ARM Reverse Engineering – Hacking Double Variables

Let’s review our code.

int main(void) {

            double myNumber = 1337.77;

 

            std::cout << myNumber << std::endl;

 

            return 0;

}

Let’s debug!

Let’s set a breakpoint at main+24 and continue.

We see the strd r2, [r11, #-12] and we have to fully understand that this means we are storing the value at the offset of -12 from register r11 into r2. Let’s now examine what exactly resides there.

Voila! We see 1337.77 at that offset location or specifically stored into 0x7efff230 in memory.

Let’s step into twice which executes the vldr d0, [r11, #-12] as we understand that 1337.77 will now be loaded into the double precision math coprocessor d0 register. Let’s now print the value at that location below.

Let’s hack the d0 register!

Now let’s reexamine the value inside d0.

Let’s continue.

Successfully hacked!

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