linux-kernel - Re: [PATCH v3 04/10] rust: list: add struct with prev/next pointers

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAH5fLggKphE3f=Jv+pfXc+_qjsGBVpXw_F4fOJiAi6vNtJ5x+Q@mail.gmail.com>
Date: Thu, 1 Aug 2024 11:42:48 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: Miguel Ojeda <ojeda@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, Wedson Almeida Filho <wedsonaf@...il.com>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Andreas Hindborg <a.hindborg@...sung.com>, Marco Elver <elver@...gle.com>, Coly Li <colyli@...e.de>, 
	Paolo Abeni <pabeni@...hat.com>, Pierre Gondois <pierre.gondois@....com>, 
	Ingo Molnar <mingo@...nel.org>, Jakub Kicinski <kuba@...nel.org>, Wei Yang <richard.weiyang@...il.com>, 
	Matthew Wilcox <willy@...radead.org>, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, Kees Cook <kees@...nel.org>
Subject: Re: [PATCH v3 04/10] rust: list: add struct with prev/next pointers

On Wed, Jul 31, 2024 at 8:41 PM Benno Lossin <benno.lossin@...ton.me> wrote:
>
> On 23.07.24 10:22, Alice Ryhl wrote:
> > +/// The prev/next pointers for an item in a linked list.
> > +///
> > +/// # Invariants
> > +///
> > +/// The fields are null if and only if this item is not in a list.
> > +#[repr(transparent)]
> > +pub struct ListLinks<const ID: u64 = 0> {
> > +    #[allow(dead_code)]
> > +    inner: Opaque<ListLinksFields>,
>
> Do you really need `Opaque`? Or would `UnsafeCell` be enough? (If it is
> enough and you change this, be aware that `Opaque` is `!Unpin`, so if
> you intend for `ListLinks` to also be `!Unpin`, then you need a
> `PhantomPinned`)

I need the `!Unpin` part for aliasing.

> > +}
> > +
> > +// SAFETY: The next/prev fields of a ListLinks can be moved across thread boundaries.
>
> Why? This is not a justification.

What would you say?

> > +unsafe impl<const ID: u64> Send for ListLinks<ID> {}
> > +// SAFETY: The type is opaque so immutable references to a ListLinks are useless. Therefore, it's
> > +// okay to have immutable access to a ListLinks from several threads at once.
>
> You don't need to argue via `Opaque`, the type doesn't expose any
> `&self` functions, so there are no functions to consider.

I'm not arguing via the `Opaque` type. I'm just using "opaque" as a
normal english word with its normal meaning.

Alice