Re: [PATCH 1/4] ubsan: Move cc-option tests into Kconfig

[Nathan Chancellor]

On Fri, Oct 02, 2020 at 03:15:24PM -0700, Kees Cook wrote:
> Instead of doing if/endif blocks with cc-option calls in the UBSAN
> Makefile, move all the tests into Kconfig and use the Makefile to
> collect the results.
> 
> Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Link: https://lore.kernel.org/lkml/CAHk-=wjPasyJrDuwDnpHJS2TuQfExwe=px-SzLeN8GFMAQJPmQ@xxxxxxxxxxxxxx/

I tested menuconfig to make sure all the flags when CONFIG_UBSAN_MISC is
flipped.

Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Tested-by: Nathan Chancellor <natechancellor@xxxxxxxxx>

One comment below.

> ---
>  lib/Kconfig.ubsan      | 48 +++++++++++++++++++++++++++++++++++++++-
>  scripts/Makefile.ubsan | 50 ++++++++++++++----------------------------
>  2 files changed, 64 insertions(+), 34 deletions(-)
> 
> diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
> index 58f8d03d037b..c0b801871e0b 100644
> --- a/lib/Kconfig.ubsan
> +++ b/lib/Kconfig.ubsan
> @@ -36,10 +36,17 @@ config UBSAN_KCOV_BROKEN
>  	  See https://bugs.llvm.org/show_bug.cgi?id=45831 for the status
>  	  in newer releases.
>  
> +config CC_HAS_UBSAN_BOUNDS
> +	def_bool $(cc-option,-fsanitize=bounds)
> +
> +config CC_HAS_UBSAN_ARRAY_BOUNDS
> +	def_bool $(cc-option,-fsanitize=array-bounds)
> +
>  config UBSAN_BOUNDS
>  	bool "Perform array index bounds checking"
>  	default UBSAN
>  	depends on !UBSAN_KCOV_BROKEN
> +	depends on CC_HAS_UBSAN_ARRAY_BOUNDS || CC_HAS_UBSAN_BOUNDS
>  	help
>  	  This option enables detection of directly indexed out of bounds
>  	  array accesses, where the array size is known at compile time.
> @@ -47,11 +54,17 @@ config UBSAN_BOUNDS
>  	  to the {str,mem}*cpy() family of functions (that is addressed
>  	  by CONFIG_FORTIFY_SOURCE).
>  
> +config CC_ARG_UBSAN_BOUNDS
> +	string
> +	default "-fsanitize=array-bounds" if CC_HAS_UBSAN_ARRAY_BOUNDS
> +	default "-fsanitize=bounds"
> +	depends on UBSAN_BOUNDS
> +
>  config UBSAN_LOCAL_BOUNDS
>  	bool "Perform array local bounds checking"
>  	depends on UBSAN_TRAP
> -	depends on CC_IS_CLANG
>  	depends on !UBSAN_KCOV_BROKEN
> +	depends on $(cc-option,-fsanitize=local-bounds)
>  	help
>  	  This option enables -fsanitize=local-bounds which traps when an
>  	  exception/error is detected. Therefore, it should be enabled only
> @@ -69,6 +82,38 @@ config UBSAN_MISC
>  	  own Kconfig options. Disable this if you only want to have
>  	  individually selected checks.
>  
> +config UBSAN_SHIFT
> +	def_bool UBSAN_MISC
> +	depends on $(cc-option,-fsanitize=shift)
> +
> +config UBSAN_DIV_ZERO
> +	def_bool UBSAN_MISC
> +	depends on $(cc-option,-fsanitize=integer-divide-by-zero)
> +
> +config UBSAN_UNREACHABLE
> +	def_bool UBSAN_MISC
> +	depends on $(cc-option,-fsanitize=unreachable)
> +
> +config UBSAN_SIGNED_OVERFLOW
> +	def_bool UBSAN_MISC
> +	depends on $(cc-option,-fsanitize=signed-integer-overflow)
> +
> +config UBSAN_UNSIGNED_OVERFLOW
> +	def_bool UBSAN_MISC
> +	depends on $(cc-option,-fsanitize=unsigned-integer-overflow)
> +
> +config UBSAN_OBJECT_SIZE
> +	def_bool UBSAN_MISC
> +	depends on $(cc-option,-fsanitize=object-size)
> +
> +config UBSAN_BOOL
> +	def_bool UBSAN_MISC
> +	depends on $(cc-option,-fsanitize=bool)
> +
> +config UBSAN_ENUM
> +	def_bool UBSAN_MISC
> +	depends on $(cc-option,-fsanitize=enum)
> +
>  config UBSAN_SANITIZE_ALL
>  	bool "Enable instrumentation for the entire kernel"
>  	depends on ARCH_HAS_UBSAN_SANITIZE_ALL
> @@ -89,6 +134,7 @@ config UBSAN_ALIGNMENT
>  	bool "Enable checks for pointers alignment"
>  	default !HAVE_EFFICIENT_UNALIGNED_ACCESS
>  	depends on !UBSAN_TRAP
> +	depends on $(cc-option,-fsanitize=alignment)
>  	help
>  	  This option enables the check of unaligned memory accesses.
>  	  Enabling this option on architectures that support unaligned
> diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan
> index 9716dab06bc7..72862da47baf 100644
> --- a/scripts/Makefile.ubsan
> +++ b/scripts/Makefile.ubsan
> @@ -1,37 +1,21 @@
>  # SPDX-License-Identifier: GPL-2.0
>  
> -export CFLAGS_UBSAN :=
> +# -fsanitize=* options makes GCC less smart than usual and
> +# increases the number of 'maybe-uninitialized' false-positives.
> +ubsan-cflags-$(CONFIG_UBSAN) += $(call cc-disable-warning, maybe-uninitialized)

