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I see a lot of interesting techniques here. I couldn't figure out is how writes are prevented to code areas in the sandbox. I'd guess they mark pages with code-bundles as read-only but I don't see any specific mention of it.

(The article does mention that the guard pages are set to no read/write/execute)

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The trampolines are located in a segment of the address space which is marked as read-only, presumably by the MMU.

The validator also needs to prevent modifications to the program's own code, otherwise it could, say, remove the breakpoint instruction from the start of a data bundle.

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