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TOMOYO Linux Cross Reference
Linux/arch/powerpc/mm/fault.c

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  1 /*
  2  *  PowerPC version
  3  *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
  4  *
  5  *  Derived from "arch/i386/mm/fault.c"
  6  *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  7  *
  8  *  Modified by Cort Dougan and Paul Mackerras.
  9  *
 10  *  Modified for PPC64 by Dave Engebretsen (engebret@ibm.com)
 11  *
 12  *  This program is free software; you can redistribute it and/or
 13  *  modify it under the terms of the GNU General Public License
 14  *  as published by the Free Software Foundation; either version
 15  *  2 of the License, or (at your option) any later version.
 16  */
 17 
 18 #include <linux/signal.h>
 19 #include <linux/sched.h>
 20 #include <linux/sched/task_stack.h>
 21 #include <linux/kernel.h>
 22 #include <linux/errno.h>
 23 #include <linux/string.h>
 24 #include <linux/types.h>
 25 #include <linux/pagemap.h>
 26 #include <linux/ptrace.h>
 27 #include <linux/mman.h>
 28 #include <linux/mm.h>
 29 #include <linux/interrupt.h>
 30 #include <linux/highmem.h>
 31 #include <linux/extable.h>
 32 #include <linux/kprobes.h>
 33 #include <linux/kdebug.h>
 34 #include <linux/perf_event.h>
 35 #include <linux/ratelimit.h>
 36 #include <linux/context_tracking.h>
 37 #include <linux/hugetlb.h>
 38 #include <linux/uaccess.h>
 39 
 40 #include <asm/firmware.h>
 41 #include <asm/page.h>
 42 #include <asm/pgtable.h>
 43 #include <asm/mmu.h>
 44 #include <asm/mmu_context.h>
 45 #include <asm/siginfo.h>
 46 #include <asm/debug.h>
 47 
 48 static inline bool notify_page_fault(struct pt_regs *regs)
 49 {
 50         bool ret = false;
 51 
 52 #ifdef CONFIG_KPROBES
 53         /* kprobe_running() needs smp_processor_id() */
 54         if (!user_mode(regs)) {
 55                 preempt_disable();
 56                 if (kprobe_running() && kprobe_fault_handler(regs, 11))
 57                         ret = true;
 58                 preempt_enable();
 59         }
 60 #endif /* CONFIG_KPROBES */
 61 
 62         if (unlikely(debugger_fault_handler(regs)))
 63                 ret = true;
 64 
 65         return ret;
 66 }
 67 
 68 /*
 69  * Check whether the instruction inst is a store using
 70  * an update addressing form which will update r1.
 71  */
 72 static bool store_updates_sp(unsigned int inst)
 73 {
 74         /* check for 1 in the rA field */
 75         if (((inst >> 16) & 0x1f) != 1)
 76                 return false;
 77         /* check major opcode */
 78         switch (inst >> 26) {
 79         case OP_STWU:
 80         case OP_STBU:
 81         case OP_STHU:
 82         case OP_STFSU:
 83         case OP_STFDU:
 84                 return true;
 85         case OP_STD:    /* std or stdu */
 86                 return (inst & 3) == 1;
 87         case OP_31:
 88                 /* check minor opcode */
 89                 switch ((inst >> 1) & 0x3ff) {
 90                 case OP_31_XOP_STDUX:
 91                 case OP_31_XOP_STWUX:
 92                 case OP_31_XOP_STBUX:
 93                 case OP_31_XOP_STHUX:
 94                 case OP_31_XOP_STFSUX:
 95                 case OP_31_XOP_STFDUX:
 96                         return true;
 97                 }
 98         }
 99         return false;
100 }
101 /*
102  * do_page_fault error handling helpers
103  */
104 
105 static int
106 __bad_area_nosemaphore(struct pt_regs *regs, unsigned long address, int si_code)
107 {
108         /*
109          * If we are in kernel mode, bail out with a SEGV, this will
110          * be caught by the assembly which will restore the non-volatile
111          * registers before calling bad_page_fault()
112          */
113         if (!user_mode(regs))
114                 return SIGSEGV;
115 
116         _exception(SIGSEGV, regs, si_code, address);
117 
118         return 0;
119 }
120 
121 static noinline int bad_area_nosemaphore(struct pt_regs *regs, unsigned long address)
122 {
123         return __bad_area_nosemaphore(regs, address, SEGV_MAPERR);
124 }
125 
126 static int __bad_area(struct pt_regs *regs, unsigned long address, int si_code)
127 {
128         struct mm_struct *mm = current->mm;
129 
130         /*
131          * Something tried to access memory that isn't in our memory map..
