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

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
   4  * Copyright (C) 2002- 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   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 const char *ptrace_reg_name(int idx)
  32 {
  33 #define R(n) case HOST_##n: return #n
  34
  35         switch (idx) {
  36 #ifdef __x86_64__
  37         R(BX);
  38         R(CX);
  39         R(DI);
  40         R(SI);
  41         R(DX);
  42         R(BP);
  43         R(AX);
  44         R(R8);
  45         R(R9);
  46         R(R10);
  47         R(R11);
  48         R(R12);
  49         R(R13);
  50         R(R14);
  51         R(R15);
  52         R(ORIG_AX);
  53         R(CS);
  54         R(SS);
  55         R(EFLAGS);
  56 #elif defined(__i386__)
  57         R(IP);
  58         R(SP);
  59         R(EFLAGS);
  60         R(AX);
  61         R(BX);
  62         R(CX);
  63         R(DX);
  64         R(SI);
  65         R(DI);
  66         R(BP);
  67         R(CS);
  68         R(SS);
  69         R(DS);
  70         R(FS);
  71         R(ES);
  72         R(GS);
  73         R(ORIG_AX);
  74 #endif
  75         }
  76         return "";
  77 }
  78
  79 static int ptrace_dump_regs(int pid)
  80 {
  81         unsigned long regs[MAX_REG_NR];
  82         int i;
  83
  84         if (ptrace(PTRACE_GETREGS, pid, 0, regs) < 0)
  85                 return -errno;
  86
  87         printk(UM_KERN_ERR "Stub registers -\n");
  88         for (i = 0; i < ARRAY_SIZE(regs); i++) {
  89                 const char *regname = ptrace_reg_name(i);
  90
  91                 printk(UM_KERN_ERR "\t%s\t(%2d): %lx\n", regname, i, regs[i]);
  92         }
  93
  94         return 0;
  95 }
  96
  97 /*
  98  * Signals that are OK to receive in the stub - we'll just continue it.
  99  * SIGWINCH will happen when UML is inside a detached screen.
 100  */
 101 #define STUB_SIG_MASK ((1 << SIGALRM) | (1 << SIGWINCH))
 102
 103 /* Signals that the stub will finish with - anything else is an error */
 104 #define STUB_DONE_MASK (1 << SIGTRAP)
 105
 106 void wait_stub_done(int pid)
 107 {
 108         int n, status, err;
 109
 110         while (1) {
 111                 CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
 112                 if ((n < 0) || !WIFSTOPPED(status))
 113                         goto bad_wait;
 114
 115                 if (((1 << WSTOPSIG(status)) & STUB_SIG_MASK) == 0)
 116                         break;
 117
 118                 err = ptrace(PTRACE_CONT, pid, 0, 0);
 119                 if (err) {
 120                         printk(UM_KERN_ERR "wait_stub_done : continue failed, "
 121                                "errno = %d\n", errno);
 122                         fatal_sigsegv();
 123                 }
 124         }
 125
 126         if (((1 << WSTOPSIG(status)) & STUB_DONE_MASK) != 0)
 127                 return;
 128
 129 bad_wait:
 130         err = ptrace_dump_regs(pid);
 131         if (err)
 132                 printk(UM_KERN_ERR "Failed to get registers from stub, "
 133                        "errno = %d\n", -err);
 134         printk(UM_KERN_ERR "wait_stub_done : failed to wait for SIGTRAP, "
 135                "pid = %d, n = %d, errno = %d, status = 0x%x\n", pid, n, errno,
 136                status);
 137         fatal_sigsegv();
 138 }
 139
 140 extern unsigned long current_stub_stack(void);
 141
 142 static void get_skas_faultinfo(int pid, struct faultinfo *fi, unsigned long *aux_fp_regs)
 143 {
 144         int err;
 145
 146         err = get_fp_registers(pid, aux_fp_regs);
 147         if (err < 0) {
 148                 printk(UM_KERN_ERR "save_fp_registers returned %d\n",
 149                        err);
 150                 fatal_sigsegv();
 151         }
 152         err = ptrace(PTRACE_CONT, pid, 0, SIGSEGV);
 153         if (err) {
 154                 printk(UM_KERN_ERR "Failed to continue stub, pid = %d, "
 155                        "errno = %d\n", pid, errno);
 156                 fatal_sigsegv();
 157         }
 158         wait_stub_done(pid);
 159
 160         /*
 161          * faultinfo is prepared by the stub_segv_handler at start of
 162          * the stub stack page. We just have to copy it.
