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Date: Wed, 7 Nov 2018 17:04:58 +0000
From: Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH v10 05/22] kasan: add CONFIG_KASAN_GENERIC and
 CONFIG_KASAN_SW_TAGS
Message-ID: <20181107170458.jirk2b3tszrcagbt@lakrids.cambridge.arm.com>
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 <ea8f0391d7befab4afec34d2a009028cd9e0f326.1541525354.git.andreyknvl@google.com>
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To: Andrey Konovalov <andreyknvl@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>, Alexander Potapenko <glider@google.com>, Dmitry Vyukov <dvyukov@google.com>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, Christoph Lameter <cl@linux.com>, Andrew Morton <akpm@linux-foundation.org>, Nick Desaulniers <ndesaulniers@google.com>, Marc Zyngier <marc.zyngier@arm.com>, Dave Martin <dave.martin@arm.com>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, "Eric W . Biederman" <ebiederm@xmission.com>, Ingo Molnar <mingo@kernel.org>, Paul Lawrence <paullawrence@google.com>, Geert Uytterhoeven <geert@linux-m68k.org>, Arnd Bergmann <arnd@arndb.de>, "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Kate Stewart <kstewart@linuxfoundation.org>, Mike Rapoport <rppt@linux.vnet.ibm.com>, kasan-dev@googlegroups.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-sparse@vger.kernel.org, linux-mm@kvack.org, linux-kbuild@vger.kernel.org, Kostya Serebryany <kcc@google.com>, Evgeniy Stepanov <eugenis@google.com>, Lee Smith <Lee.Smith@arm.com>, Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>, Jacob Bramley <Jacob.Bramley@arm.com>, Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>, Jann Horn <jannh@google.com>, Mark Brand <markbrand@google.com>, Chintan Pandya <cpandya@codeaurora.org>, Vishwath Mohan <vishwath@google.com>

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@virtuozzo.com>
> Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> ---
>  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.