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 <asm/current.h>
  10 #include <asm/pgtable.h>
  11 #include <asm/tlbflush.h>
  12 #include "arch.h"
  13 #include "as-layout.h"
  14 #include "kern_util.h"
  15 #include "os.h"
  16 #include "sysdep/sigcontext.h"
  17
  18 /*
  19  * Note this is constrained to return 0, -EFAULT, -EACCESS, -ENOMEM by
  20  * segv().
  21  */
  22 int handle_page_fault(unsigned long address, unsigned long ip,
  23                       int is_write, int is_user, int *code_out)
  24 {
  25         struct mm_struct *mm = current->mm;
  26         struct vm_area_struct *vma;
  27         pgd_t *pgd;
  28         pud_t *pud;
  29         pmd_t *pmd;
  30         pte_t *pte;
  31         int err = -EFAULT;
  32
  33         *code_out = SEGV_MAPERR;
  34
  35         /*
  36          * If the fault was during atomic operation, don't take the fault, just
  37          * fail.
  38          */
  39         if (in_atomic())
  40                 goto out_nosemaphore;
  41
  42         down_read(&mm->mmap_sem);
  43         vma = find_vma(mm, address);
  44         if (!vma)
  45                 goto out;
  46         else if (vma->vm_start <= address)
  47                 goto good_area;
  48         else if (!(vma->vm_flags & VM_GROWSDOWN))
  49                 goto out;
  50         else if (is_user && !ARCH_IS_STACKGROW(address))
  51                 goto out;
  52         else if (expand_stack(vma, address))
  53                 goto out;
  54
  55 good_area:
  56         *code_out = SEGV_ACCERR;
  57         if (is_write && !(vma->vm_flags & VM_WRITE))
  58                 goto out;
  59
  60         /* Don't require VM_READ|VM_EXEC for write faults! */
  61         if (!is_write && !(vma->vm_flags & (VM_READ | VM_EXEC)))
  62                 goto out;
  63
  64         do {
  65                 int fault;
  66 survive:
  67                 fault = handle_mm_fault(mm, vma, address, is_write);
  68                 if (unlikely(fault & VM_FAULT_ERROR)) {
  69                         if (fault & VM_FAULT_OOM) {
  70                                 err = -ENOMEM;
  71                                 goto out_of_memory;
  72                         } else if (fault & VM_FAULT_SIGBUS) {
  73                                 err = -EACCES;
  74                                 goto out;
  75                         }
  76                         BUG();
  77                 }
  78                 if (fault & VM_FAULT_MAJOR)
  79                         current->maj_flt++;
  80                 else
  81                         current->min_flt++;
  82
  83                 pgd = pgd_offset(mm, address);
  84                 pud = pud_offset(pgd, address);
  85                 pmd = pmd_offset(pud, address);
  86                 pte = pte_offset_kernel(pmd, address);
  87         } while (!pte_present(*pte));
  88         err = 0;
  89         /*
  90          * The below warning was added in place of
  91          *      pte_mkyoung(); if (is_write) pte_mkdirty();
  92          * If it's triggered, we'd see normally a hang here (a clean pte is
  93          * marked read-only to emulate the dirty bit).
  94          * However, the generic code can mark a PTE writable but clean on a
  95          * concurrent read fault, triggering this harmlessly. So comment it out.
  96          */
  97 #if 0
  98         WARN_ON(!pte_young(*pte) || (is_write && !pte_dirty(*pte)));
  99 #endif
 100         flush_tlb_page(vma, address);
 101 out:
 102         up_read(&mm->mmap_sem);
 103 out_nosemaphore:
 104         return err;
 105
 106 /*
 107  * We ran out of memory, or some other thing happened to us that made
 108  * us unable to handle the page fault gracefully.
 109  */
 110 out_of_memory:
 111         if (is_global_init(current)) {
 112                 up_read(&mm->mmap_sem);
 113                 yield();
 114                 down_read(&mm->mmap_sem);
 115                 goto survive;
 116         }
 117         goto out;
 118 }
 119
 120 static void bad_segv(struct faultinfo fi, unsigned long ip)
 121 {
 122         struct siginfo si;
 123
 124         si.si_signo = SIGSEGV;
 125         si.si_code = SEGV_ACCERR;
 126         si.si_addr = (void __user *) FAULT_ADDRESS(fi);
 127         current->thread.arch.faultinfo = fi;
 128         force_sig_info(SIGSEGV, &si, current);
 129 }
 130
 131 static void segv_handler(int sig, struct uml_pt_regs *regs)
 132 {
 133         struct faultinfo * fi = UPT_FAULTINFO(regs);
 134
 135         if (UPT_IS_USER(regs) && !SEGV_IS_FIXABLE(fi)) {
 136                 bad_segv(*fi, UPT_IP(regs));
 137                 return;
 138         }
 139         segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs);
 140 }
 141
 142 /*
 143  * We give a *copy* of the faultinfo in the regs to segv.
