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@xxxxxxxxxx> Thanks for continuing to chase this down. Reviewed-by: Kees Cook <kees@xxxxxxxxxx> -- Kees Cook
