WORD SetupLDT(WORD seg, DWORD ldtbase)
{
LDT_ENTRY EvilLdt;
DWORD base = ldtbase;
DWORD limit = 0;
int ret;
EvilLdt.BaseLow = base & 0xFFFF;
EvilLdt.HighWord.Bytes.BaseMid = base >> 16;
EvilLdt.HighWord.Bytes.BaseHi = base >> 24;
EvilLdt.LimitLow = (limit >> 12) & 0xFFFF;
EvilLdt.HighWord.Bits.LimitHi = limit >> 28;
EvilLdt.HighWord.Bits.Granularity = 1; // 0/1, if 1, limit=(limit<<12)|FFF
EvilLdt.HighWord.Bits.Default_Big = 1; // 0=16bit 1=32bit
EvilLdt.HighWord.Bits.Reserved_0 = 0; // 0/1
EvilLdt.HighWord.Bits.Sys = 0; // 0/1
EvilLdt.HighWord.Bits.Pres = 1; // 0/1 (presence bit)
EvilLdt.HighWord.Bits.Dpl = 3; // only 3 allowed :-(
EvilLdt.HighWord.Bits.Type = 23; // [16..27]
ret = NtSetLdtEntries( seg,
*(DWORD*)&EvilLdt,
*(((DWORD*)&EvilLdt)+1),
0,0,0);
if (ret < 0) {
printf("[-] Set ldt error : %08X.\n", ret);
exit(0);
}
return seg;
}
NTSTATUS Dirtbox::AllocateLdtEntry(PWORD Selector, DWORD Base, DWORD LimitSize)
{
DWORD Limit = Base + LimitSize;
LDT_ENTRY LdtEntry;
EnterCriticalSection(&ThreadingLock);
// Locate a free LDT entry
int i;
for(i = 0; i < MAXIMUM_XBOX_THREADS; i++)
if(FreeDescriptors[i])
break;
if(i == MAXIMUM_XBOX_THREADS)
{
LeaveCriticalSection(&ThreadingLock);
DebugPrint("AllocateLdtEntry: Could not locate free LDT entry.");
return STATUS_TOO_MANY_THREADS;
}
// Set up selector information
LdtEntry.BaseLow = (WORD)(Base & 0xFFFF);
LdtEntry.HighWord.Bits.BaseMid = (Base >> 16) & 0xFF;
LdtEntry.HighWord.Bits.BaseHi = (Base >> 24) & 0xFF;
LdtEntry.HighWord.Bits.Type = 0x13; // RW data segment
LdtEntry.HighWord.Bits.Dpl = 3; // user segment
LdtEntry.HighWord.Bits.Pres = 1; // present
LdtEntry.HighWord.Bits.Sys = 0;
LdtEntry.HighWord.Bits.Reserved_0 = 0;
LdtEntry.HighWord.Bits.Default_Big = 1; // 386 segment
LdtEntry.HighWord.Bits.Granularity = 0; // byte-level granularity
LdtEntry.LimitLow = (WORD)(Limit & 0xFFFF);
LdtEntry.HighWord.Bits.LimitHi = (Limit >> 16) & 0xF;
WORD Sel = ((i + 1) << 3) | 0x7;
// Allocate selector
NTSTATUS Res = NtSetLdtEntries(Sel, LdtEntry, 0, 0, 0);
if(!NT_SUCCESS(Res))
{
LeaveCriticalSection(&ThreadingLock);
DebugPrint("AllocateLdtEntry: Could not set LDT entries.");
return Res;
}
FreeDescriptors[i] = FALSE;
*Selector = Sel;
LeaveCriticalSection(&ThreadingLock);
return STATUS_SUCCESS;
}
NTSTATUS Dirtbox::FreeLdtEntry(WORD Selector)
{
LDT_ENTRY LdtEntry;
EnterCriticalSection(&ThreadingLock);
memset(&LdtEntry, 0, sizeof(LDT_ENTRY));
NTSTATUS Res = NtSetLdtEntries(Selector, LdtEntry, 0, 0, 0);
if (!NT_SUCCESS(Res))
{
LeaveCriticalSection(&ThreadingLock);
DebugPrint("FreeLdtEntry: Could not set LDT entries.");
return Res;
}
FreeDescriptors[(Selector >> 3)-1] = TRUE;
LeaveCriticalSection(&ThreadingLock);
return STATUS_SUCCESS;
}
