User-space memory editing programs

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

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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.

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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.

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It has no reason to segfault; OS (kernel, ...) API is used to write. Segfault occurs (get signalled) from OS when a process attempts to access it's own memory in a bad way (char[] overflow).

About the games: well, if a value is stored at an address, and gets read sometimes, then it could be modified before next reading occurs.

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You can use WinAPI WriteProcessMemory to write to memory space of other process.

Also read some PE/COFF documentation and use VirtualQueryEx and ReadProcessMemory to know what and where to write.