SIMD-0089: Programify Feature Gate Program (#89)

* simd: programify feature gate program (2)

* clarify a few points

* add SIMD number

* add recent sync feedback

* add specific upgrade authority details

* review feedback

* drop instruction code snippet

* remove Jump from multi-sig

proposals/0089-programify-feature-gate-program.md

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+---
+simd: '0089'
+title: Programify Feature Gate Program 
+authors:
+  - Joe Caulfield
+category: Standard
+type: Core
+status: Draft
+created: 2023-11-21
+feature: (fill in with feature tracking issues once accepted)
+supersedes: '0077'
+---
+
+## Summary
+
+This proposal suggests replacing the non-existent native program at address
+`Feature111111111111111111111111111111111111` with a Core BPF Program, as
+described in
+[SIMD 0088](https://github.com/solana-foundation/solana-improvement-documents/pull/88).
+
+Feature accounts are already assigned the owner program address
+`Feature111111111111111111111111111111111111`. Deploying a Core BPF program at
+this address would provide engineers with the capability to revoke pending
+feature activations.
+
+**Note:** The process by which core contributors *activate* features would
+remain completely unchanged.
+
+## Motivation
+
+Currently, a feature is queued for activation by a keypair holder creating an
+empty account and assigning it to the
+`Feature111111111111111111111111111111111111` program.
+
+Because there is no actual program implementation at this address, the queuing
+is irreversible; if the runtime knows about a feature gate at some address, it
+will activate it at the next epoch boundary. This means there is no recourse in
+the case of a mistaken queuing, discovery of a bug, or simply a desire to manage
+the cadence and schedule of activations.
+
+A fully-implemented Core BPF program would take ownership of those accounts and
+support revoking queued features, giving engineers more flexibility and
+safeguards.
+
+## Alternatives Considered
+
+The Feature Gate program could instead be implemented as a built-in native
+program, rather than a Core BPF program. However, this would mean any changes to
+the program would need to be implemented by all validator clients in
+coordination. This makes upgrading the program cumbersome.
+
+With the Feature Gate program instead implemented as a Core BPF program, any
+changes need only be done once, eliminating this duplication of work.
+
+## New Terminology
+
+- Feature Gate program: The Core BPF program that all feature accounts will be
+  assigned to, with address `Feature111111111111111111111111111111111111`.
+
+## Detailed Design
+
+The Feature Gate program shall be a Core BPF program whose upgrade authority
+will be a multi-sig authority with keyholders from Solana Labs and potentially
+Jito.
+
+The program shall initially be designed to support one instruction:
+`RevokePendingActivation`. Any other instructions or functionality this program
+may support in the future will be proposed and discussed separately.
+
+When this instruction is invoked by a feature key-holder, the program will
+reallocate the account to zero, assign it back to the System Program, and defund
+its lamports balance. As a result, the runtime will no longer recognize this
+feature as pending, since it will no longer be owned by
+`Feature111111111111111111111111111111111111`.
+
+The official process outlined in 
+[SIMD 0088](https://github.com/solana-foundation/solana-improvement-documents/pull/88)
+for migrating a native program to Core BPF will be used to enable this new
+program, with the addition of the `RevokePendingActivation` instruction as a
+separate BPF prgoram-upgrade step.
+
+1. Migrate the native no-op program at
+   `Feature111111111111111111111111111111111111` to a Core BPF no-op, with the
+   new program's upgrade authority set to the Feature Gate multi-sig.
+2. Upgrade the Core BPF no-op to add the `RevokePendingActivation` instruction
+   using the new multi-sig authorization.
+
+Because the only change to the program is the addition of the
+`RevokePendingActivation` instruction, these steps will enable Core BPF Feature
+Gate without any changes to the existing feature activation process.
+
+## Impact
+
+Core contributors are positively impacted by this change, since the ability to
+revoke pending feature activations is a significant security advantage.
+
+There is otherwise no change to the activation process whatsoever. This includes
+queuing features for activation with the CLI and the timing of their activation
+by the runtime.
+
+## Security Considerations
+
+Currently the accounts used for feature-gating are owned by a program ID that
+does not have any implementation. This means that there is no on-chain authority
+that can modify feature accounts once they've been created under
+`Feature111111111111111111111111111111111111`. This allows the runtime to
+confidently update their state upon activation.
+
+With this proposal, a live BPF program - which can accept instructions from
+anyone and execute code - will be the owner of these accounts. This creates some
+risk if *both* the program's processor code as well as a secure system for
+upgrading the program are not properly managed.
+
+However, this program's upgrades will be protected by a multi-sig authority.
+Thoroughly reviewed and safe processor code should mitigate any new risks
+associated with this change.
+
+## Backwards Compatibility
+
+This change is 100% backwards compatible with the existing feature activation
+process. It *only* adds the ability to revoke pending activations.