user_fixup.c

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/* user_fixup.c: Fix up user copy faults.
 *
 * Copyright (C) 2004 David S. Miller <[email protected]>
 */

#include <linux/compiler.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/errno.h>
#include <linux/module.h>

#include <asm/uaccess.h>

/* Calculating the exact fault address when using
 * block loads and stores can be very complicated.
 *
 * Instead of trying to be clever and handling all
 * of the cases, just fix things up simply here.
 */

static unsigned long compute_size(unsigned long start, unsigned long size, unsigned long *offset)
{
    unsigned long fault_addr = current_thread_info()->fault_address;
    unsigned long end = start + size;

    if (fault_addr < start || fault_addr >= end) {
        *offset = 0;
    } else {
        *offset = fault_addr - start;
        size = end - fault_addr;
    }
    return size;
}

unsigned long copy_from_user_fixup(void *to, const void __user *from, unsigned long size)
{
    unsigned long offset;

    size = compute_size((unsigned long) from, size, &offset);
    if (likely(size))
        memset(to + offset, 0, size);

    return size;
}
EXPORT_SYMBOL(copy_from_user_fixup);

unsigned long copy_to_user_fixup(void __user *to, const void *from, unsigned long size)
{
    unsigned long offset;

    return compute_size((unsigned long) to, size, &offset);
}
EXPORT_SYMBOL(copy_to_user_fixup);

unsigned long copy_in_user_fixup(void __user *to, void __user *from, unsigned long size)
{
    unsigned long fault_addr = current_thread_info()->fault_address;
    unsigned long start = (unsigned long) to;
    unsigned long end = start + size;

    if (fault_addr >= start && fault_addr < end)
        return end - fault_addr;

    start = (unsigned long) from;
    end = start + size;
    if (fault_addr >= start && fault_addr < end)
        return end - fault_addr;

    return size;
}
EXPORT_SYMBOL(copy_in_user_fixup);