l4v VS wuffs

> C/C++ can be made memory safe

.. but it's much harder to prove your work is memory safe. sel4 is memory safe C, for example. The safety is achieved by a large external theorem prover and a synced copy written in Haskell. https://github.com/seL4/l4v

Typechecks are form of proof. It's easier to write provably safe Rust than provably safe C because the proofs and checker are integrated.

You can't really retrofit safety to C. The best that can be achieved is sel4, which while it is written in C has a separate proof of its correctness: https://github.com/seL4/l4v

The proof is much, much more work than the microkernel itself. A proof for something as large as webP might take decades.

When something like the seL4 microkernel is formally verified, the remaining bugs should only be bugs in the specification, not the implementation.

seL4 specifications and proofs are not a programming language.

Yes, especially 'logically impossible' when you dig into the details. From the blogpost:

> and the kernel modifications to seL4 that can reclaim the memory used by the rootserver.

MMMMMMMMMMMkkkkkk. So you then have to ask: were these changes also formally verified? There's a metric ton of kernel changes here: https://github.com/AmbiML/sparrow-kernel/commits/sparrow but I don't see a fork of https://github.com/seL4/l4v anywhere inside AmbiML.

I mean, it does also claim to be "almost entirely written in Rust", which is true if you ignore almost the entire OS part of the OS (the kernel and the minimal seL4 runtime).

Probably the only way to prevent this type of issue in an automated fashion is to change your perspective from proving that a bug exists, to proving that it doesn't exist. That is, you define some properties that your program must satisfy to be considered correct. Then, when you make optimizations such as bulk receiver fast-path, you must prove (to the static analysis tool) that your optimizations to not break any of the required properties. You also need to properly specify the required properties in a way that they are actually useful for what people want the code to do.

All of this is incredibly difficult, and an open area of research. Probably the biggest example of this approach is the Sel4 microkernel. To put the difficulty in perspective, I checkout out some of the sel4 repositories did a quick line count.

The repository for the microkernel itself [0] has 276,541

The testsuite [1] has 26,397

The formal verification repo [2] has 1,583,410, over 5 times as much as the source code.

That is not to say that formal verification takes 5x the work. You also have to write your source-code in such a way that it is ammenable to being formally verified, which makes it more difficult to write, and limits what you can reasonably do.

Having said that, this approach can be done in a less severe way. For instance, type systems are essentially a simple form of formal verification. There are entire classes of bugs that are simply impossible in a properly typed programs; and more advanced type systems can eliminate a larger class of bugs. Although, to get the full benefit, you still need to go out of your way to encode some invariant into the type system. You also find that mainstream languages that try to go in this direction always contain some sort of escape hatch to let the programmer assert a portion of code is correct without needing to convince the verifier.

[0] https://github.com/seL4/seL4

[1] https://github.com/seL4/sel4test

[2] https://github.com/seL4/l4v

I mean, just look at the commits with "fix" in the specs folder: https://github.com/seL4/l4v/commits/master?after=4f0bbd4fcbc...

Maybe this is what you are looking for:

https://github.com/google/wuffs

"Wuffs is a memory-safe programming language (and a standard library written in that language) for Wrangling Untrusted File Formats Safely."

It could author its format parsers in https://github.com/google/wuffs, and make them BSD-like open source to maximize adoption.

An even bigger change: It could allow users to choose their iMessage client freely. Why not open up the protocol? I’m sure a security focused client would be popular and in the grand scheme of things easy to author.

Perhaps they could open up more of the OS and apps. Perhaps their claims about the security of users and the App Store is kind of BS.

This is one of the reasons I'm a big fan of wuffs[0] - it specifically targets dealing with formats like pictures, safely, and the result drops in to a C codebase to make the compat/migration story easy.

[0] https://github.com/google/wuffs

There are already huffman-decoding and some parts of webp algorithms in https://github.com/google/wuffs (language that finds missing bounds checks during compilations). In contrary, according to readme, this language allows to write more optimized code (compared to C). WEBP decoding is stated as a midterm target in the roadmap.

Specifically, since performance is crucial for this type of work, it should be written in WUFFS. WUFFS doesn't emit bounds checks (as Java does and as Rust would where it's unclear why something should be in bounds at runtime) it just rejects programs where it can't see why the indexes are in-bounds.

https://github.com/google/wuffs

You can explicitly write the same checks and meet this requirement, but chances are since you believe you're producing a high performance piece of software which doesn't need checks you'll instead be pulled up by the fact the WUFFS tooling won't accept your code and discover you got it wrong.

This is weaker than full blown formal verification, but not for the purpose we care about in program safety, thus a big improvement on humans writing LGTM.

> parsing encoded files tends to introduce vulnerabilities

If we are talking about binary formats, now there are systematic solutions like https://github.com/google/wuffs that protect against vulnerabilities. But SQLite is not just a format - it's an evolving ecosystem with constantly added features. And the most prominent issue was not even in core, it was in FTS3. What will SQLite add next? More json-related functions? Maybe BSON? It is useful, but does not help in this situation.

