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Linux/arch/powerpc/mm/fault.c

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  1 // SPDX-License-Identifier: GPL-2.0-or-later
  2 /*
  3  *  PowerPC version
  4  *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
  5  *
  6  *  Derived from "arch/i386/mm/fault.c"
  7  *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  8  *
  9  *  Modified by Cort Dougan and Paul Mackerras.
 10  *
 11  *  Modified for PPC64 by Dave Engebretsen (engebret@ibm.com)
 12  */
 13 
 14 #include <linux/signal.h>
 15 #include <linux/sched.h>
 16 #include <linux/sched/task_stack.h>
 17 #include <linux/kernel.h>
 18 #include <linux/errno.h>
 19 #include <linux/string.h>
 20 #include <linux/types.h>
 21 #include <linux/pagemap.h>
 22 #include <linux/ptrace.h>
 23 #include <linux/mman.h>
 24 #include <linux/mm.h>
 25 #include <linux/interrupt.h>
 26 #include <linux/highmem.h>
 27 #include <linux/extable.h>
 28 #include <linux/kprobes.h>
 29 #include <linux/kdebug.h>
 30 #include <linux/perf_event.h>
 31 #include <linux/ratelimit.h>
 32 #include <linux/context_tracking.h>
 33 #include <linux/hugetlb.h>
 34 #include <linux/uaccess.h>
 35 
 36 #include <asm/firmware.h>
 37 #include <asm/page.h>
 38 #include <asm/pgtable.h>
 39 #include <asm/mmu.h>
 40 #include <asm/mmu_context.h>
 41 #include <asm/siginfo.h>
 42 #include <asm/debug.h>
 43 #include <asm/kup.h>
 44 
 45 /*
 46  * Check whether the instruction inst is a store using
 47  * an update addressing form which will update r1.
 48  */
 49 static bool store_updates_sp(unsigned int inst)
 50 {
 51         /* check for 1 in the rA field */
 52         if (((inst >> 16) & 0x1f) != 1)
 53                 return false;
 54         /* check major opcode */
 55         switch (inst >> 26) {
 56         case OP_STWU:
 57         case OP_STBU:
 58         case OP_STHU:
 59         case OP_STFSU:
 60         case OP_STFDU:
 61                 return true;
 62         case OP_STD:    /* std or stdu */
 63                 return (inst & 3) == 1;
 64         case OP_31:
 65                 /* check minor opcode */
 66                 switch ((inst >> 1) & 0x3ff) {
 67                 case OP_31_XOP_STDUX:
 68                 case OP_31_XOP_STWUX:
 69                 case OP_31_XOP_STBUX:
 70                 case OP_31_XOP_STHUX:
 71                 case OP_31_XOP_STFSUX:
 72                 case OP_31_XOP_STFDUX:
 73                         return true;
 74                 }
 75         }
 76         return false;
 77 }
 78 /*
 79  * do_page_fault error handling helpers
 80  */
 81 
 82 static int
 83 __bad_area_nosemaphore(struct pt_regs *regs, unsigned long address, int si_code)
 84 {
 85         /*
 86          * If we are in kernel mode, bail out with a SEGV, this will
 87          * be caught by the assembly which will restore the non-volatile
 88          * registers before calling bad_page_fault()
 89          */
 90         if (!user_mode(regs))
 91                 return SIGSEGV;
 92 
 93         _exception(SIGSEGV, regs, si_code, address);
 94 
 95         return 0;
 96 }
 97 
 98 static noinline int bad_area_nosemaphore(struct pt_regs *regs, unsigned long address)
 99 {
100         return __bad_area_nosemaphore(regs, address, SEGV_MAPERR);
101 }
102 
103 static int __bad_area(struct pt_regs *regs, unsigned long address, int si_code)
104 {
105         struct mm_struct *mm = current->mm;
106 
107         /*
108          * Something tried to access memory that isn't in our memory map..
109          * Fix it, but check if it's kernel or user first..