132          * Fix it, but check if it's kernel or user first..
133          */
134         up_read(&mm->mmap_sem);
135 
136         return __bad_area_nosemaphore(regs, address, si_code);
137 }
138 
139 static noinline int bad_area(struct pt_regs *regs, unsigned long address)
140 {
141         return __bad_area(regs, address, SEGV_MAPERR);
142 }
143 
144 static int bad_key_fault_exception(struct pt_regs *regs, unsigned long address,
145                                     int pkey)
146 {
147         /*
148          * If we are in kernel mode, bail out with a SEGV, this will
149          * be caught by the assembly which will restore the non-volatile
150          * registers before calling bad_page_fault()
151          */
152         if (!user_mode(regs))
153                 return SIGSEGV;
154 
155         _exception_pkey(regs, address, pkey);
156 
157         return 0;
158 }
159 
160 static noinline int bad_access(struct pt_regs *regs, unsigned long address)
161 {
162         return __bad_area(regs, address, SEGV_ACCERR);
163 }
164 
165 static int do_sigbus(struct pt_regs *regs, unsigned long address,
166                      vm_fault_t fault)
167 {
168         if (!user_mode(regs))
169                 return SIGBUS;
170 
171         current->thread.trap_nr = BUS_ADRERR;
172 #ifdef CONFIG_MEMORY_FAILURE
173         if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
174                 unsigned int lsb = 0; /* shutup gcc */
175 
176                 pr_err("MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
177                         current->comm, current->pid, address);
178 
179                 if (fault & VM_FAULT_HWPOISON_LARGE)
180                         lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
181                 if (fault & VM_FAULT_HWPOISON)
182                         lsb = PAGE_SHIFT;
183 
184                 force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb,
185                                  current);
186                 return 0;
187         }
188 
189 #endif
190         force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address, current);
191         return 0;
192 }
193 
194 static int mm_fault_error(struct pt_regs *regs, unsigned long addr,
195                                 vm_fault_t fault)
196 {
197         /*
198          * Kernel page fault interrupted by SIGKILL. We have no reason to
199          * continue processing.
200          */
201         if (fatal_signal_pending(current) && !user_mode(regs))
202                 return SIGKILL;
203 
204         /* Out of memory */
205         if (fault & VM_FAULT_OOM) {
206                 /*
207                  * We ran out of memory, or some other thing happened to us that
208                  * made us unable to handle the page fault gracefully.
209                  */
210                 if (!user_mode(regs))
211                         return SIGSEGV;
212                 pagefault_out_of_memory();
213         } else {
214                 if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
215                              VM_FAULT_HWPOISON_LARGE))
216                         return do_sigbus(regs, addr, fault);
217                 else if (fault & VM_FAULT_SIGSEGV)
218                         return bad_area_nosemaphore(regs, addr);
219                 else
220                         BUG();
221         }
222         return 0;
223 }
224 
225 /* Is this a bad kernel fault ? */
226 static bool bad_kernel_fault(bool is_exec, unsigned long error_code,
227                              unsigned long address)
228 {
229         /* NX faults set DSISR_PROTFAULT on the 8xx, DSISR_NOEXEC_OR_G on others */
230         if (is_exec && (error_code & (DSISR_NOEXEC_OR_G | DSISR_KEYFAULT |
231                                       DSISR_PROTFAULT))) {
232                 printk_ratelimited(KERN_CRIT "kernel tried to execute"
233                                    " exec-protected page (%lx) -"
234                                    "exploit attempt? (uid: %d)\n",
235                                    address, from_kuid(&init_user_ns,
236                                                       current_uid()));
237         }
238         return is_exec || (address >= TASK_SIZE);
239 }
240 
241 static bool bad_stack_expansion(struct pt_regs *regs, unsigned long address,
242                                 struct vm_area_struct *vma, unsigned int flags,
243                                 bool *must_retry)
244 {
245         /*
246          * N.B. The POWER/Open ABI allows programs to access up to
247          * 288 bytes below the stack pointer.
