For more context: we have historically required the crypto instructions because
1. We make heavy use of sha256 in blobfs, where such content-hashing is on the critical path of loading all binaries, and we believe that in the absence of hardware acceleration, product owners will likely find that their performance requirements are difficult to attain and may seek to resolve those issues by compromising core security invariants, which we do not wish to encourage
2. For protecting mutable storage, both reads and writes go through AES-XTS, either in zxcrypt or fxfs-crypt. For similar reasons, we want AES instructions to be accelerated, so that protection of user data is not something that we are motivated to compromise for performance reasons.
3. In any product, we expect to do TLS for a variety of purposes (software updates, time sync, communications with servers, etc.), and don't want poor TLS performance to be a reason that people are later motivated to avoid TLS/use weak ciphersuites/etc.
Since we do not want product owners to be motivated to disable fairly fundamental security features of the system, we have endeavored to ensure that the hardware baseline is likely to adequately support performance requirements, including through the requirement of the ARM crypto instructions on such boards.
-- https://fuchsia-review.googlesource.com/c/fuchsia/+/808670?t... marking the relevant CPU as not supporting crypto instructions.