memory-write

Problem

This problem comes from pwn.college: Assembly Crash Course ⤴.

We will now set some values in memory dynamically before each run. On each run, the values will change. This means you will need to do some type of formulaic operation with registers. We will tell you which registers are set beforehand and where you should put the result. In most cases, it’s rax.

In this level, you will be working with memory. This will require you to read or write to things stored linearly in memory. If you are confused, go look at the linear addressing module in ‘ike. You may also be asked to dereference things, possibly multiple times, to things we dynamically put in memory for your use.

Please perform the following: Place the value stored in rax to 0x404000.

Solution

.intel_syntax noprefix
.global _start

_start:
  mov [0x40400], rax

This time, the value inside rax is placed inside memory address 0x404000.