User-space memory editing programs

Question

How do programs that edit memory of other processes work, such as Cheat Engine and iHaxGamez? My understanding is that a process reading from (let alone writing to) another process' memory is immediate grounds for a segmentation fault.

Answer 1

Gaining access to another processes memory under linux is fairly straightforward (assuming you have sufficient user privileges).

For example the file /dev/mem will provide access to the entire memory space of cpu. Details of the mappings for an individual process can be found in /proc/<pid>/maps.

Another example has been given here.

Answer 2

The operation system's hardware abstraction layer usually offers functions to manipulate the memory of other processes. In Windows, the corresponding functions are ReadProcessMemory and WriteProcessMemory.