Is this just to force -Wno-maybe-uninitialized even when W=2?
-Wmaybe-uninitialized is already disabled globally after
commit 78a5255ffb6a ("Stop the ad-hoc games with
-Wno-maybe-initialized"). I feel like it might be worth a comment in
case that changes in the future but maybe that is a bit much.

> -ifdef CONFIG_UBSAN_ALIGNMENT
> -      CFLAGS_UBSAN += $(call cc-option, -fsanitize=alignment)
> -endif
> +# Enable available and selected UBSAN features.
> +ubsan-cflags-$(CONFIG_UBSAN_ALIGNMENT)		+= -fsanitize=alignment
> +ubsan-cflags-$(CONFIG_UBSAN_BOUNDS)		+= $(CONFIG_CC_ARG_UBSAN_BOUNDS)
> +ubsan-cflags-$(CONFIG_UBSAN_LOCAL_BOUNDS)	+= -fsanitize=local-bounds
> +ubsan-cflags-$(CONFIG_UBSAN_SHIFT)		+= -fsanitize=shift
> +ubsan-cflags-$(CONFIG_UBSAN_DIV_ZERO)		+= -fsanitize=integer-divide-by-zero
> +ubsan-cflags-$(CONFIG_UBSAN_UNREACHABLE)	+= -fsanitize=unreachable
> +ubsan-cflags-$(CONFIG_UBSAN_SIGNED_OVERFLOW)	+= -fsanitize=signed-integer-overflow
> +ubsan-cflags-$(CONFIG_UBSAN_UNSIGNED_OVERFLOW)	+= -fsanitize=unsigned-integer-overflow
> +ubsan-cflags-$(CONFIG_UBSAN_OBJECT_SIZE)	+= -fsanitize=object-size
> +ubsan-cflags-$(CONFIG_UBSAN_BOOL)		+= -fsanitize=bool
> +ubsan-cflags-$(CONFIG_UBSAN_ENUM)		+= -fsanitize=enum
> +ubsan-cflags-$(CONFIG_UBSAN_TRAP)		+= -fsanitize-undefined-trap-on-error
>  
> -ifdef CONFIG_UBSAN_BOUNDS
> -      ifdef CONFIG_CC_IS_CLANG
> -            CFLAGS_UBSAN += -fsanitize=array-bounds
> -      else
> -            CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds)
> -      endif
> -endif
> -
> -ifdef CONFIG_UBSAN_LOCAL_BOUNDS
> -      CFLAGS_UBSAN += -fsanitize=local-bounds
> -endif
> -
> -ifdef CONFIG_UBSAN_MISC
> -      CFLAGS_UBSAN += $(call cc-option, -fsanitize=shift)
> -      CFLAGS_UBSAN += $(call cc-option, -fsanitize=integer-divide-by-zero)
> -      CFLAGS_UBSAN += $(call cc-option, -fsanitize=unreachable)
> -      CFLAGS_UBSAN += $(call cc-option, -fsanitize=signed-integer-overflow)
> -      CFLAGS_UBSAN += $(call cc-option, -fsanitize=object-size)
> -      CFLAGS_UBSAN += $(call cc-option, -fsanitize=bool)
> -      CFLAGS_UBSAN += $(call cc-option, -fsanitize=enum)
> -endif
> -
> -ifdef CONFIG_UBSAN_TRAP
> -      CFLAGS_UBSAN += $(call cc-option, -fsanitize-undefined-trap-on-error)
> -endif
> -
> -      # -fsanitize=* options makes GCC less smart than usual and
> -      # increase number of 'maybe-uninitialized false-positives
> -      CFLAGS_UBSAN += $(call cc-option, -Wno-maybe-uninitialized)
> +export CFLAGS_UBSAN := $(ubsan-cflags-y)
> -- 
> 2.25.1