kasan: improve and simplify Kconfig.kasan

Turn 'KASAN' into a menuconfig, to avoid cluttering its parent menu with
the suboptions if enabled.  Use 'if KASAN ...  endif' instead of having to
'depend on KASAN' for each entry.
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Walter Wu <walter-zh.wu@mediatek.com>
Link: http://lkml.kernel.org/r/20200629104157.3242503-1-elver@google.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/Kconfig.kasan

@@ -18,7 +18,7 @@ config CC_HAS_KASAN_SW_TAGS
 config CC_HAS_WORKING_NOSANITIZE_ADDRESS
 	def_bool !CC_IS_GCC || GCC_VERSION >= 80300
 
-config KASAN
+menuconfig KASAN
 	bool "KASAN: runtime memory debugger"
 	depends on (HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC) || \
 		   (HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS)
@@ -29,9 +29,10 @@ config KASAN
 	  designed to find out-of-bounds accesses and use-after-free bugs.
 	  See Documentation/dev-tools/kasan.rst for details.
 
+if KASAN
+
 choice
 	prompt "KASAN mode"
-	depends on KASAN
 	default KASAN_GENERIC
 	help
 	  KASAN has two modes: generic KASAN (similar to userspace ASan,
@@ -88,7 +89,6 @@ endchoice
 
 choice
 	prompt "Instrumentation type"
-	depends on KASAN
 	default KASAN_OUTLINE
 
 config KASAN_OUTLINE
@@ -113,7 +113,6 @@ endchoice
 
 config KASAN_STACK_ENABLE
 	bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
-	depends on KASAN
 	help
 	  The LLVM stack address sanitizer has a know problem that
 	  causes excessive stack usage in a lot of functions, see
@@ -134,7 +133,7 @@ config KASAN_STACK
 
 config KASAN_S390_4_LEVEL_PAGING
 	bool "KASan: use 4-level paging"
-	depends on KASAN && S390
+	depends on S390
 	help
 	  Compiling the kernel with KASan disables automatic 3-level vs
 	  4-level paging selection. 3-level paging is used by default (up
@@ -151,7 +150,7 @@ config KASAN_SW_TAGS_IDENTIFY
 
 config KASAN_VMALLOC
 	bool "Back mappings in vmalloc space with real shadow memory"
-	depends on KASAN && HAVE_ARCH_KASAN_VMALLOC
+	depends on HAVE_ARCH_KASAN_VMALLOC
 	help
 	  By default, the shadow region for vmalloc space is the read-only
 	  zero page. This means that KASAN cannot detect errors involving
@@ -164,8 +163,10 @@ config KASAN_VMALLOC
 
 config TEST_KASAN
 	tristate "Module for testing KASAN for bug detection"
-	depends on m && KASAN
+	depends on m
 	help
 	  This is a test module doing various nasty things like
 	  out of bounds accesses, use after free. It is useful for testing
 	  kernel debugging features like KASAN.
+
+endif # KASAN