248          * The kernel signal delivery code writes up to about 1.5kB
249          * below the stack pointer (r1) before decrementing it.
250          * The exec code can write slightly over 640kB to the stack
251          * before setting the user r1.  Thus we allow the stack to
252          * expand to 1MB without further checks.
253          */
254         if (address + 0x100000 < vma->vm_end) {
255                 unsigned int __user *nip = (unsigned int __user *)regs->nip;
256                 /* get user regs even if this fault is in kernel mode */
257                 struct pt_regs *uregs = current->thread.regs;
258                 if (uregs == NULL)
259                         return true;
260 
261                 /*
262                  * A user-mode access to an address a long way below
263                  * the stack pointer is only valid if the instruction
264                  * is one which would update the stack pointer to the
265                  * address accessed if the instruction completed,
266                  * i.e. either stwu rs,n(r1) or stwux rs,r1,rb
267                  * (or the byte, halfword, float or double forms).
268                  *
269                  * If we don't check this then any write to the area
270                  * between the last mapped region and the stack will
271                  * expand the stack rather than segfaulting.
272                  */
273                 if (address + 2048 >= uregs->gpr[1])
274                         return false;
275 
276                 if ((flags & FAULT_FLAG_WRITE) && (flags & FAULT_FLAG_USER) &&
277                     access_ok(nip, sizeof(*nip))) {
278                         unsigned int inst;
279                         int res;
280 
281                         pagefault_disable();
282                         res = __get_user_inatomic(inst, nip);
283                         pagefault_enable();
284                         if (!res)
285                                 return !store_updates_sp(inst);
286                         *must_retry = true;
287                 }
288                 return true;
289         }
290         return false;
291 }
292 
293 static bool access_error(bool is_write, bool is_exec,
294                          struct vm_area_struct *vma)
295 {
296         /*
297          * Allow execution from readable areas if the MMU does not
298          * provide separate controls over reading and executing.
299          *
300          * Note: That code used to not be enabled for 4xx/BookE.
301          * It is now as I/D cache coherency for these is done at
302          * set_pte_at() time and I see no reason why the test
303          * below wouldn't be valid on those processors. This -may-
304          * break programs compiled with a really old ABI though.
305          */
306         if (is_exec) {
307                 return !(vma->vm_flags & VM_EXEC) &&
308                         (cpu_has_feature(CPU_FTR_NOEXECUTE) ||
309                          !(vma->vm_flags & (VM_READ | VM_WRITE)));
310         }
311 
312         if (is_write) {
313                 if (unlikely(!(vma->vm_flags & VM_WRITE)))
314                         return true;
315                 return false;
316         }
317 
318         if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))))
319                 return true;
320         /*
321          * We should ideally do the vma pkey access check here. But in the
322          * fault path, handle_mm_fault() also does the same check. To avoid
323          * these multiple checks, we skip it here and handle access error due
324          * to pkeys later.
325          */
326         return false;
327 }
328 
329 #ifdef CONFIG_PPC_SMLPAR
330 static inline void cmo_account_page_fault(void)
331 {
332         if (firmware_has_feature(FW_FEATURE_CMO)) {
333                 u32 page_ins;
334 
335                 preempt_disable();
336                 page_ins = be32_to_cpu(get_lppaca()->page_ins);
337                 page_ins += 1 << PAGE_FACTOR;
338                 get_lppaca()->page_ins = cpu_to_be32(page_ins);
339                 preempt_enable();
340         }
341 }
342 #else
343 static inline void cmo_account_page_fault(void) { }
344 #endif /* CONFIG_PPC_SMLPAR */
345 
346 #ifdef CONFIG_PPC_BOOK3S
347 static void sanity_check_fault(bool is_write, bool is_user,
348                                unsigned long error_code, unsigned long address)
349 {
350         /*
351          * Userspace trying to access kernel address, we get PROTFAULT for that.
