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_counter.h>
  33
  34 #include <asm/firmware.h>
  35 #include <asm/page.h>
  36 #include <asm/pgtable.h>
  37 #include <asm/mmu.h>
  38 #include <asm/mmu_context.h>
  39 #include <asm/system.h>
  40 #include <asm/uaccess.h>
  41 #include <asm/tlbflush.h>
  42 #include <asm/siginfo.h>
  43
  44
  45 #ifdef CONFIG_KPROBES
  46 static inline int notify_page_fault(struct pt_regs *regs)
  47 {
  48         int ret = 0;
  49
  50         /* kprobe_running() needs smp_processor_id() */
  51         if (!user_mode(regs)) {
  52                 preempt_disable();
  53                 if (kprobe_running() && kprobe_fault_handler(regs, 11))
  54                         ret = 1;
  55                 preempt_enable();
  56         }
  57
  58         return ret;
  59 }
  60 #else
  61 static inline int notify_page_fault(struct pt_regs *regs)
  62 {
  63         return 0;
  64 }
  65 #endif
  66
  67 /*
  68  * Check whether the instruction at regs->nip is a store using
  69  * an update addressing form which will update r1.
  70  */
  71 static int store_updates_sp(struct pt_regs *regs)
  72 {
  73         unsigned int inst;
  74
  75         if (get_user(inst, (unsigned int __user *)regs->nip))
  76                 return 0;
  77         /* check for 1 in the rA field */
  78         if (((inst >> 16) & 0x1f) != 1)
  79                 return 0;
  80         /* check major opcode */
  81         switch (inst >> 26) {
  82         case 37:        /* stwu */
  83         case 39:        /* stbu */
  84         case 45:        /* sthu */
  85         case 53:        /* stfsu */
  86         case 55:        /* stfdu */
  87                 return 1;
  88         case 62:        /* std or stdu */
  89                 return (inst & 3) == 1;
  90         case 31:
  91                 /* check minor opcode */
  92                 switch ((inst >> 1) & 0x3ff) {
  93                 case 181:       /* stdux */
  94                 case 183:       /* stwux */
  95                 case 247:       /* stbux */
  96                 case 439:       /* sthux */
  97                 case 695:       /* stfsux */
  98                 case 759:       /* stfdux */
  99                         return 1;
 100                 }
 101         }
 102         return 0;
 103 }
 104
 105 /*
 106  * For 600- and 800-family processors, the error_code parameter is DSISR
 107  * for a data fault, SRR1 for an instruction fault. For 400-family processors
 108  * the error_code parameter is ESR for a data fault, 0 for an instruction
 109  * fault.
 110  * For 64-bit processors, the error_code parameter is
 111  *  - DSISR for a non-SLB data access fault,
 112  *  - SRR1 & 0x08000000 for a non-SLB instruction access fault
 113  *  - 0 any SLB fault.
 114  *
 115  * The return value is 0 if the fault was handled, or the signal
 116  * number if this is a kernel fault that can't be handled here.
 117  */
 118 int __kprobes do_page_fault(struct pt_regs *regs, unsigned long address,
 119                             unsigned long error_code)
 120 {
 121         struct vm_area_struct * vma;
 122         struct mm_struct *mm = current->mm;
 123         siginfo_t info;
 124         int code = SEGV_MAPERR;
 125         int is_write = 0, ret;
 126         int trap = TRAP(regs);
 127         int is_exec = trap == 0x400;
 128
 129 #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
 130         /*
 131          * Fortunately the bit assignments in SRR1 for an instruction
 132          * fault and DSISR for a data fault are mostly the same for the
 133          * bits we are interested in.  But there are some bits which
 134          * indicate errors in DSISR but can validly be set in SRR1.
 135          */
 136         if (trap == 0x400)
 137                 error_code &= 0x48200000;
 138         else
 139                 is_write = error_code & DSISR_ISSTORE;
 140 #else
 141         is_write = error_code & ESR_DST;
 142 #endif /* CONFIG_4xx || CONFIG_BOOKE */
 143
 144         if (notify_page_fault(regs))
 145                 return 0;
 146
 147         if (unlikely(debugger_fault_handler(regs)))
 148                 return 0;
 149
 150         /* On a kernel SLB miss we can only check for a valid exception entry */
 151         if (!user_mode(regs) && (address >= TASK_SIZE))
 152                 return SIGSEGV;
 153
 154 #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
 155         if (error_code & DSISR_DABRMATCH) {
 156                 /* DABR match */
 157                 do_dabr(regs, address, error_code);
 158                 return 0;
 159         }
 160 #endif /* !(CONFIG_4xx || CONFIG_BOOKE)*/
 161
 162         if (in_atomic() || mm == NULL) {
 163                 if (!user_mode(regs))
 164                         return SIGSEGV;
 165                 /* in_atomic() in user mode is really bad,
 166                    as is current->mm == NULL. */
 167                 printk(KERN_EMERG "Page fault in user mode with "
 168                        "in_atomic() = %d mm = %p\n", in_atomic(), mm);
 169                 printk(KERN_EMERG "NIP = %lx  MSR = %lx\n",
 170                        regs->nip, regs->msr);
 171                 die("Weird page fault", regs, SIGSEGV);
 172         }
 173
 174         perf_swcounter_event(PERF_COUNT_SW_PAGE_FAULTS, 1, 0, regs, address);
 175
 176         /* When running in the kernel we expect faults to occur only to
 177          * addresses in user space.  All other faults represent errors in the
 178          * kernel and should generate an OOPS.  Unfortunately, in the case of an
 179          * erroneous fault occurring in a code path which already holds mmap_sem
 180          * we will deadlock attempting to validate the fault against the
 181          * address space.  Luckily the kernel only validly references user
 182          * space from well defined areas of code, which are listed in the
 183          * exceptions table.
