puf: fix transmit-only UART HAL and add an interactive INTERACTIVE=1 demo mode

[dgarske]

No description provided.

[Copilot]

Pull request overview

This PR updates the PUF STM32H5 example to support a UART RX path (previously TX-only) and introduces an optional interactive demo build mode (INTERACTIVE=1) that provides a UART-driven menu for stepping through enrollment/reconstruction and a controlled noise sweep.

Changes:

• Extend the bare-metal USART3 HAL to configure RX (PD9), enable RE, and add blocking uart_getc() plus uart_drain().
• Add a new interactive demo program (main_interactive.c) and a Makefile switch to build it.
• Document the new interactive mode and its behavior in puf/README.md.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
puf/stm32.c	Adds USART3 RX support (PD9 AF7 + RE) and input helpers for interactive UART menu.
puf/README.md	Documents INTERACTIVE=1 build and the interactive UART menu/demo behavior.
puf/Makefile	Adds INTERACTIVE switch to select main_interactive.c and forces PUF_TEST=1 when interactive.
puf/main_interactive.c	New UART-driven interactive PUF demo with enrollment, reconstruction, helper dump, and noise sweep.

Suppressed comments (2)

puf/main_interactive.c:269

• wolfCrypt_Init() return value is ignored; if initialization fails, the demo continues and calls wolfCrypt/PUF APIs in an undefined state. Capture and handle the error (at least print and halt) like main.c does.

    hal_init();
    wolfCrypt_Init();

puf/main_interactive.c:196

• Return values from the two wc_PufDeriveKey() calls are ignored. If derivation fails, the demo prints/uses whatever is left in k1/k2. Propagate and handle the error before printing the keys.

    wc_PufDeriveKey(&ctx, (const byte*)"nv-integrity", 12, k1, sizeof(k1));
    wc_PufDeriveKey(&ctx, (const byte*)"device-identity", 15, k2, sizeof(k2));
    printf("  same silicon, same helper data, two HKDF contexts:\r\n");

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[aidangarske]

Skoll Code Review

Scan type: review

Overall recommendation: REQUEST_CHANGES
Findings: 10 total — 9 posted, 1 skipped
9 finding(s) posted as inline comments (see file-level comments below)

Posted findings

• [High] Mode switching can silently leave the wrong firmware in Build — puf/Makefile:64-68
• [High] INTERACTIVE does not override a command-line PUF_TEST=0 — puf/Makefile:37
• [High] Interactive mode does not build with the supported stable wolfSSL — puf/main_interactive.c:84
• [High] Rejected blobs are committed as enrolled global state — puf/main_interactive.c:314-345
• [Medium] A loaded prior-boot blob invalidates the controlled noise sweep — puf/main_interactive.c:155-170
• [Medium] The recovery checksum is never verified — puf/main_interactive.c:292-318
• [Medium] A health-band pass is presented as proof of a cold-boot readout — puf/main_interactive.c:396-397
• [Medium] The new interactive target is not compiled by CI — puf/Makefile:64-65
• [Low] README lists option 4 twice — puf/README.md:81-82

Skipped findings

• [Medium] wolfCrypt initialization failure is ignored

Review generated by Skoll

[aidangarske]

Do we want to add some CI for the PUF work we have now or at least build it in CI?