source: trunk/packages/xen-3.1/xen-3.1/linux-2.6-xen-sparse/arch/i386/kernel/ldt-xen.c @ 34

/*
 * 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 <linux/slab.h>

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

#ifdef CONFIG_SMP /* avoids "defined but not used" warnig */
static void flush_ldt(void *null)
{
        if (current->active_mm)
                load_LDT(&current->active_mm->context);
}
#endif

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

        if (mincount <= pc->size)
                return 0;
        oldsize = pc->size;
        mincount = (mincount+511)&(~511);
        if (mincount*LDT_ENTRY_SIZE > PAGE_SIZE)
                newldt = vmalloc(mincount*LDT_ENTRY_SIZE);
        else
                newldt = kmalloc(mincount*LDT_ENTRY_SIZE, 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);
        pc->ldt = newldt;
        wmb();
        pc->size = mincount;
        wmb();

        if (reload) {
#ifdef CONFIG_SMP
                cpumask_t mask;
                preempt_disable();
#endif
                make_pages_readonly(
                        pc->ldt,
                        (pc->size * LDT_ENTRY_SIZE) / PAGE_SIZE,
                        XENFEAT_writable_descriptor_tables);
                load_LDT(pc);
#ifdef CONFIG_SMP
                mask = cpumask_of_cpu(smp_processor_id());
                if (!cpus_equal(current->mm->cpu_vm_mask, mask))
                        smp_call_function(flush_ldt, NULL, 1, 1);
                preempt_enable();
#endif
        }
        if (oldsize) {
                make_pages_writable(
                        oldldt,
                        (oldsize * LDT_ENTRY_SIZE) / PAGE_SIZE,
                        XENFEAT_writable_descriptor_tables);
                if (oldsize*LDT_ENTRY_SIZE > PAGE_SIZE)
                        vfree(oldldt);
                else
                        kfree(oldldt);
        }
        return 0;
}

static inline int copy_ldt(mm_context_t *new, mm_context_t *old)
{
        int err = alloc_ldt(new, old->size, 0);
        if (err < 0)
                return err;
        memcpy(new->ldt, old->ldt, old->size*LDT_ENTRY_SIZE);
        make_pages_readonly(
                new->ldt,
                (new->size * LDT_ENTRY_SIZE) / PAGE_SIZE,
                XENFEAT_writable_descriptor_tables);
        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;

        init_MUTEX(&mm->context.sem);
        mm->context.size = 0;
        mm->context.has_foreign_mappings = 0;
        old_mm = current->mm;
        if (old_mm && old_mm->context.size > 0) {
                down(&old_mm->context.sem);
                retval = copy_ldt(&mm->context, &old_mm->context);
                up(&old_mm->context.sem);
        }
        return retval;
}

/*
 * No need to lock the MM as we are the last user
 */
void destroy_context(struct mm_struct *mm)
{
        if (mm->context.size) {
                if (mm == current->active_mm)
                        clear_LDT();
                make_pages_writable(
                        mm->context.ldt,
                        (mm->context.size * LDT_ENTRY_SIZE) / PAGE_SIZE,
                        XENFEAT_writable_descriptor_tables);
                if (mm->context.size*LDT_ENTRY_SIZE > PAGE_SIZE)
                        vfree(mm->context.ldt);
                else
                        kfree(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;

        down(&mm->context.sem);
        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;
        up(&mm->context.sem);
        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)
{
        int err;
        unsigned long size;
        void *address;

        err = 0;
        address = &default_ldt[0];
        size = 5*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 __user * ptr, unsigned long bytecount, int oldmode)
{
        struct mm_struct * mm = current->mm;
        __u32 entry_1, entry_2;
        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;
        }

        down(&mm->context.sem);
        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)) {
                        entry_1 = 0;
                        entry_2 = 0;
                        goto install;
                }
        }

        entry_1 = LDT_entry_a(&ldt_info);
        entry_2 = LDT_entry_b(&ldt_info);
        if (oldmode)
                entry_2 &= ~(1 << 20);

        /* Install the new entry ...  */
install:
        error = write_ldt_entry(mm->context.ldt, ldt_info.entry_number,
                                entry_1, entry_2);

out_unlock:
        up(&mm->context.sem);
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;
}