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Custom Processing Unit: Tracing and Patching Intel Atom Microcode
Discover the secrets of Intel Atom microcode updates, including tracing, patching, and decryption, to unlock custom CPU behavior and control flow redirection.
- The microcode update is done using an undocumented instruction that returns random data.
- The CR bus is a critical component that allows CPU internal components to interact with each other.
- Intel’s CPUs have a secret stored in the CR bus that can be accessed through the L dot component.
- The microcode sequencer can be accessed through the L dot and allows modification of microcode.
- The microcode can be decrypted and the decrypted content can be modified.
- The matching patch mechanism allows the CPU to redirect control flow to microcode ROM.
- By tracing the microcode update routine, the CPU’s internal state can be reconstructed.
- The microcode updates can be patched to implement custom CPU behavior.
- The CPU’s secret keys can be used to decrypt the microcode updates.
- The CR bus is used to communicate between CPU internal components.
- The CPU’s microcode can be analyzed to understand how it works.
- By hooking the microcode update routine, the CPU’s internal state can be observed.
- The microcode update can be used to implement custom CPU functionality.
- The CPU’s microcode can be patched to implement custom CPU behavior.