root/arch/x86/kernel/ldt.c

DEFINITIONS

1. flush_ldt
2. alloc_ldt
3. copy_ldt
4. init_new_context
5. destroy_context
6. read_ldt
7. read_default_ldt
8. write_ldt
9. sys_modify_ldt

/*
 * Copyright (C) 1992 Krishna Balasubramanian and Linus Torvalds
 * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
 * Copyright (C) 2002 Andi Kleen
 *
 * This handles calls from both 32bit and 64bit mode.
 */

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

#include <asm/uaccess.h>
#include <asm/system.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 (!cpus_equal(current->mm->cpu_vm_mask,
                                cpumask_of_cpu(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;
}