110          */
111         up_read(&mm->mmap_sem);
112 
113         return __bad_area_nosemaphore(regs, address, si_code);
114 }
115 
116 static noinline int bad_area(struct pt_regs *regs, unsigned long address)
117 {
118         return __bad_area(regs, address, SEGV_MAPERR);
119 }
120 
121 static int bad_key_fault_exception(struct pt_regs *regs, unsigned long address,
122                                     int pkey)
123 {
124         /*
125          * If we are in kernel mode, bail out with a SEGV, this will
126          * be caught by the assembly which will restore the non-volatile
127          * registers before calling bad_page_fault()
128          */
129         if (!user_mode(regs))
130                 return SIGSEGV;
131 
132         _exception_pkey(regs, address, pkey);
133 
134         return 0;
135 }
136 
137 static noinline int bad_access(struct pt_regs *regs, unsigned long address)
138 {
139         return __bad_area(regs, address, SEGV_ACCERR);
140 }
141 
142 static int do_sigbus(struct pt_regs *regs, unsigned long address,
143                      vm_fault_t fault)
144 {
145         if (!user_mode(regs))
146                 return SIGBUS;
147 
148         current->thread.trap_nr = BUS_ADRERR;
149 #ifdef CONFIG_MEMORY_FAILURE
150         if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
151                 unsigned int lsb = 0; /* shutup gcc */
152 
153                 pr_err("MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
154                         current->comm, current->pid, address);
155 
156                 if (fault & VM_FAULT_HWPOISON_LARGE)
157                         lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
158                 if (fault & VM_FAULT_HWPOISON)
159                         lsb = PAGE_SHIFT;
160 
161                 force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb);
162                 return 0;
163         }
164 
165 #endif
166         force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
167         return 0;
168 }
169 
170 static int mm_fault_error(struct pt_regs *regs, unsigned long addr,
171                                 vm_fault_t fault)
172 {
173         /*
174          * Kernel page fault interrupted by SIGKILL. We have no reason to
175          * continue processing.
176          */
177         if (fatal_signal_pending(current) && !user_mode(regs))
178                 return SIGKILL;
179 
180         /* Out of memory */
181         if (fault & VM_FAULT_OOM) {
182                 /*
183                  * We ran out of memory, or some other thing happened to us that
184                  * made us unable to handle the page fault gracefully.
185                  */
186                 if (!user_mode(regs))
187                         return SIGSEGV;
188                 pagefault_out_of_memory();
189         } else {
190                 if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
191                              VM_FAULT_HWPOISON_LARGE))
192                         return do_sigbus(regs, addr, fault);
193                 else if (fault & VM_FAULT_SIGSEGV)
194                         return bad_area_nosemaphore(regs, addr);
195                 else
196                         BUG();
197         }
198         return 0;
199 }
200 
201 /* Is this a bad kernel fault ? */
202 static bool bad_kernel_fault(struct pt_regs *regs, unsigned long error_code,
203                              unsigned long address, bool is_write)
204 {
205         int is_exec = TRAP(regs) == 0x400;
206 
207         /* NX faults set DSISR_PROTFAULT on the 8xx, DSISR_NOEXEC_OR_G on others */
208         if (is_exec && (error_code & (DSISR_NOEXEC_OR_G | DSISR_KEYFAULT |
209                                       DSISR_PROTFAULT))) {
210                 pr_crit_ratelimited("kernel tried to execute %s page (%lx) - exploit attempt? (uid: %d)\n",
211                                     address >= TASK_SIZE ? "exec-protected" : "user",
212                                     address,
213                                     from_kuid(&init_user_ns, current_uid()));
214 
215                 // Kernel exec fault is always bad
216                 return true;
217         }
218 
219         if (!is_exec && address < TASK_SIZE && (error_code & DSISR_PROTFAULT) &&
220             !search_exception_tables(regs->nip)) {
221                 pr_crit_ratelimited("Kernel attempted to access user page (%lx) - exploit attempt? (uid: %d)\n",
222                                     address,
223                                     from_kuid(&init_user_ns, current_uid()));
224         }
225 
226         // Kernel fault on kernel address is bad
227         if (address >= TASK_SIZE)
228                 return true;
229 
230         // Fault on user outside of certain regions (eg. copy_tofrom_user()) is bad
231         if (!search_exception_tables(regs->nip))
232                 return true;
233 
234         // Read/write fault in a valid region (the exception table search passed
235         // above), but blocked by KUAP is bad, it can never succeed.