 163          */
 164         memcpy(fi, (void *)current_stub_stack(), sizeof(*fi));
 165
 166         err = put_fp_registers(pid, aux_fp_regs);
 167         if (err < 0) {
 168                 printk(UM_KERN_ERR "put_fp_registers returned %d\n",
 169                        err);
 170                 fatal_sigsegv();
 171         }
 172 }
 173
 174 static void handle_segv(int pid, struct uml_pt_regs *regs, unsigned long *aux_fp_regs)
 175 {
 176         get_skas_faultinfo(pid, &regs->faultinfo, aux_fp_regs);
 177         segv(regs->faultinfo, 0, 1, NULL);
 178 }
 179
 180 /*
 181  * To use the same value of using_sysemu as the caller, ask it that value
 182  * (in local_using_sysemu
 183  */
 184 static void handle_trap(int pid, struct uml_pt_regs *regs,
 185                         int local_using_sysemu)
 186 {
 187         int err, status;
 188
 189         if ((UPT_IP(regs) >= STUB_START) && (UPT_IP(regs) < STUB_END))
 190                 fatal_sigsegv();
 191
 192         if (!local_using_sysemu)
 193         {
 194                 err = ptrace(PTRACE_POKEUSER, pid, PT_SYSCALL_NR_OFFSET,
 195                              __NR_getpid);
 196                 if (err < 0) {
 197                         printk(UM_KERN_ERR "handle_trap - nullifying syscall "
 198                                "failed, errno = %d\n", errno);
 199                         fatal_sigsegv();
 200                 }
 201
 202                 err = ptrace(PTRACE_SYSCALL, pid, 0, 0);
 203                 if (err < 0) {
 204                         printk(UM_KERN_ERR "handle_trap - continuing to end of "
 205                                "syscall failed, errno = %d\n", errno);
 206                         fatal_sigsegv();
 207                 }
 208
 209                 CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
 210                 if ((err < 0) || !WIFSTOPPED(status) ||
 211                     (WSTOPSIG(status) != SIGTRAP + 0x80)) {
 212                         err = ptrace_dump_regs(pid);
 213                         if (err)
 214                                 printk(UM_KERN_ERR "Failed to get registers "
 215                                        "from process, errno = %d\n", -err);
 216                         printk(UM_KERN_ERR "handle_trap - failed to wait at "
 217                                "end of syscall, errno = %d, status = %d\n",
 218                                errno, status);
 219                         fatal_sigsegv();
 220                 }
 221         }
 222
 223         handle_syscall(regs);
 224 }
 225
 226 extern char __syscall_stub_start[];
 227
 228 /**
 229  * userspace_tramp() - userspace trampoline
 230  * @stack:      pointer to the new userspace stack page, can be NULL, if? FIXME:
 231  *
 232  * The userspace trampoline is used to setup a new userspace process in start_userspace() after it was clone()'ed.
 233  * This function will run on a temporary stack page.
 234  * It ptrace()'es itself, then
 235  * Two pages are mapped into the userspace address space:
 236  * - STUB_CODE (with EXEC), which contains the skas stub code
 237  * - 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.
 238  * Also for the userspace process a SIGSEGV handler is installed to catch pagefaults in the userspace process.
 239  * And last the process stops itself to give control to the UML kernel for this userspace process.
