arch/powerpc/mm/fault.c

   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/kernel.h>
  21 #include <linux/errno.h>
  22 #include <linux/string.h>
  23 #include <linux/types.h>
  24 #include <linux/ptrace.h>
  25 #include <linux/mman.h>
  26 #include <linux/mm.h>
  27 #include <linux/interrupt.h>
  28 #include <linux/highmem.h>
  29 #include <linux/module.h>
  30 #include <linux/kprobes.h>
  31 #include <linux/kdebug.h>
  32
  33 #include <asm/page.h>
  34 #include <asm/pgtable.h>
  35 #include <asm/mmu.h>
  36 #include <asm/mmu_context.h>
  37 #include <asm/system.h>
  38 #include <asm/uaccess.h>
  39 #include <asm/tlbflush.h>
  40 #include <asm/siginfo.h>
  41
  42
  43 #ifdef CONFIG_KPROBES
  44 static inline int notify_page_fault(struct pt_regs *regs)
  45 {
  46         int ret = 0;
  47
  48         /* kprobe_running() needs smp_processor_id() */
  49         if (!user_mode(regs)) {
  50                 preempt_disable();
  51                 if (kprobe_running() && kprobe_fault_handler(regs, 11))
  52                         ret = 1;
  53                 preempt_enable();
  54         }
  55
  56         return ret;
  57 }
  58 #else
  59 static inline int notify_page_fault(struct pt_regs *regs)
  60 {
  61         return 0;
  62 }
  63 #endif
  64
  65 /*
  66  * Check whether the instruction at regs->nip is a store using
  67  * an update addressing form which will update r1.
  68  */
  69 static int store_updates_sp(struct pt_regs *regs)
  70 {
  71         unsigned int inst;
  72
  73         if (get_user(inst, (unsigned int __user *)regs->nip))
  74                 return 0;
  75         /* check for 1 in the rA field */
  76         if (((inst >> 16) & 0x1f) != 1)
  77                 return 0;
  78         /* check major opcode */
  79         switch (inst >> 26) {
  80         case 37:        /* stwu */
  81         case 39:        /* stbu */
  82         case 45:        /* sthu */
  83         case 53:        /* stfsu */
  84         case 55:        /* stfdu */
  85                 return 1;
  86         case 62:        /* std or stdu */
  87                 return (inst & 3) == 1;
  88         case 31:
  89                 /* check minor opcode */
  90                 switch ((inst >> 1) & 0x3ff) {
  91                 case 181:       /* stdux */
  92                 case 183:       /* stwux */
  93                 case 247:       /* stbux */
  94                 case 439:       /* sthux */
  95                 case 695:       /* stfsux */
  96                 case 759:       /* stfdux */
  97                         return 1;
  98                 }
  99         }
 100         return 0;
 101 }
 102
 103 /*
 104  * For 600- and 800-family processors, the error_code parameter is DSISR
 105  * for a data fault, SRR1 for an instruction fault. For 400-family processors
 106  * the error_code parameter is ESR for a data fault, 0 for an instruction
 107  * fault.
 108  * For 64-bit processors, the error_code parameter is
 109  *  - DSISR for a non-SLB data access fault,
 110  *  - SRR1 & 0x08000000 for a non-SLB instruction access fault
 111  *  - 0 any SLB fault.
 112  *
 113  * The return value is 0 if the fault was handled, or the signal
 114  * number if this is a kernel fault that can't be handled here.
 115  */
 116 int __kprobes do_page_fault(struct pt_regs *regs, unsigned long address,
 117                             unsigned long error_code)
 118 {
 119         struct vm_area_struct * vma;
 120         struct mm_struct *mm = current->mm;
 121         siginfo_t info;
 122         int code = SEGV_MAPERR;
 123         int is_write = 0, ret;
 124         int trap = TRAP(regs);
 125         int is_exec = trap == 0x400;
 126
 127 #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
 128         /*
 129          * Fortunately the bit assignments in SRR1 for an instruction
 130          * fault and DSISR for a data fault are mostly the same for the
 131          * bits we are interested in.  But there are some bits which
 132          * indicate errors in DSISR but can validly be set in SRR1.
