arch/arm/kernel/signal.c

   1 /*
   2  *  linux/arch/arm/kernel/signal.c
   3  *
   4  *  Copyright (C) 1995-2009 Russell King
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2 as
   8  * published by the Free Software Foundation.
   9  */
  10 #include <linux/errno.h>
  11 #include <linux/random.h>
  12 #include <linux/signal.h>
  13 #include <linux/personality.h>
  14 #include <linux/uaccess.h>
  15 #include <linux/tracehook.h>
  16 #include <linux/uprobes.h>
  17
  18 #include <asm/elf.h>
  19 #include <asm/cacheflush.h>
  20 #include <asm/traps.h>
  21 #include <asm/ucontext.h>
  22 #include <asm/unistd.h>
  23 #include <asm/vfp.h>
  24
  25 extern const unsigned long sigreturn_codes[7];
  26
  27 static unsigned long signal_return_offset;
  28
  29 #ifdef CONFIG_CRUNCH
  30 static int preserve_crunch_context(struct crunch_sigframe __user *frame)
  31 {
  32         char kbuf[sizeof(*frame) + 8];
  33         struct crunch_sigframe *kframe;
  34
  35         /* the crunch context must be 64 bit aligned */
  36         kframe = (struct crunch_sigframe *)((unsigned long)(kbuf + 8) & ~7);
  37         kframe->magic = CRUNCH_MAGIC;
  38         kframe->size = CRUNCH_STORAGE_SIZE;
  39         crunch_task_copy(current_thread_info(), &kframe->storage);
  40         return __copy_to_user(frame, kframe, sizeof(*frame));
  41 }
  42
  43 static int restore_crunch_context(struct crunch_sigframe __user *frame)
  44 {
  45         char kbuf[sizeof(*frame) + 8];
  46         struct crunch_sigframe *kframe;
  47
  48         /* the crunch context must be 64 bit aligned */
  49         kframe = (struct crunch_sigframe *)((unsigned long)(kbuf + 8) & ~7);
  50         if (__copy_from_user(kframe, frame, sizeof(*frame)))
  51                 return -1;
  52         if (kframe->magic != CRUNCH_MAGIC ||
  53             kframe->size != CRUNCH_STORAGE_SIZE)
  54                 return -1;
  55         crunch_task_restore(current_thread_info(), &kframe->storage);
  56         return 0;
  57 }
  58 #endif
  59
  60 #ifdef CONFIG_IWMMXT
  61
  62 static int preserve_iwmmxt_context(struct iwmmxt_sigframe *frame)
  63 {
  64         char kbuf[sizeof(*frame) + 8];
  65         struct iwmmxt_sigframe *kframe;
  66
  67         /* the iWMMXt context must be 64 bit aligned */
  68         kframe = (struct iwmmxt_sigframe *)((unsigned long)(kbuf + 8) & ~7);
  69         kframe->magic = IWMMXT_MAGIC;
  70         kframe->size = IWMMXT_STORAGE_SIZE;
  71         iwmmxt_task_copy(current_thread_info(), &kframe->storage);
  72         return __copy_to_user(frame, kframe, sizeof(*frame));
  73 }
  74
  75 static int restore_iwmmxt_context(struct iwmmxt_sigframe *frame)
  76 {
  77         char kbuf[sizeof(*frame) + 8];
  78         struct iwmmxt_sigframe *kframe;
  79
  80         /* the iWMMXt context must be 64 bit aligned */
  81         kframe = (struct iwmmxt_sigframe *)((unsigned long)(kbuf + 8) & ~7);
  82         if (__copy_from_user(kframe, frame, sizeof(*frame)))
  83                 return -1;
  84         if (kframe->magic != IWMMXT_MAGIC ||
  85             kframe->size != IWMMXT_STORAGE_SIZE)
  86                 return -1;
  87         iwmmxt_task_restore(current_thread_info(), &kframe->storage);
  88         return 0;
  89 }
  90
  91 #endif
  92
  93 #ifdef CONFIG_VFP
  94
  95 static int preserve_vfp_context(struct vfp_sigframe __user *frame)
  96 {
  97         const unsigned long magic = VFP_MAGIC;
  98         const unsigned long size = VFP_STORAGE_SIZE;
  99         int err = 0;
 100
 101         __put_user_error(magic, &frame->magic, err);
 102         __put_user_error(size, &frame->size, err);
 103
 104         if (err)
 105                 return -EFAULT;
 106
 107         return vfp_preserve_user_clear_hwstate(&frame->ufp, &frame->ufp_exc);
 108 }
 109
 110 static int restore_vfp_context(struct vfp_sigframe __user *frame)
 111 {
 112         unsigned long magic;
 113         unsigned long size;
 114         int err = 0;
 115
 116         __get_user_error(magic, &frame->magic, err);
 117         __get_user_error(size, &frame->size, err);
 118
 119         if (err)
 120                 return -EFAULT;
 121         if (magic != VFP_MAGIC || size != VFP_STORAGE_SIZE)
 122                 return -EINVAL;
 123
 124         return vfp_restore_user_hwstate(&frame->ufp, &frame->ufp_exc);
 125 }
 126
 127 #endif
 128
 129 /*
 130  * Do a signal return; undo the signal stack.  These are aligned to 64-bit.
