linux/arch/sparc/kernel/signal.c
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   1/*  linux/arch/sparc/kernel/signal.c
   2 *
   3 *  Copyright (C) 1991, 1992  Linus Torvalds
   4 *  Copyright (C) 1995 David S. Miller (davem@caip.rutgers.edu)
   5 *  Copyright (C) 1996 Miguel de Icaza (miguel@nuclecu.unam.mx)
   6 *  Copyright (C) 1997 Eddie C. Dost   (ecd@skynet.be)
   7 */
   8
   9#include <linux/sched.h>
  10#include <linux/kernel.h>
  11#include <linux/signal.h>
  12#include <linux/errno.h>
  13#include <linux/wait.h>
  14#include <linux/ptrace.h>
  15#include <linux/unistd.h>
  16#include <linux/mm.h>
  17#include <linux/tty.h>
  18#include <linux/smp.h>
  19#include <linux/binfmts.h>      /* do_coredum */
  20#include <linux/bitops.h>
  21#include <linux/tracehook.h>
  22
  23#include <asm/uaccess.h>
  24#include <asm/ptrace.h>
  25#include <asm/pgalloc.h>
  26#include <asm/pgtable.h>
  27#include <asm/cacheflush.h>     /* flush_sig_insns */
  28
  29#define _BLOCKABLE (~(sigmask(SIGKILL) | sigmask(SIGSTOP)))
  30
  31extern void fpsave(unsigned long *fpregs, unsigned long *fsr,
  32                   void *fpqueue, unsigned long *fpqdepth);
  33extern void fpload(unsigned long *fpregs, unsigned long *fsr);
  34
  35struct signal_frame {
  36        struct sparc_stackf     ss;
  37        __siginfo_t             info;
  38        __siginfo_fpu_t __user  *fpu_save;
  39        unsigned long           insns[2] __attribute__ ((aligned (8)));
  40        unsigned int            extramask[_NSIG_WORDS - 1];
  41        unsigned int            extra_size; /* Should be 0 */
  42        __siginfo_fpu_t         fpu_state;
  43};
  44
  45struct rt_signal_frame {
  46        struct sparc_stackf     ss;
  47        siginfo_t               info;
  48        struct pt_regs          regs;
  49        sigset_t                mask;
  50        __siginfo_fpu_t __user  *fpu_save;
  51        unsigned int            insns[2];
  52        stack_t                 stack;
  53        unsigned int            extra_size; /* Should be 0 */
  54        __siginfo_fpu_t         fpu_state;
  55};
  56
  57/* Align macros */
  58#define SF_ALIGNEDSZ  (((sizeof(struct signal_frame) + 7) & (~7)))
  59#define RT_ALIGNEDSZ  (((sizeof(struct rt_signal_frame) + 7) & (~7)))
  60
  61static int _sigpause_common(old_sigset_t set)
  62{
  63        set &= _BLOCKABLE;
  64        spin_lock_irq(&current->sighand->siglock);
  65        current->saved_sigmask = current->blocked;
  66        siginitset(&current->blocked, set);
  67        recalc_sigpending();
  68        spin_unlock_irq(&current->sighand->siglock);
  69
  70        current->state = TASK_INTERRUPTIBLE;
  71        schedule();
  72        set_thread_flag(TIF_RESTORE_SIGMASK);
  73
  74        return -ERESTARTNOHAND;
  75}
  76
  77asmlinkage int sys_sigsuspend(old_sigset_t set)
  78{
  79        return _sigpause_common(set);
  80}
  81
  82static inline int
  83restore_fpu_state(struct pt_regs *regs, __siginfo_fpu_t __user *fpu)
  84{
  85        int err;
  86#ifdef CONFIG_SMP
  87        if (test_tsk_thread_flag(current, TIF_USEDFPU))
  88                regs->psr &= ~PSR_EF;
  89#else
  90        if (current == last_task_used_math) {
  91                last_task_used_math = NULL;
  92                regs->psr &= ~PSR_EF;
  93        }
  94#endif
  95        set_used_math();
  96        clear_tsk_thread_flag(current, TIF_USEDFPU);
  97
  98        if (!access_ok(VERIFY_READ, fpu, sizeof(*fpu)))
  99                return -EFAULT;
 100
 101        err = __copy_from_user(&current->thread.float_regs[0], &fpu->si_float_regs[0],
 102                               (sizeof(unsigned long) * 32));
 103        err |= __get_user(current->thread.fsr, &fpu->si_fsr);
 104        err |= __get_user(current->thread.fpqdepth, &fpu->si_fpqdepth);
 105        if (current->thread.fpqdepth != 0)
 106                err |= __copy_from_user(&current->thread.fpqueue[0],
 107                                        &fpu->si_fpqueue[0],
 108                                        ((sizeof(unsigned long) +