236         if (bad_kuap_fault(regs, is_write))
237                 return true;
238 
239         // What's left? Kernel fault on user in well defined regions (extable
240         // matched), and allowed by KUAP in the faulting context.
241         return false;
242 }
243 
244 static bool bad_stack_expansion(struct pt_regs *regs, unsigned long address,
245                                 struct vm_area_struct *vma, unsigned int flags,
246                                 bool *must_retry)
247 {
248         /*
249          * N.B. The POWER/Open ABI allows programs to access up to
250          * 288 bytes below the stack pointer.
251          * The kernel signal delivery code writes up to about 1.5kB
252          * below the stack pointer (r1) before decrementing it.
253          * The exec code can write slightly over 640kB to the stack
254          * before setting the user r1.  Thus we allow the stack to
255          * expand to 1MB without further checks.
256          */
257         if (address + 0x100000 < vma->vm_end) {
258                 unsigned int __user *nip = (unsigned int __user *)regs->nip;
259                 /* get user regs even if this fault is in kernel mode */
260                 struct pt_regs *uregs = current->thread.regs;
261                 if (uregs == NULL)
262                         return true;
263 
264                 /*
265                  * A user-mode access to an address a long way below
266                  * the stack pointer is only valid if the instruction
267                  * is one which would update the stack pointer to the
268                  * address accessed if the instruction completed,
269                  * i.e. either stwu rs,n(r1) or stwux rs,r1,rb
270                  * (or the byte, halfword, float or double forms).
271                  *
272                  * If we don't check this then any write to the area
273                  * between the last mapped region and the stack will
274                  * expand the stack rather than segfaulting.
275                  */
276                 if (address + 2048 >= uregs->gpr[1])
277                         return false;
278 
279                 if ((flags & FAULT_FLAG_WRITE) && (flags & FAULT_FLAG_USER) &&
280                     access_ok(nip, sizeof(*nip))) {
281                         unsigned int inst;
282                         int res;
283 
284                         pagefault_disable();
285                         res = __get_user_inatomic(inst, nip);
286                         pagefault_enable();
287                         if (!res)
288                                 return !store_updates_sp(inst);
289                         *must_retry = true;
290                 }
291                 return true;
292         }
293         return false;
294 }
295 
296 static bool access_error(bool is_write, bool is_exec,
297                          struct vm_area_struct *vma)
298 {
299         /*
300          * Allow execution from readable areas if the MMU does not
301          * provide separate controls over reading and executing.
302          *
303          * Note: That code used to not be enabled for 4xx/BookE.
304          * It is now as I/D cache coherency for these is done at
305          * set_pte_at() time and I see no reason why the test
306          * below wouldn't be valid on those processors. This -may-
307          * break programs compiled with a really old ABI though.
308          */
309         if (is_exec) {
310                 return !(vma->vm_flags & VM_EXEC) &&
311                         (cpu_has_feature(CPU_FTR_NOEXECUTE) ||
312                          !(vma->vm_flags & (VM_READ | VM_WRITE)));
313         }
314 
315         if (is_write) {
316                 if (unlikely(!(vma->vm_flags & VM_WRITE)))
317                         return true;
318                 return false;
319         }
320 
321         if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))))
322                 return true;
323         /*
324          * We should ideally do the vma pkey access check here. But in the
325          * fault path, handle_mm_fault() also does the same check. To avoid
326          * these multiple checks, we skip it here and handle access error due
327          * to pkeys later.
328          */
329         return false;
330 }
331 
332 #ifdef CONFIG_PPC_SMLPAR
333 static inline void cmo_account_page_fault(void)
334 {
335         if (firmware_has_feature(FW_FEATURE_CMO)) {
336                 u32 page_ins;
337 
338                 preempt_disable();
339                 page_ins = be32_to_cpu(get_lppaca()->page_ins);
340                 page_ins += 1 << PAGE_FACTOR;
341                 get_lppaca()->page_ins = cpu_to_be32(page_ins);
342                 preempt_enable();
343         }
344 }
345 #else
346 static inline void cmo_account_page_fault(void) { }
347 #endif /* CONFIG_PPC_SMLPAR */
348 
349 #ifdef CONFIG_PPC_BOOK3S
350 static void sanity_check_fault(bool is_write, bool is_user,
351                                unsigned long error_code, unsigned long address)
352 {
353         /*
354          * Userspace trying to access kernel address, we get PROTFAULT for that.
