arch/microblaze/mm/fault.c

   1 /*
   2  *  arch/microblaze/mm/fault.c
   3  *
   4  *    Copyright (C) 2007 Xilinx, Inc.  All rights reserved.
   5  *
   6  *  Derived from "arch/ppc/mm/fault.c"
   7  *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
   8  *
   9  *  Derived from "arch/i386/mm/fault.c"
  10  *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  11  *
  12  *  Modified by Cort Dougan and Paul Mackerras.
  13  *
  14  * This file is subject to the terms and conditions of the GNU General
  15  * Public License.  See the file COPYING in the main directory of this
  16  * archive for more details.
  17  *
  18  */
  19
  20 #include <linux/extable.h>
  21 #include <linux/signal.h>
  22 #include <linux/sched.h>
  23 #include <linux/kernel.h>
  24 #include <linux/errno.h>
  25 #include <linux/string.h>
  26 #include <linux/types.h>
  27 #include <linux/ptrace.h>
  28 #include <linux/mman.h>
  29 #include <linux/mm.h>
  30 #include <linux/interrupt.h>
  31
  32 #include <asm/page.h>
  33 #include <asm/pgtable.h>
  34 #include <asm/mmu.h>
  35 #include <linux/mmu_context.h>
  36 #include <linux/uaccess.h>
  37 #include <asm/exceptions.h>
  38
  39 static unsigned long pte_misses;        /* updated by do_page_fault() */
  40 static unsigned long pte_errors;        /* updated by do_page_fault() */
  41
  42 /*
  43  * Check whether the instruction at regs->pc is a store using
  44  * an update addressing form which will update r1.
  45  */
  46 static int store_updates_sp(struct pt_regs *regs)
  47 {
  48         unsigned int inst;
  49
  50         if (get_user(inst, (unsigned int __user *)regs->pc))
  51                 return 0;
  52         /* check for 1 in the rD field */
  53         if (((inst >> 21) & 0x1f) != 1)
  54                 return 0;
  55         /* check for store opcodes */
  56         if ((inst & 0xd0000000) == 0xd0000000)
  57                 return 1;
  58         return 0;
  59 }
  60
  61
  62 /*
  63  * bad_page_fault is called when we have a bad access from the kernel.
  64  * It is called from do_page_fault above and from some of the procedures
  65  * in traps.c.
  66  */
  67 void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
  68 {
  69         const struct exception_table_entry *fixup;
  70 /* MS: no context */
  71         /* Are we prepared to handle this fault?  */
  72         fixup = search_exception_tables(regs->pc);
  73         if (fixup) {
  74                 regs->pc = fixup->fixup;
  75                 return;
  76         }
  77
  78         /* kernel has accessed a bad area */
  79         die("kernel access of bad area", regs, sig);
  80 }
  81
  82 /*
  83  * The error_code parameter is ESR for a data fault,
  84  * 0 for an instruction fault.
  85  */
  86 void do_page_fault(struct pt_regs *regs, unsigned long address,
  87                    unsigned long error_code)
  88 {
  89         struct vm_area_struct *vma;
  90         struct mm_struct *mm = current->mm;
  91         int code = SEGV_MAPERR;
  92         int is_write = error_code & ESR_S;
  93         vm_fault_t fault;
  94         unsigned int flags = FAULT_FLAG_DEFAULT;
  95
  96         regs->ear = address;
  97         regs->esr = error_code;
  98
  99         /* On a kernel SLB miss we can only check for a valid exception entry */
 100         if (unlikely(kernel_mode(regs) && (address >= TASK_SIZE))) {
 101                 pr_warn("kernel task_size exceed");
 102                 _exception(SIGSEGV, regs, code, address);
 103         }
 104
 105         /* for instr TLB miss and instr storage exception ESR_S is undefined */
 106         if ((error_code & 0x13) == 0x13 || (error_code & 0x11) == 0x11)
 107                 is_write = 0;
 108
 109         if (unlikely(faulthandler_disabled() || !mm)) {
 110                 if (kernel_mode(regs))
 111                         goto bad_area_nosemaphore;
 112
 113                 /* faulthandler_disabled() in user mode is really bad,
 114                    as is current->mm == NULL. */
 115                 pr_emerg("Page fault in user mode with faulthandler_disabled(), mm = %p\n",
 116                          mm);
 117                 pr_emerg("r15 = %lx  MSR = %lx\n",
 118                        regs->r15, regs->msr);
 119                 die("Weird page fault", regs, SIGSEGV);
 120         }
 121
 122         if (user_mode(regs))
 123                 flags |= FAULT_FLAG_USER;
 124
 125         /* When running in the kernel we expect faults to occur only to
 126          * addresses in user space.  All other faults represent errors in the
 127          * kernel and should generate an OOPS.  Unfortunately, in the case of an
 128          * erroneous fault occurring in a code path which already holds mmap_sem
 129          * we will deadlock attempting to validate the fault against the
 130          * address space.  Luckily the kernel only validly references user
 131          * space from well defined areas of code, which are listed in the
 132          * exceptions table.
 133          *
 134          * As the vast majority of faults will be valid we will only perform
 135          * the source reference check when there is a possibility of a deadlock.
 136          * Attempt to lock the address space, if we cannot we then validate the
 137          * source.  If this is invalid we can skip the address space check,
 138          * thus avoiding the deadlock.
