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Comment by roschdal | Hacker News Reader

JIT compilation is unsecure.

So what, are you willing to go away from von-neumann architecture where instructions are data and data are instructions, i.e. the instruction-data hominocity that underpins JIT compilation? Are you willing to go to a pseudo-Harvard architecture where the ability of JIT compiling is soft locked by other means like VM or strong code authentication or policy protection, which is what Apple is doing.

Fun fact: even Apple themselves have JIT. JavaScriptCore on iOS has JIT, it's just that the App Store policies forbid any application submissions with JIT or trying to mmap/mprotect an executable region. There used to be apps on TrollStore that runs JIT

Typo: it is Homoiconicity, not hominocity. I typed too fast

You're entirely correct because JIT requires violating Write xor Execute security policy. This is the reason on iOS, it is limited to Apple shipped software.

https://en.wikipedia.org/wiki/W%5EX

The wiki page mentions this is only a minor problem. Because everyone just writes, then switches and executes.

But this means that you have to decide who is allowed to switch.

GrapheneOS heavily restricts JIT usage, too:

> - Android Runtime Just-In-Time (JIT) compilation/profiling is fully disabled and replaced with full ahead-of-time (AOT) compilation. The only JIT compilation in the base OS is the V8 JavaScript JIT which is disabled by default for the Vanadium browser with per-site exception support.

> - Dynamic code loading for both native code or Java/Kotlin classes is blocked for nearly the entire base OS. […]

> - Dynamic code loading for both native code or Java/Kotlin classes can be disabled for user installed apps via 3 exploit protection toggles: […]

https://grapheneos.org/features

No, it isn't. JITs don't grant capabilities abilities an equivalent interpreter doesn't already have.

Allowing code execution allows code execution, that's it, that's the entirety of it.

It is the core of ClickHouse for example, for many years. Is it secure enough in your opinion?

Maybe, but surely there are users who are willing to trust all users of their db instance.

The issue is that it restricts from locking-down and securing the system with Write xor Execute memory. So it has system wide implication.

https://en.wikipedia.org/wiki/W%5EX

W^X is typically per mapping, not per memory page and does not interfere with JIT compilation.

Sure, but it still means that the OS has to decide who is allowed to do it and to what extent. Sophisticated worms like Stuxnet would be much harder with strict W^X for example, since CVE-2010-2568 and the like would be much harder to execute.

> Sure, but it still means that the OS has to decide who is allowed to do it and to what extent

It has to do that anyway?

Only if it wants to allow Writable Memory to become Executable, or basically, allow JIT.

How do you propose preventing that without a check?

Signed binaries with the proper assigned OS capabilities.

Yes, but with JIT, you can't really verify what the application does upfront. That is the entire point.

Capabilities are a way to control that, and the point being that only responsible proven applications get the certificate, hence how it all goes on iOS.

You're making the assumption that "responsible" is something provable, but that is not the case, it is specially not easy to prove software is secure from tampering its behaviour.

For that there is bytecode verification as intermediate step, and if you want to go crazy with security, hardware memory tagging with capabilities.

Which at this point most companies would rather save money and forbid JIT altogether.

Note that mainframes and micros have JIT environments that aren't at the same safety level as regular desktop PCs.

For example,

https://medium.com/@dhemanthc/ibm-i-architecture-how-timi-an...

Nonsense, there's no "system wide implications". Mappings are per process, and W^X is just a strategy to help harden individual processes, not the entire system. There's no herd immunity here.

JITs do not grant the ability to bypass any OS/system sandboxes. The lack of W^X doesn't do that, either. If a process opts out of W^X, such as to enable a JIT, it's voluntarily making itself less hardened, but at the end of the day this isn't any more meaningful than the program being allowed to be written in, say, C, which also voluntarily reduces the processes security hardening.

You don’t understand OP’s point because you’re assuming vulnerabilities don’t exist. That is utter nonsense.

In rust, is jit equivalent to an "unsafe" block ?

Read the code in the post. Everything is written in unsafe Rust. The assembly itself knows no memory safety at all and is completely up to the programmer skill whether it can be trusted to not mess up.

Machine code is insecure, we should all run interpreted code in a formally verified interpreter.

Alternatively, only allow for the execution of cryptographly signed static linked binaries, this naturally includes the interpreter above.

If we are sprinkling formal verification on things, we can sprinkle it on a JIT.

But then we'd have to admit that it's not the JIT that's a problem, it's the lack of guardrails and analysis features in the machine code interfaces that higher level languages expose!

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