352          */
353         if (is_user && address >= TASK_SIZE) {
354                 pr_crit_ratelimited("%s[%d]: User access of kernel address (%lx) - exploit attempt? (uid: %d)\n",
355                                    current->comm, current->pid, address,
356                                    from_kuid(&init_user_ns, current_uid()));
357                 return;
358         }
359 
360         /*
361          * For hash translation mode, we should never get a
362          * PROTFAULT. Any update to pte to reduce access will result in us
363          * removing the hash page table entry, thus resulting in a DSISR_NOHPTE
364          * fault instead of DSISR_PROTFAULT.
365          *
366          * A pte update to relax the access will not result in a hash page table
367          * entry invalidate and hence can result in DSISR_PROTFAULT.
368          * ptep_set_access_flags() doesn't do a hpte flush. This is why we have
369          * the special !is_write in the below conditional.
370          *
371          * For platforms that doesn't supports coherent icache and do support
372          * per page noexec bit, we do setup things such that we do the
373          * sync between D/I cache via fault. But that is handled via low level
374          * hash fault code (hash_page_do_lazy_icache()) and we should not reach
375          * here in such case.
376          *
377          * For wrong access that can result in PROTFAULT, the above vma->vm_flags
378          * check should handle those and hence we should fall to the bad_area
379          * handling correctly.
380          *
381          * For embedded with per page exec support that doesn't support coherent
382          * icache we do get PROTFAULT and we handle that D/I cache sync in
383          * set_pte_at while taking the noexec/prot fault. Hence this is WARN_ON
384          * is conditional for server MMU.
385          *
386          * For radix, we can get prot fault for autonuma case, because radix
387          * page table will have them marked noaccess for user.
388          */
389         if (radix_enabled() || is_write)
390                 return;
391 
392         WARN_ON_ONCE(error_code & DSISR_PROTFAULT);
393 }
394 #else
395 static void sanity_check_fault(bool is_write, bool is_user,
396                                unsigned long error_code, unsigned long address) { }
397 #endif /* CONFIG_PPC_BOOK3S */
398 
399 /*
400  * Define the correct "is_write" bit in error_code based
401  * on the processor family
402  */
403 #if (defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
404 #define page_fault_is_write(__err)      ((__err) & ESR_DST)
405 #define page_fault_is_bad(__err)        (0)
406 #else
407 #define page_fault_is_write(__err)      ((__err) & DSISR_ISSTORE)
408 #if defined(CONFIG_PPC_8xx)
409 #define page_fault_is_bad(__err)        ((__err) & DSISR_NOEXEC_OR_G)
410 #elif defined(CONFIG_PPC64)
411 #define page_fault_is_bad(__err)        ((__err) & DSISR_BAD_FAULT_64S)
412 #else
413 #define page_fault_is_bad(__err)        ((__err) & DSISR_BAD_FAULT_32S)
414 #endif
415 #endif
416 
417 /*
418  * For 600- and 800-family processors, the error_code parameter is DSISR
419  * for a data fault, SRR1 for an instruction fault. For 400-family processors
420  * the error_code parameter is ESR for a data fault, 0 for an instruction
421  * fault.
422  * For 64-bit processors, the error_code parameter is
423  *  - DSISR for a non-SLB data access fault,
424  *  - SRR1 & 0x08000000 for a non-SLB instruction access fault
425  *  - 0 any SLB fault.
426  *
427  * The return value is 0 if the fault was handled, or the signal
428  * number if this is a kernel fault that can't be handled here.