 184          *
 185          * As the vast majority of faults will be valid we will only perform
 186          * the source reference check when there is a possibility of a deadlock.
 187          * Attempt to lock the address space, if we cannot we then validate the
 188          * source.  If this is invalid we can skip the address space check,
 189          * thus avoiding the deadlock.
 190          */
 191         if (!down_read_trylock(&mm->mmap_sem)) {
 192                 if (!user_mode(regs) && !search_exception_tables(regs->nip))
 193                         goto bad_area_nosemaphore;
 194
 195                 down_read(&mm->mmap_sem);
 196         }
 197
 198         vma = find_vma(mm, address);
 199         if (!vma)
 200                 goto bad_area;
 201         if (vma->vm_start <= address)
 202                 goto good_area;
 203         if (!(vma->vm_flags & VM_GROWSDOWN))
 204                 goto bad_area;
 205
 206         /*
 207          * N.B. The POWER/Open ABI allows programs to access up to
 208          * 288 bytes below the stack pointer.
 209          * The kernel signal delivery code writes up to about 1.5kB
 210          * below the stack pointer (r1) before decrementing it.
 211          * The exec code can write slightly over 640kB to the stack
 212          * before setting the user r1.  Thus we allow the stack to
 213          * expand to 1MB without further checks.
 214          */
 215         if (address + 0x100000 < vma->vm_end) {
 216                 /* get user regs even if this fault is in kernel mode */
 217                 struct pt_regs *uregs = current->thread.regs;
 218                 if (uregs == NULL)
 219                         goto bad_area;
 220
 221                 /*
 222                  * A user-mode access to an address a long way below
 223                  * the stack pointer is only valid if the instruction
 224                  * is one which would update the stack pointer to the
 225                  * address accessed if the instruction completed,
 226                  * i.e. either stwu rs,n(r1) or stwux rs,r1,rb
 227                  * (or the byte, halfword, float or double forms).
 228                  *
 229                  * If we don't check this then any write to the area
 230                  * between the last mapped region and the stack will
 231                  * expand the stack rather than segfaulting.
 232                  */
 233                 if (address + 2048 < uregs->gpr[1]
 234                     && (!user_mode(regs) || !store_updates_sp(regs)))
 235                         goto bad_area;
 236         }
 237         if (expand_stack(vma, address))
 238                 goto bad_area;
 239
 240 good_area:
 241         code = SEGV_ACCERR;
 242 #if defined(CONFIG_6xx)
 243         if (error_code & 0x95700000)
 244                 /* an error such as lwarx to I/O controller space,
 245                    address matching DABR, eciwx, etc. */
 246                 goto bad_area;
 247 #endif /* CONFIG_6xx */
 248 #if defined(CONFIG_8xx)
 249         /* The MPC8xx seems to always set 0x80000000, which is
 250          * "undefined".  Of those that can be set, this is the only
 251          * one which seems bad.
 252          */
 253         if (error_code & 0x10000000)
 254                 /* Guarded storage error. */
 255                 goto bad_area;
 256 #endif /* CONFIG_8xx */
 257
 258         if (is_exec) {
 259 #ifdef CONFIG_PPC_STD_MMU
 260                 /* Protection fault on exec go straight to failure on
 261                  * Hash based MMUs as they either don't support per-page
 262                  * execute permission, or if they do, it's handled already
 263                  * at the hash level. This test would probably have to
 264                  * be removed if we change the way this works to make hash
 265                  * processors use the same I/D cache coherency mechanism
 266                  * as embedded.
 267                  */
 268                 if (error_code & DSISR_PROTFAULT)
 269                         goto bad_area;
 270 #endif /* CONFIG_PPC_STD_MMU */
 271
 272                 /*
 273                  * Allow execution from readable areas if the MMU does not
 274                  * provide separate controls over reading and executing.
 275                  *
 276                  * Note: That code used to not be enabled for 4xx/BookE.
