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/*
* 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 <asm/uaccess.h>
#include <asm/system.h>
#include <asm/ldt.h>
#include <asm/desc.h>
/*
* read_ldt() is not really atomic - this is not a problem since
* synchronization of reads and writes done to the LDT has to be
* assured by user-space anyway. Writes are atomic, to protect
* the security checks done on new descriptors.
*/
static int read_ldt(void * ptr, unsigned long bytecount)
{
int err;
unsigned long size;
struct mm_struct * mm = current->mm;
err = 0;
if (!mm->segments)
goto out;
size = LDT_ENTRIES*LDT_ENTRY_SIZE;
if (size > bytecount)
size = bytecount;
err = size;
if (copy_to_user(ptr, mm->segments, size))
err = -EFAULT;
out:
return err;
}
static int write_ldt(void * ptr, unsigned long bytecount, int oldmode)
{
struct mm_struct * mm = current->mm;
__u32 entry_1, entry_2, *lp;
int error;
struct modify_ldt_ldt_s 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;
}
/*
* Horrible dependencies! Try to get rid of this. This is wrong,
* as it only reloads the ldt for the first process with this
* mm. The implications are that you should really make sure that
* you have a ldt before you do the first clone(), otherwise
* you get strange behaviour (the kernel is safe, it's just user
* space strangeness).
*
* we have two choices: either we preallocate the LDT descriptor
* and can do a shared modify_ldt(), or we postallocate it and do
* an smp message pass to update it. Currently we are a bit
* un-nice to user-space and reload the LDT only on the next
* schedule. (only an issue on SMP)
*
* the GDT index of the LDT is allocated dynamically, and is
* limited by MAX_LDT_DESCRIPTORS.
*/
down(&mm->mmap_sem);
if (!mm->segments) {
error = -ENOMEM;
mm->segments = vmalloc(LDT_ENTRIES*LDT_ENTRY_SIZE);
if (!mm->segments)
goto out_unlock;
if (atomic_read(&mm->mm_users) > 1)
printk(KERN_WARNING "LDT allocated for cloned task!\n");
/*
* Possibly do an SMP cross-call to other CPUs to reload
* their LDTs?
*/
load_LDT(mm);
}
lp = (__u32 *) ((ldt_info.entry_number << 3) + (char *) mm->segments);
/* Allow LDTs to be cleared by the user. */
if (ldt_info.base_addr == 0 && ldt_info.limit == 0) {
if (oldmode ||
(ldt_info.contents == 0 &&
ldt_info.read_exec_only == 1 &&
ldt_info.seg_32bit == 0 &&
ldt_info.limit_in_pages == 0 &&
ldt_info.seg_not_present == 1 &&
ldt_info.useable == 0 )) {
entry_1 = 0;
entry_2 = 0;
goto install;
}
}
entry_1 = ((ldt_info.base_addr & 0x0000ffff) << 16) |
(ldt_info.limit & 0x0ffff);
entry_2 = (ldt_info.base_addr & 0xff000000) |
((ldt_info.base_addr & 0x00ff0000) >> 16) |
(ldt_info.limit & 0xf0000) |
((ldt_info.read_exec_only ^ 1) << 9) |
(ldt_info.contents << 10) |
((ldt_info.seg_not_present ^ 1) << 15) |
(ldt_info.seg_32bit << 22) |
(ldt_info.limit_in_pages << 23) |
0x7000;
if (!oldmode)
entry_2 |= (ldt_info.useable << 20);
/* Install the new entry ... */
install:
*lp = entry_1;
*(lp+1) = entry_2;
error = 0;
out_unlock:
up(&mm->mmap_sem);
out:
return error;
}
asmlinkage int sys_modify_ldt(int func, void *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 0x11:
ret = write_ldt(ptr, bytecount, 0);
break;
}
return ret;
}
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