Another way of thinking about the problem is that right now every line of code within a process runs with the same permissions. If we could restrict what 3rd party libraries can do - via checks either at build time or runtime - then supply chain attacks like this would be much harder to pull off.
I agree that it wouldn’t stop this library from injecting backdoors into decompressed executables. But I still think it would be a big help anyway. It would stop this attack from working.
At the big picture, we need to acknowledge that we can’t implicitly trust opensource libraries on the internet. They are written by strangers, and if you wouldn’t invite them into your home you shouldn’t give them permission to execute arbitrary code with user level permissions on your computer.
I don’t think there are any one size fits all answers here. And I can’t see a way to make your “tainted output” idea work. But even so, cutting down the trusted surface area from “leftpad can cryptolocker your computer” to “Leftpad could return bad output” sounds like it would move us in the right direction.
And by scratch I mean "without modern hardware" given supply chain attacks also apply to the hardware you build from.
We (obviously) put too much trust in little libraries like xz. I don't see a world in which people start using fewer dependencies in their projects. So given that, I think anything which makes 3rd party dependencies safer than they are now is a good thing. Hence the proposal.
The downside is it adds more complexity. Is that complexity worth it? Hard to say. Thats still worth talking about.
The goal is to restrict what included libraries can do. As you say, in languages like Rust, Go or Swift, the mechanism to do this would also need to work with statically linked code to work. And thats quite tricky, because there are no isolation boundaries between functions in executables.
It should still be possible to build something like this. It would just be inconvenient. In rust, swift and go you'd probably want to implement something like this at compile time.
In rust, I'd start by banning unsafe in dependencies. (Or whitelisting which projects are allowed to use unsafe code.) Then add special annotations on all the methods in the standard library which need special permissions to run. For example, File::open, fork, exec, networking, and so on. In cargo.toml, add a way to specify which permissions your child libraries get. "Import serde, but give it no OS permissions". When you compile your program, the compiler can look at the call tree of each function to see what actually gets called, and make sure the permissions match up. If you call a function in serde which in turn calls File::open (directly or indirectly), and you didn't explicitly allow that, the program should fail to compile.
It should be fine for serde to contain some utility function that calls the banned File::open, so long as the utility function isn't called.
Permissions should be in a tree. As you get further out in the dependency tree, libraries get fewer permissions. If I pass permissions {X,Y} to serde, serde can pass permission {X} to one of its dependencies in turn. But serde can't pass permission {Q} to its dependency - since it doesn't have that capability itself.
Any libraries which use unsafe are sort of trusted to do everything. You might need to insist that any package which calls unsafe code is actively whitelisted by the cargo.toml file in the project root.
Inconvenient is quite the understatement. Designing and implementing something like this for each and every language compiler/runtime requires hugely more effort than doing it on the OS level. The likelihood of mistakes is also far greater.
Perhaps it's worth exploring whether it can be done on the LLVM level so that at least some languages can share an implementation.
