Below MI – IBM I for Hackers
IBM i system offers full control over hardware and software, utilizing Machine Interface for abstract development and memory safety. It operates on POWER CPU with 64-bit big-endian architecture, featuring unique security levels and Single-Level Storage for memory management. Control flow is managed through register conventions and stack operations. The system lacks memory safety, allowing out-of-bounds memory access. Security levels range from no security to C2 level, with Security Level 40 recommended. The writeup delves into memory management, control flow, and security mechanisms for evaluating memory safety and exploitation.
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IBM i is a system with full control over hardware and software, using the Machine Interface (MI) for abstract development and memory safety. The platform operates on the POWER CPU with 64-bit big-endian architecture and unique security levels. Single-Level Storage (SLS) treats memory as a single virtual address space, impacting memory safety violations. The system uses thick pointers and segment identifiers for memory management. Control flow between program functions is managed through register conventions and stack operations. The system lacks memory safety, allowing for out-of-bounds memory access. Program objects in SLS have fixed virtual addresses, changing only upon recompilation. The platform's security levels range from no security to C2 level security, with Security Level 40 being the recommended minimum. The writeup provides technical insights into IBM i's memory management, control flow, and security mechanisms, crucial for evaluating memory safety issues and exploitation on the platform.
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6 commentsthe as/400 design is pretty interesting, just because it's so different from currently popular systems. if you're familiar with unix and you study vms or windows 11, you won't learn that much, because vms and unix are almost identical. os/400 is a much weirder beast, and its design doesn't just have disadvantages relative to more widely used system architectures, but also advantages—even if, in the end, the disadvantages turned out to be more important
The ABI described is the same as the AIX ABI. R1 is the stack pointer and R31 is the frame pointer, when needed.
The system is cool. But the majority of jobs are underpaid in comparison to the open source stacks. And they wonder why there is a lack of new blood.
There are many articles out there claiming COBOL/Mainframe/AS400/“ancient” programmers are retiring and the orgs want to pay you big bucks to replace them. For the most part they are just parlor tricks to try and get a cost savings on new grads.
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