VOID DriveMapInstallInt13Handler(PDRIVE_MAP_LIST DriveMap)
{
ULONG* RealModeIVT = (ULONG*)0x00000000;
USHORT* BiosLowMemorySize = (USHORT*)0x00000413;
if (!DriveMapInstalled)
{
// Get the old INT 13h handler address from the vector table
OldInt13HandlerAddress = RealModeIVT[0x13];
// Decrease the size of low memory
(*BiosLowMemorySize)--;
// Get linear address for drive map handler
DriveMapHandlerAddress = (ULONG)(*BiosLowMemorySize) << 10;
// Convert to segment:offset style address
DriveMapHandlerSegOff = (DriveMapHandlerAddress << 12) & 0xffff0000;
}
// Copy the drive map structure to the proper place
RtlCopyMemory(&DriveMapInt13HandlerMapList, DriveMap, sizeof(DRIVE_MAP_LIST));
// Set the address of the BIOS INT 13h handler
DriveMapOldInt13HandlerAddress = OldInt13HandlerAddress;
// Copy the code to our reserved area
RtlCopyMemory((PVOID)DriveMapHandlerAddress, &DriveMapInt13HandlerStart, ((ULONG)&DriveMapInt13HandlerEnd - (ULONG)&DriveMapInt13HandlerStart));
// Update the IVT
RealModeIVT[0x13] = DriveMapHandlerSegOff;
CacheInvalidateCacheData();
DriveMapInstalled = TRUE;
}
VOID DriveMapRemoveInt13Handler(VOID)
{
ULONG* RealModeIVT = (ULONG*)0x00000000;
USHORT* BiosLowMemorySize = (USHORT*)0x00000413;
if (DriveMapInstalled)
{
// Get the old INT 13h handler address from the vector table
RealModeIVT[0x13] = OldInt13HandlerAddress;
// Increase the size of low memory
(*BiosLowMemorySize)++;
CacheInvalidateCacheData();
DriveMapInstalled = FALSE;
}
}