 109                                        (sizeof(unsigned long *)))*16));
 110        return err;
 111}
 112
 113asmlinkage void do_sigreturn(struct pt_regs *regs)
 114{
 115        struct signal_frame __user *sf;
 116        unsigned long up_psr, pc, npc;
 117        sigset_t set;
 118        __siginfo_fpu_t __user *fpu_save;
 119        int err;
 120
 121        /* Always make any pending restarted system calls return -EINTR */
 122        current_thread_info()->restart_block.fn = do_no_restart_syscall;
 123
 124        synchronize_user_stack();
 125
 126        sf = (struct signal_frame __user *) regs->u_regs[UREG_FP];
 127
 128        /* 1. Make sure we are not getting garbage from the user */
 129        if (!access_ok(VERIFY_READ, sf, sizeof(*sf)))
 130                goto segv_and_exit;
 131
 132        if (((unsigned long) sf) & 3)
 133                goto segv_and_exit;
 134
 135        err = __get_user(pc,  &sf->info.si_regs.pc);
 136        err |= __get_user(npc, &sf->info.si_regs.npc);
 137
 138        if ((pc | npc) & 3)
 139                goto segv_and_exit;
 140
 141        /* 2. Restore the state */
 142        up_psr = regs->psr;
 143        err |= __copy_from_user(regs, &sf->info.si_regs, sizeof(struct pt_regs));
 144
 145        /* User can only change condition codes and FPU enabling in %psr. */
 146        regs->psr = (up_psr & ~(PSR_ICC | PSR_EF))
 147                  | (regs->psr & (PSR_ICC | PSR_EF));
 148
 149        /* Prevent syscall restart.  */
 150        pt_regs_clear_syscall(regs);
 151
 152        err |= __get_user(fpu_save, &sf->fpu_save);
 153
 154        if (fpu_save)
 155                err |= restore_fpu_state(regs, fpu_save);
 156
 157        /* This is pretty much atomic, no amount locking would prevent
 158         * the races which exist anyways.
 159         */
 160        err |= __get_user(set.sig[0], &sf->info.si_mask);
 161        err |= __copy_from_user(&set.sig[1], &sf->extramask,
 162                                (_NSIG_WORDS-1) * sizeof(unsigned int));
 163                           
 164        if (err)
 165                goto segv_and_exit;
 166
 167        sigdelsetmask(&set, ~_BLOCKABLE);
 168        spin_lock_irq(&current->sighand->siglock);
 169        current->blocked = set;
 170        recalc_sigpending();
 171        spin_unlock_irq(&current->sighand->siglock);
 172        return;
 173
 174segv_and_exit:
 175        force_sig(SIGSEGV, current);
 176}
 177
 178asmlinkage void do_rt_sigreturn(struct pt_regs *regs)
 179{
 180        struct rt_signal_frame __user *sf;
 181        unsigned int psr, pc, npc;
 182        __siginfo_fpu_t __user *fpu_save;
 183        mm_segment_t old_fs;
 184        sigset_t set;
 185        stack_t st;
 186        int err;
 187
 188        synchronize_user_stack();
 189        sf = (struct rt_signal_frame __user *) regs->u_regs[UREG_FP];
 190        if (!access_ok(VERIFY_READ, sf, sizeof(*sf)) ||
 191            (((unsigned long) sf) & 0x03))
 192                goto segv;
 193
 194        err = __get_user(pc, &sf->regs.pc);
 195        err |= __get_user(npc, &sf->regs.npc);
 196        err |= ((pc | npc) & 0x03);
 197
 198        err |= __get_user(regs->y, &sf->regs.y);
 199        err |= __get_user(psr, &sf->regs.psr);
 200
 201        err |= __copy_from_user(&regs->u_regs[UREG_G1],
 202                                &sf->regs.u_regs[UREG_G1], 15 * sizeof(u32));
 203
 204        regs->psr = (regs->psr & ~PSR_ICC) | (psr & PSR_ICC);
 205
 206        /* Prevent syscall restart.  */
 207        pt_regs_clear_syscall(regs);
 208
 209        err |= __get_user(fpu_save, &sf->fpu_save);
 210
 211        if (fpu_save)
 212                err |= restore_fpu_state(regs, fpu_save);
 213        err |= __copy_from_user(&set, &sf->mask, sizeof(sigset_t));
 214        
 215        err |= __copy_from_user(&st, &sf->stack, sizeof(stack_t));
 216        
 217        if (err)
 218                goto segv;
 219                
 220        regs->pc = pc;
 221        regs->npc = npc;
 222        
 223        /* It is more difficult to avoid calling this function than to
 224         * call it and ignore errors.
