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 #include <linux/perf_event.h>
  33 #include <linux/magic.h>
  34
  35 #include <asm/firmware.h>
  36 #include <asm/page.h>
  37 #include <asm/pgtable.h>
  38 #include <asm/mmu.h>
  39 #include <asm/mmu_context.h>
  40 #include <asm/system.h>
  41 #include <asm/uaccess.h>
  42 #include <asm/tlbflush.h>
  43 #include <asm/siginfo.h>
  44 #include <mm/mmu_decl.h>
  45
  46 #ifdef CONFIG_KPROBES
  47 static inline int notify_page_fault(struct pt_regs *regs)
  48 {
  49         int ret = 0;
  50
  51         /* kprobe_running() needs smp_processor_id() */
  52         if (!user_mode(regs)) {
  53                 preempt_disable();
  54                 if (kprobe_running() && kprobe_fault_handler(regs, 11))
  55                         ret = 1;
  56                 preempt_enable();
  57         }
  58
  59         return ret;
  60 }
  61 #else
  62 static inline int notify_page_fault(struct pt_regs *regs)
  63 {
  64         return 0;
  65 }
  66 #endif
  67
  68 /*
  69  * Check whether the instruction at regs->nip is a store using
  70  * an update addressing form which will update r1.
  71  */
  72 static int store_updates_sp(struct pt_regs *regs)
  73 {
  74         unsigned int inst;
  75
  76         if (get_user(inst, (unsigned int __user *)regs->nip))
  77                 return 0;
  78         /* check for 1 in the rA field */
  79         if (((inst >> 16) & 0x1f) != 1)
  80                 return 0;
  81         /* check major opcode */
  82         switch (inst >> 26) {
  83         case 37:        /* stwu */
  84         case 39:        /* stbu */
  85         case 45:        /* sthu */
  86         case 53:        /* stfsu */
  87         case 55:        /* stfdu */
  88                 return 1;
  89         case 62:        /* std or stdu */
  90                 return (inst & 3) == 1;
  91         case 31:
  92                 /* check minor opcode */
  93                 switch ((inst >> 1) & 0x3ff) {
  94                 case 181:       /* stdux */
  95                 case 183:       /* stwux */
  96                 case 247:       /* stbux */
  97                 case 439:       /* sthux */
  98                 case 695:       /* stfsux */
  99                 case 759:       /* stfdux */
 100                         return 1;
 101                 }
 102         }
 103         return 0;
 104 }
 105
 106 /*
 107  * For 600- and 800-family processors, the error_code parameter is DSISR
 108  * for a data fault, SRR1 for an instruction fault. For 400-family processors
 109  * the error_code parameter is ESR for a data fault, 0 for an instruction
 110  * fault.
 111  * For 64-bit processors, the error_code parameter is
 112  *  - DSISR for a non-SLB data access fault,
 113  *  - SRR1 & 0x08000000 for a non-SLB instruction access fault
 114  *  - 0 any SLB fault.
 115  *
 116  * The return value is 0 if the fault was handled, or the signal
 117  * number if this is a kernel fault that can't be handled here.
 118  */
 119 int __kprobes do_page_fault(struct pt_regs *regs, unsigned long address,
 120                             unsigned long error_code)
 121 {
 122         struct vm_area_struct * vma;
 123         struct mm_struct *mm = current->mm;
 124         siginfo_t info;
 125         int code = SEGV_MAPERR;
 126         int is_write = 0, ret;
 127         int trap = TRAP(regs);
 128         int is_exec = trap == 0x400;
 129
 130 #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
 131         /*
 132          * Fortunately the bit assignments in SRR1 for an instruction
 133          * fault and DSISR for a data fault are mostly the same for the
 134          * bits we are interested in.  But there are some bits which
 135          * indicate errors in DSISR but can validly be set in SRR1.
 136          */
 137         if (trap == 0x400)
 138                 error_code &= 0x48200000;
 139         else
 140                 is_write = error_code & DSISR_ISSTORE;
 141 #else
 142         is_write = error_code & ESR_DST;
 143 #endif /* CONFIG_4xx || CONFIG_BOOKE */
 144
 145         if (notify_page_fault(regs))
 146                 return 0;
 147
 148         if (unlikely(debugger_fault_handler(regs)))
 149                 return 0;
 150
 151         /* On a kernel SLB miss we can only check for a valid exception entry */
 152         if (!user_mode(regs) && (address >= TASK_SIZE))
 153                 return SIGSEGV;
 154
 155 #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE) || \
 156                              defined(CONFIG_PPC_BOOK3S_64))
 157         if (error_code & DSISR_DABRMATCH) {
 158                 /* DABR match */
 159                 do_dabr(regs, address, error_code);
 160                 return 0;
 161         }
 162 #endif
 163
 164         if (in_atomic() || mm == NULL) {
 165                 if (!user_mode(regs))
 166                         return SIGSEGV;
 167                 /* in_atomic() in user mode is really bad,
 168                    as is current->mm == NULL. */
 169                 printk(KERN_EMERG "Page fault in user mode with "
 170                        "in_atomic() = %d mm = %p\n", in_atomic(), mm);
 171                 printk(KERN_EMERG "NIP = %lx  MSR = %lx\n",
 172                        regs->nip, regs->msr);
 173                 die("Weird page fault", regs, SIGSEGV);
 174         }
 175
 176         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, 0, regs, address);
 177
 178         /* When running in the kernel we expect faults to occur only to
 179          * addresses in user space.  All other faults represent errors in the
 180          * kernel and should generate an OOPS.  Unfortunately, in the case of an
 181          * erroneous fault occurring in a code path which already holds mmap_sem
 182          * we will deadlock attempting to validate the fault against the
 183          * address space.  Luckily the kernel only validly references user
 184          * space from well defined areas of code, which are listed in the
 185          * exceptions table.
