arch/um/kernel/trap.c

   1 /*
   2  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   3  * Licensed under the GPL
   4  */
   5
   6 #include <linux/mm.h>
   7 #include <linux/sched.h>
   8 #include <linux/hardirq.h>
   9 #include <linux/module.h>
  10 #include <linux/uaccess.h>
  11 #include <asm/current.h>
  12 #include <asm/pgtable.h>
  13 #include <asm/tlbflush.h>
  14 #include <arch.h>
  15 #include <as-layout.h>
  16 #include <kern_util.h>
  17 #include <os.h>
  18 #include <skas.h>
  19
  20 /*
  21  * Note this is constrained to return 0, -EFAULT, -EACCESS, -ENOMEM by
  22  * segv().
  23  */
  24 int handle_page_fault(unsigned long address, unsigned long ip,
  25                       int is_write, int is_user, int *code_out)
  26 {
  27         struct mm_struct *mm = current->mm;
  28         struct vm_area_struct *vma;
  29         pgd_t *pgd;
  30         pud_t *pud;
  31         pmd_t *pmd;
  32         pte_t *pte;
  33         int err = -EFAULT;
  34         unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
  35
  36         *code_out = SEGV_MAPERR;
  37
  38         /*
  39          * If the fault was with pagefaults disabled, don't take the fault, just
  40          * fail.
  41          */
  42         if (faulthandler_disabled())
  43                 goto out_nosemaphore;
  44
  45         if (is_user)
  46                 flags |= FAULT_FLAG_USER;
  47 retry:
  48         down_read(&mm->mmap_sem);
  49         vma = find_vma(mm, address);
  50         if (!vma)
  51                 goto out;
  52         else if (vma->vm_start <= address)
  53                 goto good_area;
  54         else if (!(vma->vm_flags & VM_GROWSDOWN))
  55                 goto out;
  56         else if (is_user && !ARCH_IS_STACKGROW(address))
  57                 goto out;
  58         else if (expand_stack(vma, address))
  59                 goto out;
  60
  61 good_area:
  62         *code_out = SEGV_ACCERR;
  63         if (is_write) {
  64                 if (!(vma->vm_flags & VM_WRITE))
  65                         goto out;
  66                 flags |= FAULT_FLAG_WRITE;
  67         } else {
  68                 /* Don't require VM_READ|VM_EXEC for write faults! */
  69                 if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
  70                         goto out;
  71         }
  72
  73         do {
  74                 int fault;
  75
  76                 fault = handle_mm_fault(vma, address, flags);
  77
  78                 if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
  79                         goto out_nosemaphore;
  80
  81                 if (unlikely(fault & VM_FAULT_ERROR)) {
  82                         if (fault & VM_FAULT_OOM) {
  83                                 goto out_of_memory;
  84                         } else if (fault & VM_FAULT_SIGSEGV) {
  85                                 goto out;
  86                         } else if (fault & VM_FAULT_SIGBUS) {
  87                                 err = -EACCES;
  88                                 goto out;
  89                         }
  90                         BUG();
  91                 }
  92                 if (flags & FAULT_FLAG_ALLOW_RETRY) {
  93                         if (fault & VM_FAULT_MAJOR)
  94                                 current->maj_flt++;
  95                         else
  96                                 current->min_flt++;
  97                         if (fault & VM_FAULT_RETRY) {
  98                                 flags &= ~FAULT_FLAG_ALLOW_RETRY;
  99                                 flags |= FAULT_FLAG_TRIED;
 100
 101                                 goto retry;
 102                         }
 103                 }
 104
 105                 pgd = pgd_offset(mm, address);
 106                 pud = pud_offset(pgd, address);
 107                 pmd = pmd_offset(pud, address);
 108                 pte = pte_offset_kernel(pmd, address);
 109         } while (!pte_present(*pte));
 110         err = 0;
 111         /*
 112          * The below warning was added in place of
 113          *      pte_mkyoung(); if (is_write) pte_mkdirty();
 114          * If it's triggered, we'd see normally a hang here (a clean pte is
 115          * marked read-only to emulate the dirty bit).