 131  */
 132 struct sigframe {
 133         struct ucontext uc;
 134         unsigned long retcode[2];
 135 };
 136
 137 struct rt_sigframe {
 138         struct siginfo info;
 139         struct sigframe sig;
 140 };
 141
 142 static int restore_sigframe(struct pt_regs *regs, struct sigframe __user *sf)
 143 {
 144         struct aux_sigframe __user *aux;
 145         sigset_t set;
 146         int err;
 147
 148         err = __copy_from_user(&set, &sf->uc.uc_sigmask, sizeof(set));
 149         if (err == 0)
 150                 set_current_blocked(&set);
 151
 152         __get_user_error(regs->ARM_r0, &sf->uc.uc_mcontext.arm_r0, err);
 153         __get_user_error(regs->ARM_r1, &sf->uc.uc_mcontext.arm_r1, err);
 154         __get_user_error(regs->ARM_r2, &sf->uc.uc_mcontext.arm_r2, err);
 155         __get_user_error(regs->ARM_r3, &sf->uc.uc_mcontext.arm_r3, err);
 156         __get_user_error(regs->ARM_r4, &sf->uc.uc_mcontext.arm_r4, err);
 157         __get_user_error(regs->ARM_r5, &sf->uc.uc_mcontext.arm_r5, err);
 158         __get_user_error(regs->ARM_r6, &sf->uc.uc_mcontext.arm_r6, err);
 159         __get_user_error(regs->ARM_r7, &sf->uc.uc_mcontext.arm_r7, err);
 160         __get_user_error(regs->ARM_r8, &sf->uc.uc_mcontext.arm_r8, err);
 161         __get_user_error(regs->ARM_r9, &sf->uc.uc_mcontext.arm_r9, err);
 162         __get_user_error(regs->ARM_r10, &sf->uc.uc_mcontext.arm_r10, err);
 163         __get_user_error(regs->ARM_fp, &sf->uc.uc_mcontext.arm_fp, err);
 164         __get_user_error(regs->ARM_ip, &sf->uc.uc_mcontext.arm_ip, err);
 165         __get_user_error(regs->ARM_sp, &sf->uc.uc_mcontext.arm_sp, err);
 166         __get_user_error(regs->ARM_lr, &sf->uc.uc_mcontext.arm_lr, err);
 167         __get_user_error(regs->ARM_pc, &sf->uc.uc_mcontext.arm_pc, err);
 168         __get_user_error(regs->ARM_cpsr, &sf->uc.uc_mcontext.arm_cpsr, err);
 169
 170         err |= !valid_user_regs(regs);
 171
 172         aux = (struct aux_sigframe __user *) sf->uc.uc_regspace;
 173 #ifdef CONFIG_CRUNCH
 174         if (err == 0)
 175                 err |= restore_crunch_context(&aux->crunch);
 176 #endif
 177 #ifdef CONFIG_IWMMXT
 178         if (err == 0 && test_thread_flag(TIF_USING_IWMMXT))
 179                 err |= restore_iwmmxt_context(&aux->iwmmxt);
 180 #endif
 181 #ifdef CONFIG_VFP
 182         if (err == 0)
 183                 err |= restore_vfp_context(&aux->vfp);
 184 #endif
 185
 186         return err;
 187 }
 188
 189 asmlinkage int sys_sigreturn(struct pt_regs *regs)
 190 {
 191         struct sigframe __user *frame;
 192
 193         /* Always make any pending restarted system calls return -EINTR */
 194         current->restart_block.fn = do_no_restart_syscall;
 195
 196         /*
 197          * Since we stacked the signal on a 64-bit boundary,
 198          * then 'sp' should be word aligned here.  If it's
 199          * not, then the user is trying to mess with us.
