Fix randao mix processing in Gloas (#4728)

h/t @StefanBratanov for finding this

Author: potuz

specs/gloas/beacon-chain.md

@@ -191,6 +191,7 @@ class ExecutionPayloadBid(Container):
     parent_block_hash: Hash32
     parent_block_root: Root
     block_hash: Hash32
+    prev_randao: Bytes32
     fee_recipient: ExecutionAddress
     gas_limit: uint64
     builder_index: ValidatorIndex
@@ -984,6 +985,7 @@ def process_execution_payload_bid(state: BeaconState, block: BeaconBlock) -> Non
     # Verify that the bid is for the right parent block
     assert bid.parent_block_hash == state.latest_block_hash
     assert bid.parent_block_root == block.parent_root
+    assert bid.prev_randao == get_randao_mix(state, get_current_epoch(state))
 
     # Record the pending payment if there is some payment
     if amount > 0:
@@ -1253,6 +1255,7 @@ def process_execution_payload(
     committed_bid = state.latest_execution_payload_bid
     assert envelope.builder_index == committed_bid.builder_index
     assert committed_bid.blob_kzg_commitments_root == hash_tree_root(envelope.blob_kzg_commitments)
+    assert committed_bid.prev_randao == payload.prev_randao
 
     # Verify the withdrawals root
     assert hash_tree_root(payload.withdrawals) == state.latest_withdrawals_root
@@ -1263,8 +1266,6 @@ def process_execution_payload(
     assert committed_bid.block_hash == payload.block_hash
     # Verify consistency of the parent hash with respect to the previous execution payload
     assert payload.parent_hash == state.latest_block_hash
-    # Verify prev_randao
-    assert payload.prev_randao == get_randao_mix(state, get_current_epoch(state))
     # Verify timestamp
     assert payload.timestamp == compute_time_at_slot(state, state.slot)
     # Verify commitments are under limit

tests/core/pyspec/eth2spec/test/gloas/block_processing/test_process_execution_payload.py

@@ -169,7 +169,7 @@ def prepare_execution_payload_envelope(
     )
 
 
-def setup_state_with_payload_bid(spec, state, builder_index=None, value=None):
+def setup_state_with_payload_bid(spec, state, builder_index=None, value=None, prev_randao=None):
     """
     Helper to setup state with a committed execution payload bid.
     This simulates the state after process_execution_payload_bid has run.
@@ -180,12 +180,16 @@ def setup_state_with_payload_bid(spec, state, builder_index=None, value=None):
     if value is None:
         value = spec.Gwei(0)
 
+    if prev_randao is None:
+        prev_randao = spec.get_randao_mix(state, spec.get_current_epoch(state))
+
     # Create and set the latest execution payload bid
     kzg_list = spec.List[spec.KZGCommitment, spec.MAX_BLOB_COMMITMENTS_PER_BLOCK]()
     bid = spec.ExecutionPayloadBid(
         parent_block_hash=state.latest_block_hash,
         parent_block_root=state.latest_block_header.hash_tree_root(),
         block_hash=spec.Hash32(),
+        prev_randao=prev_randao,
         fee_recipient=spec.ExecutionAddress(),
         gas_limit=spec.uint64(60000000),
         builder_index=builder_index,
@@ -837,6 +841,38 @@ def test_process_execution_payload_wrong_prev_randao(spec, state):
     yield from run_execution_payload_processing(spec, state, signed_envelope, valid=False)
 
 
+@with_gloas_and_later
+@spec_state_test
+@always_bls
+def test_process_execution_payload_bid_prev_randao_mismatch(spec, state):
+    """
+    Test that committed_bid.prev_randao must equal payload.prev_randao
+    """
+    proposer_index = spec.get_beacon_proposer_index(state)
+    # Use a different validator as builder
+    builder_index = (proposer_index + 1) % len(state.validators)
+    make_validator_builder(spec, state, builder_index)
+
+    # Setup bid with one prev_randao value
+    bid_prev_randao = spec.Bytes32(b"\x11" * 32)
+    setup_state_with_payload_bid(
+        spec, state, builder_index, spec.Gwei(2300000), prev_randao=bid_prev_randao
+    )
+
+    execution_payload = build_empty_execution_payload(spec, state)
+    execution_payload.block_hash = state.latest_execution_payload_bid.block_hash
+    execution_payload.gas_limit = state.latest_execution_payload_bid.gas_limit
+    execution_payload.parent_hash = state.latest_block_hash
+    # Set payload with a different prev_randao value
+    execution_payload.prev_randao = spec.Bytes32(b"\x22" * 32)
+
+    signed_envelope = prepare_execution_payload_envelope(
+        spec, state, builder_index=builder_index, execution_payload=execution_payload
+    )
+
+    yield from run_execution_payload_processing(spec, state, signed_envelope, valid=False)
+
+
 @with_gloas_and_later
 @spec_state_test
 @always_bls

tests/core/pyspec/eth2spec/test/gloas/block_processing/test_process_execution_payload_bid.py

