno;
 539                 printk(UM_KERN_ERR "copy_context_skas0 : PTRACE_OLDSETOPTIONS "
 540                        "failed, errno = %d\n", errno);
 541                 goto out_kill;
 542         }
 543
 544         return pid;
 545
 546  out_kill:
 547         os_kill_ptraced_process(pid, 1);
 548         return err;
 549 }
 550
 551 void new_thread(void *stack, jmp_buf *buf, void (*handler)(void))
 552 {
 553         (*buf)[0].JB_IP = (unsigned long) handler;
 554         (*buf)[0].JB_SP = (unsigned long) stack + UM_THREAD_SIZE -
 555                 sizeof(void *);
 556 }
 557
 558 #define INIT_JMP_NEW_THREAD 0
 559 #define INIT_JMP_CALLBACK 1
 560 #define INIT_JMP_HALT 2
 561 #define INIT_JMP_REBOOT 3
 562
 563 void switch_threads(jmp_buf *me, jmp_buf *you)
 564 {
 565         if (UML_SETJMP(me) == 0)
 566                 UML_LONGJMP(you, 1);
 567 }
 568
 569 static jmp_buf initial_jmpbuf;
 570
 571 /* XXX Make these percpu */
 572 static void (*cb_proc)(void *arg);
 573 static void *cb_arg;
 574 static jmp_buf *cb_back;
 575
 576 int start_idle_thread(void *stack, jmp_buf *switch_buf)
 577 {
 578         int n;
 579
 580         set_handler(SIGWINCH);
 581
 582         /*
 583          * Can't use UML_SETJMP or UML_LONGJMP here because they save
 584          * and restore signals, with the possible side-effect of
 585          * trying to handle any signals which came when they were
 586          * blocked, which can't be done on this stack.
 587          * Signals must be blocked when jumping back here and restored
 588          * after returning to the jumper.
 589          */
 590         n = setjmp(initial_jmpbuf);
 591         switch (n) {
 592         case INIT_JMP_NEW_THREAD:
 593                 (*switch_buf)[0].JB_IP = (unsigned long) uml_finishsetup;
 594                 (*switch_buf)[0].JB_SP = (unsigned long) stack +
 595                         UM_THREAD_SIZE - sizeof(void *);
 596                 break;
 597         case INIT_JMP_CALLBACK:
 598                 (*cb_proc)(cb_arg);
 599                 longjmp(*cb_back, 1);
 600                 break;
 601         case INIT_JMP_HALT:
 602                 kmalloc_ok = 0;
 603                 return 0;
 604         case INIT_JMP_REBOOT:
 605                 kmalloc_ok = 0;
 606                 return 1;
 607         default:
 608                 printk(UM_KERN_ERR "Bad sigsetjmp return in "
 609                        "start_idle_thread - %d\n", n);
 610                 fatal_sigsegv();
 611         }
 612         longjmp(*switch_buf, 1);
 613
 614         /* unreachable */
 615         printk(UM_KERN_ERR "impossible long jump!");
 616         fatal_sigsegv();
 617         return 0;
 618 }
 619
 620 void initial_thread_cb_skas(void (*proc)(void *), void *arg)
 621 {
 622         jmp_buf here;
 623
 624         cb_proc = proc;
 625         cb_arg = arg;
 626         cb_back = &here;
 627
 628         block_signals();
 629         if (UML_SETJMP(&here) == 0)
 630                 UML_LONGJMP(&initial_jmpbuf, INIT_JMP_CALLBACK);
 631         unblock_signals();
 632
 633         cb_proc = NULL;
 634         cb_arg = NULL;
 635         cb_back = NULL;
 636 }
 637
 638 void halt_skas(void)
 639 {
 640         block_signals();
 641         UML_LONGJMP(&initial_jmpbuf, INIT_JMP_HALT);
 642 }
 643
 644 void reboot_skas(void)
 645 {
 646         block_signals();
 647         UML_LONGJMP(&initial_jmpbuf, INIT_JMP_REBOOT);
 648 }
 649
 650 void __switch_mm(struct mm_id *mm_idp)
 651 {
 652         userspace_pid[0] = mm_idp->u.pid;
 653 }