Compromising the code that is then most likely run in a test instead of compromising a build script is just a very slight inconvenience for the attacker.
I share the dislike for arbitrary build scripts but restricting them will not help the supply chain issue in a significant way.
Also there are several ways to control build.rs execution in the Cargo ecosystem as well, for example with cargo-deny.
You’re right about attackers being able to change runtime code.
pnpm does have some other features to prevent supply chain attacks, so there is still something to learn from other ecosystems. For example pnpm has a cooldown period for new dependencies and can prevent trust policy downgrades (eg new version published without build provenance where older versions did have it). See https://pnpm.io/supply-chain-security
> pnpm has a cooldown period for new dependencies
Cargo has `min-publish-age` in nightly, and it's currently heading towards stabilization: https://github.com/rust-lang/cargo/pull/17335
Disallow lists are ineffective - better to disallow by default and require opt in.
Also, crates.io can defer serving up newly uploaded scripts that have a new build.rs / proc-macro dependency and warn publicly that a version introduces it.
Restricting build scripts 100% will help mitigate the impact, just not if you only deny it once. And they can develop other things like sandboxing for build scripts by default and escaping that to be the exception that has to be explicitly allowed.
The problem is that build scripts run automatically without user consent or intevention.
`cargo add` is sufficient to compromise you, before you have a chance to even vet the code.
`cargo add` just modifies your Cargo.toml, it doesn't build anything.