[PATCH v4 1/2] rust: SHADOW_CALL_STACK is incompatible with Rust

[Alice Ryhl]

When using the shadow call stack sanitizer, all code must be compiled
with the -ffixed-x18 flag, but this flag is not currently being passed
to Rust. This results in crashes that are extremely difficult to debug.

To ensure that nobody else has to go through the same debugging session
that I had to, prevent configurations that enable both SHADOW_CALL_STACK
and RUST.

It is rather common for people to backport 724a75ac9542 ("arm64: rust:
Enable Rust support for AArch64"), so I recommend applying this fix all
the way back to 6.1.

Cc: <stable at vger.kernel.org> # 6.1 and later
Fixes: 724a75ac9542 ("arm64: rust: Enable Rust support for AArch64")
Signed-off-by: Alice Ryhl <aliceryhl at google.com>
---
 init/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/init/Kconfig b/init/Kconfig
index b0238c4b6e79..914edf51b068 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1909,6 +1909,7 @@ config RUST
 	depends on !MODVERSIONS
 	depends on !GCC_PLUGINS
 	depends on !RANDSTRUCT
+	depends on !SHADOW_CALL_STACK
 	depends on !DEBUG_INFO_BTF || PAHOLE_HAS_LANG_EXCLUDE
 	help
 	  Enables Rust support in the kernel.

-- 
2.46.0.rc1.232.g9752f9e123-goog