fault.c

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/*
 * linux/arch/unicore32/mm/fault.c
 *
 * Code specific to PKUnity SoC and UniCore ISA
 *
 * Copyright (C) 2001-2010 GUAN Xue-tao
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#include <linux/module.h>
#include <linux/signal.h>
#include <linux/mm.h>
#include <linux/hardirq.h>
#include <linux/init.h>
#include <linux/kprobes.h>
#include <linux/uaccess.h>
#include <linux/page-flags.h>
#include <linux/sched.h>
#include <linux/io.h>

#include <asm/pgtable.h>
#include <asm/tlbflush.h>

/*
 * Fault status register encodings.  We steal bit 31 for our own purposes.
 */
#define FSR_LNX_PF      (1 << 31)

static inline int fsr_fs(unsigned int fsr)
{
    /* xyabcde will be abcde+xy */
    return (fsr & 31) + ((fsr & (3 << 5)) >> 5);
}

/*
 * This is useful to dump out the page tables associated with
 * 'addr' in mm 'mm'.
 */
void show_pte(struct mm_struct *mm, unsigned long addr)
{
    pgd_t *pgd;

    if (!mm)
        mm = &init_mm;

    printk(KERN_ALERT "pgd = %p\n", mm->pgd);
    pgd = pgd_offset(mm, addr);
    printk(KERN_ALERT "[%08lx] *pgd=%08lx", addr, pgd_val(*pgd));

    do {
        pmd_t *pmd;
        pte_t *pte;

        if (pgd_none(*pgd))
            break;

        if (pgd_bad(*pgd)) {
            printk("(bad)");
            break;
        }

        pmd = pmd_offset((pud_t *) pgd, addr);
        if (PTRS_PER_PMD != 1)
            printk(", *pmd=%08lx", pmd_val(*pmd));

        if (pmd_none(*pmd))
            break;

        if (pmd_bad(*pmd)) {
            printk("(bad)");
            break;
        }

        /* We must not map this if we have highmem enabled */
        if (PageHighMem(pfn_to_page(pmd_val(*pmd) >> PAGE_SHIFT)))
            break;

        pte = pte_offset_map(pmd, addr);
        printk(", *pte=%08lx", pte_val(*pte));
        pte_unmap(pte);
    } while (0);

    printk("\n");
}

/*
 * Oops.  The kernel tried to access some page that wasn't present.
 */
static void __do_kernel_fault(struct mm_struct *mm, unsigned long addr,
        unsigned int fsr, struct pt_regs *regs)
{
    /*
     * Are we prepared to handle this kernel fault?
     */
    if (fixup_exception(regs))
        return;

    /*
     * No handler, we'll have to terminate things with extreme prejudice.
     */
    bust_spinlocks(1);
    printk(KERN_ALERT
           "Unable to handle kernel %s at virtual address %08lx\n",
           (addr < PAGE_SIZE) ? "NULL pointer dereference" :
           "paging request", addr);

    show_pte(mm, addr);
    die("Oops", regs, fsr);
    bust_spinlocks(0);
    do_exit(SIGKILL);
}

/*
 * Something tried to access memory that isn't in our memory map..
 * User mode accesses just cause a SIGSEGV
 */
static void __do_user_fault(struct task_struct *tsk, unsigned long addr,
        unsigned int fsr, unsigned int sig, int code,
        struct pt_regs *regs)
{
    struct siginfo si;

    tsk->thread.address = addr;
    tsk->thread.error_code = fsr;
    tsk->thread.trap_no = 14;
    si.si_signo = sig;
    si.si_errno = 0;
    si.si_code = code;
    si.si_addr = (void __user *)addr;
    force_sig_info(sig, &si, tsk);
}

void do_bad_area(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
    struct task_struct *tsk = current;
    struct mm_struct *mm = tsk->active_mm;

    /*
     * If we are in kernel mode at this point, we
     * have no context to handle this fault with.
     */
    if (user_mode(regs))
        __do_user_fault(tsk, addr, fsr, SIGSEGV, SEGV_MAPERR, regs);
    else
        __do_kernel_fault(mm, addr, fsr, regs);
}

#define VM_FAULT_BADMAP     0x010000
#define VM_FAULT_BADACCESS  0x020000

/*
 * Check that the permissions on the VMA allow for the fault which occurred.
 * If we encountered a write fault, we must have write permission, otherwise
 * we allow any permission.
 */
static inline bool access_error(unsigned int fsr, struct vm_area_struct *vma)
{
    unsigned int mask = VM_READ | VM_WRITE | VM_EXEC;

    if (!(fsr ^ 0x12))  /* write? */
        mask = VM_WRITE;
    if (fsr & FSR_LNX_PF)
        mask = VM_EXEC;

    return vma->vm_flags & mask ? false : true;
}

static int __do_pf(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
        unsigned int flags, struct task_struct *tsk)
{
    struct vm_area_struct *vma;
    int fault;

    vma = find_vma(mm, addr);
    fault = VM_FAULT_BADMAP;
    if (unlikely(!vma))
        goto out;
    if (unlikely(vma->vm_start > addr))
        goto check_stack;