 240  *
 241  * Return: Always zero, otherwise the current userspace process is ended with non null exit() call
 242  */
 243 static int userspace_tramp(void *stack)
 244 {
 245         void *addr;
 246         int fd;
 247         unsigned long long offset;
 248
 249         ptrace(PTRACE_TRACEME, 0, 0, 0);
 250
 251         signal(SIGTERM, SIG_DFL);
 252         signal(SIGWINCH, SIG_IGN);
 253
 254         fd = phys_mapping(uml_to_phys(__syscall_stub_start), &offset);
 255         addr = mmap64((void *) STUB_CODE, UM_KERN_PAGE_SIZE,
 256                       PROT_EXEC, MAP_FIXED | MAP_PRIVATE, fd, offset);
 257         if (addr == MAP_FAILED) {
 258                 printk(UM_KERN_ERR "mapping mmap stub at 0x%lx failed, "
 259                        "errno = %d\n", STUB_CODE, errno);
 260                 exit(1);
 261         }
 262
 263         if (stack != NULL) {
 264                 fd = phys_mapping(uml_to_phys(stack), &offset);
 265                 addr = mmap((void *) STUB_DATA,
 266                             UM_KERN_PAGE_SIZE, PROT_READ | PROT_WRITE,
 267                             MAP_FIXED | MAP_SHARED, fd, offset);
 268                 if (addr == MAP_FAILED) {
 269                         printk(UM_KERN_ERR "mapping segfault stack "
 270                                "at 0x%lx failed, errno = %d\n",
 271                                STUB_DATA, errno);
 272                         exit(1);
 273                 }
 274         }
 275         if (stack != NULL) {
 276                 struct sigaction sa;
 277
 278                 unsigned long v = STUB_CODE +
 279                                   (unsigned long) stub_segv_handler -
 280                                   (unsigned long) __syscall_stub_start;
 281
 282                 set_sigstack((void *) STUB_DATA, UM_KERN_PAGE_SIZE);
 283                 sigemptyset(&sa.sa_mask);
 284                 sa.sa_flags = SA_ONSTACK | SA_NODEFER | SA_SIGINFO;
 285                 sa.sa_sigaction = (void *) v;
 286                 sa.sa_restorer = NULL;
 287                 if (sigaction(SIGSEGV, &sa, NULL) < 0) {
 288                         printk(UM_KERN_ERR "userspace_tramp - setting SIGSEGV "
 289                                "handler failed - errno = %d\n", errno);
 290                         exit(1);
 291                 }
 292         }
 293
 294         kill(os_getpid(), SIGSTOP);
 295         return 0;
 296 }
 297
 298 int userspace_pid[NR_CPUS];
 299 int kill_userspace_mm[NR_CPUS];
 300
 301 /**
 302  * start_userspace() - prepare a new userspace process
 303  * @stub_stack: pointer to the stub stack. Can be NULL, if? FIXME:
 304  *
 305  * Setups a new temporary stack page that is used while userspace_tramp() runs
 306  * Clones the kernel process into a new userspace process, with FDs only.
 307  *
 308  * Return: When positive: the process id of the new userspace process,
 309  *         when negative: an error number.
 310  * FIXME: can PIDs become negative?!
 311  */
 312 int start_userspace(unsigned long stub_stack)
 313 {
 314         void *stack;
 315         unsigned long sp;
 316         int pid, status, n, flags, err;
 317
 318         /* setup a temporary stack page */
 319         stack = mmap(NULL, UM_KERN_PAGE_SIZE,
 320                      PROT_READ | PROT_WRITE | PROT_EXEC,
 321                      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 322         if (stack == MAP_FAILED) {
 323                 err = -errno;
 324                 printk(UM_KERN_ERR "start_userspace : mmap failed, "
 325                        "errno = %d\n", errno);
 326                 return err;
 327         }
 328
 329         /* set stack pointer to the end of the stack page, so it can grow downwards */
 330         sp = (unsigned long)stack + UM_KERN_PAGE_SIZE;
 331
 332         flags = CLONE_FILES | SIGCHLD;
 333
 334         /* clone into new userspace process */
 335         pid = clone(userspace_tramp, (void *) sp, flags, (void *) stub_stack);
 336         if (pid < 0) {
 337                 err = -errno;
 338                 printk(UM_KERN_ERR "start_userspace : clone failed, "
 339                        "errno = %d\n", errno);
 340                 return err;
 341         }
 342
 343         do {
 344                 CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
 345                 if (n < 0) {
 346                         err = -errno;
 347                         printk(UM_KERN_ERR "start_userspace : wait failed, "
 348                                "errno = %d\n", errno);
 349                         goto out_kill;
 350                 }
 351         } while (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGALRM));
 352
 353         if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP)) {
 354                 err = -EINVAL;
 355                 printk(UM_KERN_ERR "start_userspace : expected SIGSTOP, got "
 356                        "status = %d\n", status);
 357                 goto out_kill;
 358         }
 359
 360         if (ptrace(PTRACE_OLDSETOPTIONS, pid, NULL,
 361                    (void *) PTRACE_O_TRACESYSGOOD) < 0) {
 362                 err = -errno;
 363                 printk(UM_KERN_ERR "start_userspace : PTRACE_OLDSETOPTIONS "
 364                        "failed, errno = %d\n", errno);
 365                 goto out_kill;
 366         }
 367
 368         if (munmap(stack, UM_KERN_PAGE_SIZE) < 0) {
 369                 err = -errno;
 370                 printk(UM_KERN_ERR "start_userspace : munmap failed, "
 371                        "errno = %d\n", errno);
 372                 goto out_kill;
 373         }
 374
 375         return pid;
 376
 377  out_kill:
 378         os_kill_ptraced_process(pid, 1);
 379         return err;
 380 }
 381
 382 void userspace(struct uml_pt_regs *regs, unsigned long *aux_fp_regs)
 383 {
 384         int err, status, op, pid = userspace_pid[0];
 385         /* To prevent races if using_sysemu changes under us.*/
 386         int local_using_sysemu;
 387         siginfo_t si;
 388
 389         /* Handle any immediate reschedules or signals */
 390         interrupt_end();
 391
 392         while (1) {
 393                 if (kill_userspace_mm[0])
 394                         fatal_sigsegv();
 395
 396                 /*
 397                  * This can legitimately fail if the process loads a
 398                  * bogus value into a segment register.  It will
 399                  * segfault and PTRACE_GETREGS will read that value
 400                  * out of the process.  However, PTRACE_SETREGS will
 401                  * fail.  In this case, there is nothing to do but
 402                  * just kill the process.
