/*
 *  ReactOS kernel
 *  Copyright (C) 2000  ReactOS Team
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
/*
 * PROJECT:         ReactOS kernel
 * FILE:            ntoskrnl/ke/i386/ldt.c
 * PURPOSE:         LDT managment
 * PROGRAMMER:      David Welch (welch@cwcom.net)
 * UPDATE HISTORY:
 *                  Created 22/05/98
 */

/* INCLUDES *****************************************************************/

#include <ddk/ntddk.h>
#include <internal/ke.h>
#include <internal/ps.h>
#include <internal/i386/segment.h>

#define NDEBUG
#include <internal/debug.h>

/* GLOBALS *******************************************************************/

static KSPIN_LOCK LdtLock;

/* FUNCTIONS *****************************************************************/

BOOL PspIsDescriptorValid(PLDT_ENTRY ldt_entry)
{
  ULONG Base, SegLimit;
  /* 
     Allow invalid descriptors.
  */
  if(!ldt_entry->HighWord.Bits.Type &&
     !ldt_entry->HighWord.Bits.Dpl)
       return TRUE;

  /* eliminate system descriptors and code segments other than
     execute and execute/read and DPL<3 descriptors */
  if(!(ldt_entry->HighWord.Bits.Type & 0x10) ||
     (ldt_entry->HighWord.Bits.Type & 0x8 &&
      ldt_entry->HighWord.Bits.Type & 0x4) ||
     ldt_entry->HighWord.Bits.Dpl != 3 ||
     ldt_entry->HighWord.Bits.Reserved_0) return FALSE;

  if(!ldt_entry->HighWord.Bits.Pres) return TRUE;

  Base=ldt_entry->BaseLow | (ldt_entry->HighWord.Bytes.BaseMid << 16) |
             (ldt_entry->HighWord.Bytes.BaseHi << 24);

  SegLimit=ldt_entry->LimitLow |
                 (ldt_entry->HighWord.Bits.LimitHi << 16);

  if(ldt_entry->HighWord.Bits.Type & 0x4)
  {
    SegLimit=(ldt_entry->HighWord.Bits.Default_Big) ? -1 : (USHORT)-1;

  } else if(ldt_entry->HighWord.Bits.Granularity)
  {
    SegLimit=(SegLimit << 12) | 0xfff;
  }

  return ((Base + SegLimit > (ULONG) MmHighestUserAddress) ||
          (Base > Base+SegLimit) ? FALSE : TRUE);
}

NTSTATUS STDCALL
NtSetLdtEntries (ULONG Selector1,
		 LDT_ENTRY LdtEntry1,
		 ULONG Selector2,
		 LDT_ENTRY LdtEntry2)
{
  KIRQL oldIrql;
  ULONG NewLdtSize = sizeof(LDT_ENTRY);
  PUSHORT LdtDescriptor;
  ULONG LdtBase;
  ULONG LdtLimit;

  if((Selector1 & ~0xffff) || (Selector2 & ~0xffff)) return STATUS_INVALID_LDT_DESCRIPTOR;

  Selector1 &= ~0x7;
  Selector2 &= ~0x7;

  if((Selector1 && !PspIsDescriptorValid(&LdtEntry1)) ||
     (Selector2 && !PspIsDescriptorValid(&LdtEntry2))) return STATUS_INVALID_LDT_DESCRIPTOR;
  if(!(Selector1 || Selector2)) return STATUS_SUCCESS;

  NewLdtSize += (Selector1 >= Selector2) ? Selector1 : Selector2;

  KeAcquireSpinLock(&LdtLock, &oldIrql);

  LdtDescriptor = (PUSHORT) &KeGetCurrentProcess()->LdtDescriptor[0];
  LdtBase = LdtDescriptor[1] |
                  ((LdtDescriptor[2] & 0xff) << 16) |
                  ((LdtDescriptor[3] & ~0xff) << 16);
  LdtLimit = LdtDescriptor[0] |
                   ((LdtDescriptor[3] & 0xf) << 16);

  if(LdtLimit < (NewLdtSize - 1))
  {
    /* allocate new ldt, copy old one there, set gdt ldt entry to new
       values and load ldtr register and free old ldt */

    ULONG NewLdtBase = (ULONG) ExAllocatePool(NonPagedPool,
                                              NewLdtSize);

    if(!NewLdtBase)
    {
      KeReleaseSpinLock(&LdtLock, oldIrql);
      return STATUS_INSUFFICIENT_RESOURCES;
    }

    if(LdtBase)
    {
      memcpy((PVOID) NewLdtBase, (PVOID) LdtBase, LdtLimit+1);
    }

    LdtDescriptor[0] = (--NewLdtSize) & 0xffff;
    LdtDescriptor[1] = NewLdtBase & 0xffff;
    LdtDescriptor[2] = ((NewLdtBase & 0xff0000) >> 16) | 0x8200;
    LdtDescriptor[3] = ((NewLdtSize & 0xf0000) >> 16) |
                       ((NewLdtBase & 0xff000000) >> 16);

    KeSetGdtSelector(LDT_SELECTOR,
                     ((PULONG) LdtDescriptor)[0],
                     ((PULONG) LdtDescriptor)[1]);

    __asm__("lldtw %%ax" 
            : /* no output */
            : "a" (LDT_SELECTOR));

    if(LdtBase)
    {
      ExFreePool((PVOID) LdtBase);
    }

    LdtBase = NewLdtBase;
  }

  if(Selector1)
  {
    memcpy((PVOID) LdtBase + Selector1,
           &LdtEntry1,
           sizeof(LDT_ENTRY));
  }

  if(Selector2)
  {
    memcpy((PVOID) LdtBase + Selector2,
           &LdtEntry2,
           sizeof(LDT_ENTRY));
  }

  KeReleaseSpinLock(&LdtLock, oldIrql);
  return STATUS_SUCCESS;
}

VOID
Ki386InitializeLdt(VOID)
{
  PUSHORT Gdt = KeGetCurrentKPCR()->GDT;
  unsigned int base, length;

  /*
   * Set up an a descriptor for the LDT
   */
  base = length = 0;
  
  Gdt[(LDT_SELECTOR / 2) + 0] = (length & 0xFFFF);
  Gdt[(LDT_SELECTOR / 2) + 1] = (base & 0xFFFF);
  Gdt[(LDT_SELECTOR / 2) + 2] = ((base & 0xFF0000) >> 16) | 0x8200;
  Gdt[(LDT_SELECTOR / 2) + 3] = ((length & 0xF0000) >> 16) |
    ((base & 0xFF000000) >> 16);
}