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_thread_info()->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_thread_info()->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 /*
 322  * translate the signal
 323  */
 324 static inline int map_sig(int sig)
 325 {
 326         struct thread_info *thread = current_thread_info();
 327         if (sig < 32 && thread->exec_domain && thread->exec_domain->signal_invmap)
 328                 sig = thread->exec_domain->signal_invmap[sig];
 329         return sig;
 330 }
 331
 332 static int
 333 setup_return(struct pt_regs *regs, struct ksignal *ksig,
 334              unsigned long __user *rc, void __user *frame)
 335 {
 336         unsigned long handler = (unsigned long)ksig->ka.sa.sa_handler;
 337         unsigned long retcode;
 338         int thumb = 0;
 339         unsigned long cpsr = regs->ARM_cpsr & ~(PSR_f | PSR_E_BIT);
 340
 341         cpsr |= PSR_ENDSTATE;
 342
 343         /*
 344          * Maybe we need to deliver a 32-bit signal to a 26-bit task.
 345          */
 346         if (ksig->ka.sa.sa_flags & SA_THIRTYTWO)
 347                 cpsr = (cpsr & ~MODE_MASK) | USR_MODE;
 348
 349 #ifdef CONFIG_ARM_THUMB
 350         if (elf_hwcap & HWCAP_THUMB) {
 351                 /*
 352                  * The LSB of the handler determines if we're going to
 353                  * be using THUMB or ARM mode for this signal handler.
 354                  */
 355                 thumb = handler & 1;
 356
 357 #if __LINUX_ARM_ARCH__ >= 7
 358                 /*
 359                  * Clear the If-Then Thumb-2 execution state
 360                  * ARM spec requires this to be all 000s in ARM mode
 361                  * Snapdragon S4/Krait misbehaves on a Thumb=>ARM
 362                  * signal transition without this.
 363                  */
 364                 cpsr &= ~PSR_IT_MASK;
 365 #endif
 366
 367                 if (thumb) {
 368                         cpsr |= PSR_T_BIT;
 369                 } else
 370                         cpsr &= ~PSR_T_BIT;
 371         }
 372 #endif
 373
 374         if (ksig->ka.sa.sa_flags & SA_RESTORER) {
 375                 retcode = (unsigned long)ksig->ka.sa.sa_restorer;
 376         } else {
 377                 unsigned int idx = thumb << 1;
 378
 379                 if (ksig->ka.sa.sa_flags & SA_SIGINFO)
 380                         idx += 3;
 381
 382                 /*
 383                  * Put the sigreturn code on the stack no matter which return
 384                  * mechanism we use in order to remain ABI compliant
 385                  */
 386                 if (__put_user(sigreturn_codes[idx],   rc) ||
 387                     __put_user(sigreturn_codes[idx+1], rc+1))
 388                         return 1;
 389
 390 #ifdef CONFIG_MMU
 391                 if (cpsr & MODE32_BIT) {
 392                         struct mm_struct *mm = current->mm;
 393
 394                         /*
 395                          * 32-bit code can use the signal return page
 396                          * except when the MPU has protected the vectors
 397                          * page from PL0
 398                          */
 399                         retcode = mm->context.sigpage + signal_return_offset +
 400                                   (idx << 2) + thumb;
 401                 } else
 402 #endif
 403                 {
 404                         /*
 405                          * Ensure that the instruction cache sees
 406                          * the return code written onto the stack.
 407                          */
 408                         flush_icache_range((unsigned long)rc,
 409                                            (unsigned long)(rc + 2));
 410
 411                         retcode = ((unsigned long)rc) + thumb;
 412                 }
 413         }
 414
 415         regs->ARM_r0 = map_sig(ksig->sig);
 416         regs->ARM_sp = (unsigned long)frame;
 417         regs->ARM_lr = retcode;
 418         regs->ARM_pc = handler;
 419         regs->ARM_cpsr = cpsr;
 420
 421         return 0;
 422 }
 423
 424 static int
 425 setup_frame(struct ksignal *ksig, sigset_t *set, struct pt_regs *regs)
 426 {
 427         struct sigframe __user *frame = get_sigframe(ksig, regs, sizeof(*frame));
 428         int err = 0;
 429
 430         if (!frame)
 431                 return 1;
 432
 433         /*
 434          * Set uc.uc_flags to a value which sc.trap_no would never have.
