linux-kernel - Re: [PATCH 1/2] cfi: add CONFIG_CFI_ICALL_NORMALIZE

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Message-ID: <CAH5fLgi6OPLGNztKeM7pD3v7_NG6SrPrhXi8H0tFn6Rx-eVgcw@mail.gmail.com>
Date: Tue, 30 Jul 2024 18:10:45 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nicolas Schier <nicolas@...sle.eu>, Sami Tolvanen <samitolvanen@...gle.com>, 
	Peter Zijlstra <peterz@...radead.org>, Miguel Ojeda <ojeda@...nel.org>, Kees Cook <kees@...nel.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>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...sung.com>, 
	Matthew Maurer <mmaurer@...gle.com>, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 1/2] cfi: add CONFIG_CFI_ICALL_NORMALIZE_INTEGERS

On Tue, Jul 30, 2024 at 1:38 PM Miguel Ojeda
<miguel.ojeda.sandonis@...il.com> wrote:
>
> On Tue, Jul 30, 2024 at 11:40 AM Alice Ryhl <aliceryhl@...gle.com> wrote:
> >
> > Introduce a Kconfig option for enabling the experimental option to
> > normalize integer types. This ensures that integer types of the same
> > size and signedness are considered compatible by the Control Flow
> > Integrity sanitizer.
> >
> > This option exists for compatibility with Rust, as C and Rust do not
> > have the same set of integer types. There are cases where C has two
> > different integer types of the same size and alignment, but Rust only
> > has one integer type of that size and alignment. When Rust calls into
> > C functions using such types in their signature, this results in CFI
> > failures.
> >
> > This patch introduces a dedicated option for this because it is
> > undesirable to have CONFIG_RUST affect CC_FLAGS in this way.
>
> Is there any case where we would want CFI_ICALL_NORMALIZE_INTEGERS
> when Rust is not enabled, then? If not, is the idea here to make this
> an explicit extra question in the config before enabling Rust? Or why
> wouldn't it be done automatically?

I'm adding this flag to make the bringup process for RUST easier.

I'm working on enabling RUST in a new branch. We're eventually going
to have both RUST and CFI_ICALL_NORMALIZE_INTEGERS enabled in our
build, but the path to getting there is complex and we would like to
turn on CFI_ICALL_NORMALIZE_INTEGERS first, and then turn on RUST
later. Both options are non-trivial to turn on and I want to
disentangle them.

Alice