Pausable precompiles

[RomanHodulak]

Description

Introduces pausable precompiles for stopping the engine when it hits a precompiled function. This is useful for emergency cases.

Performance / NEAR gas cost considerations

Increases gas cost by a few Tgas because of additional storage read operation to load the few bytes of paused precompiles flags.

Testing

Every added module is covered by a set of unit tests covering every conceived test scenario.

Then there is a module in engine-tests containing a set of functional tests that checks several test scenarios on the wasm binary. For example, there is a test case hitting a paused precompile during a smart contract execution that expects the error ERR_PAUSED.

How should this be reviewed

You should consider the administrative engine smart contract methods this feature is going to be controlled by. Take a look at test scenarios to get an idea. Separately from that, there is the mechanism of ensuring calling a paused precompile throws an error, which you should observe.

Additional information

I have some thoughts considering the use-cases/usefulness of the engine smart contract API of this feature:

Engine smart contract method interface

The current interface is like this:

As an admin I want to pause modexp, its associated flag is 0b000000000010000. To pause it I need to run:

pause_precompiles(0b000000000010000)

The cause of the issue that made me pause modexp is resolved, now I run:

resume_precompiles(0b000000000010000)

Seems pretty inconvenient to need to know the right binary flag. Maybe it would be better to accept a list of stringified versions? So the previous example would run like this:

pause_precompiles(["MODEXP"])

resume_precompiles(["MODEXP"])

Also, when you hit invalid string, the error message could include a list of all possible precompile strings.

pause_precompiles(["MODXP"])

Invalid precompile "MODXP", pick one or more from this list: "MODEXP", "BLAKE2F", ...

Reading the current state from the engine smart contract

The paused_precompiles method returns u32, where each 1-bit identifies a paused precompile. Same as above, more human friendly would be to return a list:

paused_precompiles() -> Vec<String>

For example, outputs:

["MODEXP", "BLAKE2F", ...]

[joshuajbouw]

Make sure CI is working please.

[mrLSD]

@RomanHodulak it looks like Gast cost increased?

[joshuajbouw]

Please fix CI @RomanHodulak.

Just note that gas increases are not ideal. If gas must be increased, its important to note in the PR why it is increasing / decreasing.

[mooori]

As an admin I want to pause modexp, its associated flag is 0b000000000010000. To pause it I need to run:

pause_precompiles(0b000000000010000)

The cause of the issue that made me pause modexp is resolved, now I run:

resume_precompiles(0b000000000010000)

Seems pretty inconvenient to need to know the right binary flag.

The bitflags crate could be helpful here.

[joshuajbouw]

As noted in call, be sure to update https://github.com/aurora-is-near/aurora-cli as well with the new methods.

[joshuajbouw]

This looks like a well introduced feature which will be helpful. Great job!

[birchmd]

Nice work overall. I think there are some details in the API design that need a second look though.

[birchmd]

Looks good! Thanks for addressing my comments.

[joshuajbouw]

Sorry I broke the mergabiity :(, can you fix this @RomanHodulak ?