 225         */
 226        old_fs = get_fs();
 227        set_fs(KERNEL_DS);
 228        do_sigaltstack((const stack_t __user *) &st, NULL, (unsigned long)sf);
 229        set_fs(old_fs);
 230
 231        sigdelsetmask(&set, ~_BLOCKABLE);
 232        spin_lock_irq(&current->sighand->siglock);
 233        current->blocked = set;
 234        recalc_sigpending();
 235        spin_unlock_irq(&current->sighand->siglock);
 236        return;
 237segv:
 238        force_sig(SIGSEGV, current);
 239}
 240
 241/* Checks if the fp is valid */
 242static inline int invalid_frame_pointer(void __user *fp, int fplen)
 243{
 244        if ((((unsigned long) fp) & 7) ||
 245            !__access_ok((unsigned long)fp, fplen) ||
 246            ((sparc_cpu_model == sun4 || sparc_cpu_model == sun4c) &&
 247             ((unsigned long) fp < 0xe0000000 && (unsigned long) fp >= 0x20000000)))
 248                return 1;
 249        
 250        return 0;
 251}
 252
 253static inline void __user *get_sigframe(struct sigaction *sa, struct pt_regs *regs, unsigned long framesize)
 254{
 255        unsigned long sp = regs->u_regs[UREG_FP];
 256
 257        /*
 258         * If we are on the alternate signal stack and would overflow it, don't.
 259         * Return an always-bogus address instead so we will die with SIGSEGV.
 260         */
 261        if (on_sig_stack(sp) && !likely(on_sig_stack(sp - framesize)))
 262                return (void __user *) -1L;
 263
 264        /* This is the X/Open sanctioned signal stack switching.  */
 265        if (sa->sa_flags & SA_ONSTACK) {
 266                if (sas_ss_flags(sp) == 0)
 267                        sp = current->sas_ss_sp + current->sas_ss_size;
 268        }
 269
 270        /* Always align the stack frame.  This handles two cases.  First,
 271         * sigaltstack need not be mindful of platform specific stack
 272         * alignment.  Second, if we took this signal because the stack
 273         * is not aligned properly, we'd like to take the signal cleanly
 274         * and report that.
 275         */
 276        sp &= ~7UL;
 277
 278        return (void __user *)(sp - framesize);
 279}
 280
 281static inline int
 282save_fpu_state(struct pt_regs *regs, __siginfo_fpu_t __user *fpu)
 283{
 284        int err = 0;
 285#ifdef CONFIG_SMP
 286        if (test_tsk_thread_flag(current, TIF_USEDFPU)) {
 287                put_psr(get_psr() | PSR_EF);
 288                fpsave(&current->thread.float_regs[0], &current->thread.fsr,
 289                       &current->thread.fpqueue[0], &current->thread.fpqdepth);
 290                regs->psr &= ~(PSR_EF);
 291                clear_tsk_thread_flag(current, TIF_USEDFPU);
 292        }
 293#else
 294        if (current == last_task_used_math) {
 295                put_psr(get_psr() | PSR_EF);
 296                fpsave(&current->thread.float_regs[0], &current->thread.fsr,
 297                       &current->thread.fpqueue[0], &current->thread.fpqdepth);
 298                last_task_used_math = NULL;
 299                regs->psr &= ~(PSR_EF);
 300        }
 301#endif
 302        err |= __copy_to_user(&fpu->si_float_regs[0],
 303                              &current->thread.float_regs[0],
 304                              (sizeof(unsigned long) * 32));
 305        err |= __put_user(current->thread.fsr, &fpu->si_fsr);
 306        err |= __put_user(current->thread.fpqdepth, &fpu->si_fpqdepth);
 307        if (current->thread.fpqdepth != 0)
 308                err |= __copy_to_user(&fpu->si_fpqueue[0],
 309                                      &current->thread.fpqueue[0],
 310                                      ((sizeof(unsigned long) +
 311                                      (sizeof(unsigned long *)))*16));
 312        clear_used_math();
 313        return err;
 314}
 315
 316static void setup_frame(struct k_sigaction *ka, struct pt_regs *regs,