 116          * However, the generic code can mark a PTE writable but clean on a
 117          * concurrent read fault, triggering this harmlessly. So comment it out.
 118          */
 119 #if 0
 120         WARN_ON(!pte_young(*pte) || (is_write && !pte_dirty(*pte)));
 121 #endif
 122         flush_tlb_page(vma, address);
 123 out:
 124         up_read(&mm->mmap_sem);
 125 out_nosemaphore:
 126         return err;
 127
 128 out_of_memory:
 129         /*
 130          * We ran out of memory, call the OOM killer, and return the userspace
 131          * (which will retry the fault, or kill us if we got oom-killed).
 132          */
 133         up_read(&mm->mmap_sem);
 134         if (!is_user)
 135                 goto out_nosemaphore;
 136         pagefault_out_of_memory();
 137         return 0;
 138 }
 139 EXPORT_SYMBOL(handle_page_fault);
 140
 141 static void show_segv_info(struct uml_pt_regs *regs)
 142 {
 143         struct task_struct *tsk = current;
 144         struct faultinfo *fi = UPT_FAULTINFO(regs);
 145
 146         if (!unhandled_signal(tsk, SIGSEGV))
 147                 return;
 148
 149         if (!printk_ratelimit())
 150                 return;
 151
 152         printk("%s%s[%d]: segfault at %lx ip %p sp %p error %x",
 153                 task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
 154                 tsk->comm, task_pid_nr(tsk), FAULT_ADDRESS(*fi),
 155                 (void *)UPT_IP(regs), (void *)UPT_SP(regs),
 156                 fi->error_code);
 157
 158         print_vma_addr(KERN_CONT " in ", UPT_IP(regs));
 159         printk(KERN_CONT "\n");
 160 }
 161
 162 static void bad_segv(struct faultinfo fi, unsigned long ip)
 163 {
 164         struct siginfo si;
 165
 166         si.si_signo = SIGSEGV;
 167         si.si_code = SEGV_ACCERR;
 168         si.si_addr = (void __user *) FAULT_ADDRESS(fi);
 169         current->thread.arch.faultinfo = fi;
 170         force_sig_info(SIGSEGV, &si, current);
 171 }
 172
 173 void fatal_sigsegv(void)
 174 {
 175         force_sigsegv(SIGSEGV, current);
 176         do_signal(&current->thread.regs);
 177         /*
 178          * This is to tell gcc that we're not returning - do_signal
 179          * can, in general, return, but in this case, it's not, since
 180          * we just got a fatal SIGSEGV queued.
 181          */
 182         os_dump_core();
 183 }
 184
 185 void segv_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
 186 {
 187         struct faultinfo * fi = UPT_FAULTINFO(regs);
 188
 189         if (UPT_IS_USER(regs) && !SEGV_IS_FIXABLE(fi)) {
 190                 show_segv_info(regs);
 191                 bad_segv(*fi, UPT_IP(regs));
 192                 return;
 193         }
 194         segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs);
 195 }
 196
 197 /*
 198  * We give a *copy* of the faultinfo in the regs to segv.
 199  * This must be done, since nesting SEGVs could overwrite
 200  * the info in the regs. A pointer to the info then would
 201  * give us bad data!
 202  */
 203 unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
 204                    struct uml_pt_regs *regs)
 205 {
 206         struct siginfo si;
 207         jmp_buf *catcher;
 208         int err;
 209         int is_write = FAULT_WRITE(fi);
 210         unsigned long address = FAULT_ADDRESS(fi);
 211
 212         if (!is_user && regs)
 213                 current->thread.segv_regs = container_of(regs, struct pt_regs, regs);
 214
 215         if (!is_user && (address >= start_vm) && (address < end_vm)) {
 216                 flush_tlb_kernel_vm();
 217                 goto out;
 218         }
 219         else if (current->mm == NULL) {
 220                 show_regs(container_of(regs, struct pt_regs, regs));
 221                 panic("Segfault with no mm");
 222         }
 223         else if (!is_user && address > PAGE_SIZE && address < TASK_SIZE) {
 224                 show_regs(container_of(regs, struct pt_regs, regs));
 225                 panic("Kernel tried to access user memory at addr 0x%lx, ip 0x%lx",
 226                        address, ip);
 227         }
 228
 229         if (SEGV_IS_FIXABLE(&fi))
 230                 err = handle_page_fault(address, ip, is_write, is_user,
 231                                         &si.si_code);
 232         else {
 233                 err = -EFAULT;
 234                 /*
 235                  * A thread accessed NULL, we get a fault, but CR2 is invalid.