 403                  */
 404                 if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp)) {
 405                         printk(UM_KERN_ERR "userspace - ptrace set regs "
 406                                "failed, errno = %d\n", errno);
 407                         fatal_sigsegv();
 408                 }
 409
 410                 if (put_fp_registers(pid, regs->fp)) {
 411                         printk(UM_KERN_ERR "userspace - ptrace set fp regs "
 412                                "failed, errno = %d\n", errno);
 413                         fatal_sigsegv();
 414                 }
 415
 416                 /* Now we set local_using_sysemu to be used for one loop */
 417                 local_using_sysemu = get_using_sysemu();
 418
 419                 op = SELECT_PTRACE_OPERATION(local_using_sysemu,
 420                                              singlestepping(NULL));
 421
 422                 if (ptrace(op, pid, 0, 0)) {
 423                         printk(UM_KERN_ERR "userspace - ptrace continue "
 424                                "failed, op = %d, errno = %d\n", op, errno);
 425                         fatal_sigsegv();
 426                 }
 427
 428                 CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
 429                 if (err < 0) {
 430                         printk(UM_KERN_ERR "userspace - wait failed, "
 431                                "errno = %d\n", errno);
 432                         fatal_sigsegv();
 433                 }
 434
 435                 regs->is_user = 1;
 436                 if (ptrace(PTRACE_GETREGS, pid, 0, regs->gp)) {
 437                         printk(UM_KERN_ERR "userspace - PTRACE_GETREGS failed, "
 438                                "errno = %d\n", errno);
 439                         fatal_sigsegv();
 440                 }
 441
 442                 if (get_fp_registers(pid, regs->fp)) {
 443                         printk(UM_KERN_ERR "userspace -  get_fp_registers failed, "
 444                                "errno = %d\n", errno);
 445                         fatal_sigsegv();
 446                 }
 447
 448                 UPT_SYSCALL_NR(regs) = -1; /* Assume: It's not a syscall */
 449
 450                 if (WIFSTOPPED(status)) {
 451                         int sig = WSTOPSIG(status);
 452
 453                         /* These signal handlers need the si argument.
 454                          * The SIGIO and SIGALARM handlers which constitute the
 455                          * majority of invocations, do not use it.
