We only use AES to generate a wallet encryption key from the user password. In #7689 we ditched the OpenSSL implementation for our own. It intentionally does not use special CPU instructions like AES-NI, because performance is not an issue for our use case. Instead it is based on an existing C implementation that’s known to be constant-time.
We already have a fuzzer that checks an encryption - decryption round trip.
On CPU’s that support it, we could add an additional fuzz target that uses AES-NI on one side of the round trip. We only need the 256 bit variant. The fuzzer probably only needs to support one platform, such as Intel’s AES-NI.
Botan has a c++ implementation: https://github.com/randombit/botan/blob/master/src/lib/block/aes/aes_ni/aes_ni.cpp#L523-L601