stackleak: Support Clang stack depth tracking

Wire up stackleak to Clang's proposed[1] stack depth tracking callback
option. While __noinstr already contained __no_sanitize_coverage, it was
still needed for __init and __head section markings. This is needed to
make sure the callback is not executed in unsupported contexts.

Link: llvm/llvm-project#138323 [1]
Signed-off-by: Kees Cook <[email protected]>
Message-Id: <[email protected]>

Author: kees

arch/x86/include/asm/init.h

@@ -5,7 +5,7 @@
 #if defined(CONFIG_CC_IS_CLANG) && CONFIG_CLANG_VERSION < 170000
 #define __head	__section(".head.text") __no_sanitize_undefined __no_stack_protector
 #else
-#define __head	__section(".head.text") __no_sanitize_undefined
+#define __head	__section(".head.text") __no_sanitize_undefined __no_sanitize_coverage
 #endif
 
 struct x86_mapping_info {

include/linux/init.h

@@ -49,7 +49,9 @@
 
 /* These are for everybody (although not all archs will actually
    discard it in modules) */
-#define __init		__section(".init.text") __cold  __latent_entropy __noinitretpoline
+#define __init		__section(".init.text") __cold __latent_entropy	\
+						__noinitretpoline	\
+						__no_sanitize_coverage
 #define __initdata	__section(".init.data")
 #define __initconst	__section(".init.rodata")
 #define __exitdata	__section(".exit.data")

scripts/Makefile.ubsan

@@ -22,3 +22,15 @@ ubsan-integer-wrap-cflags-$(CONFIG_UBSAN_INTEGER_WRAP)     +=	\
 	-fsanitize=implicit-unsigned-integer-truncation		\
 	-fsanitize-ignorelist=$(srctree)/scripts/integer-wrap-ignore.scl
 export CFLAGS_UBSAN_INTEGER_WRAP := $(ubsan-integer-wrap-cflags-y)
+
+ifdef CONFIG_CC_IS_CLANG
+stackleak-cflags-$(CONFIG_STACKLEAK)	+=	\
+	-fsanitize-coverage=stack-depth		\
+	-fsanitize-coverage-stack-depth-callback-min=$(CONFIG_STACKLEAK_TRACK_MIN_SIZE)
+export STACKLEAK_CFLAGS := $(stackleak-cflags-y)
+ifdef CONFIG_STACKLEAK
+    DISABLE_STACKLEAK		:= -fno-sanitize-coverage=stack-depth
+endif
+export DISABLE_STACKLEAK
+KBUILD_CFLAGS += $(STACKLEAK_CFLAGS)
+endif

security/Kconfig.hardening

@@ -158,10 +158,13 @@ config GCC_PLUGIN_STRUCTLEAK_VERBOSE
 	  initialized. Since not all existing initializers are detected
 	  by the plugin, this can produce false positive warnings.
 
+config CC_HAS_SANCOV_STACK_DEPTH_CALLBACK
+	def_bool $(cc-option,-fsanitize-coverage-stack-depth-callback-min=1)
+
 config STACKLEAK
 	bool "Poison kernel stack before returning from syscalls"
 	depends on HAVE_ARCH_STACKLEAK
-	depends on GCC_PLUGINS
+	depends on GCC_PLUGINS || CC_HAS_SANCOV_STACK_DEPTH_CALLBACK
 	help
 	  This option makes the kernel erase the kernel stack before
 	  returning from system calls. This has the effect of leaving