Comment by hedora
2 years ago
One of the more under-appreciated features of Rust is that it traps on integer overflow / underflow by default.
It’s too bad OpenBSD doesn’t have a good Rust story for the core system. (I understand their reasoning, but it’s still too bad.)
I wonder how hard it would be to backport the integer behavior to C. (C++ would be easy: Use templates.) Perhaps they could add a compiler directive that causes vanilla integer overflow/wraparound to trap, then add annotations or a special library call that supports modulo arithmetic as expected.
Look, I get as much as the next guy that Rust brings a lot of niceties. But what we are talking about here is a project that clocks in at just over 19,000,000 lines of C (`wc -l $(find src -name '*.c' -or -name '*.h')`), code heritage going back more than 40 years, an explicit commitment to a very rich set of platforms [1], and a very limited amount of manpower compared to projects such as Linux with their insane level of corporate backing. "Just rewrite it in and/or integrate Rust" is neither easy nor safe in that it overturns everything that is already there and tested.
[1]: https://www.openbsd.org/plat.html
As for improving upon C. I can not speak for OpenBSD as a project, but I am sure that there would be ample excitement to produce a minimal, solid C compiler with experimental security features to then serve as the default compiler for the project (heck, OpenBSD already ships with a number of less common security-related compiler flags from what I recall). Sadly, I doubt there is either funding or the hands to make that a reality.
This is all true, but this just means that any security focused OS for the next 40 years should consider Rust
Rust brings niceties, but this implies no requirement for considering Rust.
Implying that OpenBSD has not considered Rust? There is plenty of discussion on misc@ already (for example [1]) and while it certainly can be "ranty", I am sure if one reads it in good faith you get a fairly nuanced picture.
[1]: https://marc.info/?l=openbsd-misc&m=151233210523661&w=2
Look, I think a lot of programmers and managers fail to understand the number of factors one needs to consider and how it scales with the complexity of your codebase and what it interacts with. If you want to rewrite your video processing service which you wrote together with five or so contributors and is say 20,000 lines of C++ into Rust, that is one thing. Take a step back and consider the number of users and what you interact with, it all seems rather manageable and you can probably be backwards compatible with respect to your users. In terms of time, maybe a few months? Maybe even six? For a single programmer that now needs to learn proper Rust.
Now, instead consider what an operating system is and the surface with which it interacts. The absolutely metric ton of hardware, the heap of standards, the massive load of hacks that are documented and undocumented, the large amount of users, the number of contributors and their experience, the platforms that you support, all the software that is written for your operating system to make it useful, etc. OpenBSD is famous (infamous?) for being willing to break things to do "the right thing". But they are also famous (infamous, again?) for being very conservative, which I think is understandable given their security focus and (relatively) low amount of manpower. Rust has certainly been considered, but it is far from the only consideration. This is akin to walking into a multi-million dollar company that has a fully functioning service or piece of software that they have been selling for decades and suggest to management that maybe we should start moving it all from C# to Rust next week, while being blissfully unaware of everything else the company is beholden to. Spoiler, it will not work out that way.
Furthermore, it is somewhat tiring that Rust keeps being touted as the final revelation when it comes to writing safer code. Guess what, there were plenty of projects before Rust that introduced safety in various forms (and at various costs) and there will be plenty of projects after Rust that will do the same. Yes, it is an amazing piece of technology, but it is equally plausible that its influence may not end up in it eating the world; rather give birth to something else or bring some of its thinking into other languages. Only time will tell and worse may end up being better yet again.
So to me, what any operating system (security focused or not) should do is to consider their (limited) options given their own goals and situation. Which is something I have seen plenty of evidence that a project of the age of OpenBSD is doing and successfully so.
Personally, I am keeping an eye on Redox and look forward to see what lessons will be learnt from their take of what an operating system can be. But for my servers and desktop I have and continue (for now?) to run a healthy mix of Linux and BSD while getting work done.
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IMHO the biggest blocker for Rust inside OpenBSD is that the project already has killed C developers and moving (some stuff) to Rust will need time and effort that could be put into other problems.
If they had to stabilize some parts, probably the answer would be different.
> IMHO the biggest blocker for Rust inside OpenBSD is that the project already has killed C developers and moving (some stuff) to Rust will need time and effort that could be put into other problems.
I'm all for dropping C in favor of Rust for new projects, but killing C developers is going a bit too far, don't you think?
> One of the more under-appreciated features of Rust is that it traps on integer overflow / underflow by default.
I think this is only true on debug builds, with --release (which most Rust binaries an end-user uses should be compiled with) it just wraps [1] [2]
[1] https://github.com/rust-lang/rfcs/blob/26197104b7bb9a5a35db2... [2] https://stackoverflow.com/a/60238510
There are compiler flags that OpenBSD could be using but aren't, which would have caught this bug without needing to convert the codebase to Rust. Using -Wconversion would have warned on the mismatched signedness of the MAX macro argument (the unsigned integer, sysno) and its result (being assigned to npins, a signed integer). Alternatively, adding -fsanitize=implicit-integer-sign-change, or a UBSan flag that includes this, would detect this at runtime for the actual range of values that end up causing a change of sign.
Though, these would also be triggered by statements like:
Due to the pins array being of unsigned int, so all this sort of code would need to be fixed too.
In this case more important than any runtime overflow/underflow checks is the fact that the compiler will check that comparison operands are of the same type instead of inserting an implicit cast. Instead the programmer is forced to insert an explicit conversion like .try_into().unwrap(), which clearly suggests the possibility of an error. And if the error isn't handled, it will panic.
https://play.rust-lang.org/?version=stable&mode=debug&editio...
A similar warning could be enabled in GCC using the flag -Wsign-compare.
>I wonder how hard it would be to backport the integer behavior to C.
Clang and gcc have flags that can make integer overflow trap.