 133          */
 134         if (trap == 0x400)
 135                 error_code &= 0x48200000;
 136         else
 137                 is_write = error_code & DSISR_ISSTORE;
 138 #else
 139         is_write = error_code & ESR_DST;
 140 #endif /* CONFIG_4xx || CONFIG_BOOKE */
 141
 142         if (notify_page_fault(regs))
 143                 return 0;
 144
 145         if (unlikely(debugger_fault_handler(regs)))
 146                 return 0;
 147
 148         /* On a kernel SLB miss we can only check for a valid exception entry */
 149         if (!user_mode(regs) && (address >= TASK_SIZE))
 150                 return SIGSEGV;
 151
 152 #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
 153         if (error_code & DSISR_DABRMATCH) {
 154                 /* DABR match */
 155                 do_dabr(regs, address, error_code);
 156                 return 0;
 157         }
 158 #endif /* !(CONFIG_4xx || CONFIG_BOOKE)*/
 159
 160         if (in_atomic() || mm == NULL) {
 161                 if (!user_mode(regs))
 162                         return SIGSEGV;
 163                 /* in_atomic() in user mode is really bad,
 164                    as is current->mm == NULL. */
 165                 printk(KERN_EMERG "Page fault in user mode with "
 166                        "in_atomic() = %d mm = %p\n", in_atomic(), mm);
 167                 printk(KERN_EMERG "NIP = %lx  MSR = %lx\n",
 168                        regs->nip, regs->msr);
 169                 die("Weird page fault", regs, SIGSEGV);
 170         }
 171
 172         /* When running in the kernel we expect faults to occur only to
 173          * addresses in user space.  All other faults represent errors in the
 174          * kernel and should generate an OOPS.  Unfortunately, in the case of an
 175          * erroneous fault occurring in a code path which already holds mmap_sem
 176          * we will deadlock attempting to validate the fault against the
 177          * address space.  Luckily the kernel only validly references user
 178          * space from well defined areas of code, which are listed in the
 179          * exceptions table.
 180          *
 181          * As the vast majority of faults will be valid we will only perform
 182          * the source reference check when there is a possibility of a deadlock.
 183          * Attempt to lock the address space, if we cannot we then validate the
 184          * source.  If this is invalid we can skip the address space check,
 185          * thus avoiding the deadlock.
 186          */
 187         if (!down_read_trylock(&mm->mmap_sem)) {
 188                 if (!user_mode(regs) && !search_exception_tables(regs->nip))
 189                         goto bad_area_nosemaphore;
 190
 191                 down_read(&mm->mmap_sem);
 192         }
 193
 194         vma = find_vma(mm, address);
 195         if (!vma)
 196                 goto bad_area;
 197         if (vma->vm_start <= address)
 198                 goto good_area;
 199         if (!(vma->vm_flags & VM_GROWSDOWN))
 200                 goto bad_area;
 201
 202         /*
 203          * N.B. The POWER/Open ABI allows programs to access up to
 204          * 288 bytes below the stack pointer.
 205          * The kernel signal delivery code writes up to about 1.5kB
 206          * below the stack pointer (r1) before decrementing it.
 207          * The exec code can write slightly over 640kB to the stack
 208          * before setting the user r1.  Thus we allow the stack to
 209          * expand to 1MB without further checks.
 210          */
 211         if (address + 0x100000 < vma->vm_end) {
 212                 /* get user regs even if this fault is in kernel mode */
 213                 struct pt_regs *uregs = current->thread.regs;
 214                 if (uregs == NULL)
 215                         goto bad_area;
 216
 217                 /*
 218                  * A user-mode access to an address a long way below
 219                  * the stack pointer is only valid if the instruction
 220                  * is one which would update the stack pointer to the
 221                  * address accessed if the instruction completed,
 222                  * i.e. either stwu rs,n(r1) or stwux rs,r1,rb
 223                  * (or the byte, halfword, float or double forms).
 224                  *
 225                  * If we don't check this then any write to the area
 226                  * between the last mapped region and the stack will
 227                  * expand the stack rather than segfaulting.
 228                  */
 229                 if (address + 2048 < uregs->gpr[1]
 230                     && (!user_mode(regs) || !store_updates_sp(regs)))
 231                         goto bad_area;
 232         }
 233         if (expand_stack(vma, address))
 234                 goto bad_area;
 235
 236 good_area:
 237         code = SEGV_ACCERR;
 238 #if defined(CONFIG_6xx)
 239         if (error_code & 0x95700000)
 240                 /* an error such as lwarx to I/O controller space,
 241                    address matching DABR, eciwx, etc. */
 242                 goto bad_area;
 243 #endif /* CONFIG_6xx */
 244 #if defined(CONFIG_8xx)
 245         /* The MPC8xx seems to always set 0x80000000, which is
 246          * "undefined".  Of those that can be set, this is the only
 247          * one which seems bad.
 248          */
 249         if (error_code & 0x10000000)
 250                 /* Guarded storage error. */
 251                 goto bad_area;
 252 #endif /* CONFIG_8xx */
 253
 254         if (is_exec) {
 255 #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
 256                 /* protection fault */
 257                 if (error_code & DSISR_PROTFAULT)
 258                         goto bad_area;
 259                 /*
 260                  * Allow execution from readable areas if the MMU does not
 261                  * provide separate controls over reading and executing.
