/*
 * linux/kernel/ldt.c
 *
 * Copyright (C) 1992 Krishna Balasubramanian and Linus Torvalds
 * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
 */

#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/smp_lock.h>
#include <linux/vmalloc.h>

#include <asm/uaccess.h>
#include <asm/system.h>
#include <asm/ldt.h>
#include <asm/desc.h>

/*
 * read_ldt() is not really atomic - this is not a problem since
 * synchronization of reads and writes done to the LDT has to be
 * assured by user-space anyway. Writes are atomic, to protect
 * the security checks done on new descriptors.
 */
static int read_ldt(void * ptr, unsigned long bytecount)
{
    int err;
    unsigned long size;
    struct mm_struct * mm = current->mm;

    err = 0;
    if (!mm->context.segments)
        goto out;

    size = LDT_ENTRIES*LDT_ENTRY_SIZE;
    if (size > bytecount)
        size = bytecount;

    err = size;
    if (copy_to_user(ptr, mm->context.segments, size))
        err = -EFAULT;
 out:
    return err;
}

static int read_default_ldt(void * ptr, unsigned long bytecount)
{
    int err;
    unsigned long size;
    void *address;

    err = 0;
    address = &default_ldt[0];
    size = sizeof(struct desc_struct);
    if (size > bytecount)
        size = bytecount;

    err = size;
    if (copy_to_user(ptr, address, size))
        err = -EFAULT;

    return err;
}

static int write_ldt(void * ptr, unsigned long bytecount, int oldmode)
{
    struct mm_struct * mm = current->mm;
    __u32 entry_1, entry_2, *lp;
    unsigned long phys_lp, max_limit;
    int error;
    struct modify_ldt_ldt_s ldt_info;

    error = -EINVAL;
    if (bytecount != sizeof(ldt_info))
        goto out;
    error = -EFAULT; 	
    if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
        goto out;

    error = -EINVAL;
    if (ldt_info.entry_number >= LDT_ENTRIES)
        goto out;
    if (ldt_info.contents == 3) {
        if (oldmode)
            goto out;
        if (ldt_info.seg_not_present == 0)
            goto out;
    }

    /*
     * This makes our tests for overlap with Xen space easier. There's no good
     * reason to have a user segment starting this high anyway.
     */
    if (ldt_info.base_addr >= PAGE_OFFSET)
        goto out;

    down_write(&mm->mmap_sem);
    if (!mm->context.segments) {
        void * segments = vmalloc(LDT_ENTRIES*LDT_ENTRY_SIZE);
        error = -ENOMEM;
        if (!segments)
            goto out_unlock;
        memset(segments, 0, LDT_ENTRIES*LDT_ENTRY_SIZE);
        make_pages_readonly(segments, (LDT_ENTRIES*LDT_ENTRY_SIZE)/PAGE_SIZE);
        wmb();
        mm->context.segments = segments;
        mm->context.cpuvalid = 1UL << smp_processor_id();
        load_LDT(mm);
        flush_page_update_queue();
    }

    lp = (__u32 *)((ldt_info.entry_number<<3) + (char *)mm->context.segments);
    phys_lp = arbitrary_virt_to_phys(lp);

    /* Allow LDTs to be cleared by the user. */
    if (ldt_info.base_addr == 0 && ldt_info.limit == 0) {
        if (oldmode ||
            (ldt_info.contents == 0		&&
             ldt_info.read_exec_only == 1	&&
             ldt_info.seg_32bit == 0		&&
             ldt_info.limit_in_pages == 0	&&
             ldt_info.seg_not_present == 1	&&
             ldt_info.useable == 0 )) {
            entry_1 = 0;
            entry_2 = 0;
            goto install;
        }
    }

    max_limit = HYPERVISOR_VIRT_START - ldt_info.base_addr;
    if ( ldt_info.limit_in_pages )
        max_limit >>= PAGE_SHIFT;
    max_limit--;
    if ( (ldt_info.limit & 0xfffff) > (max_limit & 0xfffff) )
        ldt_info.limit = max_limit;

    entry_1 = ((ldt_info.base_addr & 0x0000ffff) << 16) |
        (ldt_info.limit & 0x0ffff);
    entry_2 = (ldt_info.base_addr & 0xff000000) |
        ((ldt_info.base_addr & 0x00ff0000) >> 16) |
        (ldt_info.limit & 0xf0000) |
        ((ldt_info.read_exec_only ^ 1) << 9) |
        (ldt_info.contents << 10) |
        ((ldt_info.seg_not_present ^ 1) << 15) |
        (ldt_info.seg_32bit << 22) |
        (ldt_info.limit_in_pages << 23) |
        0x7000;
    if (!oldmode)
        entry_2 |= (ldt_info.useable << 20);

    /* Install the new entry ...  */
 install:
    error = HYPERVISOR_update_descriptor(phys_lp, entry_1, entry_2);

 out_unlock:
    up_write(&mm->mmap_sem);
 out:
    return error;
}

asmlinkage int sys_modify_ldt(int func, void *ptr, unsigned long bytecount)
{
    int ret = -ENOSYS;

    switch (func) {
    case 0:
        ret = read_ldt(ptr, bytecount);
        break;
    case 1:
        ret = write_ldt(ptr, bytecount, 1);
        break;
    case 2:
        ret = read_default_ldt(ptr, bytecount);
        break;
    case 0x11:
        ret = write_ldt(ptr, bytecount, 0);
        break;
    }
    return ret;
}