mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-18 17:36:11 +00:00
367 lines
5.7 KiB
NASM
367 lines
5.7 KiB
NASM
.286c
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.model small
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.code
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org 100h
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start:
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jmp install
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old_si dw 0
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old_bx dw 0
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old_cx dw 0
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old_dx dw 0
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es_main dw 0
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num_ff dw 0
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last_pag dw 0
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viroff dw 0
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count db 0
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scan_seg dw 0
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mes db 'Found !','$'
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filnm db 15 dup(0)
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buffer db 'NCMAIN.EXE',0h,0h,0h,0h,0h
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db 'QA.COM',
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db 64 dup (0)
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include datagame.inc
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int_21h_entry:
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pushf ; Push flags
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sti ; Enable interrupts
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cmp ah,4Bh ;
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jne loc_24 ; Jump if equal
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cmp al,0
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je loc_25
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loc_24:
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popf ; Pop flags
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db 0EAh
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old_21h_off dw ?
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old_21h_seg dw ?
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loc_25:
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mov cs:old_bx,bx
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push ax
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push cx
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push di
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push es
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push ds
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push si
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push dx
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mov si,dx
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loc_205:
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inc si
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cmp byte ptr ds:[si],0
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jne loc_205
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mov bh,0
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loc_206:
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inc bh
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dec si
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cmp byte ptr ds:[si],'\'
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jne loc_206
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inc si
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dec bh
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push cs
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pop es
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xor cx,cx
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mov bl,-1
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loc_94:
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inc bl
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lea di,cs:buffer
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mov ax,15
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mul bl
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add di,ax
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push si
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mov cl,bh
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rep cmpsb
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pop si
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je loc_57
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cmp bl,4
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jne loc_94
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jmp short loc_95
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loc_57:
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mov byte ptr cs:count,0
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jmp loc_fin
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loc_95:
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mov cl,bh
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lea di,cs:filnm
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repne movsb
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sub si,3
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cmp word ptr ds:[si],'XE'
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jne loc_47
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lea ax,cs:only_exe
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mov byte ptr bl,cs:only_exe_count
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jmp short loc_files
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loc_47:
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cmp word ptr ds:[si],'OC'
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je loc_79
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lea ax,cs:ov_pi
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mov byte ptr bl,cs:ov_pi_count
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jmp short loc_files
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loc_79:
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lea ax,cs:com_exe
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mov byte ptr bl,cs:com_exe_count
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loc_files:
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mov cs:viroff,ax
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mov byte ptr cs:count,bl
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mov ah,3dh
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xor al,al
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int 21h ; file is open for reading
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jc loc_fin
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mov bx,ax
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mov ah,42h
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xor cx,cx
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mov dx,cx
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mov al,2
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int 21h ; seek to the end
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mov cs:num_ff,dx ; save number of 64k
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mov cs:last_pag,ax ; save length of last page
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mov ah,3eh
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int 21h ; close the file
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loc_fin:
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pop dx
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pop si
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pop ds
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pop es
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pop di
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pop cx
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pop ax
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loc_en:
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mov bx,cs:old_bx
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jmp loc_24
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message:
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mov dx,si
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mov ah,09h
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int 21h
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lea dx,mes
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mov ah,09h
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int 21h
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ret
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int_4b_scan:
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mov old_bx,bx
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mov old_dx,dx
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push cs
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pop ds
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add dx,10h ; dx = Start seg
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call scanvir
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jc loc_vir
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mov ax,old_bx
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mov dx,old_dx
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mov ds,dx
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mov es,dx
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retf
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loc_vir:
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; call message
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pop dx
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pop ds
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mov dx,old_dx
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push dx
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xor dx,dx
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push dx
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retf
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scanvir:
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; dx = segment for scan (offset = 0)
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; cs:viroff = offset of virtable
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; ds = segment of virtable
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; cs:count = number of viruses
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; cs:num_ff = number of 64k
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; cs:last_pag = number of bytes in last page
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; return bit c if virus is founded
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; ds:si points to the viruses name
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; bp,es,di,bx,ax,dx <20><><EFBFBD><EFBFBD><EFBFBD>
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mov cs:es_main,dx ; es_main = Start_seg
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mov bp,cs:viroff ; bp - pointer to virus table
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mov bh,0
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loc_5:
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cmp byte ptr cs:count,bh
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jne loc_61
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ret
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loc_61:
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inc bh
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mov di,cs:es_main ;
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mov es,di ;
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xor di,di ;
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mov dx,cs:num_ff ;
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mov si,cs:[bp] ; si points to this viruses pattern
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lodsb
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mov bl,al ; bl - counter of characters in virus pattern
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sub bl,1
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lodsb ; al - first char of pattern
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jmp loc_12 ; go to search
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loc_9:
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cmp dx,-1 ; virus is ended ?
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jne loc_15 ; no
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add bp,2 ; bp points to the next virus
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jmp loc_5
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loc_15:
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xor di,di ; di points to the beginning of the next segment
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mov cx,es ;
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add cx,1000h ;
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mov es,cx ; es points to the next segment
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loc_12:
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cmp dx,0 ; we'll work with last page ?
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je loc_2 ; yes
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mov cx,0ffffh ; cx = maximum counter
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jmp loc_10
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loc_2:
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mov cx,cs:last_pag ;
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loc_10:
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repne scasb ; search for first char
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je loc_13 ; found
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dec dx ; decrement of the counter of 64k
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jmp loc_9 ; go to the preparing for the search in next segment
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loc_13:
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mov cs:old_cx,cx ;
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mov cs:old_si,si
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push di
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push es
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cmp di,0fff0h
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jbe loc_7
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mov cx,es
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inc cx
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mov es,cx
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sub di,10h
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loc_7:
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xor cx,cx
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mov cl,bl
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repz cmpsb
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jne loc_11
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pop es
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pop di
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jmp loc_89 ; found !
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loc_11:
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mov si,cs:old_si
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pop es
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pop di
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mov cx,cs:old_cx
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jmp loc_10
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loc_er:
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loc_89:
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stc
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ret
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pattern:
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db 08eh
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db 0c2h
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db 08eh
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db 0dah
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db 08bh
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db 0c3h
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db 0cbh
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install:
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int 5
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cli ; set new stack
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mov ax,cs
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mov ss,ax
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mov bx,offset n
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add bx,50h
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mov sp,bx
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sti
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xor ax,ax
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push ax
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pop ds ; ds=0
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cli
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mov di,ds:[21h*4]
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mov ax,ds:[21h*4+2]
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mov cs:old_21h_off,di
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mov cs:old_21h_seg,ax
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mov di,ds:[31h*4]
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mov ax,ds:[31h*4+2]
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push ax
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pop es
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mov ds:[21h*4],offset int_21h_entry
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mov ds:[21h*4+2],cs
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sti
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; find 'MZ'
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mov cx,-1
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cld
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mov byte ptr al,4dh
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loc_lo:
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repne scasb
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jne loc_err
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cmp byte ptr es:[di],5ah
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jne loc_lo
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loc_loop:
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; 'MZ' found
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push cs
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pop ds
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lea si,cs:pattern
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inc si
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mov byte ptr al,cs:[si-1]
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inc si
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loc_loop1:
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dec si
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repne scasb
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jne loc_err
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push cx
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mov cx,6
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rep cmpsb
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pop cx
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jnz loc_loop1
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suc_end:
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mov byte ptr es:[di-5],0eah
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mov es:[di-4],offset int_4b_scan
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mov es:[di-2],cs
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loc_err:
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mov dx,offset install
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int 27h
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n:
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dw 50 dup (0)
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end start |