 186          *
 187          * As the vast majority of faults will be valid we will only perform
 188          * the source reference check when there is a possibility of a deadlock.
 189          * Attempt to lock the address space, if we cannot we then validate the
 190          * source.  If this is invalid we can skip the address space check,
 191          * thus avoiding the deadlock.
 192          */
 193         if (!down_read_trylock(&mm->mmap_sem)) {
 194                 if (!user_mode(regs) && !search_exception_tables(regs->nip))
 195                         goto bad_area_nosemaphore;
 196
 197                 down_read(&mm->mmap_sem);
 198         }
 199
 200         vma = find_vma(mm, address);
 201         if (!vma)
 202                 goto bad_area;
 203         if (vma->vm_start <= address)
 204                 goto good_area;
 205         if (!(vma->vm_flags & VM_GROWSDOWN))
 206                 goto bad_area;
 207
 208         /*
 209          * N.B. The POWER/Open ABI allows programs to access up to
 210          * 288 bytes below the stack pointer.
 211          * The kernel signal delivery code writes up to about 1.5kB
 212          * below the stack pointer (r1) before decrementing it.
 213          * The exec code can write slightly over 640kB to the stack
 214          * before setting the user r1.  Thus we allow the stack to
 215          * expand to 1MB without further checks.
 216          */
 217         if (address + 0x100000 < vma->vm_end) {
 218                 /* get user regs even if this fault is in kernel mode */
 219                 struct pt_regs *uregs = current->thread.regs;
 220                 if (uregs == NULL)
 221                         goto bad_area;
 222
 223                 /*
 224                  * A user-mode access to an address a long way below
 225                  * the stack pointer is only valid if the instruction
 226                  * is one which would update the stack pointer to the
 227                  * address accessed if the instruction completed,
 228                  * i.e. either stwu rs,n(r1) or stwux rs,r1,rb
 229                  * (or the byte, halfword, float or double forms).
 230                  *
 231                  * If we don't check this then any write to the area
 232                  * between the last mapped region and the stack will
 233                  * expand the stack rather than segfaulting.
 234                  */
 235                 if (address + 2048 < uregs->gpr[1]
 236                     && (!user_mode(regs) || !store_updates_sp(regs)))
 237                         goto bad_area;
 238         }
 239         if (expand_stack(vma, address))
 240                 goto bad_area;
 241
 242 good_area:
 243         code = SEGV_ACCERR;
 244 #if defined(CONFIG_6xx)
 245         if (error_code & 0x95700000)
 246                 /* an error such as lwarx to I/O controller space,
 247                    address matching DABR, eciwx, etc. */
 248                 goto bad_area;
 249 #endif /* CONFIG_6xx */
 250 #if defined(CONFIG_8xx)
 251         /* 8xx sometimes need to load a invalid/non-present TLBs.
 252          * These must be invalidated separately as linux mm don't.
 253          */
 254         if (error_code & 0x40000000) /* no translation? */
 255                 _tlbil_va(address, 0, 0, 0);
 256
 257         /* The MPC8xx seems to always set 0x80000000, which is
 258          * "undefined".  Of those that can be set, this is the only
 259          * one which seems bad.
 260          */
 261         if (error_code & 0x10000000)
 262                 /* Guarded storage error. */
 263                 goto bad_area;
 264 #endif /* CONFIG_8xx */
 265
 266         if (is_exec) {
 267 #ifdef CONFIG_PPC_STD_MMU
 268                 /* Protection fault on exec go straight to failure on
 269                  * Hash based MMUs as they either don't support per-page
 270                  * execute permission, or if they do, it's handled already
 271                  * at the hash level. This test would probably have to
 272                  * be removed if we change the way this works to make hash
 273                  * processors use the same I/D cache coherency mechanism
 274                  * as embedded.
