Re: [PATCH v11 2/3] rust: add parameter support to the `module!` macro

[Andreas Hindborg <a.hindborg@kernel.org>]

"Alice Ryhl" <aliceryhl@google.com> writes:

> On Mon, May 05, 2025 at 11:55:33AM +0200, Andreas Hindborg wrote:
>> "Alice Ryhl" <aliceryhl@google.com> writes:
>>
>> > On Fri, May 02, 2025 at 02:16:35PM +0200, Andreas Hindborg wrote:
>> > It would be a use-after-free to
>> > access it during module teardown. For example, what if I access this
>> > static during its own destructor? Or during the destructor of another
>> > module parameter?
>>
>> Yes, that is a problem.
>>
>> We can get around it for now by just not calling `free` for now. We only
>> support simple types that do not need drop. I think we would have to
>> seal the `ModuleParam` trait for this.
>>
>> For a proper solution, we could
>>  - Require a token to read the parameter.
>>  - Synchronize on a module private field and return an option from the
>>    parameter getter. This would require module exit to run before param
>>    free. I think this is the case, but I did not check.
>>  - Use a `Revocable` and revoke the parameter in `free`.
>>
>> Any other ideas or comments on the outlined solutions?
>
> I think the simplest you can do right now is
>
> trait ModuleParam: Copy

Cool 👍

>
> so that it can't contain any non-trivial values. That way you don't need
> Drop either.
>
> Long term, I think we need a way to detect whether it's safe to access
> module globals. The exact same problem applies to the existing global
> for the module itself - except it's worse there because we can't access
> that one during init either.

Yep.



Best regards,
Andreas Hindborg