kbuild: rust: Enable KASAN support

Rust supports KASAN via LLVM, but prior to this patch, the flags aren't
set properly.
Suggested-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Matthew Maurer <mmaurer@google.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Link: https://lore.kernel.org/r/20240820194910.187826-4-mmaurer@google.com
[ Applied "SW_TAGS KASAN" nit. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

scripts/Makefile.kasan

@@ -12,6 +12,11 @@ endif
 KASAN_SHADOW_OFFSET ?= $(CONFIG_KASAN_SHADOW_OFFSET)
 
 cc-param = $(call cc-option, -mllvm -$(1), $(call cc-option, --param $(1)))
+rustc-param = $(call rustc-option, -Cllvm-args=-$(1),)
+
+check-args = $(foreach arg,$(2),$(call $(1),$(arg)))
+
+kasan_params :=
 
 ifdef CONFIG_KASAN_STACK
 	stack_enable := 1
@@ -41,39 +46,59 @@ CFLAGS_KASAN := $(call cc-option, -fsanitize=kernel-address \
 		$(call cc-option, -fsanitize=kernel-address \
 		-mllvm -asan-mapping-offset=$(KASAN_SHADOW_OFFSET)))
 
-# Now, add other parameters enabled similarly in both GCC and Clang.
-# As some of them are not supported by older compilers, use cc-param.
-CFLAGS_KASAN += $(call cc-param,asan-instrumentation-with-call-threshold=$(call_threshold)) \
-		$(call cc-param,asan-stack=$(stack_enable)) \
-		$(call cc-param,asan-instrument-allocas=1) \
-		$(call cc-param,asan-globals=1)
+# The minimum supported `rustc` version has a minimum supported LLVM
+# version late enough that we can assume support for -asan-mapping-offset.
+RUSTFLAGS_KASAN := -Zsanitizer=kernel-address \
+		   -Zsanitizer-recover=kernel-address \
+		   -Cllvm-args=-asan-mapping-offset=$(KASAN_SHADOW_OFFSET)
+
+# Now, add other parameters enabled similarly in GCC, Clang, and rustc.
+# As some of them are not supported by older compilers, these will be filtered
+# through `cc-param` or `rust-param` as applicable.
+kasan_params += asan-instrumentation-with-call-threshold=$(call_threshold) \
+		asan-stack=$(stack_enable) \
+		asan-instrument-allocas=1 \
+		asan-globals=1
 
 # Instrument memcpy/memset/memmove calls by using instrumented __asan_mem*()
 # instead. With compilers that don't support this option, compiler-inserted
 # memintrinsics won't be checked by KASAN on GENERIC_ENTRY architectures.
-CFLAGS_KASAN += $(call cc-param,asan-kernel-mem-intrinsic-prefix=1)
+kasan_params += asan-kernel-mem-intrinsic-prefix=1
 
 endif # CONFIG_KASAN_GENERIC
 
 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
+
 ifdef CONFIG_KASAN_INLINE
-	instrumentation_flags := $(call cc-param,hwasan-mapping-offset=$(KASAN_SHADOW_OFFSET))
+	kasan_params += hwasan-mapping-offset=$(KASAN_SHADOW_OFFSET)
 else
-	instrumentation_flags := $(call cc-param,hwasan-instrument-with-calls=1)
+	kasan_params += hwasan-instrument-with-calls=1
 endif
 
-CFLAGS_KASAN := -fsanitize=kernel-hwaddress \
-		$(call cc-param,hwasan-instrument-stack=$(stack_enable)) \
-		$(call cc-param,hwasan-use-short-granules=0) \
-		$(call cc-param,hwasan-inline-all-checks=0) \
-		$(instrumentation_flags)
+kasan_params += hwasan-instrument-stack=$(stack_enable) \
+		hwasan-use-short-granules=0 \
+		hwasan-inline-all-checks=0
 
 # Instrument memcpy/memset/memmove calls by using instrumented __hwasan_mem*().
 ifeq ($(call clang-min-version, 150000)$(call gcc-min-version, 130000),y)
-	CFLAGS_KASAN += $(call cc-param,hwasan-kernel-mem-intrinsic-prefix=1)
+	kasan_params += hwasan-kernel-mem-intrinsic-prefix=1
 endif
 
 endif # CONFIG_KASAN_SW_TAGS
 
-export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE
+# Add all as-supported KASAN LLVM parameters requested by the configuration.
+CFLAGS_KASAN += $(call check-args, cc-param, $(kasan_params))
+
+ifdef CONFIG_RUST
+	# Avoid calling `rustc-param` unless Rust is enabled.
+	RUSTFLAGS_KASAN += $(call check-args, rustc-param, $(kasan_params))
+endif # CONFIG_RUST
+
+export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE RUSTFLAGS_KASAN

scripts/Makefile.lib

@@ -167,6 +167,9 @@ ifneq ($(CONFIG_KASAN_HW_TAGS),y)
 _c_flags += $(if $(patsubst n%,, \
 		$(KASAN_SANITIZE_$(target-stem).o)$(KASAN_SANITIZE)$(is-kernel-object)), \
 		$(CFLAGS_KASAN), $(CFLAGS_KASAN_NOSANITIZE))
+_rust_flags += $(if $(patsubst n%,, \
+		$(KASAN_SANITIZE_$(target-stem).o)$(KASAN_SANITIZE)$(is-kernel-object)), \
+		$(RUSTFLAGS_KASAN))
 endif
 endif
 

scripts/generate_rust_target.rs

@@ -207,7 +207,7 @@ fn main() {
         }
         ts.push("features", features);
         ts.push("llvm-target", "x86_64-linux-gnu");
-        ts.push("supported-sanitizers", ["kcfi"]);
+        ts.push("supported-sanitizers", ["kcfi", "kernel-address"]);
         ts.push("target-pointer-width", "64");
     } else if cfg.has("X86_32") {
         // This only works on UML, as i386 otherwise needs regparm support in rustc