 200          */
 201         if (regs->ARM_sp & 7)
 202                 goto badframe;
 203
 204         frame = (struct sigframe __user *)regs->ARM_sp;
 205
 206         if (!access_ok(VERIFY_READ, frame, sizeof (*frame)))
 207                 goto badframe;
 208
 209         if (restore_sigframe(regs, frame))
 210                 goto badframe;
 211
 212         return regs->ARM_r0;
 213
 214 badframe:
 215         force_sig(SIGSEGV, current);
 216         return 0;
 217 }
 218
 219 asmlinkage int sys_rt_sigreturn(struct pt_regs *regs)
 220 {
 221         struct rt_sigframe __user *frame;
 222
 223         /* Always make any pending restarted system calls return -EINTR */
 224         current->restart_block.fn = do_no_restart_syscall;
 225
 226         /*
 227          * Since we stacked the signal on a 64-bit boundary,
 228          * then 'sp' should be word aligned here.  If it's
 229          * not, then the user is trying to mess with us.
 230          */
 231         if (regs->ARM_sp & 7)
 232                 goto badframe;
 233
 234         frame = (struct rt_sigframe __user *)regs->ARM_sp;
 235
 236         if (!access_ok(VERIFY_READ, frame, sizeof (*frame)))
 237                 goto badframe;
 238
 239         if (restore_sigframe(regs, &frame->sig))
 240                 goto badframe;
 241
 242         if (restore_altstack(&frame->sig.uc.uc_stack))
 243                 goto badframe;
 244
 245         return regs->ARM_r0;
 246
 247 badframe:
 248         force_sig(SIGSEGV, current);
 249         return 0;
 250 }
 251
 252 static int
 253 setup_sigframe(struct sigframe __user *sf, struct pt_regs *regs, sigset_t *set)
 254 {
 255         struct aux_sigframe __user *aux;
 256         int err = 0;
 257
 258         __put_user_error(regs->ARM_r0, &sf->uc.uc_mcontext.arm_r0, err);
 259         __put_user_error(regs->ARM_r1, &sf->uc.uc_mcontext.arm_r1, err);
 260         __put_user_error(regs->ARM_r2, &sf->uc.uc_mcontext.arm_r2, err);
 261         __put_user_error(regs->ARM_r3, &sf->uc.uc_mcontext.arm_r3, err);
 262         __put_user_error(regs->ARM_r4, &sf->uc.uc_mcontext.arm_r4, err);
 263         __put_user_error(regs->ARM_r5, &sf->uc.uc_mcontext.arm_r5, err);
 264         __put_user_error(regs->ARM_r6, &sf->uc.uc_mcontext.arm_r6, err);
 265         __put_user_error(regs->ARM_r7, &sf->uc.uc_mcontext.arm_r7, err);
 266         __put_user_error(regs->ARM_r8, &sf->uc.uc_mcontext.arm_r8, err);
 267         __put_user_error(regs->ARM_r9, &sf->uc.uc_mcontext.arm_r9, err);
 268         __put_user_error(regs->ARM_r10, &sf->uc.uc_mcontext.arm_r10, err);
 269         __put_user_error(regs->ARM_fp, &sf->uc.uc_mcontext.arm_fp, err);
 270         __put_user_error(regs->ARM_ip, &sf->uc.uc_mcontext.arm_ip, err);
 271         __put_user_error(regs->ARM_sp, &sf->uc.uc_mcontext.arm_sp, err);
 272         __put_user_error(regs->ARM_lr, &sf->uc.uc_mcontext.arm_lr, err);
 273         __put_user_error(regs->ARM_pc, &sf->uc.uc_mcontext.arm_pc, err);
 274         __put_user_error(regs->ARM_cpsr, &sf->uc.uc_mcontext.arm_cpsr, err);
 275
 276         __put_user_error(current->thread.trap_no, &sf->uc.uc_mcontext.trap_no, err);
 277         __put_user_error(current->thread.error_code, &sf->uc.uc_mcontext.error_code, err);
 278         __put_user_error(current->thread.address, &sf->uc.uc_mcontext.fault_address, err);
 279         __put_user_error(set->sig[0], &sf->uc.uc_mcontext.oldmask, err);
 280
 281         err |= __copy_to_user(&sf->uc.uc_sigmask, set, sizeof(*set));
 282
 283         aux = (struct aux_sigframe __user *) sf->uc.uc_regspace;
 284 #ifdef CONFIG_CRUNCH
 285         if (err == 0)
 286                 err |= preserve_crunch_context(&aux->crunch);
 287 #endif
 288 #ifdef CONFIG_IWMMXT
 289         if (err == 0 && test_thread_flag(TIF_USING_IWMMXT))
 290                 err |= preserve_iwmmxt_context(&aux->iwmmxt);
 291 #endif
 292 #ifdef CONFIG_VFP
 293         if (err == 0)
 294                 err |= preserve_vfp_context(&aux->vfp);
 295 #endif