 317                        int signo, sigset_t *oldset)
 318{
 319        struct signal_frame __user *sf;
 320        int sigframe_size, err;
 321
 322        /* 1. Make sure everything is clean */
 323        synchronize_user_stack();
 324
 325        sigframe_size = SF_ALIGNEDSZ;
 326        if (!used_math())
 327                sigframe_size -= sizeof(__siginfo_fpu_t);
 328
 329        sf = (struct signal_frame __user *)
 330                get_sigframe(&ka->sa, regs, sigframe_size);
 331
 332        if (invalid_frame_pointer(sf, sigframe_size))
 333                goto sigill_and_return;
 334
 335        if (current_thread_info()->w_saved != 0)
 336                goto sigill_and_return;
 337
 338        /* 2. Save the current process state */
 339        err = __copy_to_user(&sf->info.si_regs, regs, sizeof(struct pt_regs));
 340        
 341        err |= __put_user(0, &sf->extra_size);
 342
 343        if (used_math()) {
 344                err |= save_fpu_state(regs, &sf->fpu_state);
 345                err |= __put_user(&sf->fpu_state, &sf->fpu_save);
 346        } else {
 347                err |= __put_user(0, &sf->fpu_save);
 348        }
 349
 350        err |= __put_user(oldset->sig[0], &sf->info.si_mask);
 351        err |= __copy_to_user(sf->extramask, &oldset->sig[1],
 352                              (_NSIG_WORDS - 1) * sizeof(unsigned int));
 353        err |= __copy_to_user(sf, (char *) regs->u_regs[UREG_FP],
 354                              sizeof(struct reg_window));
 355        if (err)
 356                goto sigsegv;
 357        
 358        /* 3. signal handler back-trampoline and parameters */
 359        regs->u_regs[UREG_FP] = (unsigned long) sf;
 360        regs->u_regs[UREG_I0] = signo;
 361        regs->u_regs[UREG_I1] = (unsigned long) &sf->info;
 362        regs->u_regs[UREG_I2] = (unsigned long) &sf->info;
 363
 364        /* 4. signal handler */
 365        regs->pc = (unsigned long) ka->sa.sa_handler;
 366        regs->npc = (regs->pc + 4);
 367
 368        /* 5. return to kernel instructions */
 369        if (ka->ka_restorer)
 370                regs->u_regs[UREG_I7] = (unsigned long)ka->ka_restorer;
 371        else {
 372                regs->u_regs[UREG_I7] = (unsigned long)(&(sf->insns[0]) - 2);
 373
 374                /* mov __NR_sigreturn, %g1 */
 375                err |= __put_user(0x821020d8, &sf->insns[0]);
 376
 377                /* t 0x10 */
 378                err |= __put_user(0x91d02010, &sf->insns[1]);
 379                if (err)
 380                        goto sigsegv;
 381
 382                /* Flush instruction space. */
 383                flush_sig_insns(current->mm, (unsigned long) &(sf->insns[0]));
 384        }
 385        return;
 386
 387sigill_and_return:
 388        do_exit(SIGILL);
 389sigsegv:
 390        force_sigsegv(signo, current);
 391}
 392
 393static void setup_rt_frame(struct k_sigaction *ka, struct pt_regs *regs,
 394                           int signo, sigset_t *oldset, siginfo_t *info)
 395{
 396        struct rt_signal_frame __user *sf;
 397        int sigframe_size;
 398        unsigned int psr;
 399        int err;
 400
 401        synchronize_user_stack();
 402        sigframe_size = RT_ALIGNEDSZ;
 403        if (!used_math())
 404                sigframe_size -= sizeof(__siginfo_fpu_t);
 405        sf = (struct rt_signal_frame __user *)
 406                get_sigframe(&ka->sa, regs, sigframe_size);
 407        if (invalid_frame_pointer(sf, sigframe_size))
 408                goto sigill;
 409        if (current_thread_info()->w_saved != 0)
 410                goto sigill;
 411
 412        err  = __put_user(regs->pc, &sf->regs.pc);
 413        err |= __put_user(regs->npc, &sf->regs.npc);
 414        err |= __put_user(regs->y, &sf->regs.y);
 415        psr = regs->psr;
 416        if (used_math())
 417                psr |= PSR_EF;
