linux/arch/i386/kernel/ldt.c
Jeremy Fitzhardinge e5e3a04289 [PATCH] i386: remove default_ldt, and simplify ldt-setting.
This patch removes the default_ldt[] array, as it has been unused since
iBCS stopped being supported.  This means it is now possible to actually
set an empty LDT segment.

In order to deal with this, the set_ldt_desc/load_LDT pair has been
replaced with a single set_ldt() operation which is responsible for both
setting up the LDT descriptor in the GDT, and reloading the LDT register.
If there are no LDT entries, the LDT register is loaded with a NULL
descriptor.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Andi Kleen <ak@suse.de>
Acked-by: Zachary Amsden <zach@vmware.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
2006-12-07 02:14:01 +01:00

252 lines
5.1 KiB
C

/*
* linux/arch/i386/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();
load_LDT(pc);
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();
#else
load_LDT(pc);
#endif
}
if (oldsize) {
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);
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;
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();
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;
err = 0;
size = 5*sizeof(struct desc_struct);
if (size > bytecount)
size = bytecount;
err = size;
if (clear_user(ptr, 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:
write_ldt_entry(mm->context.ldt, ldt_info.entry_number, entry_1, entry_2);
error = 0;
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;
}