 277                  * It is now as I/D cache coherency for these is done at
 278                  * set_pte_at() time and I see no reason why the test
 279                  * below wouldn't be valid on those processors. This -may-
 280                  * break programs compiled with a really old ABI though.
 281                  */
 282                 if (!(vma->vm_flags & VM_EXEC) &&
 283                     (cpu_has_feature(CPU_FTR_NOEXECUTE) ||
 284                      !(vma->vm_flags & (VM_READ | VM_WRITE))))
 285                         goto bad_area;
 286         /* a write */
 287         } else if (is_write) {
 288                 if (!(vma->vm_flags & VM_WRITE))
 289                         goto bad_area;
 290         /* a read */
 291         } else {
 292                 /* protection fault */
 293                 if (error_code & 0x08000000)
 294                         goto bad_area;
 295                 if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
 296                         goto bad_area;
 297         }
 298
 299         /*
 300          * If for any reason at all we couldn't handle the fault,
 301          * make sure we exit gracefully rather than endlessly redo
 302          * the fault.
 303          */
 304  survive:
 305         ret = handle_mm_fault(mm, vma, address, is_write);
 306         if (unlikely(ret & VM_FAULT_ERROR)) {
 307                 if (ret & VM_FAULT_OOM)
 308                         goto out_of_memory;
 309                 else if (ret & VM_FAULT_SIGBUS)
 310                         goto do_sigbus;
 311                 BUG();
 312         }
 313         if (ret & VM_FAULT_MAJOR) {
 314                 current->maj_flt++;
 315                 perf_swcounter_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, 0,
 316                                      regs, address);
 317 #ifdef CONFIG_PPC_SMLPAR
 318                 if (firmware_has_feature(FW_FEATURE_CMO)) {
 319                         preempt_disable();
 320                         get_lppaca()->page_ins += (1 << PAGE_FACTOR);
 321                         preempt_enable();
 322                 }
 323 #endif
 324         } else {
 325                 current->min_flt++;
 326                 perf_swcounter_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, 0,
 327                                      regs, address);
 328         }
 329         up_read(&mm->mmap_sem);
 330         return 0;
 331
 332 bad_area:
 333         up_read(&mm->mmap_sem);
 334
 335 bad_area_nosemaphore:
 336         /* User mode accesses cause a SIGSEGV */
 337         if (user_mode(regs)) {
 338                 _exception(SIGSEGV, regs, code, address);
 339                 return 0;
 340         }
 341
 342         if (is_exec && (error_code & DSISR_PROTFAULT)
 343             && printk_ratelimit())
 344                 printk(KERN_CRIT "kernel tried to execute NX-protected"
 345                        " page (%lx) - exploit attempt? (uid: %d)\n",
 346                        address, current_uid());
 347
 348         return SIGSEGV;
 349
 350 /*
 351  * We ran out of memory, or some other thing happened to us that made
 352  * us unable to handle the page fault gracefully.
 353  */
 354 out_of_memory:
 355         up_read(&mm->mmap_sem);
 356         if (is_global_init(current)) {
 357                 yield();
 358                 down_read(&mm->mmap_sem);
 359                 goto survive;
 360         }
 361         printk("VM: killing process %s\n", current->comm);
 362         if (user_mode(regs))
 363                 do_group_exit(SIGKILL);
 364         return SIGKILL;
 365
 366 do_sigbus:
 367         up_read(&mm->mmap_sem);
 368         if (user_mode(regs)) {
 369                 info.si_signo = SIGBUS;
 370                 info.si_errno = 0;
 371                 info.si_code = BUS_ADRERR;
 372                 info.si_addr = (void __user *)address;
 373                 force_sig_info(SIGBUS, &info, current);
 374                 return 0;
 375         }
 376         return SIGBUS;
 377 }
 378
 379 /*
 380  * bad_page_fault is called when we have a bad access from the kernel.
 381  * It is called from the DSI and ISI handlers in head.S and from some
 382  * of the procedures in traps.c.
 383  */
 384 void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
 385 {
 386         const struct exception_table_entry *entry;
 387
 388         /* Are we prepared to handle this fault?  */
 389         if ((entry = search_exception_tables(regs->nip)) != NULL) {
 390                 regs->nip = entry->fixup;
 391                 return;
 392         }
 393
 394         /* kernel has accessed a bad area */
 395
 396         switch (regs->trap) {
 397         case 0x300:
 398         case 0x380:
 399                 printk(KERN_ALERT "Unable to handle kernel paging request for "
 400                         "data at address 0x%08lx\n", regs->dar);
 401                 break;
 402         case 0x400:
 403         case 0x480:
 404                 printk(KERN_ALERT "Unable to handle kernel paging request for "
 405                         "instruction fetch\n");
 406                 break;
 407         default:
 408                 printk(KERN_ALERT "Unable to handle kernel paging request for "
 409                         "unknown fault\n");
 410                 break;
 411         }
 412         printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
 413                 regs->nip);
 414
 415         die("Kernel access of bad area", regs, sig);
 416 }