sanitize precompile input

EIPS/eip-4788.md

@@ -85,6 +85,9 @@ sstore(HISTORY_STORAGE_ADDRESS, root_index, parent_beacon_block_root)
 Beginning at the execution timestamp `FORK_TIMESTAMP`, a "stateful" precompile is deployed at `HISTORY_STORAGE_ADDRESS`.
 
 Callers of the precompile should provide the `timestamp` they are querying encoded as 32 bytes in big-endian format.
+Clients **MUST** sanitize this input call data to the precompile.
+If the input is _more_ than 32 bytes, the precompile only takes the first 32 bytes of the input buffer and ignores the rest.
+If the input is _less_ than 32 bytes, the precompile should revert.
 
 Given this input, the precompile reduces the `timestamp` in the same way during the write routine and first checks if
 the `timestamp` recorded in the ring buffer matches the one supplied by the caller.
@@ -97,6 +100,10 @@ In pseudocode:
 
 ```python
 timestamp = evm.calldata[:32]
+if len(timestamp) != 32:
+    evm.revert()
+    return
+
 timestamp_reduced = to_uint64_be(timestamp) % HISTORICAL_ROOTS_LENGTH
 timestamp_index = to_uint256_be(timestamp_reduced)