linux-kernel - Re: [PATCH v7 7/7] rust: enable `clippy::ref_as

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: <CAJ-ks9n3BdKkfCpMXhE8M8Sx4B5rASoNvbmA4zPU3rmPQwZCiQ@mail.gmail.com>
Date: Thu, 27 Mar 2025 15:44:09 -0400
From: Tamir Duberstein <tamird@...il.com>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nicolas Schier <nicolas@...sle.eu>, Miguel Ojeda <ojeda@...nel.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
	Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Brendan Higgins <brendan.higgins@...ux.dev>, David Gow <davidgow@...gle.com>, 
	Rae Moar <rmoar@...gle.com>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Luis Chamberlain <mcgrof@...nel.org>, Russ Weight <russ.weight@...ux.dev>, Rob Herring <robh@...nel.org>, 
	Saravana Kannan <saravanak@...gle.com>, Abdiel Janulgue <abdiel.janulgue@...il.com>, 
	Daniel Almeida <daniel.almeida@...labora.com>, Robin Murphy <robin.murphy@....com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	FUJITA Tomonori <fujita.tomonori@...il.com>, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com, 
	linux-pci@...r.kernel.org, linux-block@...r.kernel.org, 
	devicetree@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	netdev@...r.kernel.org
Subject: Re: [PATCH v7 7/7] rust: enable `clippy::ref_as_ptr` lint

On Thu, Mar 27, 2025 at 10:15 AM Tamir Duberstein <tamird@...il.com> wrote:
>
> On Wed, Mar 26, 2025 at 6:15 PM Benno Lossin <benno.lossin@...ton.me> wrote:
> >
> > On Wed Mar 26, 2025 at 11:09 PM CET, Tamir Duberstein wrote:
> > > On Wed, Mar 26, 2025 at 5:09 PM Benno Lossin <benno.lossin@...ton.me> wrote:
> > >> On Wed Mar 26, 2025 at 8:06 PM CET, Tamir Duberstein wrote:
> > >> > On Wed, Mar 26, 2025 at 1:36 PM Benno Lossin <benno.lossin@...ton.me> wrote:
> > >> >> On Wed Mar 26, 2025 at 5:57 PM CET, Tamir Duberstein wrote:
> > >> >> >
> > >> >> > Yeah, we should do this - but again: not relevant in this discussion.
> > >> >>
> > >> >> I think it's pretty relevant.
> > >> >
> > >> > It's not relevant because we're no longer talking about transmuting
> > >> > pointer to pointer. The two options are:
> > >> > 1. transmute reference to reference.
> > >> > 2. coerce reference to pointer, `as` cast pointer to pointer (triggers
> > >> > `ptr_as_ptr`), reborrow pointer to reference.
> > >> >
> > >> > If anyone can help me understand why (2) is better than (1), I'd
> > >> > certainly appreciate it.
> > >>
> > >> I am very confident that (2) is correct. With (1) I'm not sure (see
> > >> above), so that's why I mentioned it.
> > >
> > > Can you help me understand why you're confident about (2) but not (1)?
> >
> > My explanation from above explains why I'm not confident about (1):
> >
> >     For ptr-to-int transmutes, I know that they will probably remove
> >     provenance, hence I am a bit cautious about using them for ptr-to-ptr or
> >     ref-to-ref.
> >
> > The reason I'm confident about (2) is that that is the canonical way to
> > cast the type of a reference pointing to an `!Sized` value.
>
> Do you have a citation, other than the transmute doc?

Turns out this appeases clippy:

diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs
index 80a9782b1c6e..7a6fc78fc314 100644
--- a/rust/kernel/uaccess.rs
+++ b/rust/kernel/uaccess.rs
@@ -240,9 +240,10 @@ pub fn read_raw(&mut self, out: &mut
[MaybeUninit<u8>]) -> Result {
     /// Fails with [`EFAULT`] if the read happens on a bad address,
or if the read goes out of
     /// bounds of this [`UserSliceReader`]. This call may modify
`out` even if it returns an error.
     pub fn read_slice(&mut self, out: &mut [u8]) -> Result {
+        let out: *mut [u8] = out;
         // SAFETY: The types are compatible and `read_raw` doesn't
write uninitialized bytes to
         // `out`.
-        let out = unsafe { &mut *(out as *mut [u8] as *mut
[MaybeUninit<u8>]) };
+        let out = unsafe { &mut *(out as *mut [MaybeUninit<u8>]) };
         self.read_raw(out)
     }

Benno, would that work for you? Same in str.rs, of course.