arch/nds32/mm/fault.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 // Copyright (C) 2005-2017 Andes Technology Corporation
   3
   4 #include <linux/extable.h>
   5 #include <linux/module.h>
   6 #include <linux/signal.h>
   7 #include <linux/ptrace.h>
   8 #include <linux/mm.h>
   9 #include <linux/init.h>
  10 #include <linux/hardirq.h>
  11 #include <linux/uaccess.h>
  12 #include <linux/perf_event.h>
  13
  14 #include <asm/pgtable.h>
  15 #include <asm/tlbflush.h>
  16
  17 extern void die(const char *str, struct pt_regs *regs, long err);
  18
  19 /*
  20  * This is useful to dump out the page tables associated with
  21  * 'addr' in mm 'mm'.
  22  */
  23 void show_pte(struct mm_struct *mm, unsigned long addr)
  24 {
  25         pgd_t *pgd;
  26         if (!mm)
  27                 mm = &init_mm;
  28
  29         pr_alert("pgd = %p\n", mm->pgd);
  30         pgd = pgd_offset(mm, addr);
  31         pr_alert("[%08lx] *pgd=%08lx", addr, pgd_val(*pgd));
  32
  33         do {
  34                 pmd_t *pmd;
  35
  36                 if (pgd_none(*pgd))
  37                         break;
  38
  39                 if (pgd_bad(*pgd)) {
  40                         pr_alert("(bad)");
  41                         break;
  42                 }
  43
  44                 pmd = pmd_offset(pgd, addr);
  45 #if PTRS_PER_PMD != 1
  46                 pr_alert(", *pmd=%08lx", pmd_val(*pmd));
  47 #endif
  48
  49                 if (pmd_none(*pmd))
  50                         break;
  51
  52                 if (pmd_bad(*pmd)) {
  53                         pr_alert("(bad)");
  54                         break;
  55                 }
  56
  57                 if (IS_ENABLED(CONFIG_HIGHMEM))
  58                 {
  59                         pte_t *pte;
  60                         /* We must not map this if we have highmem enabled */
  61                         pte = pte_offset_map(pmd, addr);
  62                         pr_alert(", *pte=%08lx", pte_val(*pte));
  63                         pte_unmap(pte);
  64                 }
  65         } while (0);
  66
  67         pr_alert("\n");
  68 }
  69
  70 void do_page_fault(unsigned long entry, unsigned long addr,
  71                    unsigned int error_code, struct pt_regs *regs)
  72 {
  73         struct task_struct *tsk;
  74         struct mm_struct *mm;
  75         struct vm_area_struct *vma;
  76         int si_code;
  77         vm_fault_t fault;
  78         unsigned int mask = VM_READ | VM_WRITE | VM_EXEC;
  79         unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
  80
  81         error_code = error_code & (ITYPE_mskINST | ITYPE_mskETYPE);
  82         tsk = current;
  83         mm = tsk->mm;
  84         si_code = SEGV_MAPERR;
  85         /*
  86          * We fault-in kernel-space virtual memory on-demand. The
  87          * 'reference' page table is init_mm.pgd.
  88          *
  89          * NOTE! We MUST NOT take any locks for this case. We may
  90          * be in an interrupt or a critical region, and should
  91          * only copy the information from the master page table,
  92          * nothing more.
  93          */
  94         if (addr >= TASK_SIZE) {
  95                 if (user_mode(regs))
  96                         goto bad_area_nosemaphore;
  97
  98                 if (addr >= TASK_SIZE && addr < VMALLOC_END
  99                     && (entry == ENTRY_PTE_NOT_PRESENT))
 100                         goto vmalloc_fault;
 101                 else
 102                         goto no_context;
 103         }
 104
 105         /* Send a signal to the task for handling the unalignment access. */
 106         if (entry == ENTRY_GENERAL_EXCPETION
 107             && error_code == ETYPE_ALIGNMENT_CHECK) {
 108                 if (user_mode(regs))
 109                         goto bad_area_nosemaphore;
 110                 else
 111                         goto no_context;
 112         }
 113
 114         /*
 115          * If we're in an interrupt or have no user
 116          * context, we must not take the fault..
 117          */
 118         if (unlikely(faulthandler_disabled() || !mm))
 119                 goto no_context;
 120
 121         /*
 122          * As per x86, we may deadlock here. However, since the kernel only
 123          * validly references user space from well defined areas of the code,
 124          * we can bug out early if this is from code which shouldn't.