355          */
356         if (is_user && address >= TASK_SIZE) {
357                 pr_crit_ratelimited("%s[%d]: User access of kernel address (%lx) - exploit attempt? (uid: %d)\n",
358                                    current->comm, current->pid, address,
359                                    from_kuid(&init_user_ns, current_uid()));
360                 return;
361         }
362 
363         /*
364          * For hash translation mode, we should never get a
365          * PROTFAULT. Any update to pte to reduce access will result in us
366          * removing the hash page table entry, thus resulting in a DSISR_NOHPTE
367          * fault instead of DSISR_PROTFAULT.
368          *
369          * A pte update to relax the access will not result in a hash page table
370          * entry invalidate and hence can result in DSISR_PROTFAULT.
371          * ptep_set_access_flags() doesn't do a hpte flush. This is why we have
372          * the special !is_write in the below conditional.
373          *
374          * For platforms that doesn't supports coherent icache and do support
375          * per page noexec bit, we do setup things such that we do the
376          * sync between D/I cache via fault. But that is handled via low level
377          * hash fault code (hash_page_do_lazy_icache()) and we should not reach
378          * here in such case.
379          *
380          * For wrong access that can result in PROTFAULT, the above vma->vm_flags
381          * check should handle those and hence we should fall to the bad_area
382          * handling correctly.
383          *
384          * For embedded with per page exec support that doesn't support coherent
385          * icache we do get PROTFAULT and we handle that D/I cache sync in
386          * set_pte_at while taking the noexec/prot fault. Hence this is WARN_ON
387          * is conditional for server MMU.
388          *
389          * For radix, we can get prot fault for autonuma case, because radix
390          * page table will have them marked noaccess for user.
391          */
392         if (radix_enabled() || is_write)
393                 return;
394 
395         WARN_ON_ONCE(error_code & DSISR_PROTFAULT);
396 }
397 #else
398 static void sanity_check_fault(bool is_write, bool is_user,
399                                unsigned long error_code, unsigned long address) { }
400 #endif /* CONFIG_PPC_BOOK3S */
401 
402 /*
403  * Define the correct "is_write" bit in error_code based
404  * on the processor family
405  */
406 #if (defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
407 #define page_fault_is_write(__err)      ((__err) & ESR_DST)
408 #define page_fault_is_bad(__err)        (0)
409 #else
410 #define page_fault_is_write(__err)      ((__err) & DSISR_ISSTORE)
411 #if defined(CONFIG_PPC_8xx)
412 #define page_fault_is_bad(__err)        ((__err) & DSISR_NOEXEC_OR_G)
413 #elif defined(CONFIG_PPC64)
414 #define page_fault_is_bad(__err)        ((__err) & DSISR_BAD_FAULT_64S)
415 #else
416 #define page_fault_is_bad(__err)        ((__err) & DSISR_BAD_FAULT_32S)
417 #endif
418 #endif
419 
420 /*
421  * For 600- and 800-family processors, the error_code parameter is DSISR
422  * for a data fault, SRR1 for an instruction fault. For 400-family processors
423  * the error_code parameter is ESR for a data fault, 0 for an instruction
424  * fault.
425  * For 64-bit processors, the error_code parameter is
426  *  - DSISR for a non-SLB data access fault,
427  *  - SRR1 & 0x08000000 for a non-SLB instruction access fault
428  *  - 0 any SLB fault.
429  *
430  * The return value is 0 if the fault was handled, or the signal
431  * number if this is a kernel fault that can't be handled here.