 275                  */
 276                 if (error_code & DSISR_PROTFAULT)
 277                         goto bad_area;
 278 #endif /* CONFIG_PPC_STD_MMU */
 279
 280                 /*
 281                  * Allow execution from readable areas if the MMU does not
 282                  * provide separate controls over reading and executing.
 283                  *
 284                  * Note: That code used to not be enabled for 4xx/BookE.
 285                  * It is now as I/D cache coherency for these is done at
 286                  * set_pte_at() time and I see no reason why the test
 287                  * below wouldn't be valid on those processors. This -may-
 288                  * break programs compiled with a really old ABI though.
 289                  */
 290                 if (!(vma->vm_flags & VM_EXEC) &&
 291                     (cpu_has_feature(CPU_FTR_NOEXECUTE) ||
 292                      !(vma->vm_flags & (VM_READ | VM_WRITE))))
 293                         goto bad_area;
 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         ret = handle_mm_fault(mm, vma, address, is_write ? FAULT_FLAG_WRITE : 0);
 313         if (unlikely(ret & VM_FAULT_ERROR)) {
 314                 if (ret & VM_FAULT_OOM)
 315                         goto out_of_memory;
 316                 else if (ret & VM_FAULT_SIGBUS)
 317                         goto do_sigbus;
 318                 BUG();
 319         }
 320         if (ret & VM_FAULT_MAJOR) {
 321                 current->maj_flt++;
 322                 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, 0,
 323                                      regs, address);
 324 #ifdef CONFIG_PPC_SMLPAR
 325                 if (firmware_has_feature(FW_FEATURE_CMO)) {
 326                         preempt_disable();
 327                         get_lppaca()->page_ins += (1 << PAGE_FACTOR);
 328                         preempt_enable();
 329                 }
 330 #endif
 331         } else {
 332                 current->min_flt++;
 333                 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, 0,
 334                                      regs, address);
 335         }
 336         up_read(&mm->mmap_sem);
 337         return 0;
 338
 339 bad_area:
 340         up_read(&mm->mmap_sem);
 341
 342 bad_area_nosemaphore:
 343         /* User mode accesses cause a SIGSEGV */
 344         if (user_mode(regs)) {
 345                 _exception(SIGSEGV, regs, code, address);
 346                 return 0;
 347         }
 348
 349         if (is_exec && (error_code & DSISR_PROTFAULT)
 350             && printk_ratelimit())
 351                 printk(KERN_CRIT "kernel tried to execute NX-protected"
 352                        " page (%lx) - exploit attempt? (uid: %d)\n",
 353                        address, current_uid());
 354
 355         return SIGSEGV;
 356
 357 /*
 358  * We ran out of memory, or some other thing happened to us that made
 359  * us unable to handle the page fault gracefully.
 360  */
 361 out_of_memory:
 362         up_read(&mm->mmap_sem);
 363         if (!user_mode(regs))
 364                 return SIGKILL;
 365         pagefault_out_of_memory();
 366         return 0;
 367
 368 do_sigbus:
 369         up_read(&mm->mmap_sem);
 370         if (user_mode(regs)) {
 371                 info.si_signo = SIGBUS;
 372                 info.si_errno = 0;
 373                 info.si_code = BUS_ADRERR;
 374                 info.si_addr = (void __user *)address;
 375                 force_sig_info(SIGBUS, &info, current);
 376                 return 0;
 377         }
 378         return SIGBUS;
 379 }
 380
 381 /*
 382  * bad_page_fault is called when we have a bad access from the kernel.
 383  * It is called from the DSI and ISI handlers in head.S and from some
 384  * of the procedures in traps.c.
 385  */
 386 void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
 387 {
 388         const struct exception_table_entry *entry;
 389         unsigned long *stackend;
 390
 391         /* Are we prepared to handle this fault?  */
 392         if ((entry = search_exception_tables(regs->nip)) != NULL) {
 393                 regs->nip = entry->fixup;
 394                 return;
 395         }
 396
 397         /* kernel has accessed a bad area */
 398
 399         switch (regs->trap) {
 400         case 0x300:
 401         case 0x380:
 402                 printk(KERN_ALERT "Unable to handle kernel paging request for "
 403                         "data at address 0x%08lx\n", regs->dar);
 404                 break;
 405         case 0x400:
 406         case 0x480:
 407                 printk(KERN_ALERT "Unable to handle kernel paging request for "
 408                         "instruction fetch\n");
 409                 break;
 410         default:
 411                 printk(KERN_ALERT "Unable to handle kernel paging request for "
 412                         "unknown fault\n");
 413                 break;
 414         }
 415         printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
 416                 regs->nip);
 417
 418         stackend = end_of_stack(current);
 419         if (current != &init_task && *stackend != STACK_END_MAGIC)
 420                 printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");
 421
 422         die("Kernel access of bad area", regs, sig);
 423 }