linux-kernel - Re: [PATCH 2/2] rust: cfi: add support for CFI

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Message-ID: <CAH5fLgjU87JsdwFv9umd0U3vLv=-UPiE6sf=F7B-RTujchcjYw@mail.gmail.com>
Date: Tue, 30 Jul 2024 18:26:45 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Sami Tolvanen <samitolvanen@...gle.com>, Masahiro Yamada <masahiroy@...nel.org>, 
	Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>, 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 2/2] rust: cfi: add support for CFI_CLANG with Rust

On Tue, Jul 30, 2024 at 6:03 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Tue, Jul 30, 2024 at 08:24:15AM -0700, Sami Tolvanen wrote:
> > On Tue, Jul 30, 2024 at 3:32 AM Peter Zijlstra <peterz@...radead.org> wrote:
> > >
> > > On Tue, Jul 30, 2024 at 09:40:12AM +0000, Alice Ryhl wrote:
> > > > From: Matthew Maurer <mmaurer@...gle.com>
> > > >
> > > > Make it possible to use the Control Flow Integrity (CFI) sanitizer when
> > > > Rust is enabled. Enabling CFI with Rust requires that CFI is configured
> > > > to normalize integer types so that all integer types of the same size
> > > > and signedness are compatible under CFI.
> > >
> > > I am assuming -- because I have to, because you're not actually saying
> > > anyting -- that this is fully compatible with the C version and all the
> > > fun and games we play with rewriting the function prologue for FineIBT
> > > and the like also work?
> >
> > Rust uses the same LLVM backend for the actual code generation, so it
> > should be fully compatible.
>
> Yes, but we also combine that with -fpatchable-function-entry= for a
> very specific effect, and I don't think I see the Rust thingy do that.

Oh, you're right. I missed this because we're not using FineIBT, and
when this patch was originally written we had not yet implemented a
Rust equivalent to -fpatchable-function-entry=. However, that flag is
now available as of rustc version 1.80.0, so it shouldn't be an issue.
I'll fix this for v2 of this series.

Thanks for catching this!

As for whether it works other than that, I've been using this on my
personal phone together with Rust Binder for several months, so it's
well tested on arm64.

Alice