linux/arch/um/kernel/trap.c
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   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 <asm/current.h>
  11#include <asm/pgtable.h>
  12#include <asm/tlbflush.h>
  13#include "arch.h"
  14#include "as-layout.h"
  15#include "kern_util.h"
  16#include "os.h"
  17#include "skas.h"
  18
  19/*
  20 * Note this is constrained to return 0, -EFAULT, -EACCESS, -ENOMEM by
  21 * segv().
  22 */
  23int handle_page_fault(unsigned long address, unsigned long ip,
  24                      int is_write, int is_user, int *code_out)
  25{
  26        struct mm_struct *mm = current->mm;
  27        struct vm_area_struct *vma;
  28        pgd_t *pgd;
  29        pud_t *pud;
  30        pmd_t *pmd;
  31        pte_t *pte;
  32        int err = -EFAULT;
  33
  34        *code_out = SEGV_MAPERR;
  35
  36        /*
  37         * If the fault was during atomic operation, don't take the fault, just
  38         * fail.
  39         */
  40        if (in_atomic())
  41                goto out_nosemaphore;
  42
  43        down_read(&mm->mmap_sem);
  44        vma = find_vma(mm, address);
  45        if (!vma)
  46                goto out;
  47        else if (vma->vm_start <= address)
  48                goto good_area;
  49        else if (!(vma->vm_flags & VM_GROWSDOWN))
  50                goto out;
  51        else if (is_user && !ARCH_IS_STACKGROW(address))
  52                goto out;
  53        else if (expand_stack(vma, address))
  54                goto out;
  55
  56good_area:
  57        *code_out = SEGV_ACCERR;
  58        if (is_write && !(vma->vm_flags & VM_WRITE))
  59                goto out;
  60
  61        /* Don't require VM_READ|VM_EXEC for write faults! */
  62        if (!is_write && !(vma->vm_flags & (VM_READ | VM_EXEC)))
  63                goto out;
  64
  65        do {
  66                int fault;
  67
  68                fault = handle_mm_fault(mm, vma, address, is_write ? FAULT_FLAG_WRITE : 0);
  69                if (unlikely(fault & VM_FAULT_ERROR)) {
  70                        if (fault & VM_FAULT_OOM) {
  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);
 101out:
 102        up_read(&mm->mmap_sem);
 103out_nosemaphore:
 104        return err;
 105
 106out_of_memory:
 107        /*
 108         * We ran out of memory, call the OOM killer, and return the userspace
 109         * (which will retry the fault, or kill us if we got oom-killed).
 110         */
 111        up_read(&mm->mmap_sem);
 112        pagefault_out_of_memory();
 113        return 0;
 114}
 115EXPORT_SYMBOL(handle_page_fault);
 116
 117static void show_segv_info(struct uml_pt_regs *regs)
 118{
 119        struct task_struct *tsk = current;
 120        struct faultinfo *fi = UPT_FAULTINFO(regs);
 121
 122        if (!unhandled_signal(tsk, SIGSEGV))
 123                return;
 124
 125        if (!printk_ratelimit())
 126                return;
 127
 128        printk("%s%s[%d]: segfault at %lx ip %p sp %p error %x",
 129                task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
 130                tsk->comm, task_pid_nr(tsk), FAULT_ADDRESS(*fi),
 131                (void *)UPT_IP(regs), (void *)UPT_SP(regs),
 132                fi->error_code);
 133
 134        print_vma_addr(KERN_CONT " in ", UPT_IP(regs));
 135        printk(KERN_CONT "\n");
 136}
 137
 138static void bad_segv(struct faultinfo fi, unsigned long ip)
 139{
 140        struct siginfo si;
 141
 142        si.si_signo = SIGSEGV;
 143        si.si_code = SEGV_ACCERR;
 144        si.si_addr = (void __user *) FAULT_ADDRESS(fi);
 145        current->thread.arch.faultinfo = fi;
 146        force_sig_info(SIGSEGV, &si, current);
 147}
 148
 149void fatal_sigsegv(void)
 150{
 151        force_sigsegv(SIGSEGV, current);
 152        do_signal();
 153        /*
 154         * This is to tell gcc that we're not returning - do_signal
 155         * can, in general, return, but in this case, it's not, since
 156         * we just got a fatal SIGSEGV queued.