429  */
430 static int __do_page_fault(struct pt_regs *regs, unsigned long address,
431                            unsigned long error_code)
432 {
433         struct vm_area_struct * vma;
434         struct mm_struct *mm = current->mm;
435         unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
436         int is_exec = TRAP(regs) == 0x400;
437         int is_user = user_mode(regs);
438         int is_write = page_fault_is_write(error_code);
439         vm_fault_t fault, major = 0;
440         bool must_retry = false;
441 
442         if (notify_page_fault(regs))
443                 return 0;
444 
445         if (unlikely(page_fault_is_bad(error_code))) {
446                 if (is_user) {
447                         _exception(SIGBUS, regs, BUS_OBJERR, address);
448                         return 0;
449                 }
450                 return SIGBUS;
451         }
452 
453         /* Additional sanity check(s) */
454         sanity_check_fault(is_write, is_user, error_code, address);
455 
456         /*
457          * The kernel should never take an execute fault nor should it
458          * take a page fault to a kernel address.
459          */
460         if (unlikely(!is_user && bad_kernel_fault(is_exec, error_code, address)))
461                 return SIGSEGV;
462 
463         /*
464          * If we're in an interrupt, have no user context or are running
465          * in a region with pagefaults disabled then we must not take the fault
466          */
467         if (unlikely(faulthandler_disabled() || !mm)) {
468                 if (is_user)
469                         printk_ratelimited(KERN_ERR "Page fault in user mode"
470                                            " with faulthandler_disabled()=%d"
471                                            " mm=%p\n",
472                                            faulthandler_disabled(), mm);
473                 return bad_area_nosemaphore(regs, address);
474         }
475 
476         /* We restore the interrupt state now */
477         if (!arch_irq_disabled_regs(regs))
478                 local_irq_enable();
479 
480         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
481 
482         if (error_code & DSISR_KEYFAULT)
483                 return bad_key_fault_exception(regs, address,
484                                                get_mm_addr_key(mm, address));
485 
486         /*
487          * We want to do this outside mmap_sem, because reading code around nip
488          * can result in fault, which will cause a deadlock when called with
489          * mmap_sem held
490          */
491         if (is_user)
492                 flags |= FAULT_FLAG_USER;
493         if (is_write)
494                 flags |= FAULT_FLAG_WRITE;
495         if (is_exec)
496                 flags |= FAULT_FLAG_INSTRUCTION;
497 
498         /* When running in the kernel we expect faults to occur only to
499          * addresses in user space.  All other faults represent errors in the
500          * kernel and should generate an OOPS.  Unfortunately, in the case of an
501          * erroneous fault occurring in a code path which already holds mmap_sem
502          * we will deadlock attempting to validate the fault against the
503          * address space.  Luckily the kernel only validly references user
504          * space from well defined areas of code, which are listed in the
505          * exceptions table.
506          *
507          * As the vast majority of faults will be valid we will only perform
508          * the source reference check when there is a possibility of a deadlock.
509          * Attempt to lock the address space, if we cannot we then validate the
510          * source.  If this is invalid we can skip the address space check,
511          * thus avoiding the deadlock.
512          */
513         if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
514                 if (!is_user && !search_exception_tables(regs->nip))
515                         return bad_area_nosemaphore(regs, address);
516 
517 retry:
518                 down_read(&mm->mmap_sem);
519         } else {
520                 /*
521                  * The above down_read_trylock() might have succeeded in
522                  * which case we'll have missed the might_sleep() from
523                  * down_read():
524                  */
525                 might_sleep();
526         }
527 
528         vma = find_vma(mm, address);
529         if (unlikely(!vma))
530                 return bad_area(regs, address);
531         if (likely(vma->vm_start <= address))
532                 goto good_area;
533         if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
534                 return bad_area(regs, address);
535 
536         /* The stack is being expanded, check if it's valid */
537         if (unlikely(bad_stack_expansion(regs, address, vma, flags,
538                                          &must_retry))) {
539                 if (!must_retry)
540                         return bad_area(regs, address);
541 
542                 up_read(&mm->mmap_sem);
543                 if (fault_in_pages_readable((const char __user *)regs->nip,
544                                             sizeof(unsigned int)))
545                         return bad_area_nosemaphore(regs, address);
546                 goto retry;
547         }
548 
549         /* Try to expand it */
550         if (unlikely(expand_stack(vma, address)))
551                 return bad_area(regs, address);
552 
553 good_area:
554         if (unlikely(access_error(is_write, is_exec, vma)))
555                 return bad_access(regs, address);
556 
557         /*
558          * If for any reason at all we couldn't handle the fault,
559          * make sure we exit gracefully rather than endlessly redo
560          * the fault.
