trap.c

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/*
 * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 * Licensed under the GPL
 */

#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/hardirq.h>
#include <linux/module.h>
#include <asm/current.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>
#include <arch.h>
#include <as-layout.h>
#include <kern_util.h>
#include <os.h>
#include <skas.h>

/*
 * Note this is constrained to return 0, -EFAULT, -EACCESS, -ENOMEM by
 * segv().
 */
int handle_page_fault(unsigned long address, unsigned long ip,
              int is_write, int is_user, int *code_out)
{
    struct mm_struct *mm = current->mm;
    struct vm_area_struct *vma;
    pgd_t *pgd;
    pud_t *pud;
    pmd_t *pmd;
    pte_t *pte;
    int err = -EFAULT;
    unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE |
                 (is_write ? FAULT_FLAG_WRITE : 0);

    *code_out = SEGV_MAPERR;

    /*
     * If the fault was during atomic operation, don't take the fault, just
     * fail.
     */
    if (in_atomic())
        goto out_nosemaphore;

retry:
    down_read(&mm->mmap_sem);
    vma = find_vma(mm, address);
    if (!vma)
        goto out;
    else if (vma->vm_start <= address)
        goto good_area;
    else if (!(vma->vm_flags & VM_GROWSDOWN))
        goto out;
    else if (is_user && !ARCH_IS_STACKGROW(address))
        goto out;
    else if (expand_stack(vma, address))
        goto out;

good_area:
    *code_out = SEGV_ACCERR;
    if (is_write && !(vma->vm_flags & VM_WRITE))
        goto out;

    /* Don't require VM_READ|VM_EXEC for write faults! */
    if (!is_write && !(vma->vm_flags & (VM_READ | VM_EXEC)))
        goto out;

    do {
        int fault;

        fault = handle_mm_fault(mm, vma, address, flags);

        if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
            goto out_nosemaphore;

        if (unlikely(fault & VM_FAULT_ERROR)) {
            if (fault & VM_FAULT_OOM) {
                goto out_of_memory;
            } else if (fault & VM_FAULT_SIGBUS) {
                err = -EACCES;
                goto out;
            }
            BUG();
        }
        if (flags & FAULT_FLAG_ALLOW_RETRY) {
            if (fault & VM_FAULT_MAJOR)
                current->maj_flt++;
            else
                current->min_flt++;
            if (fault & VM_FAULT_RETRY) {
                flags &= ~FAULT_FLAG_ALLOW_RETRY;
                flags |= FAULT_FLAG_TRIED;

                goto retry;
            }
        }

        pgd = pgd_offset(mm, address);
        pud = pud_offset(pgd, address);
        pmd = pmd_offset(pud, address);
        pte = pte_offset_kernel(pmd, address);
    } while (!pte_present(*pte));
    err = 0;
    /*
     * The below warning was added in place of
     *  pte_mkyoung(); if (is_write) pte_mkdirty();
     * If it's triggered, we'd see normally a hang here (a clean pte is
     * marked read-only to emulate the dirty bit).
     * However, the generic code can mark a PTE writable but clean on a
     * concurrent read fault, triggering this harmlessly. So comment it out.
     */
#if 0
    WARN_ON(!pte_young(*pte) || (is_write && !pte_dirty(*pte)));
#endif
    flush_tlb_page(vma, address);
out:
    up_read(&mm->mmap_sem);
out_nosemaphore:
    return err;

out_of_memory:
    /*
     * We ran out of memory, call the OOM killer, and return the userspace
     * (which will retry the fault, or kill us if we got oom-killed).
     */
    up_read(&mm->mmap_sem);
    pagefault_out_of_memory();
    return 0;
}
EXPORT_SYMBOL(handle_page_fault);

static void show_segv_info(struct uml_pt_regs *regs)
{
    struct task_struct *tsk = current;
    struct faultinfo *fi = UPT_FAULTINFO(regs);

    if (!unhandled_signal(tsk, SIGSEGV))
        return;

    if (!printk_ratelimit())
        return;

    printk("%s%s[%d]: segfault at %lx ip %p sp %p error %x",
        task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
        tsk->comm, task_pid_nr(tsk), FAULT_ADDRESS(*fi),
        (void *)UPT_IP(regs), (void *)UPT_SP(regs),
        fi->error_code);

    print_vma_addr(KERN_CONT " in ", UPT_IP(regs));
    printk(KERN_CONT "\n");
}

static void bad_segv(struct faultinfo fi, unsigned long ip)
{
    struct siginfo si;

    si.si_signo = SIGSEGV;
    si.si_code = SEGV_ACCERR;
    si.si_addr = (void __user *) FAULT_ADDRESS(fi);
    current->thread.arch.faultinfo = fi;
    force_sig_info(SIGSEGV, &si, current);
}

void fatal_sigsegv(void)
{
    force_sigsegv(SIGSEGV, current);
    do_signal();
    /*
     * This is to tell gcc that we're not returning - do_signal
     * can, in general, return, but in this case, it's not, since
     * we just got a fatal SIGSEGV queued.
     */
    os_dump_core();
}

void segv_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
{
    struct faultinfo * fi = UPT_FAULTINFO(regs);

    if (UPT_IS_USER(regs) && !SEGV_IS_FIXABLE(fi)) {
        show_segv_info(regs);
        bad_segv(*fi, UPT_IP(regs));
        return;
    }
    segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs);
}