 456                          */
 457                         switch (sig) {
 458                         case SIGSEGV:
 459                         case SIGTRAP:
 460                         case SIGILL:
 461                         case SIGBUS:
 462                         case SIGFPE:
 463                         case SIGWINCH:
 464                                 ptrace(PTRACE_GETSIGINFO, pid, 0, (struct siginfo *)&si);
 465                                 break;
 466                         }
 467
 468                         switch (sig) {
 469                         case SIGSEGV:
 470                                 if (PTRACE_FULL_FAULTINFO) {
 471                                         get_skas_faultinfo(pid,
 472                                                            &regs->faultinfo, aux_fp_regs);
 473                                         (*sig_info[SIGSEGV])(SIGSEGV, (struct siginfo *)&si,
 474                                                              regs);
 475                                 }
 476                                 else handle_segv(pid, regs, aux_fp_regs);
 477                                 break;
 478                         case SIGTRAP + 0x80:
 479                                 handle_trap(pid, regs, local_using_sysemu);
 480                                 break;
 481                         case SIGTRAP:
 482                                 relay_signal(SIGTRAP, (struct siginfo *)&si, regs);
 483                                 break;
 484                         case SIGALRM:
 485                                 break;
 486                         case SIGIO:
 487                         case SIGILL:
 488                         case SIGBUS:
 489                         case SIGFPE:
 490                         case SIGWINCH:
 491                                 block_signals_trace();
 492                                 (*sig_info[sig])(sig, (struct siginfo *)&si, regs);
 493                                 unblock_signals_trace();
 494                                 break;
 495                         default:
 496                                 printk(UM_KERN_ERR "userspace - child stopped "
 497                                        "with signal %d\n", sig);
 498                                 fatal_sigsegv();
 499                         }
 500                         pid = userspace_pid[0];
 501                         interrupt_end();
 502
 503                         /* Avoid -ERESTARTSYS handling in host */
 504                         if (PT_SYSCALL_NR_OFFSET != PT_SYSCALL_RET_OFFSET)
 505                                 PT_SYSCALL_NR(regs->gp) = -1;
 506                 }
 507         }
 508 }
 509
 510 static unsigned long thread_regs[MAX_REG_NR];
 511 static unsigned long thread_fp_regs[FP_SIZE];
 512
 513 static int __init init_thread_regs(void)
 514 {
 515         get_safe_registers(thread_regs, thread_fp_regs);
 516         /* Set parent's instruction pointer to start of clone-stub */
 517         thread_regs[REGS_IP_INDEX] = STUB_CODE +
 518                                 (unsigned long) stub_clone_handler -
 519                                 (unsigned long) __syscall_stub_start;
 520         thread_regs[REGS_SP_INDEX] = STUB_DATA + UM_KERN_PAGE_SIZE -
 521                 sizeof(void *);
 522 #ifdef __SIGNAL_FRAMESIZE
 523         thread_regs[REGS_SP_INDEX] -= __SIGNAL_FRAMESIZE;
 524 #endif
 525         return 0;
 526 }
 527
 528 __initcall(init_thread_regs);
 529
 530 int copy_context_skas0(unsigned long new_stack, int pid)
 531 {
 532         int err;
 533         unsigned long current_stack = current_stub_stack();
 534         struct stub_data *data = (struct stub_data *) current_stack;
 535         struct stub_data *child_data = (struct stub_data *) new_stack;
 536         unsigned long long new_offset;
 537         int new_fd = phys_mapping(uml_to_phys((void *)new_stack), &new_offset);
 538
 539         /*
 540          * prepare offset and fd of child's stack as argument for parent's
 541          * and child's mmap2 calls
 542          */
 543         *data = ((struct stub_data) {
 544                 .offset = MMAP_OFFSET(new_offset),
 545                 .fd     = new_fd,
 546                 .parent_err = -ESRCH,
 547                 .child_err = 0,
 548         });
 549
 550         *child_data = ((struct stub_data) {
 551                 .child_err = -ESRCH,
 552         });
 553
 554         err = ptrace_setregs(pid, thread_regs);
 555         if (err < 0) {
 556                 err = -errno;
 557                 printk(UM_KERN_ERR "copy_context_skas0 : PTRACE_SETREGS "
 558                        "failed, pid = %d, errno = %d\n", pid, -err);
 559                 return err;
 560         }
 561
 562         err = put_fp_registers(pid, thread_fp_regs);
 563         if (err < 0) {
 564                 printk(UM_KERN_ERR "copy_context_skas0 : put_fp_registers "
 565                        "failed, pid = %d, err = %d\n", pid, err);
 566                 return err;
 567         }
 568
 569         /*
 570          * Wait, until parent has finished its work: read child's pid from
 571          * parent's stack, and check, if bad result.
 572          */
 573         err = ptrace(PTRACE_CONT, pid, 0, 0);
 574         if (err) {
 575                 err = -errno;
 576                 printk(UM_KERN_ERR "Failed to continue new process, pid = %d, "
 577                        "errno = %d\n", pid, errno);
 578                 return err;
 579         }
 580
 581         wait_stub_done(pid);
 582
 583         pid = data->parent_err;
 584         if (pid < 0) {
 585                 printk(UM_KERN_ERR "copy_context_skas0 - stub-parent reports "
 586                        "error %d\n", -pid);
 587                 return pid;
 588         }
 589
 590         /*
 591          * Wait, until child has finished too: read child's result from
 592          * child's stack and check it.