 435          */
 436         __put_user_error(0x5ac3c35a, &frame->uc.uc_flags, err);
 437
 438         err |= setup_sigframe(frame, regs, set);
 439         if (err == 0)
 440                 err = setup_return(regs, ksig, frame->retcode, frame);
 441
 442         return err;
 443 }
 444
 445 static int
 446 setup_rt_frame(struct ksignal *ksig, sigset_t *set, struct pt_regs *regs)
 447 {
 448         struct rt_sigframe __user *frame = get_sigframe(ksig, regs, sizeof(*frame));
 449         int err = 0;
 450
 451         if (!frame)
 452                 return 1;
 453
 454         err |= copy_siginfo_to_user(&frame->info, &ksig->info);
 455
 456         __put_user_error(0, &frame->sig.uc.uc_flags, err);
 457         __put_user_error(NULL, &frame->sig.uc.uc_link, err);
 458
 459         err |= __save_altstack(&frame->sig.uc.uc_stack, regs->ARM_sp);
 460         err |= setup_sigframe(&frame->sig, regs, set);
 461         if (err == 0)
 462                 err = setup_return(regs, ksig, frame->sig.retcode, frame);
 463
 464         if (err == 0) {
 465                 /*
 466                  * For realtime signals we must also set the second and third
 467                  * arguments for the signal handler.
 468                  *   -- Peter Maydell <pmaydell@chiark.greenend.org.uk> 2000-12-06
 469                  */
 470                 regs->ARM_r1 = (unsigned long)&frame->info;
 471                 regs->ARM_r2 = (unsigned long)&frame->sig.uc;
 472         }
 473
 474         return err;
 475 }
 476
 477 /*
 478  * OK, we're invoking a handler
 479  */
 480 static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 481 {
 482         sigset_t *oldset = sigmask_to_save();
 483         int ret;
 484
 485         /*
 486          * Set up the stack frame
 487          */
 488         if (ksig->ka.sa.sa_flags & SA_SIGINFO)
 489                 ret = setup_rt_frame(ksig, oldset, regs);
 490         else
 491                 ret = setup_frame(ksig, oldset, regs);
 492
 493         /*
 494          * Check that the resulting registers are actually sane.
 495          */
 496         ret |= !valid_user_regs(regs);
 497
 498         signal_setup_done(ret, ksig, 0);
 499 }
 500
 501 /*
 502  * Note that 'init' is a special process: it doesn't get signals it doesn't
 503  * want to handle. Thus you cannot kill init even with a SIGKILL even by
 504  * mistake.
 505  *
 506  * Note that we go through the signals twice: once to check the signals that
 507  * the kernel can handle, and then we build all the user-level signal handling
 508  * stack-frames in one go after that.
 509  */
 510 static int do_signal(struct pt_regs *regs, int syscall)
 511 {
 512         unsigned int retval = 0, continue_addr = 0, restart_addr = 0;
 513         struct ksignal ksig;
 514         int restart = 0;
 515
 516         /*
 517          * If we were from a system call, check for system call restarting...
 518          */
 519         if (syscall) {
 520                 continue_addr = regs->ARM_pc;
 521                 restart_addr = continue_addr - (thumb_mode(regs) ? 2 : 4);
 522                 retval = regs->ARM_r0;
 523
 524                 /*
 525                  * Prepare for system call restart.  We do this here so that a
 526                  * debugger will see the already changed PSW.
