rust: add flags for shadow call stack sanitizer

As of rustc 1.80.0, the Rust compiler supports the -Zfixed-x18 flag, so
we can now use Rust with the shadow call stack sanitizer.

On older versions of Rust, it is possible to use shadow call stack by
passing -Ctarget-feature=+reserve-x18 instead of -Zfixed-x18. However,
this flag emits a warning, so this patch does not add support for that.

Currently, the compiler thinks that the aarch64-unknown-none target
doesn't support -Zsanitizer=shadow-call-stack, so the build will fail if
you enable shadow call stack in non-dynamic mode. See [2] for the
feature request to add this. Kconfig is not configured to reject this
configuration because that leads to cyclic Kconfig rules.

Link: rust-lang/rust#121972 [1]
Signed-off-by: Alice Ryhl <aliceryhl@google.com>

Author: Darksonn

Makefile

@@ -945,6 +945,7 @@ ifdef CONFIG_SHADOW_CALL_STACK
 ifndef CONFIG_DYNAMIC_SCS
 CC_FLAGS_SCS	:= -fsanitize=shadow-call-stack
 KBUILD_CFLAGS	+= $(CC_FLAGS_SCS)
+KBUILD_RUSTFLAGS += -Zsanitizer=shadow-call-stack
 endif
 export CC_FLAGS_SCS
 endif

arch/Kconfig

@@ -690,7 +690,7 @@ config SHADOW_CALL_STACK
 	bool "Shadow Call Stack"
 	depends on ARCH_SUPPORTS_SHADOW_CALL_STACK
 	depends on DYNAMIC_FTRACE_WITH_ARGS || DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
-	depends on !RUST
+	depends on !RUST || RUSTC_VERSION >= 108000
 	depends on MMU
 	help
 	  This option enables the compiler's Shadow Call Stack, which

arch/arm64/Makefile

@@ -57,9 +57,11 @@ KBUILD_AFLAGS	+= $(call cc-option,-mabi=lp64)
 ifneq ($(CONFIG_UNWIND_TABLES),y)
 KBUILD_CFLAGS	+= -fno-asynchronous-unwind-tables -fno-unwind-tables
 KBUILD_AFLAGS	+= -fno-asynchronous-unwind-tables -fno-unwind-tables
+KBUILD_RUSTFLAGS += -Cforce-unwind-tables=n
 else
 KBUILD_CFLAGS	+= -fasynchronous-unwind-tables
 KBUILD_AFLAGS	+= -fasynchronous-unwind-tables
+KBUILD_RUSTFLAGS += -Cforce-unwind-tables=y -Zuse-sync-unwind=n
 endif
 
 ifeq ($(CONFIG_STACKPROTECTOR_PER_TASK),y)
@@ -114,6 +116,7 @@ endif
 
 ifeq ($(CONFIG_SHADOW_CALL_STACK), y)
 KBUILD_CFLAGS	+= -ffixed-x18
+KBUILD_RUSTFLAGS += -Zfixed-x18
 endif
 
 ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)