libc: Refine the arc4random_buf implementation

[xiaoxiang781216]

Note: Please adhere to Contributing Guidelines.

Summary

fill the buffer with getrandom instead random pool and move the implementation to from crypto to libc

Impact

Make arc4random_buf always available

Testing

ci

[nuttxpr]

[Experimental Bot, please feedback here]

No, this PR does not fully meet the NuttX requirements.

Missing Information:

• Summary:
  • Lacks a clear explanation of why the change from random pool to getrandom is necessary. What problem does it solve?
  • Needs more detail on the functional code changes. "move the implementation from crypto to libc" is vague. Be specific about functions or modules impacted.
• Impact:
  • While "Make arc4random_buf always available" is a result, explain how this impacts users or the system. Is there a performance difference? Why is this availability important?
  • The impact sections are largely incomplete. Address all points (build, hardware, documentation, security, compatibility) with either "NO" or a "YES" + explanation.
• Testing:
  • "ci" is insufficient. Provide actual build host and target details as requested.
  • "Testing logs before/after" are missing entirely. Show evidence of the problem the PR fixes AND that it now works as intended.

Recommendations:

1. Expand the Summary: Clearly articulate the problem and solution. Provide specific code-level details.
2. Complete Impact Assessment: Address all impact points. Even if the answer is "NO", state it explicitly.
3. Provide Detailed Testing Information: Include build host/target specifics and relevant logs demonstrating the change's effect.

By providing this missing information, your PR will be much stronger and easier for reviewers to understand and approve.

[acassis]

@xiaoxiang781216 maybe we need to update the random number generation Documentation/ to explain that up_rngbuf() now is used to fill the randomness pool

[cederom]

Thank you @xiaoxiang781216 :-) Build errors :-) + documentation update needed? :-)

[xiaoxiang781216]

@xiaoxiang781216 maybe we need to update the random number generation Documentation/ to explain that up_rngbuf() now is used to fill the randomness pool

but we don't have any document which describe random pool.

[xiaoxiang781216]

Thank you @xiaoxiang781216 :-) Build errors :-) + documentation update needed? :-)

fixed.

[cederom]

@acassis: @xiaoxiang781216 maybe we need to update the random number generation Documentation/ to explain that up_rngbuf() now is used to fill the randomness pool

@xiaoxiang781216: but we don't have any document which describe random pool.

Okay then nothing to update :-P But I agree some documentation would be nice to have here (different task), random is important, for instance would random work without hardware entropy generator and with software implementation with arc4random and how that impacts security (i.e. mbedtls)? :-)

[acassis]

@xiaoxiang781216 @cederom exactly! How to integrate HW RNG, how to use pseudo random generator without HW RNG, etc

[cederom]

Okay, TODO added in Issue #14511 :-)

[lupyuen]

Sorry @xiaoxiang781216: The arm-04 build is failing at the NuttX Mirror Repo, wonder if it's because of this PR? Thanks!

Configuration/Tool: lc823450-xgevk/krndis,CONFIG_ARM_TOOLCHAIN_GNU_EABI
arm-none-eabi-ld: /github/workspace/sources/nuttx/staging//libc.a(lib_arc4random.o): in function `arc4random_buf':
/github/workspace/sources/nuttx/libs/libc/stdlib/lib_arc4random.c:111:(.text.arc4random_buf+0x26): undefined reference to `clock_systime_ticks'

https://github.com/NuttX/nuttx/actions/runs/11540264972/job/32129220872#step:7:101

Update: This error is strange. Sometimes it doesn't appear: https://github.com/NuttX/nuttx/actions/runs/11540270335

But it appears on my Home Build Server: https://gist.github.com/nuttxpr/74e46f5eca2a0cd5a234e5389d40457a#file-ci-arm-04-log-L157

[xiaoxiang781216]

@lupyuen Fix here: #14523