 296         __put_user_error(0, &aux->end_magic, err);
 297
 298         return err;
 299 }
 300
 301 static inline void __user *
 302 get_sigframe(struct ksignal *ksig, struct pt_regs *regs, int framesize)
 303 {
 304         unsigned long sp = sigsp(regs->ARM_sp, ksig);
 305         void __user *frame;
 306
 307         /*
 308          * ATPCS B01 mandates 8-byte alignment
 309          */
 310         frame = (void __user *)((sp - framesize) & ~7);
 311
 312         /*
 313          * Check that we can actually write to the signal frame.
 314          */
 315         if (!access_ok(VERIFY_WRITE, frame, framesize))
 316                 frame = NULL;
 317
 318         return frame;
 319 }
 320
 321 static int
 322 setup_return(struct pt_regs *regs, struct ksignal *ksig,
 323              unsigned long __user *rc, void __user *frame)
 324 {
 325         unsigned long handler = (unsigned long)ksig->ka.sa.sa_handler;
 326         unsigned long retcode;
 327         int thumb = 0;
 328         unsigned long cpsr = regs->ARM_cpsr & ~(PSR_f | PSR_E_BIT);
 329
 330         cpsr |= PSR_ENDSTATE;
 331
 332         /*
 333          * Maybe we need to deliver a 32-bit signal to a 26-bit task.
 334          */
 335         if (ksig->ka.sa.sa_flags & SA_THIRTYTWO)
 336                 cpsr = (cpsr & ~MODE_MASK) | USR_MODE;
 337
 338 #ifdef CONFIG_ARM_THUMB
 339         if (elf_hwcap & HWCAP_THUMB) {
 340                 /*
 341                  * The LSB of the handler determines if we're going to
 342                  * be using THUMB or ARM mode for this signal handler.
 343                  */
 344                 thumb = handler & 1;
 345
 346                 /*
 347                  * Clear the If-Then Thumb-2 execution state.  ARM spec
 348                  * requires this to be all 000s in ARM mode.  Snapdragon
 349                  * S4/Krait misbehaves on a Thumb=>ARM signal transition
 350                  * without this.
 351                  *
 352                  * We must do this whenever we are running on a Thumb-2
 353                  * capable CPU, which includes ARMv6T2.  However, we elect
 354                  * to always do this to simplify the code; this field is
 355                  * marked UNK/SBZP for older architectures.
 356                  */
 357                 cpsr &= ~PSR_IT_MASK;
 358
 359                 if (thumb) {
 360                         cpsr |= PSR_T_BIT;
 361                 } else
 362                         cpsr &= ~PSR_T_BIT;
 363         }
 364 #endif
 365
 366         if (ksig->ka.sa.sa_flags & SA_RESTORER) {
 367                 retcode = (unsigned long)ksig->ka.sa.sa_restorer;
 368         } else {
 369                 unsigned int idx = thumb << 1;
 370
 371                 if (ksig->ka.sa.sa_flags & SA_SIGINFO)
 372                         idx += 3;
 373
 374                 /*
 375                  * Put the sigreturn code on the stack no matter which return
 376                  * mechanism we use in order to remain ABI compliant
 377                  */
 378                 if (__put_user(sigreturn_codes[idx],   rc) ||
 379                     __put_user(sigreturn_codes[idx+1], rc+1))
 380                         return 1;
 381
 382 #ifdef CONFIG_MMU
 383                 if (cpsr & MODE32_BIT) {
 384                         struct mm_struct *mm = current->mm;
 385
 386                         /*
 387                          * 32-bit code can use the signal return page
 388                          * except when the MPU has protected the vectors
 389                          * page from PL0
 390                          */
 391                         retcode = mm->context.sigpage + signal_return_offset +
 392                                   (idx << 2) + thumb;
 393                 } else
 394 #endif
 395                 {
 396                         /*
 397                          * Ensure that the instruction cache sees
 398                          * the return code written onto the stack.
