/*



	    Gaara virus disinfector type 2
	--------------------------------------
	by Piotr Bania <bania.piotr@gmail.com>
	http://www.piotrbania.com
	
	
	Details:
	
	Firs of all, the disinfector checks if the GAARA is already resident
	if so you may want to clear the RAM memory. And this seems to be 
	the best way of disinfection but you will loose all your RAM programs
	unless they are archived. Anyway i made an another approach.
	Which i hope can teach you how to clear the virus.
	
	This type of disinfector is trying to find a EPO injection
	which virus made by patching the ti-gcc epilog. It's how
	it obtains it execution. The idea is simple, we are scanning
	the potencial infected file starting from entrypoint, we are
	looking for a BRA sequence of byte (of course do to the fact
	we don't have a disassembler here this may gives as a lot of
	false positives). So, next we are checking if the bra destination
	is suitable for following codintions:
	
	1) it is not negative (because Gaara body lays below)
	2) it is within the file size range
	3) it points to the virus body
	
	If following conditions are passed, we consider the BRA as na
	injection of GAARA. Then we simply reset the injection within
	the original EPILOG. And finally we are clearing GAARA marker.
	That's all, have fun!

*/



#include <tigcclib.h>

#define get_romb(x)					({(long)x = *(long*)0xC8;}) 
#define LOW_GAARA_SIZE			400



/* signatures */
unsigned char 	sig_gaara_mark[]			= {'G','A','A','R','A','X'};

/* repair */
unsigned char 	repair_bytes[]		=	{0x4E, 0x5E, 0x4E, 0x75};

unsigned short	gaara_m_offset 		= 0;
int							d_files						= 0;


void is_infected(void)
{
	unsigned long a;
	get_romb(a);
		
	if (!(a & 0xE00000))
	{
		printf("Disg: Seems the ROMCALL-JUMP-TABLE is redirected\n");
		printf("Disg: Please reset RAM to make it clean.\n");
		ngetchx();		
		
		/* well i should rewrite the ROMCALL-JUMP-TABLE ptr here by hand
		but i guess it would be a cool job for you :)*/
		return;
	}
	
	printf("Disg: Seems the RAM is clean\n");	
}


unsigned short get_sig_off(void *mem, unsigned short size, unsigned char *sig, int sig_s)
{
	
	int i,ii, found;
	for (i = 0; i < (size-3); i++)
	{	
		found = 1;
		for (ii = 0; ii < sig_s; ii++)
		{
			if (*(unsigned char*)(mem+i+ii) != sig[ii])
			{
				found = 0;
				goto next;				
			}
		}		

next:		
		if (found == 1)
		{
			if (*(char*)(mem+i+ii) == 'X')
				return 0;			// to avoid fail on itself
			return i;		
		}
			
	}	
	
	return 0;
}


int is_gaara(void *mem, unsigned short size)
{
	int i;
	unsigned long offset;
	
	printf("Disg: Scaning for the infection mark\n");

	gaara_m_offset = get_sig_off(mem,size,&sig_gaara_mark,sizeof(sig_gaara_mark)-1);
	if (gaara_m_offset != 0)
	{
					printf("Disg: File is infected with Gaara, trying to repair\n");
					return 1;			
	}

	printf("Disg: File is clean\n");
	return 0;	
}


void disinfection_two(void *mem, unsigned short size)
{
	int i = 0;
	void *where;
	void *start_scan;
	
	unsigned long dest;
	unsigned short offset;
		
		
  /* lets look for potencial BRA's */
 
	start_scan = (unsigned long)mem + 2;
	
	
	
	/* this is a bit slow and bit bruteforce, but the good point is that
	large BRA is not so heavily used in orginal programs :) */
	
	for (i = 0; i < (size-6); i++)
	{		
		/* this would be faster then sig_gaara_injection proc */
		if ((*(unsigned char*)(start_scan+i) == 0x60) && (*(unsigned char*)(start_scan+i+1) == 0x00))
		{
			/* potencial BRA is found, now let check its destination, it can be an even address */
			memcpy((void*)&offset,(void*)(start_scan+i+2),2);
			
			/* all Gaara size-jumps must be positive */
			if ((offset < 0) || (offset > size))
				continue;
				
			/* borders? */
			if ((unsigned long)((start_scan+i) + offset) > (unsigned long)(mem + size))
				continue;
			
			dest = start_scan + i + offset + 2;
	
			/* does it points to Gaara? */
			if ((*(unsigned char*)(dest) == 0x4E) && (*(unsigned char*)(dest+3) == 0x71) && \
					(*(unsigned char*)(dest+4) == 0x48))
					{
						
						printf("Disg: The virus injection was found at %lx\n",start_scan+i);
					
						/* clean the injection */
						memcpy((void*)(start_scan+i),(void*)&repair_bytes,sizeof(repair_bytes));
						
						/* and now destroy the Gaara marker, pad it with 0 */
						memset((void*)(mem + gaara_m_offset),0,5);						
					}			
		}		
	}
		  			
	printf("Disg: File is repaired\n");
	d_files++;
	return;
}




void in_infected_file(SYM_ENTRY *se)
{
	unsigned short size;
	void *mem = HeapDeref(se->handle);
	
	printf("Disg: Checking %s\n",se->name);
	
	if (!mem)
	{
		printf("Disg: Error, cannot HeapDeref();\n");
		return;		
	}
	
	size = *(unsigned short*)mem;
	
	printf("Disg: Variable size is %d bytes \n",size);
	
	if (size < LOW_GAARA_SIZE)
	{
		printf("Disg: The file is not infected (size is too low)\n");
		return;		
	}
		
	if (!is_gaara(mem,size))
		return;
				
	disinfection_two(mem,size);
	
}




void dis_loop(void)
{

	SYM_ENTRY *se;

	if (!FolderOp(NULL, FOP_LOCK | FOP_ALL_FOLDERS))
	{
		printf("Disg: Locking folder table failed\n");
		return;		
	}
		
	se = SymFindFirst(NULL, FO_RECURSE | FO_SKIP_TEMPS);
	
	while (se)
	{
			in_infected_file(se);			
			se = SymFindNext();		
	}
		
	FolderOp(NULL,FOP_UNLOCK | FOP_ALL_FOLDERS);
	
}


// Main Function
void _main(void)
{
	clrscr();
	printf("*** DISG - Gaara virus file disinfector ready.\n");
	printf("*** by Piotr Bania - http://www.piotrbania.com\n");

	is_infected();
	dis_loop();
	
	printf("Disg: Disinfection ended, %d file were disinfected\n",d_files);
	ngetchx();
}