@@ -47,6 +47,7 @@ def prepare_signed_execution_payload_bid(
     gas_limit=None,
     block_hash=None,
     blob_kzg_commitments_root=None,
+    prev_randao=None,
     valid_signature=True,
 ):
     """
@@ -88,10 +89,14 @@ def prepare_signed_execution_payload_bid(
         kzg_list = spec.List[spec.KZGCommitment, spec.MAX_BLOB_COMMITMENTS_PER_BLOCK]()
         blob_kzg_commitments_root = kzg_list.hash_tree_root()
 
+    if prev_randao is None:
+        prev_randao = spec.get_randao_mix(state, spec.get_current_epoch(state))
+
     bid = spec.ExecutionPayloadBid(
         parent_block_hash=parent_block_hash,
         parent_block_root=parent_block_root,
         block_hash=block_hash,
+        prev_randao=prev_randao,
         fee_recipient=fee_recipient,
         gas_limit=gas_limit,
         builder_index=builder_index,
@@ -821,3 +826,30 @@ def test_process_execution_payload_bid_wrong_parent_block_root(spec, state):
     block.body.signed_execution_payload_bid = signed_bid
 
     yield from run_execution_payload_bid_processing(spec, state, block, valid=False)
+
+
+@with_gloas_and_later
+@spec_state_test
+def test_process_execution_payload_bid_wrong_prev_randao(spec, state):
+    """
+    Test wrong prev_randao fails (bid.prev_randao != get_randao_mix)
+    """
+    proposer_index = spec.get_beacon_proposer_index(state)
+
+    # Create block first to advance slot
+    block = build_empty_block_for_next_slot(spec, state)
+
+    # Create bid with wrong prev_randao
+    wrong_prev_randao = spec.Bytes32(b"\x42" * 32)
+    signed_bid = prepare_signed_execution_payload_bid(
+        spec,
+        state,
+        builder_index=proposer_index,
+        slot=block.slot,
+        parent_block_root=block.parent_root,
+        prev_randao=wrong_prev_randao,
+    )
+
+    block.body.signed_execution_payload_bid = signed_bid
+
+    yield from run_execution_payload_bid_processing(spec, state, block, valid=False)

tests/core/pyspec/eth2spec/test/helpers/execution_payload.py

@@ -323,10 +323,12 @@ def build_empty_post_gloas_execution_payload_bid(spec, state):
     # to distinguish it from the genesis block hash and have
     # is_parent_node_full correctly return False
     empty_payload_hash = spec.Hash32(b"\x01" + b"\x00" * 31)
+    prev_randao = spec.get_randao_mix(state, spec.get_current_epoch(state))
     return spec.ExecutionPayloadBid(
         parent_block_hash=state.latest_block_hash,
         parent_block_root=parent_block_root,
         block_hash=empty_payload_hash,
+        prev_randao=prev_randao,
         fee_recipient=spec.ExecutionAddress(),
         gas_limit=spec.uint64(0),
         builder_index=builder_index,
@@ -362,15 +364,16 @@ def build_empty_execution_payload(spec, state, randao_mix=None):
     if is_post_gloas(spec):
         latest = state.latest_execution_payload_bid
         parent_hash = latest.parent_block_hash
+        if randao_mix is None:
+            randao_mix = state.latest_execution_payload_bid.prev_randao
     else:
         latest = state.latest_execution_payload_header
         parent_hash = latest.block_hash
+        if randao_mix is None:
+            randao_mix = spec.get_randao_mix(state, spec.get_current_epoch(state))
     timestamp = spec.compute_time_at_slot(state, state.slot)
     empty_txs = spec.List[spec.Transaction, spec.MAX_TRANSACTIONS_PER_PAYLOAD]()
 
-    if randao_mix is None:
-        randao_mix = spec.get_randao_mix(state, spec.get_current_epoch(state))
-
     payload = spec.ExecutionPayload(
         parent_hash=parent_hash,
         fee_recipient=spec.ExecutionAddress(),