561          */
562         fault = handle_mm_fault(vma, address, flags);
563 
564 #ifdef CONFIG_PPC_MEM_KEYS
565         /*
566          * we skipped checking for access error due to key earlier.
567          * Check that using handle_mm_fault error return.
568          */
569         if (unlikely(fault & VM_FAULT_SIGSEGV) &&
570                 !arch_vma_access_permitted(vma, is_write, is_exec, 0)) {
571 
572                 int pkey = vma_pkey(vma);
573 
574                 up_read(&mm->mmap_sem);
575                 return bad_key_fault_exception(regs, address, pkey);
576         }
577 #endif /* CONFIG_PPC_MEM_KEYS */
578 
579         major |= fault & VM_FAULT_MAJOR;
580 
581         /*
582          * Handle the retry right now, the mmap_sem has been released in that
583          * case.
584          */
585         if (unlikely(fault & VM_FAULT_RETRY)) {
586                 /* We retry only once */
587                 if (flags & FAULT_FLAG_ALLOW_RETRY) {
588                         /*
589                          * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
590                          * of starvation.
591                          */
592                         flags &= ~FAULT_FLAG_ALLOW_RETRY;
593                         flags |= FAULT_FLAG_TRIED;
594                         if (!fatal_signal_pending(current))
595                                 goto retry;
596                 }
597 
598                 /*
599                  * User mode? Just return to handle the fatal exception otherwise
600                  * return to bad_page_fault
601                  */
602                 return is_user ? 0 : SIGBUS;
603         }
604 
605         up_read(&current->mm->mmap_sem);
606 
607         if (unlikely(fault & VM_FAULT_ERROR))
608                 return mm_fault_error(regs, address, fault);
609 
610         /*
611          * Major/minor page fault accounting.
612          */
613         if (major) {
614                 current->maj_flt++;
615                 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs, address);
616                 cmo_account_page_fault();
617         } else {
618                 current->min_flt++;
619                 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs, address);
620         }
621         return 0;
622 }
623 NOKPROBE_SYMBOL(__do_page_fault);
624 
625 int do_page_fault(struct pt_regs *regs, unsigned long address,
626                   unsigned long error_code)
627 {
628         enum ctx_state prev_state = exception_enter();
629         int rc = __do_page_fault(regs, address, error_code);
630         exception_exit(prev_state);
631         return rc;
632 }
633 NOKPROBE_SYMBOL(do_page_fault);
634 
635 /*
636  * bad_page_fault is called when we have a bad access from the kernel.
637  * It is called from the DSI and ISI handlers in head.S and from some
638  * of the procedures in traps.c.
639  */
640 void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
641 {
642         const struct exception_table_entry *entry;
643 
644         /* Are we prepared to handle this fault?  */
645         if ((entry = search_exception_tables(regs->nip)) != NULL) {
646                 regs->nip = extable_fixup(entry);
647                 return;
648         }
649 
650         /* kernel has accessed a bad area */
651 
652         switch (TRAP(regs)) {
653         case 0x300:
654         case 0x380:
655         case 0xe00:
656                 pr_alert("BUG: %s at 0x%08lx\n",
657                          regs->dar < PAGE_SIZE ? "Kernel NULL pointer dereference" :
658                          "Unable to handle kernel data access", regs->dar);
659                 break;
660         case 0x400:
661         case 0x480:
662                 pr_alert("BUG: Unable to handle kernel instruction fetch%s",
663                          regs->nip < PAGE_SIZE ? " (NULL pointer?)\n" : "\n");
664                 break;
665         case 0x600:
666                 pr_alert("BUG: Unable to handle kernel unaligned access at 0x%08lx\n",
667                          regs->dar);
668                 break;
669         default:
670                 pr_alert("BUG: Unable to handle unknown paging fault at 0x%08lx\n",
671                          regs->dar);
672                 break;
673         }
674         printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
675                 regs->nip);
676 
677         if (task_stack_end_corrupted(current))
678                 printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");
679 
680         die("Kernel access of bad area", regs, sig);
681 }
682 

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