432  */
433 static int __do_page_fault(struct pt_regs *regs, unsigned long address,
434                            unsigned long error_code)
435 {
436         struct vm_area_struct * vma;
437         struct mm_struct *mm = current->mm;
438         unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
439         int is_exec = TRAP(regs) == 0x400;
440         int is_user = user_mode(regs);
441         int is_write = page_fault_is_write(error_code);
442         vm_fault_t fault, major = 0;
443         bool must_retry = false;
444         bool kprobe_fault = kprobe_page_fault(regs, 11);
445 
446         if (unlikely(debugger_fault_handler(regs) || kprobe_fault))
447                 return 0;
448 
449         if (unlikely(page_fault_is_bad(error_code))) {
450                 if (is_user) {
451                         _exception(SIGBUS, regs, BUS_OBJERR, address);
452                         return 0;
453                 }
454                 return SIGBUS;
455         }
456 
457         /* Additional sanity check(s) */
458         sanity_check_fault(is_write, is_user, error_code, address);
459 
460         /*
461          * The kernel should never take an execute fault nor should it
462          * take a page fault to a kernel address or a page fault to a user
463          * address outside of dedicated places
464          */
465         if (unlikely(!is_user && bad_kernel_fault(regs, error_code, address, is_write)))
466                 return SIGSEGV;
467 
468         /*
469          * If we're in an interrupt, have no user context or are running
470          * in a region with pagefaults disabled then we must not take the fault
471          */
472         if (unlikely(faulthandler_disabled() || !mm)) {
473                 if (is_user)
474                         printk_ratelimited(KERN_ERR "Page fault in user mode"
475                                            " with faulthandler_disabled()=%d"
476                                            " mm=%p\n",
477                                            faulthandler_disabled(), mm);
478                 return bad_area_nosemaphore(regs, address);
479         }
480 
481         /* We restore the interrupt state now */
482         if (!arch_irq_disabled_regs(regs))
483                 local_irq_enable();
484 
485         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
486 
487         if (error_code & DSISR_KEYFAULT)
488                 return bad_key_fault_exception(regs, address,
489                                                get_mm_addr_key(mm, address));
490 
491         /*
492          * We want to do this outside mmap_sem, because reading code around nip
493          * can result in fault, which will cause a deadlock when called with
494          * mmap_sem held
495          */
496         if (is_user)
497                 flags |= FAULT_FLAG_USER;
498         if (is_write)
499                 flags |= FAULT_FLAG_WRITE;
500         if (is_exec)
501                 flags |= FAULT_FLAG_INSTRUCTION;
502 
503         /* When running in the kernel we expect faults to occur only to
504          * addresses in user space.  All other faults represent errors in the
505          * kernel and should generate an OOPS.  Unfortunately, in the case of an
506          * erroneous fault occurring in a code path which already holds mmap_sem
507          * we will deadlock attempting to validate the fault against the
508          * address space.  Luckily the kernel only validly references user
509          * space from well defined areas of code, which are listed in the
510          * exceptions table.
511          *
512          * As the vast majority of faults will be valid we will only perform
513          * the source reference check when there is a possibility of a deadlock.
514          * Attempt to lock the address space, if we cannot we then validate the
515          * source.  If this is invalid we can skip the address space check,
516          * thus avoiding the deadlock.
517          */
518         if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
519                 if (!is_user && !search_exception_tables(regs->nip))
520                         return bad_area_nosemaphore(regs, address);
521 
522 retry:
523                 down_read(&mm->mmap_sem);
524         } else {
525                 /*
526                  * The above down_read_trylock() might have succeeded in
527                  * which case we'll have missed the might_sleep() from
528                  * down_read():
529                  */
530                 might_sleep();
531         }
532 
533         vma = find_vma(mm, address);
534         if (unlikely(!vma))
535                 return bad_area(regs, address);
536         if (likely(vma->vm_start <= address))
537                 goto good_area;
538         if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
539                 return bad_area(regs, address);
540 
541         /* The stack is being expanded, check if it's valid */
542         if (unlikely(bad_stack_expansion(regs, address, vma, flags,
543                                          &must_retry))) {
544                 if (!must_retry)
545                         return bad_area(regs, address);
546 
547                 up_read(&mm->mmap_sem);
548                 if (fault_in_pages_readable((const char __user *)regs->nip,
549                                             sizeof(unsigned int)))
550                         return bad_area_nosemaphore(regs, address);
551                 goto retry;
552         }
553 
554         /* Try to expand it */
555         if (unlikely(expand_stack(vma, address)))
556                 return bad_area(regs, address);
557 
558 good_area:
559         if (unlikely(access_error(is_write, is_exec, vma)))
560                 return bad_access(regs, address);
561 
562         /*
563          * If for any reason at all we couldn't handle the fault,
564          * make sure we exit gracefully rather than endlessly redo
565          * the fault.