 262                  */
 263                 if (!(vma->vm_flags & VM_EXEC) &&
 264                     (cpu_has_feature(CPU_FTR_NOEXECUTE) ||
 265                      !(vma->vm_flags & (VM_READ | VM_WRITE))))
 266                         goto bad_area;
 267 #else
 268                 pte_t *ptep;
 269                 pmd_t *pmdp;
 270
 271                 /* Since 4xx/Book-E supports per-page execute permission,
 272                  * we lazily flush dcache to icache. */
 273                 ptep = NULL;
 274                 if (get_pteptr(mm, address, &ptep, &pmdp)) {
 275                         spinlock_t *ptl = pte_lockptr(mm, pmdp);
 276                         spin_lock(ptl);
 277                         if (pte_present(*ptep)) {
 278                                 struct page *page = pte_page(*ptep);
 279
 280                                 if (!test_bit(PG_arch_1, &page->flags)) {
 281                                         flush_dcache_icache_page(page);
 282                                         set_bit(PG_arch_1, &page->flags);
 283                                 }
 284                                 pte_update(ptep, 0, _PAGE_HWEXEC |
 285                                            _PAGE_ACCESSED);
 286                                 _tlbie(address, mm->context.id);
 287                                 pte_unmap_unlock(ptep, ptl);
 288                                 up_read(&mm->mmap_sem);
 289                                 return 0;
 290                         }
 291                         pte_unmap_unlock(ptep, ptl);
 292                 }
 293 #endif
 294         /* a write */
 295         } else if (is_write) {
 296                 if (!(vma->vm_flags & VM_WRITE))
 297                         goto bad_area;
 298         /* a read */
 299         } else {
 300                 /* protection fault */
 301                 if (error_code & 0x08000000)
 302                         goto bad_area;
 303                 if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
 304                         goto bad_area;
 305         }
 306
 307         /*
 308          * If for any reason at all we couldn't handle the fault,
 309          * make sure we exit gracefully rather than endlessly redo
 310          * the fault.
 311          */
 312  survive:
 313         ret = handle_mm_fault(mm, vma, address, is_write);
 314         if (unlikely(ret & VM_FAULT_ERROR)) {
 315                 if (ret & VM_FAULT_OOM)
 316                         goto out_of_memory;
 317                 else if (ret & VM_FAULT_SIGBUS)
 318                         goto do_sigbus;
 319                 BUG();
 320         }
 321         if (ret & VM_FAULT_MAJOR)
 322                 current->maj_flt++;
 323         else
 324                 current->min_flt++;
 325         up_read(&mm->mmap_sem);
 326         return 0;
 327
 328 bad_area:
 329         up_read(&mm->mmap_sem);
 330
 331 bad_area_nosemaphore:
 332         /* User mode accesses cause a SIGSEGV */
 333         if (user_mode(regs)) {
 334                 _exception(SIGSEGV, regs, code, address);
 335                 return 0;
 336         }
 337
 338         if (is_exec && (error_code & DSISR_PROTFAULT)
 339             && printk_ratelimit())
 340                 printk(KERN_CRIT "kernel tried to execute NX-protected"
 341                        " page (%lx) - exploit attempt? (uid: %d)\n",
 342                        address, current->uid);
 343
 344         return SIGSEGV;
 345
 346 /*
 347  * We ran out of memory, or some other thing happened to us that made
 348  * us unable to handle the page fault gracefully.
 349  */
 350 out_of_memory:
 351         up_read(&mm->mmap_sem);
 352         if (is_global_init(current)) {
 353                 yield();
 354                 down_read(&mm->mmap_sem);
 355                 goto survive;
 356         }
 357         printk("VM: killing process %s\n", current->comm);
 358         if (user_mode(regs))
 359                 do_group_exit(SIGKILL);
 360         return SIGKILL;
 361
 362 do_sigbus:
 363         up_read(&mm->mmap_sem);
 364         if (user_mode(regs)) {
 365                 info.si_signo = SIGBUS;
 366                 info.si_errno = 0;
 367                 info.si_code = BUS_ADRERR;
 368                 info.si_addr = (void __user *)address;
 369                 force_sig_info(SIGBUS, &info, current);
 370                 return 0;
 371         }
 372         return SIGBUS;
 373 }
 374
 375 /*
 376  * bad_page_fault is called when we have a bad access from the kernel.
 377  * It is called from the DSI and ISI handlers in head.S and from some
 378  * of the procedures in traps.c.
 379  */
 380 void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
 381 {
 382         const struct exception_table_entry *entry;
 383
 384         /* Are we prepared to handle this fault?  */
 385         if ((entry = search_exception_tables(regs->nip)) != NULL) {
 386                 regs->nip = entry->fixup;
 387                 return;
 388         }
 389
 390         /* kernel has accessed a bad area */
 391
 392         switch (regs->trap) {
 393         case 0x300:
 394         case 0x380:
 395                 printk(KERN_ALERT "Unable to handle kernel paging request for "
 396                         "data at address 0x%08lx\n", regs->dar);
 397                 break;
 398         case 0x400:
 399         case 0x480:
 400                 printk(KERN_ALERT "Unable to handle kernel paging request for "
 401                         "instruction fetch\n");
 402                 break;
 403         default:
 404                 printk(KERN_ALERT "Unable to handle kernel paging request for "
 405                         "unknown fault\n");
 406                 break;
 407         }
 408         printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
 409                 regs->nip);
 410
 411         die("Kernel access of bad area", regs, sig);
 412 }