Fix buffer limit of 2000 bytes in CosmWasm

[assafmo]

• Adjust go-cosmwasm rust-to-go FFI to allow arbitrary-length buffers (Related to: Use after free in api/memory.go::receiveSlice CosmWasm/wasmvm#55)
  • This is being fixed in PR Unlimited buffers in ffi CosmWasm/wasmvm#67.
  • While working on this @reuvenpo identified and fixed many memory bugs. These are listed in the description of the PR.
  • This comment in their issue tracker describes future improvements to make buffer-passing more efficient (today there are 2 copies done in each direction, where only 1 is needed)
  • This issue describes bugs discovered in handling of out-of-gas scenarios (They are never handled correctly, and could cause UB before mitigations that the above PR put in place)
• Adjust cosmwasm runtime-to-wasm FFI to allow arbitrary-length buffers
  • Cosmwasm team is going to try doing it themselves again. @reuvenpo helped them find the right approach to implementing this:
    Call export "allocate" from db_read implementation CosmWasm/cosmwasm#245 & boxed the wasmer_instance field of Instance to make it safe to reference CosmWasm/cosmwasm#306
  • Update 2020-05-18: For now this is on hold since this turns out to be nontrivial, and there are other priorities. We expect to return to it though.
  • Update 2020-05-25: work resumed in this PR: Call export "allocate" from db_read implementation CosmWasm/cosmwasm#245
• Port the changes implemented in the cosmwasm repos to our fork

[reuvenpo]

the cosmwasm guys now have issues opened about these topics. we will see if they fix it before i do :D

[assafmo]

CosmWasm/wasmvm#67

[reuvenpo]

This is now pulled in to our repository in #262