On Tue, Aug 06, 2024 at 10:01:44AM +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 > 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. > > At the time of writing, all released rustc versions up to and including > 1.81 incorrectly think that the Rust targets aarch64-unknown-none and > riscv64-unknown-none-elf don't support -Zsanitizer=shadow-call-stack, so > the build will fail if you enable shadow call stack in non-dynamic mode. > See [1] for the relevant feature request. To avoid this compilation > failure, Kconfig is set up to reject such configurations. > > Note that because these configurations are rejected, this patch only > allows SCS to be used with arm64 and not on riscv. However, once [1] is > implemented, I will submit a follow-up patch that allows configurations > without UNWIND_PATCH_PAC_INTO_SCS on sufficiently new compilers. That > patch will implicitly allow SCS to be enabled on riscv, but this is okay > because unlike arm64, riscv does not need any flags for rustc beyond > -Zsanitizer=shadow-call-stack. > > 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 `depends on` clause is placed on `config 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. > > Link: https://github.com/rust-lang/rust/issues/121972 [1] > Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx> I'd like to make sure Ard is happy with this, but from what I can see it looks correct. Thanks! Reviewed-by: Kees Cook <kees@xxxxxxxxxx> -- Kees Cook