 236                  * This code is used in __do_copy_from_user() of TT mode.
 237                  * XXX tt mode is gone, so maybe this isn't needed any more
 238                  */
 239                 address = 0;
 240         }
 241
 242         catcher = current->thread.fault_catcher;
 243         if (!err)
 244                 goto out;
 245         else if (catcher != NULL) {
 246                 current->thread.fault_addr = (void *) address;
 247                 UML_LONGJMP(catcher, 1);
 248         }
 249         else if (current->thread.fault_addr != NULL)
 250                 panic("fault_addr set but no fault catcher");
 251         else if (!is_user && arch_fixup(ip, regs))
 252                 goto out;
 253
 254         if (!is_user) {
 255                 show_regs(container_of(regs, struct pt_regs, regs));
 256                 panic("Kernel mode fault at addr 0x%lx, ip 0x%lx",
 257                       address, ip);
 258         }
 259
 260         show_segv_info(regs);
 261
 262         if (err == -EACCES) {
 263                 si.si_signo = SIGBUS;
 264                 si.si_errno = 0;
 265                 si.si_code = BUS_ADRERR;
 266                 si.si_addr = (void __user *)address;
 267                 current->thread.arch.faultinfo = fi;
 268                 force_sig_info(SIGBUS, &si, current);
 269         } else {
 270                 BUG_ON(err != -EFAULT);
 271                 si.si_signo = SIGSEGV;
 272                 si.si_addr = (void __user *) address;
 273                 current->thread.arch.faultinfo = fi;
 274                 force_sig_info(SIGSEGV, &si, current);
 275         }
 276
 277 out:
 278         if (regs)
 279                 current->thread.segv_regs = NULL;
 280
 281         return 0;
 282 }
 283
 284 void relay_signal(int sig, struct siginfo *si, struct uml_pt_regs *regs)
 285 {
 286         struct faultinfo *fi;
 287         struct siginfo clean_si;
 288
 289         if (!UPT_IS_USER(regs)) {
 290                 if (sig == SIGBUS)
 291                         printk(KERN_ERR "Bus error - the host /dev/shm or /tmp "
 292                                "mount likely just ran out of space\n");
 293                 panic("Kernel mode signal %d", sig);
 294         }
 295
 296         arch_examine_signal(sig, regs);
 297
 298         memset(&clean_si, 0, sizeof(clean_si));
 299         clean_si.si_signo = si->si_signo;
 300         clean_si.si_errno = si->si_errno;
 301         clean_si.si_code = si->si_code;
 302         switch (sig) {
 303         case SIGILL:
 304         case SIGFPE:
 305         case SIGSEGV:
 306         case SIGBUS:
 307         case SIGTRAP:
 308                 fi = UPT_FAULTINFO(regs);
 309                 clean_si.si_addr = (void __user *) FAULT_ADDRESS(*fi);
 310                 current->thread.arch.faultinfo = *fi;
 311 #ifdef __ARCH_SI_TRAPNO
 312                 clean_si.si_trapno = si->si_trapno;
 313 #endif
 314                 break;
 315         default:
 316                 printk(KERN_ERR "Attempted to relay unknown signal %d (si_code = %d)\n",
 317                         sig, si->si_code);
 318         }
 319
 320         force_sig_info(sig, &clean_si, current);
 321 }
 322
 323 void bus_handler(int sig, struct siginfo *si, struct uml_pt_regs *regs)
 324 {
 325         if (current->thread.fault_catcher != NULL)
 326                 UML_LONGJMP(current->thread.fault_catcher, 1);
 327         else
 328                 relay_signal(sig, si, regs);
 329 }
 330
 331 void winch(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
 332 {
 333         do_IRQ(WINCH_IRQ, regs);
 334 }
 335
 336 void trap_init(void)
 337 {
 338 }