Re: [PATCH v10 05/22] kasan: add CONFIG_KASAN_GENERIC and CONFIG_KASAN_SW_TAGS

[Mark Rutland]

On Tue, Nov 06, 2018 at 06:30:20PM +0100, Andrey Konovalov wrote:
> This commit splits the current CONFIG_KASAN config option into two:
> 1. CONFIG_KASAN_GENERIC, that enables the generic KASAN mode (the one
>    that exists now);
> 2. CONFIG_KASAN_SW_TAGS, that enables the software tag-based KASAN mode.
> 
> The name CONFIG_KASAN_SW_TAGS is chosen as in the future we will have
> another hardware tag-based KASAN mode, that will rely on hardware memory
> tagging support in arm64.
> 
> With CONFIG_KASAN_SW_TAGS enabled, compiler options are changed to
> instrument kernel files with -fsantize=kernel-hwaddress (except the ones
> for which KASAN_SANITIZE := n is set).
> 
> Both CONFIG_KASAN_GENERIC and CONFIG_KASAN_SW_TAGS support both
> CONFIG_KASAN_INLINE and CONFIG_KASAN_OUTLINE instrumentation modes.
> 
> This commit also adds empty placeholder (for now) implementation of
> tag-based KASAN specific hooks inserted by the compiler and adjusts
> common hooks implementation to compile correctly with each of the
> config options.
> 
> Reviewed-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> ---
>  arch/arm64/Kconfig                  |  1 +
>  include/linux/compiler-clang.h      |  5 +-
>  include/linux/compiler-gcc.h        |  6 ++
>  include/linux/compiler_attributes.h | 13 -----
>  include/linux/kasan.h               | 16 ++++--
>  lib/Kconfig.kasan                   | 87 +++++++++++++++++++++++------
>  mm/kasan/Makefile                   |  6 +-
>  mm/kasan/generic.c                  |  2 +-
>  mm/kasan/kasan.h                    |  3 +-
>  mm/kasan/tags.c                     | 75 +++++++++++++++++++++++++
>  mm/slub.c                           |  2 +-
>  scripts/Makefile.kasan              | 27 ++++++++-
>  12 files changed, 201 insertions(+), 42 deletions(-)
>  create mode 100644 mm/kasan/tags.c
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 787d7850e064..8b331dcfb48e 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -111,6 +111,7 @@ config ARM64
>  	select HAVE_ARCH_JUMP_LABEL
>  	select HAVE_ARCH_JUMP_LABEL_RELATIVE
>  	select HAVE_ARCH_KASAN if !(ARM64_16K_PAGES && ARM64_VA_BITS_48)
> +	select HAVE_ARCH_KASAN_SW_TAGS if !(ARM64_16K_PAGES && ARM64_VA_BITS_48)

Given this relies on a compiler feature, can we please gate this on
compiler feature detection? e.g. in some common Kconfig have:

	select CC_HAS_ASAN_HWADDRESS if $(cc-option -fsanitize=kernel-hwaddress)

... and on arm64 we can do:

	select HAVE_ARCH_KASAN_SW_TAGS if !(ARM64_16K_PAGES && ARM64_VA_BITS_48)

... and core KASAN Kconfig can have:

config KASAN_SW_TAGS
	depends on HAVE_ARCH_KASAN_SW_TAGS
	depends on CC_HAS_ASAN_HWADDRESS

[...]

> +ifeq ($(call cc-option, $(CFLAGS_KASAN) -Werror),)
> +    ifneq ($(CONFIG_COMPILE_TEST),y)
> +        $(warning Cannot use CONFIG_KASAN_SW_TAGS: \
> +            -fsanitize=hwaddress is not supported by compiler)
> +    endif
> +endif

... and then this warning shouldn't be possible, and can go.

Thanks,
Mark.