Regarding traces, there are many forensics tools and even books about forensic analysis of SQLite databases. In well-designed format such tools should not exist in the first place. This is hard requirement: if it requires rewriting the whole file - then so be it.

I agree that Wuffs [1] would have been a very good alternative! If it can be made more generally. AFAIK Wuffs is still very limited, in particular it never allows dynamic allocation. Many formats, including those supported by Wuffs the library, need dynamic allocation, so Wuffs code has to be glued with unverified non-Wuffs code [2]. This only works with simpler formats.

[1] https://github.com/google/wuffs/blob/main/doc/wuffs-the-lang...

[2] https://github.com/google/wuffs/blob/main/doc/note/memory-sa...

There are efforts to do that, notably https://github.com/google/wuffs

RLBox is another interesting option that lets you sandbox C/C++ code.

I think the main reason is that security is one of those things that people don't care about until it is too late to change. They get to the point of having a fast PDF library in C++ that has all the features. Then they realise that they should have written it in a safer language but by that point it means a complete rewrite.

The same reason not enough people use Bazel. By the time most people realise they need it, you've already implemented a huge build system using Make or whatever.

I finally have time to try out wuffs (https://github.com/google/wuffs), which I first heard about here on HN. I want to develop a low-level tokenizer for SDF files, a small-molecule structure file format which started in the 1970s, with lots of, let's call it 'heritage'. Wuffs' ability to process near the data, with a coroutine-like interface, seems like a good fit.

I got the "hello-wuffs-c" example to work, which took some tinkering (see wuffs issue #24). That reads a single string and returns an unsigned int. Despite looking at the example implementations for json parsing, I can't figure out how to go from that example to something which handles multiple input buffer blocks, with string tokens that might straddle two buffers.

Nor could I find third-party examples of people using wuffs-the-language beyond basic experimentation for simple binary data. The handful of non-trivial examples I found only used wuffs-the-library, as a vendored component in a larger project.

The lack of wuffs-the-language use after several years seems a strong sign that I shouldn't look to wuffs for my project. Given the 'workarounds' in #24 are still present after 3 years, it doesn't even seem that widely internally at Google.

Does anyone here have experience to share, or pointers to related projects?

Here's an off-topic answer.

Depends on what you want your toy language to do and what sort of runtime support you'd like to lean on.

JVM is pretty good for a lot of script-y languages, does impose overhead of having a JVM around. Provides GC, Threads, Reflection, consistent semantics. Tons of tools, libraries, support.

WebAssembly is constrained (for running-in-a-browser safety reasons) but then you get to run your code in a browser, or as a service, etc, and Other People are working hard on the problem of getting your WA to go fast. That used to be a big reason for using JVM, but it turns out that Security Is Darn Hard.

I have used C in the (distant) past as an IL, and that works up to a point, implementing garbage collection can be a pain if that's a thing that you want. C compilers have had a lot of work on them over the years, and you also have access to some low-level stuff, so if you were E.G. trying to come up with a little language that had super-good performance, C might be a good choice. (See also, [Wuffs](https://github.com/google/wuffs), by Nigel Tao et al at Google).

A suggestion, if you do target C -- don't work too hard to find isomorphisms between C's data structures and YourToyLang's data structures. Back around 1990, I did my C-generating compiler for Modula-3, and a friend at Xerox PARC used C as a target for Cedar Mesa, and Hans used it in a lower-level way (so I was mapping between M-3 records and C structs, for example, Hans was not) and the lower-level way worked better -- i.e., I chose poorly. It worked, but lower-level worked better.

If you are targeting a higher-level language, Rust and Go both seem like interesting options to me. Both have the disadvantage that they are still changing slightly but you get interesting "services" from the underlying VM -- for Rust, the borrow checker, plus libraries, for Go, reflection, goroutines, and the GC, plus libraries.

Rust should get you slightly higher performance, but I'd worry that you couldn't hide the existence of the borrow checker from your toy language, especially if you wanted to interact with Rust libraries from YTL. If you wanted to learn something vaguely publishable/wider-interesting, that question right there ("can I compile a TL to Rust, touch the Rust libraries, and not expose the borrow checker? No+what-I-tried/Yes+this-worked") is not bad.

I have a minor conflict of interest suggesting Go; I work on Go, usually on the compiler, and machine-generated code makes great test data. But regarded as a VM, I am a little puzzled why it hasn't seen wider use, because the GC is great (for lower-allocation rates than Java however; JVM GC has higher throughout efficiency, but Go has tagless objects, interior pointer support, and tiny pause times. Go-the-language makes it pretty easy to allocate less.) Things Go-as-a-VM currently lacks:

- tail call elimination (JVM same)