extable.c

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#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/sort.h>
#include <asm/uaccess.h>

static inline unsigned long
ex_insn_addr(const struct exception_table_entry *x)
{
    return (unsigned long)&x->insn + x->insn;
}
static inline unsigned long
ex_fixup_addr(const struct exception_table_entry *x)
{
    return (unsigned long)&x->fixup + x->fixup;
}

int fixup_exception(struct pt_regs *regs)
{
    const struct exception_table_entry *fixup;
    unsigned long new_ip;

#ifdef CONFIG_PNPBIOS
    if (unlikely(SEGMENT_IS_PNP_CODE(regs->cs))) {
        extern u32 pnp_bios_fault_eip, pnp_bios_fault_esp;
        extern u32 pnp_bios_is_utter_crap;
        pnp_bios_is_utter_crap = 1;
        printk(KERN_CRIT "PNPBIOS fault.. attempting recovery.\n");
        __asm__ volatile(
            "movl %0, %%esp\n\t"
            "jmp *%1\n\t"
            : : "g" (pnp_bios_fault_esp), "g" (pnp_bios_fault_eip));
        panic("do_trap: can't hit this");
    }
#endif

    fixup = search_exception_tables(regs->ip);
    if (fixup) {
        new_ip = ex_fixup_addr(fixup);

        if (fixup->fixup - fixup->insn >= 0x7ffffff0 - 4) {
            /* Special hack for uaccess_err */
            current_thread_info()->uaccess_err = 1;
            new_ip -= 0x7ffffff0;
        }
        regs->ip = new_ip;
        return 1;
    }

    return 0;
}

/* Restricted version used during very early boot */
int __init early_fixup_exception(unsigned long *ip)
{
    const struct exception_table_entry *fixup;
    unsigned long new_ip;

    fixup = search_exception_tables(*ip);
    if (fixup) {
        new_ip = ex_fixup_addr(fixup);

        if (fixup->fixup - fixup->insn >= 0x7ffffff0 - 4) {
            /* uaccess handling not supported during early boot */
            return 0;
        }

        *ip = new_ip;
        return 1;
    }

    return 0;
}

/*
 * Search one exception table for an entry corresponding to the
 * given instruction address, and return the address of the entry,
 * or NULL if none is found.
 * We use a binary search, and thus we assume that the table is
 * already sorted.
 */
const struct exception_table_entry *
search_extable(const struct exception_table_entry *first,
           const struct exception_table_entry *last,
           unsigned long value)
{
    while (first <= last) {
        const struct exception_table_entry *mid;
        unsigned long addr;

        mid = ((last - first) >> 1) + first;
        addr = ex_insn_addr(mid);
        if (addr < value)
            first = mid + 1;
        else if (addr > value)
            last = mid - 1;
        else
            return mid;
        }
        return NULL;
}

/*
 * The exception table needs to be sorted so that the binary
 * search that we use to find entries in it works properly.
 * This is used both for the kernel exception table and for
 * the exception tables of modules that get loaded.
 *
 */
static int cmp_ex(const void *a, const void *b)
{
    const struct exception_table_entry *x = a, *y = b;

    /*
     * This value will always end up fittin in an int, because on
     * both i386 and x86-64 the kernel symbol-reachable address
     * space is < 2 GiB.
     *
     * This compare is only valid after normalization.
     */
    return x->insn - y->insn;
}

void sort_extable(struct exception_table_entry *start,
          struct exception_table_entry *finish)
{
    struct exception_table_entry *p;
    int i;

    /* Convert all entries to being relative to the start of the section */
    i = 0;
    for (p = start; p < finish; p++) {
        p->insn += i;
        i += 4;
        p->fixup += i;
        i += 4;
    }

    sort(start, finish - start, sizeof(struct exception_table_entry),
         cmp_ex, NULL);

    /* Denormalize all entries */
    i = 0;
    for (p = start; p < finish; p++) {
        p->insn -= i;
        i += 4;
        p->fixup -= i;
        i += 4;
    }
}

#ifdef CONFIG_MODULES
/*
 * If the exception table is sorted, any referring to the module init
 * will be at the beginning or the end.
 */
void trim_init_extable(struct module *m)
{
    /*trim the beginning*/
    while (m->num_exentries &&
           within_module_init(ex_insn_addr(&m->extable[0]), m)) {
        m->extable++;
        m->num_exentries--;
    }
    /*trim the end*/
    while (m->num_exentries &&
           within_module_init(ex_insn_addr(&m->extable[m->num_exentries-1]), m))
        m->num_exentries--;
}
#endif /* CONFIG_MODULES */