 527                  */
 528                 switch (retval) {
 529                 case -ERESTART_RESTARTBLOCK:
 530                         restart -= 2;
 531                 case -ERESTARTNOHAND:
 532                 case -ERESTARTSYS:
 533                 case -ERESTARTNOINTR:
 534                         restart++;
 535                         regs->ARM_r0 = regs->ARM_ORIG_r0;
 536                         regs->ARM_pc = restart_addr;
 537                         break;
 538                 }
 539         }
 540
 541         /*
 542          * Get the signal to deliver.  When running under ptrace, at this
 543          * point the debugger may change all our registers ...
 544          */
 545         /*
 546          * Depending on the signal settings we may need to revert the
 547          * decision to restart the system call.  But skip this if a
 548          * debugger has chosen to restart at a different PC.
 549          */
 550         if (get_signal(&ksig)) {
 551                 /* handler */
 552                 if (unlikely(restart) && regs->ARM_pc == restart_addr) {
 553                         if (retval == -ERESTARTNOHAND ||
 554                             retval == -ERESTART_RESTARTBLOCK
 555                             || (retval == -ERESTARTSYS
 556                                 && !(ksig.ka.sa.sa_flags & SA_RESTART))) {
 557                                 regs->ARM_r0 = -EINTR;
 558                                 regs->ARM_pc = continue_addr;
 559                         }
 560                 }
 561                 handle_signal(&ksig, regs);
 562         } else {
 563                 /* no handler */
 564                 restore_saved_sigmask();
 565                 if (unlikely(restart) && regs->ARM_pc == restart_addr) {
 566                         regs->ARM_pc = continue_addr;
 567                         return restart;
 568                 }
 569         }
 570         return 0;
 571 }
 572
 573 asmlinkage int
 574 do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
 575 {
 576         do {
 577                 if (likely(thread_flags & _TIF_NEED_RESCHED)) {
 578                         schedule();
 579                 } else {
 580                         if (unlikely(!user_mode(regs)))
 581                                 return 0;
 582                         local_irq_enable();
 583                         if (thread_flags & _TIF_SIGPENDING) {
 584                                 int restart = do_signal(regs, syscall);
 585                                 if (unlikely(restart)) {
 586                                         /*
 587                                          * Restart without handlers.
 588                                          * Deal with it without leaving
 589                                          * the kernel space.
 590                                          */
 591                                         return restart;
 592                                 }
 593                                 syscall = 0;
 594                         } else if (thread_flags & _TIF_UPROBE) {
 595                                 clear_thread_flag(TIF_UPROBE);
 596                                 uprobe_notify_resume(regs);
 597                         } else {
 598                                 clear_thread_flag(TIF_NOTIFY_RESUME);
 599                                 tracehook_notify_resume(regs);
 600                         }
 601                 }
 602                 local_irq_disable();
 603                 thread_flags = current_thread_info()->flags;
 604         } while (thread_flags & _TIF_WORK_MASK);
 605         return 0;
 606 }
 607
 608 struct page *get_signal_page(void)
 609 {
 610         unsigned long ptr;
 611         unsigned offset;
 612         struct page *page;
 613         void *addr;
 614
 615         page = alloc_pages(GFP_KERNEL, 0);
 616
 617         if (!page)
 618                 return NULL;
 619
 620         addr = page_address(page);
 621
 622         /* Give the signal return code some randomness */
 623         offset = 0x200 + (get_random_int() & 0x7fc);
 624         signal_return_offset = offset;
 625
 626         /*
 627          * Copy signal return handlers into the vector page, and
 628          * set sigreturn to be a pointer to these.
 629          */
 630         memcpy(addr + offset, sigreturn_codes, sizeof(sigreturn_codes));
 631
 632         ptr = (unsigned long)addr + offset;
 633         flush_icache_range(ptr, ptr + sizeof(sigreturn_codes));
 634
 635         return page;
 636 }