fault.c

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/*
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Copyright (C) 1995 - 2000 by Ralf Baechle
 */
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ptrace.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/module.h>
#include <linux/kprobes.h>
#include <linux/perf_event.h>

#include <asm/branch.h>
#include <asm/mmu_context.h>
#include <asm/uaccess.h>
#include <asm/ptrace.h>
#include <asm/highmem.h>        /* For VMALLOC_END */
#include <linux/kdebug.h>

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 */
asmlinkage void __kprobes do_page_fault(struct pt_regs *regs, unsigned long write,
                  unsigned long address)
{
    struct vm_area_struct * vma = NULL;
    struct task_struct *tsk = current;
    struct mm_struct *mm = tsk->mm;
    const int field = sizeof(unsigned long) * 2;
    siginfo_t info;
    int fault;
    unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE |
                         (write ? FAULT_FLAG_WRITE : 0);

#if 0
    printk("Cpu%d[%s:%d:%0*lx:%ld:%0*lx]\n", raw_smp_processor_id(),
           current->comm, current->pid, field, address, write,
           field, regs->cp0_epc);
#endif

#ifdef CONFIG_KPROBES
    /*
     * This is to notify the fault handler of the kprobes.  The
     * exception code is redundant as it is also carried in REGS,
     * but we pass it anyhow.
     */
    if (notify_die(DIE_PAGE_FAULT, "page fault", regs, -1,
               (regs->cp0_cause >> 2) & 0x1f, SIGSEGV) == NOTIFY_STOP)
        return;
#endif

    info.si_code = SEGV_MAPERR;

    /*
     * We fault-in kernel-space virtual memory on-demand. The
     * 'reference' page table is init_mm.pgd.
     *
     * NOTE! We MUST NOT take any locks for this case. We may
     * be in an interrupt or a critical region, and should
     * only copy the information from the master page table,
     * nothing more.
     */
#ifdef CONFIG_64BIT
# define VMALLOC_FAULT_TARGET no_context
#else
# define VMALLOC_FAULT_TARGET vmalloc_fault
#endif

    if (unlikely(address >= VMALLOC_START && address <= VMALLOC_END))
        goto VMALLOC_FAULT_TARGET;
#ifdef MODULE_START
    if (unlikely(address >= MODULE_START && address < MODULE_END))
        goto VMALLOC_FAULT_TARGET;
#endif

    /*
     * If we're in an interrupt or have no user
     * context, we must not take the fault..
     */
    if (in_atomic() || !mm)
        goto bad_area_nosemaphore;

retry:
    down_read(&mm->mmap_sem);
    vma = find_vma(mm, address);
    if (!vma)
        goto bad_area;
    if (vma->vm_start <= address)
        goto good_area;
    if (!(vma->vm_flags & VM_GROWSDOWN))
        goto bad_area;
    if (expand_stack(vma, address))
        goto bad_area;
/*
 * Ok, we have a good vm_area for this memory access, so
 * we can handle it..
 */
good_area:
    info.si_code = SEGV_ACCERR;

    if (write) {
        if (!(vma->vm_flags & VM_WRITE))
            goto bad_area;
    } else {
        if (cpu_has_rixi) {
            if (address == regs->cp0_epc && !(vma->vm_flags & VM_EXEC)) {
#if 0
                pr_notice("Cpu%d[%s:%d:%0*lx:%ld:%0*lx] XI violation\n",
                      raw_smp_processor_id(),
                      current->comm, current->pid,
                      field, address, write,
                      field, regs->cp0_epc);
#endif
                goto bad_area;
            }
            if (!(vma->vm_flags & VM_READ)) {
#if 0
                pr_notice("Cpu%d[%s:%d:%0*lx:%ld:%0*lx] RI violation\n",
                      raw_smp_processor_id(),
                      current->comm, current->pid,
                      field, address, write,
                      field, regs->cp0_epc);
#endif
                goto bad_area;
            }
        } else {
            if (!(vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)))
                goto bad_area;
        }
    }

    /*
     * If for any reason at all we couldn't handle the fault,
     * make sure we exit gracefully rather than endlessly redo
     * the fault.
     */
    fault = handle_mm_fault(mm, vma, address, flags);

    if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
        return;

    perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
    if (unlikely(fault & VM_FAULT_ERROR)) {
        if (fault & VM_FAULT_OOM)
            goto out_of_memory;
        else if (fault & VM_FAULT_SIGBUS)
            goto do_sigbus;
        BUG();
    }
    if (flags & FAULT_FLAG_ALLOW_RETRY) {
        if (fault & VM_FAULT_MAJOR) {
            perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
                          regs, address);
            tsk->maj_flt++;
        } else {
            perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
                          regs, address);
            tsk->min_flt++;
        }
        if (fault & VM_FAULT_RETRY) {
            flags &= ~FAULT_FLAG_ALLOW_RETRY;
            flags |= FAULT_FLAG_TRIED;

