//-------------------------------------------------------------------
//	iokludge.c
//
//	This module installs a 'workaround' for the x86_64 kernel's 
//	prohibition against access to x86 I/O ports by unprivileged 
//	applications.  It achieves this by installing a new handler 
//	for the 'obsolete' (and otherwise unused) exception 9 which   
//	an application may invoke without privilege restrictions if
//	the software interrupt instruction 'int $0x09' is executed.
//	(This is easy to accomplish with inline assembly language.)
//	The new exception-handler merely sets the IOPL-field in the 
//	RFLAGS register to 3, permitting 'in' and 'out' to execute.
//	The original handler is restored as this module is removed. 
//
//	     	to compile:  $ mmake iokludge.c
//	     	to install:  $ /sbin/insmod iokludge.ko
//		and remove:  $ /sbin/rmmod iokludge
//
//	NOTE: This code was written and tested for kernel 2.6.26.6.
//
//	programmer: ALLAN CRUSE
//	written on: 17 APR 2009
//-------------------------------------------------------------------

#include <linux/module.h>	// for module_init(), module_exit()

#define INT_ID		9	// this IDT-entry is no longer used  

typedef struct	{ long	lo, hi; } GATE_DESCRIPTOR;

char modname[] = "iokludge";
unsigned short 	oldidtr[5], newidtr[5];
GATE_DESCRIPTOR	*oldidt, *newidt;
unsigned long	kpage;

void load_IDTR( void *regimage )
{
	asm(" lidtq %0 " : : "m" (*(unsigned short*)regimage) );
}

//--------  INTERRUPT SERVICE ROUTINE  ------------
void isr_entry( void );
asm("	.text					");
asm("	.type	isr_entry, @function		");
asm("isr_entry:					");
asm("	orq	$0x3000, 16(%rsp)		");
asm("	iretq					");
//-------------------------------------------------

static int __init iokludge_init( void )
{
	GATE_DESCRIPTOR	oldgate, newgate;
	long long	isrlocn;

	printk( "<1>\nInstalling \'%s\' module\n", modname );

	// allocate kernel memory for a new Interrupt Descriptor Table
	kpage = get_zeroed_page( GFP_KERNEL );
	if ( !kpage ) return -ENOMEM;

	// initialize our module's global variables
	asm(" sidtq oldidtr \n sidtq newidtr ");
	memcpy( newidtr+1, &kpage, sizeof( unsigned long ) );
	oldidt = (GATE_DESCRIPTOR*)(*(unsigned long*)(oldidtr+1));
	newidt = (GATE_DESCRIPTOR*)(*(unsigned long*)(newidtr+1));
	memcpy( newidt, oldidt, 256 * sizeof( GATE_DESCRIPTOR ) );

	// setup our Interrupt Gate 
	isrlocn = (long long)isr_entry;
	oldgate = oldidt[ INT_ID ];
	oldgate.lo &= 0x0000FFFFFFFF0000L;	
	newgate.hi = (isrlocn >> 32);
	newgate.hi &= 0x00000000FFFFFFFFL;
	newgate.lo = isrlocn;
	newgate.lo &= 0x00000000FFFFFFFFL;
	newgate.lo |= (newgate.lo << 32);
	newgate.lo &= 0xFFFF00000000FFFFL;
	newgate.lo |= oldgate.lo;
	newgate.lo |= (0x6000L << 32);
	newidt[ INT_ID ] = newgate;

	// activate our new Interrupt Descriptor Table
	load_IDTR( newidtr );	
	smp_call_function( load_IDTR, newidtr, 1, 1 );
	return	0;  //SUCCESS
}


static void __exit iokludge_exit(void )
{
	// reactivate the original Interrupt Descriptor Table
	smp_call_function( load_IDTR, oldidtr, 1, 1 );
	load_IDTR( oldidtr );

	// release allocated kernel memory
	if ( kpage ) free_page( kpage );

	printk( "<1>Removing \'%s\' module\n", modname );
}

module_init( iokludge_init );
module_exit( iokludge_exit );
MODULE_LICENSE("GPL");