linux-kernel - Re: [PATCH] rust: init: remove impl Zeroable for Infallible

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-Id: <F1F3C985-9CAE-4286-B236-4AF6C0918DB5@me.com>
Date: Wed, 20 Mar 2024 21:53:42 -0700
From: Laine Taffin Altman <alexanderaltman@...com>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: Boqun Feng <boqun.feng@...il.com>,
 Miguel Ojeda <ojeda@...nel.org>,
 Alex Gaynor <alex.gaynor@...il.com>,
 Wedson Almeida Filho <wedsonaf@...il.com>,
 Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Andreas Hindborg <a.hindborg@...sung.com>,
 Alice Ryhl <aliceryhl@...gle.com>,
 Martin Rodriguez Reboredo <yakoyoku@...il.com>,
 stable@...r.kernel.org,
 rust-for-linux@...r.kernel.org,
 lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rust: init: remove impl Zeroable for Infallible

On Mar 19, 2024, at 3:34 AM, Benno Lossin <benno.lossin@...ton.me> wrote:
> On 3/19/24 06:28, Laine Taffin Altman wrote:
>> On Mar 18, 2024, at 9:39 PM, Boqun Feng <boqun.feng@...il.com> wrote:
>>> On Mon, Mar 18, 2024 at 08:17:07PM -0700, Laine Taffin Altman wrote:
>>>> On Mar 18, 2024, at 10:25 AM, Boqun Feng <boqun.feng@...il.com> wrote:
>>>>> On Wed, Mar 13, 2024 at 11:09:37PM +0000, Benno Lossin wrote:
>>>>>> From: Laine Taffin Altman <alexanderaltman@...com>
>>>>>> 
>>>>>> It is not enough for a type to be a ZST to guarantee that zeroed memory
>>>>>> is a valid value for it; it must also be inhabited. Creating a value of
>>>>>> an uninhabited type, ZST or no, is immediate UB.
>>>>>> Thus remove the implementation of `Zeroable` for `Infallible`, since
>>>>>> that type is not inhabited.
>>>>>> 
>>>>>> Cc: stable@...r.kernel.org
>>>>>> Fixes: 38cde0bd7b67 ("rust: init: add `Zeroable` trait and `init::zeroed` function")
>>>>>> Closes: https://github.com/Rust-for-Linux/pinned-init/pull/13
>>>>>> Signed-off-by: Laine Taffin Altman <alexanderaltman@...com>
>>>>>> Signed-off-by: Benno Lossin <benno.lossin@...ton.me>
>>>>> 
>>>>> I think either in the commit log or in the code comment, there better be
>>>>> a link or explanation on "(un)inhabited type". The rest looks good to
>>>>> me.
>>>> 
>>>> Would the following be okay for that purpose?
>>>> 
>>>> A type is inhabited if at least one valid value of that type exists; a
>>>> type is uninhabited if no valid values of that type exist.  The terms
>>>> "inhabited" and "uninhabited" in this sense originate in type theory,
>>>> a branch of mathematics.
>>>> 
>>>> In Rust, producing an invalid value of any type is immediate undefined
>>>> behavior (UB); this includes via zeroing memory.  Therefore, since an
>>>> uninhabited type has no valid values, producing any values at all for
>>>> it is UB.
>>>> 
>>>> The Rust standard library type `core::convert::Infallible` is
>>>> uninhabited, by virtue of having been declared as an enum with no
>>>> cases, which always produces uninhabited types in Rust.  Thus, remove
>>>> the implementation of `Zeroable` for `Infallible`, thereby avoiding
>>>> the UB.
>>>> 
>>> 
>>> Yeah, this works for me. Thanks!
>> 
>> Great!  Should it be re-sent or can the new wording be incorporated upon merge?
> 
> I can re-send it for you again, or do you want to send it yourself?
> I think it is also a good idea to add a link to [1] in the code, since
> the above explanation is rather long and fits better in the commit
> message.
> 

I’ll try and do it myself; thank you for sending the first round for me and illustrating procedures!  What Reviewed-By’s/Signed-Off-By's should I retain?

Thanks,
Laine

> -- 
> Cheers,
> Benno
> 
> [1]: https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types