 399                          */
 400                         flush_icache_range((unsigned long)rc,
 401                                            (unsigned long)(rc + 2));
 402
 403                         retcode = ((unsigned long)rc) + thumb;
 404                 }
 405         }
 406
 407         regs->ARM_r0 = ksig->sig;
 408         regs->ARM_sp = (unsigned long)frame;
 409         regs->ARM_lr = retcode;
 410         regs->ARM_pc = handler;
 411         regs->ARM_cpsr = cpsr;
 412
 413         return 0;
 414 }
 415
 416 static int
 417 setup_frame(struct ksignal *ksig, sigset_t *set, struct pt_regs *regs)
 418 {
 419         struct sigframe __user *frame = get_sigframe(ksig, regs, sizeof(*frame));
 420         int err = 0;
 421
 422         if (!frame)
 423                 return 1;
 424
 425         /*
 426          * Set uc.uc_flags to a value which sc.trap_no would never have.
 427          */
 428         __put_user_error(0x5ac3c35a, &frame->uc.uc_flags, err);
 429
 430         err |= setup_sigframe(frame, regs, set);
 431         if (err == 0)
 432                 err = setup_return(regs, ksig, frame->retcode, frame);
 433
 434         return err;
 435 }
 436
 437 static int
 438 setup_rt_frame(struct ksignal *ksig, sigset_t *set, struct pt_regs *regs)
 439 {
 440         struct rt_sigframe __user *frame = get_sigframe(ksig, regs, sizeof(*frame));
 441         int err = 0;
 442
 443         if (!frame)
 444                 return 1;
 445
 446         err |= copy_siginfo_to_user(&frame->info, &ksig->info);
 447
 448         __put_user_error(0, &frame->sig.uc.uc_flags, err);
 449         __put_user_error(NULL, &frame->sig.uc.uc_link, err);
 450
 451         err |= __save_altstack(&frame->sig.uc.uc_stack, regs->ARM_sp);
 452         err |= setup_sigframe(&frame->sig, regs, set);
 453         if (err == 0)
 454                 err = setup_return(regs, ksig, frame->sig.retcode, frame);
 455
 456         if (err == 0) {
 457                 /*
 458                  * For realtime signals we must also set the second and third
 459                  * arguments for the signal handler.
 460                  *   -- Peter Maydell <pmaydell@chiark.greenend.org.uk> 2000-12-06
 461                  */
 462                 regs->ARM_r1 = (unsigned long)&frame->info;
 463                 regs->ARM_r2 = (unsigned long)&frame->sig.uc;
 464         }
 465
 466         return err;
 467 }
 468
 469 /*
 470  * OK, we're invoking a handler
 471  */
 472 static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 473 {
 474         sigset_t *oldset = sigmask_to_save();
 475         int ret;
 476
 477         /*
 478          * Set up the stack frame
 479          */
 480         if (ksig->ka.sa.sa_flags & SA_SIGINFO)
 481                 ret = setup_rt_frame(ksig, oldset, regs);
 482         else
 483                 ret = setup_frame(ksig, oldset, regs);
 484
 485         /*
 486          * Check that the resulting registers are actually sane.
 487          */
 488         ret |= !valid_user_regs(regs);
 489
 490         signal_setup_done(ret, ksig, 0);
 491 }
 492
 493 /*
 494  * Note that 'init' is a special process: it doesn't get signals it doesn't
 495  * want to handle. Thus you cannot kill init even with a SIGKILL even by
 496  * mistake.
 497  *
 498  * Note that we go through the signals twice: once to check the signals that
 499  * the kernel can handle, and then we build all the user-level signal handling
 500  * stack-frames in one go after that.
 501  */
 502 static int do_signal(struct pt_regs *regs, int syscall)
 503 {
 504         unsigned int retval = 0, continue_addr = 0, restart_addr = 0;
 505         struct ksignal ksig;
 506         int restart = 0;
 507
 508         /*
 509          * If we were from a system call, check for system call restarting...