            /*
             * No need to up_read(&mm->mmap_sem) as we would
             * have already released it in __lock_page_or_retry
             * in mm/filemap.c.
             */

            goto retry;
        }
    }

    up_read(&mm->mmap_sem);
    return;

/*
 * Something tried to access memory that isn't in our memory map..
 * Fix it, but check if it's kernel or user first..
 */
bad_area:
    up_read(&mm->mmap_sem);

bad_area_nosemaphore:
    /* User mode accesses just cause a SIGSEGV */
    if (user_mode(regs)) {
        tsk->thread.cp0_badvaddr = address;
        tsk->thread.error_code = write;
#if 0
        printk("do_page_fault() #2: sending SIGSEGV to %s for "
               "invalid %s\n%0*lx (epc == %0*lx, ra == %0*lx)\n",
               tsk->comm,
               write ? "write access to" : "read access from",
               field, address,
               field, (unsigned long) regs->cp0_epc,
               field, (unsigned long) regs->regs[31]);
#endif
        info.si_signo = SIGSEGV;
        info.si_errno = 0;
        /* info.si_code has been set above */
        info.si_addr = (void __user *) address;
        force_sig_info(SIGSEGV, &info, tsk);
        return;
    }

no_context:
    /* Are we prepared to handle this kernel fault?  */
    if (fixup_exception(regs)) {
        current->thread.cp0_baduaddr = address;
        return;
    }

    /*
     * Oops. The kernel tried to access some bad page. We'll have to
     * terminate things with extreme prejudice.
     */
    bust_spinlocks(1);

    printk(KERN_ALERT "CPU %d Unable to handle kernel paging request at "
           "virtual address %0*lx, epc == %0*lx, ra == %0*lx\n",
           raw_smp_processor_id(), field, address, field, regs->cp0_epc,
           field,  regs->regs[31]);
    die("Oops", regs);

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;

do_sigbus:
    up_read(&mm->mmap_sem);

    /* Kernel mode? Handle exceptions or die */
    if (!user_mode(regs))
        goto no_context;
    else
    /*
     * Send a sigbus, regardless of whether we were in kernel
     * or user mode.
     */
#if 0
        printk("do_page_fault() #3: sending SIGBUS to %s for "
               "invalid %s\n%0*lx (epc == %0*lx, ra == %0*lx)\n",
               tsk->comm,
               write ? "write access to" : "read access from",
               field, address,
               field, (unsigned long) regs->cp0_epc,
               field, (unsigned long) regs->regs[31]);
#endif
    tsk->thread.cp0_badvaddr = address;
    info.si_signo = SIGBUS;
    info.si_errno = 0;
    info.si_code = BUS_ADRERR;
    info.si_addr = (void __user *) address;
    force_sig_info(SIGBUS, &info, tsk);

    return;
#ifndef CONFIG_64BIT
vmalloc_fault:
    {
        /*
         * Synchronize this task's top level page-table
         * with the 'reference' page table.
         *
         * Do _not_ use "tsk" here. We might be inside
         * an interrupt in the middle of a task switch..
         */
        int offset = __pgd_offset(address);
        pgd_t *pgd, *pgd_k;
        pud_t *pud, *pud_k;
        pmd_t *pmd, *pmd_k;
        pte_t *pte_k;

        pgd = (pgd_t *) pgd_current[raw_smp_processor_id()] + offset;
        pgd_k = init_mm.pgd + offset;

        if (!pgd_present(*pgd_k))
            goto no_context;
        set_pgd(pgd, *pgd_k);

        pud = pud_offset(pgd, address);
        pud_k = pud_offset(pgd_k, address);
        if (!pud_present(*pud_k))
            goto no_context;

        pmd = pmd_offset(pud, address);
        pmd_k = pmd_offset(pud_k, address);
        if (!pmd_present(*pmd_k))
            goto no_context;
        set_pmd(pmd, *pmd_k);

        pte_k = pte_offset_kernel(pmd_k, address);
        if (!pte_present(*pte_k))
            goto no_context;
        return;
    }
#endif
}