 418        err |= __put_user(psr, &sf->regs.psr);
 419        err |= __copy_to_user(&sf->regs.u_regs, regs->u_regs, sizeof(regs->u_regs));
 420        err |= __put_user(0, &sf->extra_size);
 421
 422        if (psr & PSR_EF) {
 423                err |= save_fpu_state(regs, &sf->fpu_state);
 424                err |= __put_user(&sf->fpu_state, &sf->fpu_save);
 425        } else {
 426                err |= __put_user(0, &sf->fpu_save);
 427        }
 428        err |= __copy_to_user(&sf->mask, &oldset->sig[0], sizeof(sigset_t));
 429        
 430        /* Setup sigaltstack */
 431        err |= __put_user(current->sas_ss_sp, &sf->stack.ss_sp);
 432        err |= __put_user(sas_ss_flags(regs->u_regs[UREG_FP]), &sf->stack.ss_flags);
 433        err |= __put_user(current->sas_ss_size, &sf->stack.ss_size);
 434        
 435        err |= __copy_to_user(sf, (char *) regs->u_regs[UREG_FP],
 436                              sizeof(struct reg_window));       
 437
 438        err |= copy_siginfo_to_user(&sf->info, info);
 439
 440        if (err)
 441                goto sigsegv;
 442
 443        regs->u_regs[UREG_FP] = (unsigned long) sf;
 444        regs->u_regs[UREG_I0] = signo;
 445        regs->u_regs[UREG_I1] = (unsigned long) &sf->info;
 446        regs->u_regs[UREG_I2] = (unsigned long) &sf->regs;
 447
 448        regs->pc = (unsigned long) ka->sa.sa_handler;
 449        regs->npc = (regs->pc + 4);
 450
 451        if (ka->ka_restorer)
 452                regs->u_regs[UREG_I7] = (unsigned long)ka->ka_restorer;
 453        else {
 454                regs->u_regs[UREG_I7] = (unsigned long)(&(sf->insns[0]) - 2);
 455
 456                /* mov __NR_sigreturn, %g1 */
 457                err |= __put_user(0x821020d8, &sf->insns[0]);
 458
 459                /* t 0x10 */
 460                err |= __put_user(0x91d02010, &sf->insns[1]);
 461                if (err)
 462                        goto sigsegv;
 463
 464                /* Flush instruction space. */
 465                flush_sig_insns(current->mm, (unsigned long) &(sf->insns[0]));
 466        }
 467        return;
 468
 469sigill:
 470        do_exit(SIGILL);
 471sigsegv:
 472        force_sigsegv(signo, current);
 473}
 474
 475static inline void
 476handle_signal(unsigned long signr, struct k_sigaction *ka,
 477              siginfo_t *info, sigset_t *oldset, struct pt_regs *regs)
 478{
 479        if (ka->sa.sa_flags & SA_SIGINFO)
 480                setup_rt_frame(ka, regs, signr, oldset, info);
 481        else
 482                setup_frame(ka, regs, signr, oldset);
 483
 484        spin_lock_irq(&current->sighand->siglock);
 485        sigorsets(&current->blocked,&current->blocked,&ka->sa.sa_mask);
 486        if (!(ka->sa.sa_flags & SA_NOMASK))
 487                sigaddset(&current->blocked, signr);
 488        recalc_sigpending();
 489        spin_unlock_irq(&current->sighand->siglock);
 490}
 491
 492static inline void syscall_restart(unsigned long orig_i0, struct pt_regs *regs,
 493                                   struct sigaction *sa)
 494{
 495        switch(regs->u_regs[UREG_I0]) {
 496        case ERESTART_RESTARTBLOCK:
 497        case ERESTARTNOHAND:
 498        no_system_call_restart:
 499                regs->u_regs[UREG_I0] = EINTR;
 500                regs->psr |= PSR_C;
 501                break;
 502        case ERESTARTSYS:
 503                if (!(sa->sa_flags & SA_RESTART))
 504                        goto no_system_call_restart;
 505                /* fallthrough */
 506        case ERESTARTNOINTR:
 507                regs->u_regs[UREG_I0] = orig_i0;
 508                regs->pc -= 4;
 509                regs->npc -= 4;
 510        }
 511}
 512
 513/* Note that 'init' is a special process: it doesn't get signals it doesn't
 514 * want to handle. Thus you cannot kill init even with a SIGKILL even by
 515 * mistake.