 510          */
 511         if (syscall) {
 512                 continue_addr = regs->ARM_pc;
 513                 restart_addr = continue_addr - (thumb_mode(regs) ? 2 : 4);
 514                 retval = regs->ARM_r0;
 515
 516                 /*
 517                  * Prepare for system call restart.  We do this here so that a
 518                  * debugger will see the already changed PSW.
 519                  */
 520                 switch (retval) {
 521                 case -ERESTART_RESTARTBLOCK:
 522                         restart -= 2;
 523                 case -ERESTARTNOHAND:
 524                 case -ERESTARTSYS:
 525                 case -ERESTARTNOINTR:
 526                         restart++;
 527                         regs->ARM_r0 = regs->ARM_ORIG_r0;
 528                         regs->ARM_pc = restart_addr;
 529                         break;
 530                 }
 531         }
 532
 533         /*
 534          * Get the signal to deliver.  When running under ptrace, at this
 535          * point the debugger may change all our registers ...
 536          */
 537         /*
 538          * Depending on the signal settings we may need to revert the
 539          * decision to restart the system call.  But skip this if a
 540          * debugger has chosen to restart at a different PC.
 541          */
 542         if (get_signal(&ksig)) {
 543                 /* handler */
 544                 if (unlikely(restart) && regs->ARM_pc == restart_addr) {
 545                         if (retval == -ERESTARTNOHAND ||
 546                             retval == -ERESTART_RESTARTBLOCK
 547                             || (retval == -ERESTARTSYS
 548                                 && !(ksig.ka.sa.sa_flags & SA_RESTART))) {
 549                                 regs->ARM_r0 = -EINTR;
 550                                 regs->ARM_pc = continue_addr;
 551                         }
 552                 }
 553                 handle_signal(&ksig, regs);
 554         } else {
 555                 /* no handler */
 556                 restore_saved_sigmask();
 557                 if (unlikely(restart) && regs->ARM_pc == restart_addr) {
 558                         regs->ARM_pc = continue_addr;
 559                         return restart;
 560                 }
 561         }
 562         return 0;
 563 }
 564
 565 asmlinkage int
 566 do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
 567 {
 568         /*
 569          * The assembly code enters us with IRQs off, but it hasn't
 570          * informed the tracing code of that for efficiency reasons.
 571          * Update the trace code with the current status.
 572          */
 573         trace_hardirqs_off();
 574         do {
 575                 if (likely(thread_flags & _TIF_NEED_RESCHED)) {
 576                         schedule();
 577                 } else {
 578                         if (unlikely(!user_mode(regs)))
 579                                 return 0;
 580                         local_irq_enable();
 581                         if (thread_flags & _TIF_SIGPENDING) {
 582                                 int restart = do_signal(regs, syscall);
 583                                 if (unlikely(restart)) {
 584                                         /*
 585                                          * Restart without handlers.
 586                                          * Deal with it without leaving
 587                                          * the kernel space.
 588                                          */
 589                                         return restart;
 590                                 }
 591                                 syscall = 0;
 592                         } else if (thread_flags & _TIF_UPROBE) {
 593                                 uprobe_notify_resume(regs);
 594                         } else {
 595                                 clear_thread_flag(TIF_NOTIFY_RESUME);
 596                                 tracehook_notify_resume(regs);
 597                         }
 598                 }
 599                 local_irq_disable();
 600                 thread_flags = current_thread_info()->flags;
 601         } while (thread_flags & _TIF_WORK_MASK);
 602         return 0;
 603 }
 604
 605 struct page *get_signal_page(void)
 606 {
 607         unsigned long ptr;
 608         unsigned offset;
 609         struct page *page;
 610         void *addr;
 611
 612         page = alloc_pages(GFP_KERNEL, 0);
 613
 614         if (!page)
 615                 return NULL;
 616
 617         addr = page_address(page);
 618
 619         /* Give the signal return code some randomness */
 620         offset = 0x200 + (get_random_int() & 0x7fc);
 621         signal_return_offset = offset;
 622
 623         /*
 624          * Copy signal return handlers into the vector page, and
 625          * set sigreturn to be a pointer to these.
 626          */
 627         memcpy(addr + offset, sigreturn_codes, sizeof(sigreturn_codes));
 628
 629         ptr = (unsigned long)addr + offset;
 630         flush_icache_range(ptr, ptr + sizeof(sigreturn_codes));
 631
 632         return page;
 633 }