566          */
567         fault = handle_mm_fault(vma, address, flags);
568 
569 #ifdef CONFIG_PPC_MEM_KEYS
570         /*
571          * we skipped checking for access error due to key earlier.
572          * Check that using handle_mm_fault error return.
573          */
574         if (unlikely(fault & VM_FAULT_SIGSEGV) &&
575                 !arch_vma_access_permitted(vma, is_write, is_exec, 0)) {
576 
577                 int pkey = vma_pkey(vma);
578 
579                 up_read(&mm->mmap_sem);
580                 return bad_key_fault_exception(regs, address, pkey);
581         }
582 #endif /* CONFIG_PPC_MEM_KEYS */
583 
584         major |= fault & VM_FAULT_MAJOR;
585 
586         /*
587          * Handle the retry right now, the mmap_sem has been released in that
588          * case.
589          */
590         if (unlikely(fault & VM_FAULT_RETRY)) {
591                 /* We retry only once */
592                 if (flags & FAULT_FLAG_ALLOW_RETRY) {
593                         /*
594                          * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
595                          * of starvation.
596                          */
597                         flags &= ~FAULT_FLAG_ALLOW_RETRY;
598                         flags |= FAULT_FLAG_TRIED;
599                         if (!fatal_signal_pending(current))
600                                 goto retry;
601                 }
602 
603                 /*
604                  * User mode? Just return to handle the fatal exception otherwise
605                  * return to bad_page_fault
606                  */
607                 return is_user ? 0 : SIGBUS;
608         }
609 
610         up_read(&current->mm->mmap_sem);
611 
612         if (unlikely(fault & VM_FAULT_ERROR))
613                 return mm_fault_error(regs, address, fault);
614 
615         /*
616          * Major/minor page fault accounting.
617          */
618         if (major) {
619                 current->maj_flt++;
620                 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs, address);
621                 cmo_account_page_fault();
622         } else {
623                 current->min_flt++;
624                 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs, address);
625         }
626         return 0;
627 }
628 NOKPROBE_SYMBOL(__do_page_fault);
629 
630 int do_page_fault(struct pt_regs *regs, unsigned long address,
631                   unsigned long error_code)
632 {
633         enum ctx_state prev_state = exception_enter();
634         int rc = __do_page_fault(regs, address, error_code);
635         exception_exit(prev_state);
636         return rc;
637 }
638 NOKPROBE_SYMBOL(do_page_fault);
639 
640 /*
641  * bad_page_fault is called when we have a bad access from the kernel.
642  * It is called from the DSI and ISI handlers in head.S and from some
643  * of the procedures in traps.c.
644  */
645 void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
646 {
647         const struct exception_table_entry *entry;
648 
649         /* Are we prepared to handle this fault?  */
650         if ((entry = search_exception_tables(regs->nip)) != NULL) {
651                 regs->nip = extable_fixup(entry);
652                 return;
653         }
654 
655         /* kernel has accessed a bad area */
656 
657         switch (TRAP(regs)) {
658         case 0x300:
659         case 0x380:
660         case 0xe00:
661                 pr_alert("BUG: %s at 0x%08lx\n",
662                          regs->dar < PAGE_SIZE ? "Kernel NULL pointer dereference" :
663                          "Unable to handle kernel data access", regs->dar);
664                 break;
665         case 0x400:
666         case 0x480:
667                 pr_alert("BUG: Unable to handle kernel instruction fetch%s",
668                          regs->nip < PAGE_SIZE ? " (NULL pointer?)\n" : "\n");
669                 break;
670         case 0x600:
671                 pr_alert("BUG: Unable to handle kernel unaligned access at 0x%08lx\n",
672                          regs->dar);
673                 break;
674         default:
675                 pr_alert("BUG: Unable to handle unknown paging fault at 0x%08lx\n",
676                          regs->dar);
677                 break;
678         }
679         printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
680                 regs->nip);
681 
682         if (task_stack_end_corrupted(current))
683                 printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");
684 
685         die("Kernel access of bad area", regs, sig);
686 }
687 

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