Code Injection - Working with Floats

This tutorial builds on the topic of Code Injection:

Let's say you have a float and some code that increases the value.

Note: SS is for singles and SD is for doubles.

What if what writes to the value is only a MOVSS. Try to find a spot above the write instruction that has an ADDSS (or a SUBSS depending on what you want to do).

//...
movss [eax+10],xmm0

Editable value

We could use a label, giving it some memory. And optionally register it so the label can be used on the table as an address.

//...
alloc(someMem, 0x400)
//...
label(someSymbol)
registerSymbol(someSymbol)
//...
someMem:
//...
movss xmm0,[someSymbol]
//...
jmp return
//...
someSymbol:
dd (float)100
//...

We could add an editable value like above but use MULSS to add a multiplier to the script.

//...
alloc(someMem, 0x400)
//...
label(someSymbol)
registerSymbol(someSymbol)
//...
someMem:
//...
mulss xmm0,[someSymbol]
//...
jmp return
//...
someSymbol:
dd (float)100
//...

Calculate a value for a Multiplier

Let's say we just can't find an ADDSS or a SUBSS, and all we have is a MOVSS.

movss [eax+10],xmm0

We can just do some math in the script, to calculate a value for a multiplier.

//...
alloc(someMem, 0x400)
//...
label(someSymbol)
registerSymbol(someSymbol)
//...
someMem:
//...
subss xmm0,[eax+10]
mulss xmm0,[someSymbol]
movss [eax+10],xmm0
//...
jmp return
//...
someSymbol:
dd (float)10
//...

Working with doubles

Let's say the game use doubles, we can use ADDSD, SUBSD, MULSD, and MOVSD instead. We just need to also make our scripts value a double.

movsd [eax+10],xmm0

So to calculate a value for a multiplier.

//...
alloc(someMem, 0x400)
//...
label(someSymbol)
registerSymbol(someSymbol)
//...
someMem:
//...
subsd xmm0,[eax+10]
mulsd xmm0,[someSymbol]
movsd [eax+10],xmm0
//...
jmp return
//...
someSymbol:
dq (double)10
//...

Working with packed instructions

So some times (especially with vectors) you'll see packed instructions, like MOVAPS, MOVUPS, ADDPS, SUBPS, MULPS. These type of instructions work on 16 bytes at a time.

SO let's say you have some code accessing the player coordinate deltas, and it's using packed instructions.

So let's add a multiplier for this.

//...
alloc(someMem, 0x400)
//...
label(someSymbol)
registerSymbol(someSymbol)
//...
someMem:
//...
mulps xmm0,[someSymbol]
//...
jmp return
//...
someSymbol:
dd (float)1.75
dd (float)1.75
dd (float)1.25
dd (float)1
//...

Calculate a value for packed instruction

Let's say we just can't find an ADDPS or a SUBPS, and all we have is a MOVUPS or a MOVAPS.

movups [eax+10],xmm0

We can just do some math in the script, to calculate a value for a multiplier.

//...
alloc(someMem, 0x400)
//...
label(someSymbol)
registerSymbol(someSymbol)
//...
someMem:
//...
subps xmm0,[eax+10]
mulps xmm0,[someSymbol]
movups [eax+10],xmm0
//...
jmp return
//...
someSymbol:
dd (float)1.75
dd (float)1.75
dd (float)1.25
dd (float)1
//...

We could use the align command and then be able to use aligned instructions. So if the injection point looks like this.

movaps [eax+10],xmm0

Then we could make a script like this.

//...
alloc(someMem, 0x400)
//...
label(someSymbol)
registerSymbol(someSymbol)
//...
someMem:
//...
subps xmm0,[eax+10]
mulps xmm0,[someSymbol]
movaps [eax+10],xmm0
//...
jmp return
//...
align 10 CC
someSymbol:
dd (float)1.75
dd (float)1.75
dd (float)1.25
dd (float)1
//...