fix: bound unauthenticated image size before RAM load

[rizlik]

ZD#21988

[Copilot]

Pull request overview

This PR addresses a security-hardening issue in wolfBoot’s RAM-load paths by bounding an unauthenticated image length (read from a decrypted-but-not-yet-authenticated header) before it can drive RAM copies/decryption. This is especially important for EXT_ENCRYPTED stream-cipher configurations where ciphertext malleability can attacker-influence the decrypted length field.

Changes:

• Introduces a shared wolfBoot_ramboot_check_size() helper to validate payload size against the RAM load region.
• Uses the helper to reject oversized images in both wolfBoot_ramboot() (RAM load) and wolfBoot_ram_decrypt() (MMU ramboot decrypt path) before copying/decrypt loops run.
• Adds new unit tests (and Makefile targets) to regress oversized length, wraparound length, and ciphertext bit-flip manipulation of the length field.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
tools/unit-tests/unit-update-ram-enc.c	Adds regression tests for encrypted/MMU RAM decrypt size-bounding (including wrap and malleation cases).
tools/unit-tests/Makefile	Adds build/run targets for the new encrypted RAM decrypt unit tests (fixed partitions + nopart/RAMBOOT_MAX_SIZE variants).
src/update_ram.c	Switches RAM-load size validation to the shared wolfBoot_ramboot_check_size() helper.
src/libwolfboot.c	Adds bounds checking in wolfBoot_ram_decrypt() before the decrypt/copy loop.
include/image.h	Adds the wolfBoot_ramboot_check_size() inline helper for consistent bounds validation.

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[dgarske]

Skoll Multi-Scan Review

Modes: review + review-securityOverall recommendation: COMMENT
Findings: 4 total — 4 posted, 0 skipped
4 finding(s) posted as inline comments (see file-level comments below)

Posted findings

• [Medium] [review] Bound-check edge cases not exercised: exact max-valid length and FIXED underflow guard — tools/unit-tests/unit-update-ram-enc.c:118-300
• [Low] [review+review-security] WOLFBOOT_RAMBOOT_MAX_SIZE silently ignored when WOLFBOOT_FIXED_PARTITIONS is also defined — src/libwolfboot.c:2418-2429
• [Low] [review-security] New length bound does not account for ENCRYPT_BLOCK_SIZE rounding of the decrypt copy loop — src/libwolfboot.c:2418-2439
• [Low] [review] Overflow-length tcase is missing its tcase_set_timeout call — tools/unit-tests/unit-update-ram-enc.c:323-326

Review generated by Skoll

[dgarske]

#802 (review)