rust: kasan: add support for Software Tag-Based KASAN

This adds support for Software Tag-Based KASAN (KASAN_SW_TAGS) when
CONFIG_RUST is enabled. This requires that rustc includes support for
the kernel-hwaddress sanitizer, which is available since 1.96.0 [1].

Unlike with clang, we need to pass -Zsanitizer-recover in addition to
-Zsanitizer because the option is not implied automatically.

Link: rust-lang/rust#153049 [1]
Reviewed-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>

Author: Darksonn

init/Kconfig

@@ -2179,7 +2179,7 @@ config RUST
 	depends on !CFI || HAVE_CFI_ICALL_NORMALIZE_INTEGERS_RUSTC
 	select CFI_ICALL_NORMALIZE_INTEGERS if CFI
 	depends on !CALL_PADDING || RUSTC_VERSION >= 108100
-	depends on !KASAN_SW_TAGS
+	depends on !KASAN_SW_TAGS || RUSTC_VERSION >= 109600
 	depends on !(MITIGATION_RETHUNK && KASAN) || RUSTC_VERSION >= 108300
 	help
 	  Enables Rust support in the kernel.

scripts/Makefile.kasan

@@ -71,8 +71,6 @@ ifdef CONFIG_KASAN_SW_TAGS
 
 CFLAGS_KASAN := -fsanitize=kernel-hwaddress
 
-# This sets flags that will enable SW_TAGS KASAN once enabled in Rust. These
-# will not work today, and is guarded against in dependencies for CONFIG_RUST.
 RUSTFLAGS_KASAN := -Zsanitizer=kernel-hwaddress \
 		   -Zsanitizer-recover=kernel-hwaddress