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