 157         */
 158        os_dump_core();
 159}
 160
 161void segv_handler(int sig, struct uml_pt_regs *regs)
 162{
 163        struct faultinfo * fi = UPT_FAULTINFO(regs);
 164
 165        if (UPT_IS_USER(regs) && !SEGV_IS_FIXABLE(fi)) {
 166                show_segv_info(regs);
 167                bad_segv(*fi, UPT_IP(regs));
 168                return;
 169        }
 170        segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs);
 171}
 172
 173/*
 174 * We give a *copy* of the faultinfo in the regs to segv.
 175 * This must be done, since nesting SEGVs could overwrite
 176 * the info in the regs. A pointer to the info then would
 177 * give us bad data!
 178 */
 179unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
 180                   struct uml_pt_regs *regs)
 181{
 182        struct siginfo si;
 183        jmp_buf *catcher;
 184        int err;
 185        int is_write = FAULT_WRITE(fi);
 186        unsigned long address = FAULT_ADDRESS(fi);
 187
 188        if (!is_user && (address >= start_vm) && (address < end_vm)) {
 189                flush_tlb_kernel_vm();
 190                return 0;
 191        }
 192        else if (current->mm == NULL) {
 193                show_regs(container_of(regs, struct pt_regs, regs));
 194                panic("Segfault with no mm");
 195        }
 196
 197        if (SEGV_IS_FIXABLE(&fi) || SEGV_MAYBE_FIXABLE(&fi))
 198                err = handle_page_fault(address, ip, is_write, is_user,
 199                                        &si.si_code);
 200        else {
 201                err = -EFAULT;
 202                /*
 203                 * A thread accessed NULL, we get a fault, but CR2 is invalid.
 204                 * This code is used in __do_copy_from_user() of TT mode.
 205                 * XXX tt mode is gone, so maybe this isn't needed any more
 206                 */
 207                address = 0;
 208        }
 209
 210        catcher = current->thread.fault_catcher;
 211        if (!err)
 212                return 0;
 213        else if (catcher != NULL) {
 214                current->thread.fault_addr = (void *) address;
 215                UML_LONGJMP(catcher, 1);
 216        }
 217        else if (current->thread.fault_addr != NULL)
 218                panic("fault_addr set but no fault catcher");
 219        else if (!is_user && arch_fixup(ip, regs))
 220                return 0;
 221
 222        if (!is_user) {
 223                show_regs(container_of(regs, struct pt_regs, regs));
 224                panic("Kernel mode fault at addr 0x%lx, ip 0x%lx",
 225                      address, ip);
 226        }
 227
 228        show_segv_info(regs);
 229
 230        if (err == -EACCES) {
 231                si.si_signo = SIGBUS;
 232                si.si_errno = 0;
 233                si.si_code = BUS_ADRERR;
 234                si.si_addr = (void __user *)address;
 235                current->thread.arch.faultinfo = fi;
 236                force_sig_info(SIGBUS, &si, current);
 237        } else {
 238                BUG_ON(err != -EFAULT);
 239                si.si_signo = SIGSEGV;
 240                si.si_addr = (void __user *) address;
 241                current->thread.arch.faultinfo = fi;
 242                force_sig_info(SIGSEGV, &si, current);
 243        }
 244        return 0;
 245}
 246
 247void relay_signal(int sig, struct uml_pt_regs *regs)
 248{
 249        if (!UPT_IS_USER(regs)) {
 250                if (sig == SIGBUS)
 251                        printk(KERN_ERR "Bus error - the host /dev/shm or /tmp "
 252                               "mount likely just ran out of space\n");
 253                panic("Kernel mode signal %d", sig);
 254        }
 255
 256        arch_examine_signal(sig, regs);
 257
 258        current->thread.arch.faultinfo = *UPT_FAULTINFO(regs);
 259        force_sig(sig, current);
 260}
 261
 262void bus_handler(int sig, struct uml_pt_regs *regs)
 263{
 264        if (current->thread.fault_catcher != NULL)
 265                UML_LONGJMP(current->thread.fault_catcher, 1);
 266        else relay_signal(sig, regs);
 267}
 268
 269void winch(int sig, struct uml_pt_regs *regs)
 270{
 271        do_IRQ(WINCH_IRQ, regs);
 272}
 273
 274void trap_init(void)
 275{
 276}
 277
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