[PATCH v3 2/2] rust: add flags for shadow call stack sanitizer

[Alice Ryhl <aliceryhl@google.com>]

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: https://github.com/rust-lang/rust/issues/121972 [1]
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
 Makefile            | 1 +
 arch/Kconfig        | 2 +-
 arch/arm64/Makefile | 3 +++
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index c11a10c8e710..4ae741601a1c 100644
--- a/Makefile
+++ b/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
diff --git a/arch/Kconfig b/arch/Kconfig
index 238448a9cb71..5a6e296df5e6 100644
--- a/arch/Kconfig
+++ b/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
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 3f0f35fd5bb7..bbf313ddd700 100644
--- a/arch/arm64/Makefile
+++ b/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)

-- 
2.45.2.803.g4e1b14247a-goog