    /*
     * Ok, we have a good vm_area for this
     * memory access, so we can handle it.
     */
good_area:
    if (access_error(fsr, vma)) {
        fault = VM_FAULT_BADACCESS;
        goto out;
    }

    /*
     * 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, addr & PAGE_MASK, flags);
    return fault;

check_stack:
    if (vma->vm_flags & VM_GROWSDOWN && !expand_stack(vma, addr))
        goto good_area;
out:
    return fault;
}

static int do_pf(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
    struct task_struct *tsk;
    struct mm_struct *mm;
    int fault, sig, code;
    unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE |
                 ((!(fsr ^ 0x12)) ? FAULT_FLAG_WRITE : 0);

    tsk = current;
    mm = tsk->mm;

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

    /*
     * As per x86, we may deadlock here.  However, since the kernel only
     * validly references user space from well defined areas of the code,
     * we can bug out early if this is from code which shouldn't.
     */
    if (!down_read_trylock(&mm->mmap_sem)) {
        if (!user_mode(regs)
            && !search_exception_tables(regs->UCreg_pc))
            goto no_context;
retry:
        down_read(&mm->mmap_sem);
    } else {
        /*
         * The above down_read_trylock() might have succeeded in
         * which case, we'll have missed the might_sleep() from
         * down_read()
         */
        might_sleep();
#ifdef CONFIG_DEBUG_VM
        if (!user_mode(regs) &&
            !search_exception_tables(regs->UCreg_pc))
            goto no_context;
#endif
    }

    fault = __do_pf(mm, addr, fsr, flags, tsk);

    /* If we need to retry but a fatal signal is pending, handle the
     * signal first. We do not need to release the mmap_sem because
     * it would already be released in __lock_page_or_retry in
     * mm/filemap.c. */
    if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
        return 0;

    if (!(fault & VM_FAULT_ERROR) && (flags & FAULT_FLAG_ALLOW_RETRY)) {
        if (fault & VM_FAULT_MAJOR)
            tsk->maj_flt++;
        else
            tsk->min_flt++;
        if (fault & VM_FAULT_RETRY) {
            /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
            * of starvation. */
            flags &= ~FAULT_FLAG_ALLOW_RETRY;
            goto retry;
        }
    }

    up_read(&mm->mmap_sem);

    /*
     * Handle the "normal" case first - VM_FAULT_MAJOR / VM_FAULT_MINOR
     */
    if (likely(!(fault &
           (VM_FAULT_ERROR | VM_FAULT_BADMAP | VM_FAULT_BADACCESS))))
        return 0;

    if (fault & VM_FAULT_OOM) {
        /*
         * We ran out of memory, call the OOM killer, and return to
         * userspace (which will retry the fault, or kill us if we
         * got oom-killed)
         */
        pagefault_out_of_memory();
        return 0;
    }

    /*
     * If we are in kernel mode at this point, we
     * have no context to handle this fault with.
     */
    if (!user_mode(regs))
        goto no_context;

    if (fault & VM_FAULT_SIGBUS) {
        /*
         * We had some memory, but were unable to
         * successfully fix up this page fault.
         */
        sig = SIGBUS;
        code = BUS_ADRERR;
    } else {
        /*
         * Something tried to access memory that
         * isn't in our memory map..
         */
        sig = SIGSEGV;
        code = fault == VM_FAULT_BADACCESS ? SEGV_ACCERR : SEGV_MAPERR;
    }

    __do_user_fault(tsk, addr, fsr, sig, code, regs);
    return 0;

no_context:
    __do_kernel_fault(mm, addr, fsr, regs);
    return 0;
}

/*
 * First Level Translation Fault Handler
 *
 * We enter here because the first level page table doesn't contain
 * a valid entry for the address.
 *
 * If the address is in kernel space (>= TASK_SIZE), then we are
 * probably faulting in the vmalloc() area.
 *
 * If the init_task's first level page tables contains the relevant
 * entry, we copy the it to this task.  If not, we send the process
 * a signal, fixup the exception, or oops the kernel.
 *
 * 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.
 */
static int do_ifault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
    unsigned int index;
    pgd_t *pgd, *pgd_k;
    pmd_t *pmd, *pmd_k;

    if (addr < TASK_SIZE)
        return do_pf(addr, fsr, regs);

    if (user_mode(regs))
        goto bad_area;

    index = pgd_index(addr);

    pgd = cpu_get_pgd() + index;
    pgd_k = init_mm.pgd + index;

    if (pgd_none(*pgd_k))
        goto bad_area;

    pmd_k = pmd_offset((pud_t *) pgd_k, addr);
    pmd = pmd_offset((pud_t *) pgd, addr);

    if (pmd_none(*pmd_k))
        goto bad_area;

    set_pmd(pmd, *pmd_k);
    flush_pmd_entry(pmd);
    return 0;

bad_area:
    do_bad_area(addr, fsr, regs);
    return 0;
}

/*
 * This abort handler always returns "fault".
 */
static int do_bad(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
    return 1;
}

static int do_good(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
    unsigned int res1, res2;

    printk("dabt exception but no error!\n");

