linux/arch/x86/kernel/ldt.c

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/*
* 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>
#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);
#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) {
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);
if (err < 0)
return err;
memcpy(new->ldt, old->ldt, old->size * 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
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;
}