Robert Allan James
09857b7228
The QEMU-verifiable slice of the real-hardware RNG driver (per FABRIC-3.md §G.2). New include/starkernel/rng.h + src/starkernel/rng/rng.c provide the single entropy entry point: rng_init() probes the backend set (v2.0.0: virtio-rng only) and, on no backend, prints a loud boot-time warning while rng_get_bytes() returns RNG_ERR_NO_BACKEND - never silently degrading to a deterministic seed. The backend-selection switch in rng.c is the exact seam v2.5.0's per-arch drivers (amd64 RDRAND, riscv64 Zkr, aarch64 peripheral) plug into without touching the call path. Consumers route through the unified layer instead of virtio-rng directly: capsule_mint.c (identity seed + drive_uuid) and kernel_main.c phase 8 (rng_init()). virtio_rng.c stays as the sole backend. Built clean on amd64/aarch64/riscv64. QEMU amd64 boot: POST 1012/0/0 + ok>, "rng: backend = virtio-rng" + "entropy: ready", Zuse identity confirmed from thumbdrive - mint/cert behavior unchanged. FABRIC-3.md §G.2 v2.0.0 slice marked BUILT+VERIFIED.
66 lines
2.7 KiB
C
66 lines
2.7 KiB
C
/*
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* rng.h — Unified entropy entry point for StarKernel
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*
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* The single place any kernel consumer (keygen, identity mint, drive_uuid,
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* certificate serials, ...) asks for entropy. All entropy flows through
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* rng_get_bytes() and never touches a backend directly.
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*
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* The set of active backends is determined at rng_init() time by probing,
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* in order, until one (or more) come up:
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* - v2.0.0 (QEMU): virtio-rng is the sole backend — there is no virtio-rng
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* on real hardware, but QEMU exposes it uniformly on all three arches
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* (amd64/aarch64/riscv64), and the paravirtualized device sidesteps the
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* per-ISA gap where no single CPU RNG covers all three models (amd64 has
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* RDRAND, riscv64 has Zkr, but QEMU's aarch64 CPU models expose neither —
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* see virtio_rng.h / vm_uuid.h for the identical finding).
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* - v2.5.0 (real hardware): real per-arch backends are inserted here without
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* touching the call path — amd64 RDRAND, riscv64 Zkr (RNDR), aarch64
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* peripheral RNG — each handled by a case in rng_init() and rng_get_bytes()
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* (grid §G.4). On QEMU all three arches stay on virtio-rng; nothing changes.
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*
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* Probe-and-refuse-loudly contract (§G.2): if no backend comes up at
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* rng_init(), the kernel prints a loud boot-time message. A later
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* rng_get_bytes() call with no backend returns -1 (RNG_ERR_NO_BACKEND) rather
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* than ever silently degrading to a deterministic throwaway — the exact failure
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* Phases A/G call out as unacceptable. Callers (e.g. capsule_mint_identity)
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* must surface that refusal as an explicit no-entropy error, never proceed with
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* a deterministic seed.
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*
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* Important ordering: rng_init() must run before any rng_get_bytes()/mint call
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* (it already does in kernel_main phase 8, ahead of Zuse boot attach, which is
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* the only mint path in v2.0.0). rng_get_bytes() with rng_init() never
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* successful returns RNG_ERR_NO_BACKEND, never blocks.
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*/
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#ifndef STARKERNEL_RNG_H
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#define STARKERNEL_RNG_H
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#include <stddef.h>
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#include <stdint.h>
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/* Return codes (negative = failure). */
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#define RNG_ERR_NO_BACKEND (-1) /* rng_init() found no working entropy source */
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/*
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* rng_init — probe and bring up the entropy backends. Returns 0 if at least
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* one backend is active (rng_get_bytes() will succeed), nonzero otherwise.
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* Prints a loud boot-time message when no backend comes up. Call once, early.
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*/
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int rng_init(void);
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/*
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* rng_ready — 1 if at least one backend is active, 0 otherwise.
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*/
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int rng_ready(void);
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/*
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* rng_get_bytes — fill buf with n bytes of real entropy, blocking until all
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* n bytes are obtained.
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*
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* Returns 0 on success (buf fully filled).
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* Returns RNG_ERR_NO_BACKEND (-1) if no backend is active.
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*/
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int rng_get_bytes(uint8_t *buf, size_t n);
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#endif /* STARKERNEL_RNG_H */
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