Re: Can the Kernel Concurrency Sanitizer Own Rust Code?

[Boqun Feng <boqun.feng@gmail.com>]

Hi Marco,

On Thu, Oct 07, 2021 at 03:01:07PM +0200, Marco Elver wrote:
> Hi Paul,
> 
> Thanks for writing up https://paulmck.livejournal.com/64970.html --
> these were also my thoughts. Similarly for KASAN.
> 
> Sanitizer integration will also, over time, provide quantitative data
> on the rate of bugs in C code, unsafe-Rust, and of course safe-Rust
> code as well as any number of interactions between them once the
> fuzzers are let loose on Rust code.
> 
> Re integrating KCSAN with Rust, this should be doable since rustc does
> support ThreadSanitizer instrumentation:
> https://rustc-dev-guide.rust-lang.org/sanitizers.html
> 
> Just need to pass all the rest of the -mllvm options to rustc as well,
> and ensure it's not attempting to link against compiler-rt. I haven't
> tried, so wouldn't know how it currently behaves.
> 

Thanks for looking into this, and I think you're right: if rustc
supports ThreadSanitizer, then basic features os KCSAN should work.

> Also of importance will be the __tsan_atomic*() instrumentation, which
> KCSAN already provides: my guess is that whatever subset of the LKMM
> Rust initially provides (looking at the current version it certainly
> is the case), the backend will lower them to LLVM atomic intrinsics
> [1], which ThreadSanitizer instrumentation turns into __tsan_atomic*()
> calls.
> [1] https://llvm.org/docs/Atomics.html
> 

Besides atomics, the counterpart of READ_ONCE() and WRITE_ONCE() should
also be looked into, IOW the core::ptr::{read,write}_volatile()
(although I don't think their semantics is completely defined since the
memory model of Rust is incomplete). There could easily be cases where
Rust-side do writes with lock critical sections while C-side do reads
out of the lock critical sections, so Rust-side need to play the
volatile game.

I'm not sure whether rustc will generate special instrumentation for
{read,write}_volatile(), if not, we need to provide something similar to
KCSAN does for READ_ONCE() and WRITE_ONCE().

Regards,
Boqun

> Thanks,
> -- Marco