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From:   Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Date:   Thu, 18 Aug 2022 18:03:04 +0200
Message-ID: <CANiq72mqutW7cDjYQv4qOYOAV6uM8kUWenquQyiG-mEw4DURJA@mail.gmail.com>
Subject: Re: [PATCH v9 06/27] rust: add C helpers
To:     Kees Cook <keescook@chromium.org>
Cc:     Miguel Ojeda <ojeda@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, patches@lists.linux.dev,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Geoffrey Thomas <geofft@ldpreload.com>,
        Wedson Almeida Filho <wedsonaf@google.com>,
        Sven Van Asbroeck <thesven73@gmail.com>,
        Gary Guo <gary@garyguo.net>, Boqun Feng <boqun.feng@gmail.com>,
        Maciej Falkowski <m.falkowski@samsung.com>,
        Wei Liu <wei.liu@kernel.org>,
        =?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>
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On Thu, Aug 18, 2022 at 1:56 AM Kees Cook <keescook@chromium.org> wrote:
>
> Perfect. It may be worth stating this explicitly with the helper. i.e.
> "This is for handling any panic!() calls in core Rust, but should not
> ever be used in the 'kernel' create; failures should be handled."

I am not sure we should say "ever", because there are sometimes
situations where we statically know a situation is impossible. Of
course, "impossible" in practice is possible -- even if it is due to a
single-event upset.

For the "statically impossible" cases, we could simply trigger UB
instead of panicking. However, while developing and debugging one
would like to detect bugs as soon as possible. Moreover, in
production, people may have use cases where killing the world is
better as soon as anything "funny" is detected, no matter what.

So we could make it configurable, so that "Rust statically impossible
panics" can be defined as UB, `make_task_dead()` or a full `BUG()`.

By the way, I should have mentioned the `unwrap()s` too, since they
are pretty much explicit panics. We don't have any in v9 either, but
we do have a couple dozens in the full code (in the 97% not submitted)
in non-test or examples code. Many are of the "statically impossible"
kind, but any that is not merits some discussion, which we can do as
we upstream the different pieces.

Cheers,
Miguel