 139          */
 140         if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
 141                 if (kernel_mode(regs) && !search_exception_tables(regs->pc))
 142                         goto bad_area_nosemaphore;
 143
 144 retry:
 145                 down_read(&mm->mmap_sem);
 146         }
 147
 148         vma = find_vma(mm, address);
 149         if (unlikely(!vma))
 150                 goto bad_area;
 151
 152         if (vma->vm_start <= address)
 153                 goto good_area;
 154
 155         if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
 156                 goto bad_area;
 157
 158         if (unlikely(!is_write))
 159                 goto bad_area;
 160
 161         /*
 162          * N.B. The ABI allows programs to access up to
 163          * a few hundred bytes below the stack pointer (TBD).
 164          * The kernel signal delivery code writes up to about 1.5kB
 165          * below the stack pointer (r1) before decrementing it.
 166          * The exec code can write slightly over 640kB to the stack
 167          * before setting the user r1.  Thus we allow the stack to
 168          * expand to 1MB without further checks.
 169          */
 170         if (unlikely(address + 0x100000 < vma->vm_end)) {
 171
 172                 /* get user regs even if this fault is in kernel mode */
 173                 struct pt_regs *uregs = current->thread.regs;
 174                 if (uregs == NULL)
 175                         goto bad_area;
 176
 177                 /*
 178                  * A user-mode access to an address a long way below
 179                  * the stack pointer is only valid if the instruction
 180                  * is one which would update the stack pointer to the
 181                  * address accessed if the instruction completed,
 182                  * i.e. either stwu rs,n(r1) or stwux rs,r1,rb
 183                  * (or the byte, halfword, float or double forms).
 184                  *
 185                  * If we don't check this then any write to the area
 186                  * between the last mapped region and the stack will
 187                  * expand the stack rather than segfaulting.
 188                  */
 189                 if (address + 2048 < uregs->r1
 190                         && (kernel_mode(regs) || !store_updates_sp(regs)))
 191                                 goto bad_area;
 192         }
 193         if (expand_stack(vma, address))
 194                 goto bad_area;
 195
 196 good_area:
 197         code = SEGV_ACCERR;
 198
 199         /* a write */
 200         if (unlikely(is_write)) {
 201                 if (unlikely(!(vma->vm_flags & VM_WRITE)))
 202                         goto bad_area;
 203                 flags |= FAULT_FLAG_WRITE;
 204         /* a read */
 205         } else {
 206                 /* protection fault */
 207                 if (unlikely(error_code & 0x08000000))
 208                         goto bad_area;
 209                 if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC))))
 210                         goto bad_area;
 211         }
 212
 213         /*
 214          * If for any reason at all we couldn't handle the fault,
 215          * make sure we exit gracefully rather than endlessly redo
 216          * the fault.
 217          */
 218         fault = handle_mm_fault(vma, address, flags);
 219
 220         if (fault_signal_pending(fault, regs))
 221                 return;
 222
 223         if (unlikely(fault & VM_FAULT_ERROR)) {
 224                 if (fault & VM_FAULT_OOM)
 225                         goto out_of_memory;
 226                 else if (fault & VM_FAULT_SIGSEGV)
 227                         goto bad_area;
 228                 else if (fault & VM_FAULT_SIGBUS)
 229                         goto do_sigbus;
 230                 BUG();
 231         }
 232
 233         if (flags & FAULT_FLAG_ALLOW_RETRY) {
 234                 if (unlikely(fault & VM_FAULT_MAJOR))
 235                         current->maj_flt++;
 236                 else
 237                         current->min_flt++;
 238                 if (fault & VM_FAULT_RETRY) {
 239                         flags |= FAULT_FLAG_TRIED;
 240
 241                         /*
 242                          * No need to up_read(&mm->mmap_sem) as we would
 243                          * have already released it in __lock_page_or_retry
 244                          * in mm/filemap.c.
 245                          */
 246
 247                         goto retry;
 248                 }
 249         }
 250
 251         up_read(&mm->mmap_sem);
 252
 253         /*
 254          * keep track of tlb+htab misses that are good addrs but
 255          * just need pte's created via handle_mm_fault()
 256          * -- Cort
 257          */
 258         pte_misses++;
 259         return;
 260
 261 bad_area:
 262         up_read(&mm->mmap_sem);
 263
 264 bad_area_nosemaphore:
 265         pte_errors++;
 266
 267         /* User mode accesses cause a SIGSEGV */
 268         if (user_mode(regs)) {
 269                 _exception(SIGSEGV, regs, code, address);
 270                 return;
 271         }
 272
 273         bad_page_fault(regs, address, SIGSEGV);
 274         return;
 275
 276 /*
 277  * We ran out of memory, or some other thing happened to us that made
 278  * us unable to handle the page fault gracefully.
 279  */
 280 out_of_memory:
 281         up_read(&mm->mmap_sem);
 282         if (!user_mode(regs))
 283                 bad_page_fault(regs, address, SIGKILL);
 284         else
 285                 pagefault_out_of_memory();
 286         return;
 287
 288 do_sigbus:
 289         up_read(&mm->mmap_sem);
 290         if (user_mode(regs)) {
 291                 force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
 292                 return;
 293         }
 294         bad_page_fault(regs, address, SIGBUS);
 295 }