 144  * This must be done, since nesting SEGVs could overwrite
 145  * the info in the regs. A pointer to the info then would
 146  * give us bad data!
 147  */
 148 unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
 149                    struct uml_pt_regs *regs)
 150 {
 151         struct siginfo si;
 152         jmp_buf *catcher;
 153         int err;
 154         int is_write = FAULT_WRITE(fi);
 155         unsigned long address = FAULT_ADDRESS(fi);
 156
 157         if (!is_user && (address >= start_vm) && (address < end_vm)) {
 158                 flush_tlb_kernel_vm();
 159                 return 0;
 160         }
 161         else if (current->mm == NULL) {
 162                 show_regs(container_of(regs, struct pt_regs, regs));
 163                 panic("Segfault with no mm");
 164         }
 165
 166         if (SEGV_IS_FIXABLE(&fi) || SEGV_MAYBE_FIXABLE(&fi))
 167                 err = handle_page_fault(address, ip, is_write, is_user,
 168                                         &si.si_code);
 169         else {
 170                 err = -EFAULT;
 171                 /*
 172                  * A thread accessed NULL, we get a fault, but CR2 is invalid.
 173                  * This code is used in __do_copy_from_user() of TT mode.
 174                  * XXX tt mode is gone, so maybe this isn't needed any more
 175                  */
 176                 address = 0;
 177         }
 178
 179         catcher = current->thread.fault_catcher;
 180         if (!err)
 181                 return 0;
 182         else if (catcher != NULL) {
 183                 current->thread.fault_addr = (void *) address;
 184                 UML_LONGJMP(catcher, 1);
 185         }
 186         else if (current->thread.fault_addr != NULL)
 187                 panic("fault_addr set but no fault catcher");
 188         else if (!is_user && arch_fixup(ip, regs))
 189                 return 0;
 190
 191         if (!is_user) {
 192                 show_regs(container_of(regs, struct pt_regs, regs));
 193                 panic("Kernel mode fault at addr 0x%lx, ip 0x%lx",
 194                       address, ip);
 195         }
 196
 197         if (err == -EACCES) {
 198                 si.si_signo = SIGBUS;
 199                 si.si_errno = 0;
 200                 si.si_code = BUS_ADRERR;
 201                 si.si_addr = (void __user *)address;
 202                 current->thread.arch.faultinfo = fi;
 203                 force_sig_info(SIGBUS, &si, current);
 204         } else if (err == -ENOMEM) {
 205                 printk(KERN_INFO "VM: killing process %s\n", current->comm);
 206                 do_exit(SIGKILL);
 207         } else {
 208                 BUG_ON(err != -EFAULT);
 209                 si.si_signo = SIGSEGV;
 210                 si.si_addr = (void __user *) address;
 211                 current->thread.arch.faultinfo = fi;
 212                 force_sig_info(SIGSEGV, &si, current);
 213         }
 214         return 0;
 215 }
 216
 217 void relay_signal(int sig, struct uml_pt_regs *regs)
 218 {
 219         if (arch_handle_signal(sig, regs))
 220                 return;
 221
 222         if (!UPT_IS_USER(regs)) {
 223                 if (sig == SIGBUS)
 224                         printk(KERN_ERR "Bus error - the host /dev/shm or /tmp "
 225                                "mount likely just ran out of space\n");
 226                 panic("Kernel mode signal %d", sig);
 227         }
 228
 229         current->thread.arch.faultinfo = *UPT_FAULTINFO(regs);
 230         force_sig(sig, current);
 231 }
 232
 233 static void bus_handler(int sig, struct uml_pt_regs *regs)
 234 {
 235         if (current->thread.fault_catcher != NULL)
 236                 UML_LONGJMP(current->thread.fault_catcher, 1);
 237         else relay_signal(sig, regs);
 238 }
 239
 240 static void winch(int sig, struct uml_pt_regs *regs)
 241 {
 242         do_IRQ(WINCH_IRQ, regs);
 243 }
 244
 245 const struct kern_handlers handlinfo_kern = {
 246         .relay_signal = relay_signal,
 247         .winch = winch,
 248         .bus_handler = bus_handler,
 249         .page_fault = segv_handler,
 250         .sigio_handler = sigio_handler,
 251         .timer_handler = timer_handler
 252 };
 253
 254 void trap_init(void)
 255 {
 256 }