CVE-2022-39354: Incorrect is_static parameter for custom stateful precompiles in SputnikVM (evm)

A custom stateful precompile can use the is_static parameter to determine if the call is executed in a static context (via STATICCALL), and thus decide if stateful operations should be done. Previously, the passed is_static parameter was incorrect – it was only set to true if the call comes from a direct STATICCALL opcode. However, once a static call context is entered, it should stay static.

The issue only impacts custom precompiles that actually uses is_static. The maintainers estimate the usage is low. However, for those affected, it can lead to possible incorrect state transitions.