ricardgb opened a new pull request, #19557:
URL: https://github.com/apache/nuttx/pull/19557
## Summary
Follow-up to the rp23xx hardware TRNG driver added in 52e84e0c0a. Two
robustness gaps in the entropy path:
1. **Health-test failures were served as entropy.** The read waited for
`EHR_VALID` and copied the block out without checking `RNG_ISR`, so a
sample that failed the CryptoCell von-Neumann / CRNGT / autocorrelation
test was returned regardless. Now a failed block is discarded and the
source re-armed; only a block that passed is returned.
2. **No startup check.** A small self-test draws a few conditioned blocks at
registration; if the source is stuck (identical blocks) it latches
`/dev/random` and `/dev/urandom` to fail with `-EIO` instead of emitting
predictable output that would silently weaken every derived key.
The read path is factored through a small `rp23xx_rng_collect()` helper
shared by the self-test.
## Impact
- rp23xx only. No API or config change (same `CONFIG_RP23XX_RNG`).
- Healthy hardware is unaffected: passing blocks are returned as before.
- A broken/stuck TRNG now fails closed (`-EIO`) rather than returning weak
entropy.
## Testing
- Built `raspberrypi-pico-2:nsh` with `CONFIG_RP23XX_RNG=y`,
`CONFIG_DEV_RANDOM=y`, `CONFIG_DEV_URANDOM_ARCH=y` (arm-none-eabi-gcc
13.2);
`tools/checkpatch.sh -c -u -m -g` passes.
- On healthy silicon the read path is unchanged from 52e84e0c0a (passing
blocks only); the failure paths (`RNG_ISR` error, stuck source) cannot be
forced on real hardware but are exercised by the discard/re-arm and
self-test logic on every read/registration.
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*Changes made with an AI agent, human-reviewed.*
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