ldt.c

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/*
 * Copyright (C) 1992 Krishna Balasubramanian and Linus Torvalds
 * Copyright (C) 1999 Ingo Molnar <[email protected]>
 * Copyright (C) 2002 Andi Kleen
 *
 * This handles calls from both 32bit and 64bit mode.
 */

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

#include <asm/ldt.h>
#include <asm/desc.h>
#include <asm/mmu_context.h>
#include <asm/syscalls.h>

#ifdef CONFIG_SMP
static void flush_ldt(void *current_mm)
{
    if (current->active_mm == current_mm)
        load_LDT(&current->active_mm->context);
}
#endif

static int alloc_ldt(mm_context_t *pc, int mincount, int reload)
{
    void *oldldt, *newldt;
    int oldsize;

    if (mincount <= pc->size)
        return 0;
    oldsize = pc->size;
    mincount = (mincount + (PAGE_SIZE / LDT_ENTRY_SIZE - 1)) &
            (~(PAGE_SIZE / LDT_ENTRY_SIZE - 1));
    if (mincount * LDT_ENTRY_SIZE > PAGE_SIZE)
        newldt = vmalloc(mincount * LDT_ENTRY_SIZE);
    else
        newldt = (void *)__get_free_page(GFP_KERNEL);

    if (!newldt)
        return -ENOMEM;

    if (oldsize)
        memcpy(newldt, pc->ldt, oldsize * LDT_ENTRY_SIZE);
    oldldt = pc->ldt;
    memset(newldt + oldsize * LDT_ENTRY_SIZE, 0,
           (mincount - oldsize) * LDT_ENTRY_SIZE);

    paravirt_alloc_ldt(newldt, mincount);

#ifdef CONFIG_X86_64
    /* CHECKME: Do we really need this ? */
    wmb();
#endif
    pc->ldt = newldt;
    wmb();
    pc->size = mincount;
    wmb();

    if (reload) {
#ifdef CONFIG_SMP
        preempt_disable();
        load_LDT(pc);
        if (!cpumask_equal(mm_cpumask(current->mm),
                   cpumask_of(smp_processor_id())))
            smp_call_function(flush_ldt, current->mm, 1);
        preempt_enable();
#else
        load_LDT(pc);
#endif
    }
    if (oldsize) {
        paravirt_free_ldt(oldldt, oldsize);
        if (oldsize * LDT_ENTRY_SIZE > PAGE_SIZE)
            vfree(oldldt);
        else
            put_page(virt_to_page(oldldt));
    }
    return 0;
}

static inline int copy_ldt(mm_context_t *new, mm_context_t *old)
{
    int err = alloc_ldt(new, old->size, 0);
    int i;

    if (err < 0)
        return err;

    for (i = 0; i < old->size; i++)
        write_ldt_entry(new->ldt, i, old->ldt + i * LDT_ENTRY_SIZE);
    return 0;
}

/*
 * we do not have to muck with descriptors here, that is
 * done in switch_mm() as needed.
 */
int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
{
    struct mm_struct *old_mm;
    int retval = 0;

    mutex_init(&mm->context.lock);
    mm->context.size = 0;
    old_mm = current->mm;
    if (old_mm && old_mm->context.size > 0) {
        mutex_lock(&old_mm->context.lock);
        retval = copy_ldt(&mm->context, &old_mm->context);
        mutex_unlock(&old_mm->context.lock);
    }
    return retval;
}

/*
 * No need to lock the MM as we are the last user
 *
 * 64bit: Don't touch the LDT register - we're already in the next thread.
 */
void destroy_context(struct mm_struct *mm)
{
    if (mm->context.size) {
#ifdef CONFIG_X86_32
        /* CHECKME: Can this ever happen ? */
        if (mm == current->active_mm)
            clear_LDT();
#endif
        paravirt_free_ldt(mm->context.ldt, mm->context.size);
        if (mm->context.size * LDT_ENTRY_SIZE > PAGE_SIZE)
            vfree(mm->context.ldt);
        else
            put_page(virt_to_page(mm->context.ldt));
        mm->context.size = 0;
    }
}

static int read_ldt(void __user *ptr, unsigned long bytecount)
{
    int err;
    unsigned long size;
    struct mm_struct *mm = current->mm;

    if (!mm->context.size)
        return 0;
    if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
        bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;

    mutex_lock(&mm->context.lock);
    size = mm->context.size * LDT_ENTRY_SIZE;
    if (size > bytecount)
        size = bytecount;

    err = 0;
    if (copy_to_user(ptr, mm->context.ldt, size))
        err = -EFAULT;
    mutex_unlock(&mm->context.lock);
    if (err < 0)
        goto error_return;
    if (size != bytecount) {
        /* zero-fill the rest */
        if (clear_user(ptr + size, bytecount - size) != 0) {
            err = -EFAULT;
            goto error_return;
        }
    }
    return bytecount;
error_return:
    return err;
}

static int read_default_ldt(void __user *ptr, unsigned long bytecount)
{
    /* CHECKME: Can we use _one_ random number ? */
#ifdef CONFIG_X86_32
    unsigned long size = 5 * sizeof(struct desc_struct);
#else
    unsigned long size = 128;
#endif
    if (bytecount > size)
        bytecount = size;
    if (clear_user(ptr, bytecount))
        return -EFAULT;
    return bytecount;
}

static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
{
    struct mm_struct *mm = current->mm;
    struct desc_struct ldt;
    int error;
    struct user_desc 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;
    }

    mutex_lock(&mm->context.lock);
    if (ldt_info.entry_number >= mm->context.size) {
        error = alloc_ldt(&current->mm->context,
                  ldt_info.entry_number + 1, 1);
        if (error < 0)
            goto out_unlock;
    }

    /* Allow LDTs to be cleared by the user. */
    if (ldt_info.base_addr == 0 && ldt_info.limit == 0) {
        if (oldmode || LDT_empty(&ldt_info)) {
            memset(&ldt, 0, sizeof(ldt));
            goto install;
        }
    }

    fill_ldt(&ldt, &ldt_info);
    if (oldmode)
        ldt.avl = 0;

    /* Install the new entry ...  */
install:
    write_ldt_entry(mm->context.ldt, ldt_info.entry_number, &ldt);
    error = 0;

out_unlock:
    mutex_unlock(&mm->context.lock);
out:
    return error;
}

asmlinkage int sys_modify_ldt(int func, void __user *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;
}