 125          */
 126         if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
 127                 if (!user_mode(regs) &&
 128                     !search_exception_tables(instruction_pointer(regs)))
 129                         goto no_context;
 130 retry:
 131                 down_read(&mm->mmap_sem);
 132         } else {
 133                 /*
 134                  * The above down_read_trylock() might have succeeded in which
 135                  * case, we'll have missed the might_sleep() from down_read().
 136                  */
 137                 might_sleep();
 138                 if (IS_ENABLED(CONFIG_DEBUG_VM)) {
 139                         if (!user_mode(regs) &&
 140                             !search_exception_tables(instruction_pointer(regs)))
 141                                 goto no_context;
 142                 }
 143         }
 144
 145         vma = find_vma(mm, addr);
 146
 147         if (unlikely(!vma))
 148                 goto bad_area;
 149
 150         if (vma->vm_start <= addr)
 151                 goto good_area;
 152
 153         if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
 154                 goto bad_area;
 155
 156         if (unlikely(expand_stack(vma, addr)))
 157                 goto bad_area;
 158
 159         /*
 160          * Ok, we have a good vm_area for this memory access, so
 161          * we can handle it..
 162          */
 163
 164 good_area:
 165         si_code = SEGV_ACCERR;
 166
 167         /* first do some preliminary protection checks */
 168         if (entry == ENTRY_PTE_NOT_PRESENT) {
 169                 if (error_code & ITYPE_mskINST)
 170                         mask = VM_EXEC;
 171                 else {
 172                         mask = VM_READ | VM_WRITE;
 173                 }
 174         } else if (entry == ENTRY_TLB_MISC) {
 175                 switch (error_code & ITYPE_mskETYPE) {
 176                 case RD_PROT:
 177                         mask = VM_READ;
 178                         break;
 179                 case WRT_PROT:
 180                         mask = VM_WRITE;
 181                         flags |= FAULT_FLAG_WRITE;
 182                         break;
 183                 case NOEXEC:
 184                         mask = VM_EXEC;
 185                         break;
 186                 case PAGE_MODIFY:
 187                         mask = VM_WRITE;
 188                         flags |= FAULT_FLAG_WRITE;
 189                         break;
 190                 case ACC_BIT:
 191                         BUG();
 192                 default:
 193                         break;
 194                 }
 195
 196         }
 197         if (!(vma->vm_flags & mask))
 198                 goto bad_area;
 199
 200         /*
 201          * If for any reason at all we couldn't handle the fault,
 202          * make sure we exit gracefully rather than endlessly redo
 203          * the fault.
 204          */
 205
 206         fault = handle_mm_fault(vma, addr, flags);
 207
 208         /*
 209          * If we need to retry but a fatal signal is pending, handle the
 210          * signal first. We do not need to release the mmap_sem because it
 211          * would already be released in __lock_page_or_retry in mm/filemap.c.
 212          */
 213         if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
 214                 if (!user_mode(regs))
 215                         goto no_context;
 216                 return;
 217         }
 218
 219         if (unlikely(fault & VM_FAULT_ERROR)) {
 220                 if (fault & VM_FAULT_OOM)
 221                         goto out_of_memory;
 222                 else if (fault & VM_FAULT_SIGBUS)
 223                         goto do_sigbus;
 224                 else
 225                         goto bad_area;
 226         }
 227
 228         /*
 229          * Major/minor page fault accounting is only done on the initial
 230          * attempt. If we go through a retry, it is extremely likely that the
 231          * page will be found in page cache at that point.
 232          */
 233         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
 234         if (flags & FAULT_FLAG_ALLOW_RETRY) {
 235                 if (fault & VM_FAULT_MAJOR) {
 236                         tsk->maj_flt++;
 237                         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ,
 238                                       1, regs, addr);
 239                 } else {
 240                         tsk->min_flt++;
 241                         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN,
 242                                       1, regs, addr);
 243                 }
 244                 if (fault & VM_FAULT_RETRY) {
 245                         flags &= ~FAULT_FLAG_ALLOW_RETRY;
 246                         flags |= FAULT_FLAG_TRIED;
 247
 248                         /* No need to up_read(&mm->mmap_sem) as we would
 249                          * have already released it in __lock_page_or_retry
 250                          * in mm/filemap.c.
 251                          */
 252                         goto retry;
 253                 }
 254         }
 255
 256         up_read(&mm->mmap_sem);
 257         return;
 258
 259         /*
 260          * Something tried to access memory that isn't in our memory map..
 261          * Fix it, but check if it's kernel or user first..
