linux-kernel - Re: [PATCH v6] rust: support for shadow call stack sanitizer

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Message-ID: <202408261311.3C191659@keescook>
Date: Mon, 26 Aug 2024 13:12:18 -0700
From: Kees Cook <kees@...nel.org>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
	Jamie Cunliffe <Jamie.Cunliffe@....com>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Conor Dooley <conor@...nel.org>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Nicolas Schier <nicolas@...sle.eu>, Marc Zyngier <maz@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Mark Brown <broonie@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Miguel Ojeda <ojeda@...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>,
	Valentin Obst <kernel@...entinobst.de>,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v6] rust: support for shadow call stack sanitizer

On Mon, Aug 26, 2024 at 02:22:52PM +0000, Alice Ryhl wrote:
> This patch adds all of the flags that are needed to support the shadow
> call stack (SCS) sanitizer with Rust, and updates Kconfig to allow only
> configurations that work.
> 
> The -Zfixed-x18 flag is required to use SCS on arm64, and requires rustc
> version 1.80.0 or greater. This restriction is reflected in Kconfig.
> 
> When CONFIG_DYNAMIC_SCS is enabled, the build will be configured to
> include unwind tables in the build artifacts. Dynamic SCS uses the
> unwind tables at boot to find all places that need to be patched. The
> -Cforce-unwind-tables=y flag ensures that unwind tables are available
> for Rust code.
> 
> In non-dynamic mode, the -Zsanitizer=shadow-call-stack flag is what
> enables the SCS sanitizer. Using this flag requires rustc version 1.82.0
> or greater on the targets used by Rust in the kernel. This restriction
> is reflected in Kconfig.
> 
> It is possible to avoid the requirement of rustc 1.80.0 by using
> -Ctarget-feature=+reserve-x18 instead of -Zfixed-x18. However, this flag
> emits a warning during the build, so this patch does not add support for
> using it and instead requires 1.80.0 or greater.
> 
> The dependency is placed on `select HAVE_RUST` to avoid a situation
> where enabling Rust silently turns off the sanitizer. Instead, turning
> on the sanitizer results in Rust being disabled. We generally do not
> want changes to CONFIG_RUST to result in any mitigations being changed
> or turned off.
> 
> At the time of writing, rustc 1.82.0 only exists via the nightly release
> channel. There is a chance that the -Zsanitizer=shadow-call-stack flag
> will end up needing 1.83.0 instead, but I think it is small.
> 
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>

Thanks for continuing to chase this down.

Reviewed-by: Kees Cook <kees@...nel.org>

-- 
Kees Cook