/*
 * We give a *copy* of the faultinfo in the regs to segv.
 * This must be done, since nesting SEGVs could overwrite
 * the info in the regs. A pointer to the info then would
 * give us bad data!
 */
unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
           struct uml_pt_regs *regs)
{
    struct siginfo si;
    jmp_buf *catcher;
    int err;
    int is_write = FAULT_WRITE(fi);
    unsigned long address = FAULT_ADDRESS(fi);

    if (!is_user && (address >= start_vm) && (address < end_vm)) {
        flush_tlb_kernel_vm();
        return 0;
    }
    else if (current->mm == NULL) {
        show_regs(container_of(regs, struct pt_regs, regs));
        panic("Segfault with no mm");
    }

    if (SEGV_IS_FIXABLE(&fi) || SEGV_MAYBE_FIXABLE(&fi))
        err = handle_page_fault(address, ip, is_write, is_user,
                    &si.si_code);
    else {
        err = -EFAULT;
        /*
         * A thread accessed NULL, we get a fault, but CR2 is invalid.
         * This code is used in __do_copy_from_user() of TT mode.
         * XXX tt mode is gone, so maybe this isn't needed any more
         */
        address = 0;
    }

    catcher = current->thread.fault_catcher;
    if (!err)
        return 0;
    else if (catcher != NULL) {
        current->thread.fault_addr = (void *) address;
        UML_LONGJMP(catcher, 1);
    }
    else if (current->thread.fault_addr != NULL)
        panic("fault_addr set but no fault catcher");
    else if (!is_user && arch_fixup(ip, regs))
        return 0;

    if (!is_user) {
        show_regs(container_of(regs, struct pt_regs, regs));
        panic("Kernel mode fault at addr 0x%lx, ip 0x%lx",
              address, ip);
    }

    show_segv_info(regs);

    if (err == -EACCES) {
        si.si_signo = SIGBUS;
        si.si_errno = 0;
        si.si_code = BUS_ADRERR;
        si.si_addr = (void __user *)address;
        current->thread.arch.faultinfo = fi;
        force_sig_info(SIGBUS, &si, current);
    } else {
        BUG_ON(err != -EFAULT);
        si.si_signo = SIGSEGV;
        si.si_addr = (void __user *) address;
        current->thread.arch.faultinfo = fi;
        force_sig_info(SIGSEGV, &si, current);
    }
    return 0;
}

void relay_signal(int sig, struct siginfo *si, struct uml_pt_regs *regs)
{
    struct faultinfo *fi;
    struct siginfo clean_si;

    if (!UPT_IS_USER(regs)) {
        if (sig == SIGBUS)
            printk(KERN_ERR "Bus error - the host /dev/shm or /tmp "
                   "mount likely just ran out of space\n");
        panic("Kernel mode signal %d", sig);
    }

    arch_examine_signal(sig, regs);

    memset(&clean_si, 0, sizeof(clean_si));
    clean_si.si_signo = si->si_signo;
    clean_si.si_errno = si->si_errno;
    clean_si.si_code = si->si_code;
    switch (sig) {
    case SIGILL:
    case SIGFPE:
    case SIGSEGV:
    case SIGBUS:
    case SIGTRAP:
        fi = UPT_FAULTINFO(regs);
        clean_si.si_addr = (void __user *) FAULT_ADDRESS(*fi);
        current->thread.arch.faultinfo = *fi;
#ifdef __ARCH_SI_TRAPNO
        clean_si.si_trapno = si->si_trapno;
#endif
        break;
    default:
        printk(KERN_ERR "Attempted to relay unknown signal %d (si_code = %d)\n",
            sig, si->si_code);
    }

    force_sig_info(sig, &clean_si, current);
}

void bus_handler(int sig, struct siginfo *si, struct uml_pt_regs *regs)
{
    if (current->thread.fault_catcher != NULL)
        UML_LONGJMP(current->thread.fault_catcher, 1);
    else
        relay_signal(sig, si, regs);
}

void winch(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
{
    do_IRQ(WINCH_IRQ, regs);
}

void trap_init(void)
{
}