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MalwareSourceCode/MSDOS/Virus.MSDOS.Unknown.tsr.asm

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2021-01-13 00:01:59 +00:00
; NOTE : This template is for .COM files only do not use for .EXE files!!
;
;
;
; Copyright 1986 by Dana Nowell - All rights reserved
;
; HISTORY:
; Version Date Name Description
; 1.0 11/10/86 dn first cut
; 1.01 11/21/86 dn Fixed memory allocation bug
; Added installation message
;
title TSR Template
NULL equ 00h
BELL equ 07h ; bell character
BACKSPACE equ 08h ; backspace character
TAB equ 09h ; tab character
LF equ 0ah ; line feed
F_FEED equ 0ch ; form feed
CR equ 0dh ; carriage return
EOF equ 1ah ; ctrl z ( end of file )
SPACE equ ' ' ; ascii space character
QUOTE equ '"'
SIGNATURE1 equ 6144h ; used for already
SIGNATURE2 equ 616eh ; resident check
DOS_INT equ 21h ; DOS function interrupt
DISP_CHAR equ 02h
GET_KEY equ 08h
DOS_SCR_MSG equ 09h
DOS_SET_INT equ 25h
DOS_RESIDENT equ 31h
DOS_GET_INT equ 35h
DOS_TERMINATE equ 4ch
DOS_STRING_TERM equ '$'
; Interrupt vectors used
HOOK_INT equ 1ch ; interrupt to be hooked ( timer tick now )
;------------------------------------------------------------------------------
;
; MACRO SECTION
;
;------------------------------------------------------------------------------
Version_msg macro
jmp short copyright_end
copyright_msg db CR, LF
db 'TSR Shell - Version 1.01', CR, LF
db 'Copyright 1986, Dana Nowell ', CR, LF, CR, LF
db 'May be distributed without license', CR, LF, '$'
copyright_end:
Msg copyright_msg
endm
Msg macro ptr
push dx
push ax
lea dx, ptr
mov ah, 09h
int 21h
pop ax
pop dx
endm
com segment para public 'code'
assume cs:com, ds:com, es:com
;------------------------------------------------------------------------------
;
; note: The PSP occurs at the beginning of the code segment
; for all programs. In COM files the code seg = data seg
;
;------------------------------------------------------------------------------
org 0
psp_start dw ? ; int 20h - possibly a block for unresolved
; externals during link ?
mem_size dw ? ; size of available memory in paragraphs
filler db ? ; reserved usually zero
dos_call db ? ; call
dd ? ; address of dos function handler
term_vector dd ? ; address of dos terminate routine
break_vector dd ? ; address of dos break routine
error_vector dd ? ; address of dos error routine
dos_reserved db 2 dup(?); reserved by dos
dos_handles db 20 dup(?) ; file handle array
environ_ptr dw ? ; seg of dos environment ( offset = 0 )
dos_work db 34 dup(?) ; dos work area
int_21h db ? ; int
db ? ; 21h
db ? ; retf ( return far )
reserved dw ? ; reserved by dos
fcb1_ext db 7 dup(?) ; fcb # 1 extension
fcb1 db 9 dup(?) ; fcb #1
fcb2_ext db 7 dup(?) ; fcb # 2 extension
fcb2 db 20 dup(?) ; fcb #2
;
; disk transfer area ( dta ) and parameter block occupy the same space
;
;
;dta db 128 dup(?) ; disk transfer area
param_len db ? ; length of parameter string ( excludes CR )
parameters db 127 dup(?) ; parameters
;------------------------------------------------------------------------------
;
; Note on standard fcb structure :
;
; The standard FCB is larger than the size reserved in the PSP if you
; intend to use to FCB data from the PSP move it to a different location.
;
;
; STANDARD STRUCTURE OF A FILE CONTROL BLOCK
;
;
; extension :
; offset length description
; -7 1 extension active flag ( 0ffh = active )
; -6 5 normally unused should be zeros
; -1 1 file attribute when extension is active
; 1 . . . . . . . 1 read-only
; 2 . . . . . . 1 . hidden
; 4 . . . . . 1 . . system
; 8 . . . . 1 . . . volume label
; 16 . . . 1 . . . . subdirectory
; 32 . . 1 . . . . . archive
; 64 . 1 . . . . . . unused
; 128 1 . . . . . . . unused
;
; fcb :
; offset length description
; 0 1 special drive number ( 1 byte )
; 0 = default
; 1 = a:
; 2 = b: etc
; 1 8 filename or device name
; 9 3 filename extension
; 12 2 current block number
; 14 2 record size
; 16 4 file size in bytes ( dos dir entry at open )
; 20 2 file date ( bit coded as in dir )
; 22 10 dos work area
; 32 1 current record number ( 0 - 127 )
; 33 4 random record number
;
;------------------------------------------------------------------------------
org 100h ; required for COM file ( skips PSP )
start:
jmp install ; install the demon
;-------------------------------------------------------------------
;
; resident data structures go here
;
;-------------------------------------------------------------------
old_int dd 0 ; original value of hooked interrupt
resident1 dw SIGNATURE1
resident2 dw SIGNATURE2
;-------------------------------------------------------------------
;
; new interrupt starts here
;
;-------------------------------------------------------------------
new_int:
pushf
sti ; must turn INT on if we're going to use them
;-------------------------------------------------------------------
;
; be well behaved and pass control to original int
;
;-------------------------------------------------------------------
popf
pushf
call dword ptr cs:old_int ; do old interrupt
iret ; bye bye
;------------------------------------------------------------------------------
;
; INSTALLATION DATA STRUCTURES AND CODE GO HERE
;
; WARNING WARNING WARNING - this area does not exist after installation
;
;------------------------------------------------------------------------------
last_resident_byte db 0 ; last resident byte
resident_flag dw 0 ; am I already resident ? ( 0 = NO )
install_msg db CR, LF, 'Installation Complete', CR, LF, '$'
already_installed_msg db CR, LF
db 'Already Installed - Installation Aborted'
db CR, LF, '$'
install proc near
Version_msg
mov al, HOOK_INT ; int to hook
mov ah, DOS_GET_INT ; get int(AL) vector ==> ES+BX
int DOS_INT ; do the int
lea si, old_int ; where to put old timer interrupt vector
mov [si], bx ; save the offset and segment
mov 2[si], es ; ( es also used in check resident )
call check_resident ; am I already resident ?
cmp resident_flag, 0
je not_resident
Msg already_installed_msg
mov ah, DOS_TERMINATE ; terminate & stay resident
mov al, 1 ; return value is 1 (already installed)
int DOS_INT ; bye-bye
not_resident:
mov dx, offset new_int ; offset of new timer interrupt
mov al, HOOK_INT ; timer tick
mov ah, DOS_SET_INT ; set int(AL) vector from DS+DX
int DOS_INT ; do the int
; program terminate and stay resident
Msg install_msg ; Display the installation message
mov dx, offset last_resident_byte
mov cl, 4 ; convert to paragraphs required to
shr dx, cl ; remain resident ( divide by 16 )
inc dx ; allow for any remainder of division
mov ah, DOS_RESIDENT ; terminate & stay resident
mov al, 0 ; return value is 0 (good return)
int DOS_INT ; bye-bye
install endp
;
; Check resident procedure
; requires es register to contain the segment address of
; the current location for the interrupt being hooked.
; use the DOS function 35h to obtain this information.
;
check_resident proc near
cmp es:resident1, SIGNATURE1
jne not_res
cmp es:resident2, SIGNATURE2
jne not_res
mov resident_flag, 1
not_res:
ret
check_resident endp
com ends
end start

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