 262          */
 263 bad_area:
 264         up_read(&mm->mmap_sem);
 265
 266 bad_area_nosemaphore:
 267
 268         /* User mode accesses just cause a SIGSEGV */
 269
 270         if (user_mode(regs)) {
 271                 tsk->thread.address = addr;
 272                 tsk->thread.error_code = error_code;
 273                 tsk->thread.trap_no = entry;
 274                 force_sig_fault(SIGSEGV, si_code, (void __user *)addr);
 275                 return;
 276         }
 277
 278 no_context:
 279
 280         /* Are we prepared to handle this kernel fault?
 281          *
 282          * (The kernel has valid exception-points in the source
 283          *  when it acesses user-memory. When it fails in one
 284          *  of those points, we find it in a table and do a jump
 285          *  to some fixup code that loads an appropriate error
 286          *  code)
 287          */
 288
 289         {
 290                 const struct exception_table_entry *entry;
 291
 292                 if ((entry =
 293                      search_exception_tables(instruction_pointer(regs))) !=
 294                     NULL) {
 295                         /* Adjust the instruction pointer in the stackframe */
 296                         instruction_pointer(regs) = entry->fixup;
 297                         return;
 298                 }
 299         }
 300
 301         /*
 302          * Oops. The kernel tried to access some bad page. We'll have to
 303          * terminate things with extreme prejudice.
 304          */
 305
 306         bust_spinlocks(1);
 307         pr_alert("Unable to handle kernel %s at virtual address %08lx\n",
 308                  (addr < PAGE_SIZE) ? "NULL pointer dereference" :
 309                  "paging request", addr);
 310
 311         show_pte(mm, addr);
 312         die("Oops", regs, error_code);
 313         bust_spinlocks(0);
 314         do_exit(SIGKILL);
 315
 316         return;
 317
 318         /*
 319          * We ran out of memory, or some other thing happened to us that made
 320          * us unable to handle the page fault gracefully.
 321          */
 322
 323 out_of_memory:
 324         up_read(&mm->mmap_sem);
 325         if (!user_mode(regs))
 326                 goto no_context;
 327         pagefault_out_of_memory();
 328         return;
 329
 330 do_sigbus:
 331         up_read(&mm->mmap_sem);
 332
 333         /* Kernel mode? Handle exceptions or die */
 334         if (!user_mode(regs))
 335                 goto no_context;
 336
 337         /*
 338          * Send a sigbus
 339          */
 340         tsk->thread.address = addr;
 341         tsk->thread.error_code = error_code;
 342         tsk->thread.trap_no = entry;
 343         force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)addr);
 344
 345         return;
 346
 347 vmalloc_fault:
 348         {
 349                 /*
 350                  * Synchronize this task's top level page-table
 351                  * with the 'reference' page table.
 352                  *
 353                  * Use current_pgd instead of tsk->active_mm->pgd
 354                  * since the latter might be unavailable if this
 355                  * code is executed in a misfortunately run irq
 356                  * (like inside schedule() between switch_mm and
 357                  *  switch_to...).
 358                  */
 359
 360                 unsigned int index = pgd_index(addr);
 361                 pgd_t *pgd, *pgd_k;
 362                 pud_t *pud, *pud_k;
 363                 pmd_t *pmd, *pmd_k;
 364                 pte_t *pte_k;
 365
 366                 pgd = (pgd_t *) __va(__nds32__mfsr(NDS32_SR_L1_PPTB)) + index;
 367                 pgd_k = init_mm.pgd + index;
 368
 369                 if (!pgd_present(*pgd_k))
 370                         goto no_context;
 371
 372                 pud = pud_offset(pgd, addr);
 373                 pud_k = pud_offset(pgd_k, addr);
 374                 if (!pud_present(*pud_k))
 375                         goto no_context;
 376
 377                 pmd = pmd_offset(pud, addr);
 378                 pmd_k = pmd_offset(pud_k, addr);
 379                 if (!pmd_present(*pmd_k))
 380                         goto no_context;
 381
 382                 if (!pmd_present(*pmd))
 383                         set_pmd(pmd, *pmd_k);
 384                 else
 385                         BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k));
 386
 387                 /*
 388                  * Since the vmalloc area is global, we don't
 389                  * need to copy individual PTE's, it is enough to
 390                  * copy the pgd pointer into the pte page of the
 391                  * root task. If that is there, we'll find our pte if
 392                  * it exists.
 393                  */
 394
 395                 /* Make sure the actual PTE exists as well to
 396                  * catch kernel vmalloc-area accesses to non-mapped
 397                  * addres. If we don't do this, this will just
 398                  * silently loop forever.
 399                  */
 400
 401                 pte_k = pte_offset_kernel(pmd_k, addr);
 402                 if (!pte_present(*pte_k))
 403                         goto no_context;
 404
 405                 return;
 406         }
 407 }