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eBoot — TLV anti-rollback fix: build, test, and reproduce

Everything below runs on a plain Linux host (or macOS). No board, no cross-compiler, no hardware needed — the native build compiles the platform-agnostic core libraries and the whole unit-test suite.

The finding and the reasoning are in PROPOSAL.md.

0. Prerequisites

# Debian / Ubuntu
sudo apt update
sudo apt install -y build-essential cmake git python3 python3-pip valgrind

# macOS (Homebrew)
brew install cmake python git

Python bits used by the script-driven suites:

pip3 install -r requirements.txt
pip3 install pytest

On newer Debian/Ubuntu, pip3 may refuse to touch system packages. Either use a virtualenv, or append --break-system-packages to the two commands.

valgrind is optional. Without it, CMake skips the 17 valgrind targets and ctest runs 21 tests instead of 38; everything else is identical.

1. Build

cd eBoot
cmake -B build -DEBLDR_BUILD_TESTS=ON -DCMAKE_BUILD_TYPE=Debug
cmake --build build --parallel

One #warning during the build is expected and intentional — it fires because no production signing key is configured, so the RFC 8032 test-vector key is being compiled in as the trust anchor.

2. Run the tests

ctest --test-dir build --output-on-failure

Expected: 100% tests passed, 0 tests failed out of 38 (21 without valgrind). The new one is test_tlv_auth, which you can run on its own:

./build/tests/eboot_test_tlv_auth
TLV authentication (anti-rollback counter)

  test_authenticated_tlv_counter_is_read                     [PASS]
  test_tampered_tlv_counter_is_rejected                      [PASS]
  test_tamper_is_invisible_to_signature_and_integrity        [PASS]
  test_unbound_tlv_area_is_not_trusted                       [PASS]
  test_image_without_tlv_area_still_reports_zero             [PASS]
  test_tlv_binding_fields_are_inside_the_signed_prefix       [PASS]
  test_oversized_tlv_len_is_rejected                         [PASS]

7/7 passed

The script-driven suites:

python3 run_all_tests.py                  # expect 33 passed
python3 tests/production_test_suite.py    # expect 1 failure: SA-6.9 (pre-existing)

SA-6.9 wants a sanitizer job in the CI workflow. It is unrelated to this change and deliberately left alone.

3. Reproduce the original vulnerability

This is the part worth doing yourself. It builds upstream, unpatched eBoot in a throwaway worktree and runs the proof of concept against it.

export EBOOT="$PWD"          # run this from the root of this archive
git worktree add /tmp/eboot-upstream 13a7a02
cd /tmp/eboot-upstream
cmake -B build -DCMAKE_BUILD_TYPE=Debug
cmake --build build --parallel
gcc -I include "$EBOOT/poc/tlv_downgrade_poc.c" -o /tmp/poc \
    build/libeboot_core.a build/libeboot_hal.a -lm
/tmp/poc

Before the fix — the downgrade succeeds:

device anti-rollback floor      : 9
read_image_counter (untampered) : rc=0 counter=3
rollback_verify(3)              : -14  (rejected, as it should be)

after rewriting 4 TLV bytes:
  signed header prefix changed? : NO
  parse_header                  : 0
  verify_integrity (SHA-256)    : 0  (still PASSES)
  read_image_counter            : rc=0 counter=9
  rollback_verify(9)            : 0  (ACCEPTED -- downgrade succeeded)

Four bytes were rewritten. The SHA-256 payload check still passes and not one byte of the signed header prefix changed — because the TLV area sits outside both.

After the fix — same binary, patched library:

cd "$EBOOT"
gcc -I include poc/tlv_downgrade_poc.c -o /tmp/poc_after \
    build/libeboot_core.a build/libeboot_hal.a -lm
/tmp/poc_after
read_image_counter (untampered) : rc=0 counter=0
rollback_verify(0)              : -14  (rejected, as it should be)
...
  read_image_counter            : rc=0 counter=0
  rollback_verify(0)            : -14  (rejected)

The image declares no authenticated TLV area, so nothing in it can raise the anti-rollback floor.

Clean up the worktree when done:

git worktree remove --force /tmp/eboot-upstream

4. Read the change

git log --oneline 13a7a02..HEAD
git diff 13a7a02 -- core/rollback.c include/eos_image.h
git show --stat HEAD~1

The substance is in three files:

File What changed
include/eos_image.h reserved[30] → tlv_len (2 B) + tlv_hash (28 B), both inside the signed prefix, plus static asserts pinning the offsets
core/rollback.c hash the declared TLV area and refuse to read a counter from one that does not match
tests/unit/test_tlv_auth.c the regression test, 7 cases

5. Optional: cross-compile check

Not required, and not something I validated. If you have the toolchain:

cmake -B build-arm -DEBLDR_BOARD=stm32f4 \
  -DCMAKE_TOOLCHAIN_FILE=toolchains/arm-none-eabi.cmake
cmake --build build-arm --parallel