 516 */
 517static void do_signal(struct pt_regs *regs, unsigned long orig_i0)
 518{
 519        struct k_sigaction ka;
 520        int restart_syscall;
 521        sigset_t *oldset;
 522        siginfo_t info;
 523        int signr;
 524
 525        if (pt_regs_is_syscall(regs) && (regs->psr & PSR_C))
 526                restart_syscall = 1;
 527        else
 528                restart_syscall = 0;
 529
 530        if (test_thread_flag(TIF_RESTORE_SIGMASK))
 531                oldset = &current->saved_sigmask;
 532        else
 533                oldset = &current->blocked;
 534
 535        signr = get_signal_to_deliver(&info, &ka, regs, NULL);
 536
 537        /* If the debugger messes with the program counter, it clears
 538         * the software "in syscall" bit, directing us to not perform
 539         * a syscall restart.
 540         */
 541        if (restart_syscall && !pt_regs_is_syscall(regs))
 542                restart_syscall = 0;
 543
 544        if (signr > 0) {
 545                if (restart_syscall)
 546                        syscall_restart(orig_i0, regs, &ka.sa);
 547                handle_signal(signr, &ka, &info, oldset, regs);
 548
 549                /* a signal was successfully delivered; the saved
 550                 * sigmask will have been stored in the signal frame,
 551                 * and will be restored by sigreturn, so we can simply
 552                 * clear the TIF_RESTORE_SIGMASK flag.
 553                 */
 554                if (test_thread_flag(TIF_RESTORE_SIGMASK))
 555                        clear_thread_flag(TIF_RESTORE_SIGMASK);
 556
 557                tracehook_signal_handler(signr, &info, &ka, regs, 0);
 558                return;
 559        }
 560        if (restart_syscall &&
 561            (regs->u_regs[UREG_I0] == ERESTARTNOHAND ||
 562             regs->u_regs[UREG_I0] == ERESTARTSYS ||
 563             regs->u_regs[UREG_I0] == ERESTARTNOINTR)) {
 564                /* replay the system call when we are done */
 565                regs->u_regs[UREG_I0] = orig_i0;
 566                regs->pc -= 4;
 567                regs->npc -= 4;
 568        }
 569        if (restart_syscall &&
 570            regs->u_regs[UREG_I0] == ERESTART_RESTARTBLOCK) {
 571                regs->u_regs[UREG_G1] = __NR_restart_syscall;
 572                regs->pc -= 4;
 573                regs->npc -= 4;
 574        }
 575
 576        /* if there's no signal to deliver, we just put the saved sigmask
 577         * back
 578         */
 579        if (test_thread_flag(TIF_RESTORE_SIGMASK)) {
 580                clear_thread_flag(TIF_RESTORE_SIGMASK);
 581                sigprocmask(SIG_SETMASK, &current->saved_sigmask, NULL);
 582        }
 583}
 584
 585void do_notify_resume(struct pt_regs *regs, unsigned long orig_i0,
 586                      unsigned long thread_info_flags)
 587{
 588        if (thread_info_flags & (_TIF_SIGPENDING | _TIF_RESTORE_SIGMASK))
 589                do_signal(regs, orig_i0);
 590        if (thread_info_flags & _TIF_NOTIFY_RESUME) {
 591                clear_thread_flag(TIF_NOTIFY_RESUME);
 592                tracehook_notify_resume(regs);
 593        }
 594}
 595
 596asmlinkage int
 597do_sys_sigstack(struct sigstack __user *ssptr, struct sigstack __user *ossptr,
 598                unsigned long sp)
 599{
 600        int ret = -EFAULT;
 601
 602        /* First see if old state is wanted. */
 603        if (ossptr) {
 604                if (put_user(current->sas_ss_sp + current->sas_ss_size,
 605                             &ossptr->the_stack) ||
 606                    __put_user(on_sig_stack(sp), &ossptr->cur_status))
 607                        goto out;
 608        }
 609
 610        /* Now see if we want to update the new state. */
 611        if (ssptr) {
 612                char *ss_sp;
 613
 614                if (get_user(ss_sp, &ssptr->the_stack))
 615                        goto out;
 616                /* If the current stack was set with sigaltstack, don't
 617                   swap stacks while we are on it.  */
 618                ret = -EPERM;
 619                if (current->sas_ss_sp && on_sig_stack(sp))
 620                        goto out;
 621
 622                /* Since we don't know the extent of the stack, and we don't
 623                   track onstack-ness, but rather calculate it, we must
 624                   presume a size.  Ho hum this interface is lossy.  */
 625                current->sas_ss_sp = (unsigned long)ss_sp - SIGSTKSZ;
 626                current->sas_ss_size = SIGSTKSZ;
 627        }
 628        ret = 0;
 629out:
 630        return ret;
 631}
 632