    __asm__ __volatile__(
            "mff %0,f0\n"
            "mff %1,f1\n"
            : "=r"(res1), "=r"(res2)
            :
            : "memory");

    printk(KERN_EMERG "r0 :%08x  r1 :%08x\n", res1, res2);
    panic("shut up\n");
    return 0;
}

static struct fsr_info {
    int (*fn) (unsigned long addr, unsigned int fsr, struct pt_regs *regs);
    int sig;
    int code;
    const char *name;
} fsr_info[] = {
    /*
     * The following are the standard Unicore-I and UniCore-II aborts.
     */
    { do_good,  SIGBUS,  0,     "no error"      },
    { do_bad,   SIGBUS,  BUS_ADRALN,    "alignment exception"   },
    { do_bad,   SIGBUS,  BUS_OBJERR,    "external exception"    },
    { do_bad,   SIGBUS,  0,     "burst operation"   },
    { do_bad,   SIGBUS,  0,     "unknown 00100"     },
    { do_ifault,    SIGSEGV, SEGV_MAPERR,   "2nd level pt non-exist"},
    { do_bad,   SIGBUS,  0,     "2nd lvl large pt non-exist" },
    { do_bad,   SIGBUS,  0,     "invalid pte"       },
    { do_pf,    SIGSEGV, SEGV_MAPERR,   "page miss"     },
    { do_bad,   SIGBUS,  0,     "middle page miss"  },
    { do_bad,   SIGBUS,  0,     "large page miss"   },
    { do_pf,    SIGSEGV, SEGV_MAPERR,   "super page (section) miss" },
    { do_bad,   SIGBUS,  0,     "unknown 01100"     },
    { do_bad,   SIGBUS,  0,     "unknown 01101"     },
    { do_bad,   SIGBUS,  0,     "unknown 01110"     },
    { do_bad,   SIGBUS,  0,     "unknown 01111"     },
    { do_bad,   SIGBUS,  0,     "addr: up 3G or IO" },
    { do_pf,    SIGSEGV, SEGV_ACCERR,   "read unreadable addr"  },
    { do_pf,    SIGSEGV, SEGV_ACCERR,   "write unwriteable addr"},
    { do_pf,    SIGSEGV, SEGV_ACCERR,   "exec unexecutable addr"},
    { do_bad,   SIGBUS,  0,     "unknown 10100"     },
    { do_bad,   SIGBUS,  0,     "unknown 10101"     },
    { do_bad,   SIGBUS,  0,     "unknown 10110"     },
    { do_bad,   SIGBUS,  0,     "unknown 10111"     },
    { do_bad,   SIGBUS,  0,     "unknown 11000"     },
    { do_bad,   SIGBUS,  0,     "unknown 11001"     },
    { do_bad,   SIGBUS,  0,     "unknown 11010"     },
    { do_bad,   SIGBUS,  0,     "unknown 11011"     },
    { do_bad,   SIGBUS,  0,     "unknown 11100"     },
    { do_bad,   SIGBUS,  0,     "unknown 11101"     },
    { do_bad,   SIGBUS,  0,     "unknown 11110"     },
    { do_bad,   SIGBUS,  0,     "unknown 11111"     }
};

void __init hook_fault_code(int nr,
        int (*fn) (unsigned long, unsigned int, struct pt_regs *),
        int sig, int code, const char *name)
{
    if (nr < 0 || nr >= ARRAY_SIZE(fsr_info))
        BUG();

    fsr_info[nr].fn   = fn;
    fsr_info[nr].sig  = sig;
    fsr_info[nr].code = code;
    fsr_info[nr].name = name;
}

/*
 * Dispatch a data abort to the relevant handler.
 */
asmlinkage void do_DataAbort(unsigned long addr, unsigned int fsr,
            struct pt_regs *regs)
{
    const struct fsr_info *inf = fsr_info + fsr_fs(fsr);
    struct siginfo info;

    if (!inf->fn(addr, fsr & ~FSR_LNX_PF, regs))
        return;

    printk(KERN_ALERT "Unhandled fault: %s (0x%03x) at 0x%08lx\n",
           inf->name, fsr, addr);

    info.si_signo = inf->sig;
    info.si_errno = 0;
    info.si_code = inf->code;
    info.si_addr = (void __user *)addr;
    uc32_notify_die("", regs, &info, fsr, 0);
}

asmlinkage void do_PrefetchAbort(unsigned long addr,
            unsigned int ifsr, struct pt_regs *regs)
{
    const struct fsr_info *inf = fsr_info + fsr_fs(ifsr);
    struct siginfo info;

    if (!inf->fn(addr, ifsr | FSR_LNX_PF, regs))
        return;

    printk(KERN_ALERT "Unhandled prefetch abort: %s (0x%03x) at 0x%08lx\n",
           inf->name, ifsr, addr);

    info.si_signo = inf->sig;
    info.si_errno = 0;
    info.si_code = inf->code;
    info.si_addr = (void __user *)addr;
    uc32_notify_die("", regs, &info, ifsr, 0);
}