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

[Will Deacon <will@kernel.org>]

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@google.com>
> ---
> Link: https://lore.kernel.org/rust-for-linux/20240808221138.873750-1-ojeda@kernel.org/ [1]
> ---
> Changes in v6:
> - Move Kconfig requirements into arch/*/Kconfig.
> - List non-dynamic SCS as supported on 1.82. This reflects newly added
>   things in rustc.
> - Link to v5: https://lore.kernel.org/r/20240806-shadow-call-stack-v5-1-26dccb829154@google.com
> 
> Changes in v5:
> - Rebase series on v6.11-rc2.
> - The first patch is no longer included as it was merged in v6.11-rc2.
> - The commit message is rewritten from scratch.
> - Link to v4: https://lore.kernel.org/r/20240729-shadow-call-stack-v4-0-2a664b082ea4@google.com
> 
> Changes in v4:
> - Move `depends on` to CONFIG_RUST.
> - Rewrite commit messages to include more context.
> - Link to v3: https://lore.kernel.org/r/20240704-shadow-call-stack-v3-0-d11c7a6ebe30@google.com
> 
> Changes in v3:
> - Use -Zfixed-x18.
> - Add logic to reject unsupported rustc versions.
> - Also include a fix to be backported.
> - Link to v2: https://lore.kernel.org/rust-for-linux/20240305-shadow-call-stack-v2-1-c7b4a3f4d616@google.com/
> 
> Changes in v2:
> - Add -Cforce-unwind-tables flag.
> - Link to v1: https://lore.kernel.org/rust-for-linux/20240304-shadow-call-stack-v1-1-f055eaf40a2c@google.com/
> ---
>  Makefile            | 1 +
>  arch/arm64/Kconfig  | 7 ++++++-
>  arch/arm64/Makefile | 3 +++
>  arch/riscv/Kconfig  | 7 ++++++-
>  init/Kconfig        | 1 -
>  5 files changed, 16 insertions(+), 3 deletions(-)

For the arm64 parts:

Acked-by: Will Deacon <will@kernel.org>

In which tree do you plan to merge this?

Cheers,

Will