 593          */
 594         wait_stub_done(pid);
 595         if (child_data->child_err != STUB_DATA) {
 596                 printk(UM_KERN_ERR "copy_context_skas0 - stub-child %d reports "
 597                        "error %ld\n", pid, data->child_err);
 598                 err = data->child_err;
 599                 goto out_kill;
 600         }
 601
 602         if (ptrace(PTRACE_OLDSETOPTIONS, pid, NULL,
 603                    (void *)PTRACE_O_TRACESYSGOOD) < 0) {
 604                 err = -errno;
 605                 printk(UM_KERN_ERR "copy_context_skas0 : PTRACE_OLDSETOPTIONS "
 606                        "failed, errno = %d\n", errno);
 607                 goto out_kill;
 608         }
 609
 610         return pid;
 611
 612  out_kill:
 613         os_kill_ptraced_process(pid, 1);
 614         return err;
 615 }
 616
 617 void new_thread(void *stack, jmp_buf *buf, void (*handler)(void))
 618 {
 619         (*buf)[0].JB_IP = (unsigned long) handler;
 620         (*buf)[0].JB_SP = (unsigned long) stack + UM_THREAD_SIZE -
 621                 sizeof(void *);
 622 }
 623
 624 #define INIT_JMP_NEW_THREAD 0
 625 #define INIT_JMP_CALLBACK 1
 626 #define INIT_JMP_HALT 2
 627 #define INIT_JMP_REBOOT 3
 628
 629 void switch_threads(jmp_buf *me, jmp_buf *you)
 630 {
 631         if (UML_SETJMP(me) == 0)
 632                 UML_LONGJMP(you, 1);
 633 }
 634
 635 static jmp_buf initial_jmpbuf;
 636
 637 /* XXX Make these percpu */
 638 static void (*cb_proc)(void *arg);
 639 static void *cb_arg;
 640 static jmp_buf *cb_back;
 641
 642 int start_idle_thread(void *stack, jmp_buf *switch_buf)
 643 {
 644         int n;
 645
 646         set_handler(SIGWINCH);
 647
 648         /*
 649          * Can't use UML_SETJMP or UML_LONGJMP here because they save
 650          * and restore signals, with the possible side-effect of
 651          * trying to handle any signals which came when they were
 652          * blocked, which can't be done on this stack.
 653          * Signals must be blocked when jumping back here and restored
 654          * after returning to the jumper.
 655          */
 656         n = setjmp(initial_jmpbuf);
 657         switch (n) {
 658         case INIT_JMP_NEW_THREAD:
 659                 (*switch_buf)[0].JB_IP = (unsigned long) uml_finishsetup;
 660                 (*switch_buf)[0].JB_SP = (unsigned long) stack +
 661                         UM_THREAD_SIZE - sizeof(void *);
 662                 break;
 663         case INIT_JMP_CALLBACK:
 664                 (*cb_proc)(cb_arg);
 665                 longjmp(*cb_back, 1);
 666                 break;
 667         case INIT_JMP_HALT:
 668                 kmalloc_ok = 0;
 669                 return 0;
 670         case INIT_JMP_REBOOT:
 671                 kmalloc_ok = 0;
 672                 return 1;
 673         default:
 674                 printk(UM_KERN_ERR "Bad sigsetjmp return in "
 675                        "start_idle_thread - %d\n", n);
 676                 fatal_sigsegv();
 677         }
 678         longjmp(*switch_buf, 1);
 679
 680         /* unreachable */
 681         printk(UM_KERN_ERR "impossible long jump!");
 682         fatal_sigsegv();
 683         return 0;
 684 }
 685
 686 void initial_thread_cb_skas(void (*proc)(void *), void *arg)
 687 {
 688         jmp_buf here;
 689
 690         cb_proc = proc;
 691         cb_arg = arg;
 692         cb_back = &here;
 693
 694         block_signals_trace();
 695         if (UML_SETJMP(&here) == 0)
 696                 UML_LONGJMP(&initial_jmpbuf, INIT_JMP_CALLBACK);
 697         unblock_signals_trace();
 698
 699         cb_proc = NULL;
 700         cb_arg = NULL;
 701         cb_back = NULL;
 702 }
 703
 704 void halt_skas(void)
 705 {
 706         block_signals_trace();
 707         UML_LONGJMP(&initial_jmpbuf, INIT_JMP_HALT);
 708 }
 709
 710 void reboot_skas(void)
 711 {
 712         block_signals_trace();
 713         UML_LONGJMP(&initial_jmpbuf, INIT_JMP_REBOOT);
 714 }
 715
 716 void __switch_mm(struct mm_id *mm_idp)
 717 {
 718         userspace_pid[0] = mm_idp->u.pid;
 719         kill_userspace_mm[0] = mm_idp->kill;
 720 }