Re: [PATCH RFC v3 36/36] net: kasan: kmsan: support CONFIG_GENERIC_CSUM on x86, enable it for KASAN/KMSAN

[Marco Elver <elver@google.com>]

On Fri, 22 Nov 2019 at 12:28, <glider@google.com> wrote:
>
> This is needed to allow memory tools like KASAN and KMSAN see the
> memory accesses from the checksum code. Without CONFIG_GENERIC_CSUM the
> tools can't see memory accesses originating from handwritten assembly
> code.
> For KASAN it's a question of detecting more bugs, for KMSAN using the C
> implementation also helps avoid false positives originating from
> seemingly uninitialized checksum values.

The files touched are only in x86. The title mentions 'net' -- is this
still accurate?

> Signed-off-by: Alexander Potapenko <glider@google.com>
> To: Alexander Potapenko <glider@google.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Michal Simek <monstr@monstr.eu>
> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Cc: Vegard Nossum <vegard.nossum@oracle.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: Randy Dunlap <rdunlap@infradead.org>
> Cc: linux-mm@kvack.org
> ---
>
> v2:
>  - dropped the "default n" (as requested by Randy Dunlap)
>
> Change-Id: I645e2c097253a8d5717ad87e2e2df6f6f67251f3
> ---
>  arch/x86/Kconfig                |  4 ++++
>  arch/x86/include/asm/checksum.h | 10 +++++++---
>  arch/x86/lib/Makefile           |  2 ++
>  3 files changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 3f83a5c53808..f497aae3dbf4 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -272,6 +272,10 @@ config GENERIC_ISA_DMA
>         def_bool y
>         depends on ISA_DMA_API
>
> +config GENERIC_CSUM
> +       bool
> +       default y if KMSAN || KASAN

When would it be desirable to use GENERIC_CSUM without KMSAN or KASAN?

If it is generally a bad idea to disable GENERIC_CSUM with KMSAN and
KASAN, does it make more sense to just remove this config option and
unconditionally (if CONFIG_K{A,M}SAN) use the asm-generic version in
checksum.h?

This would simplify this patch and avoid introducing a config option
that will likely never be set explicitly.

>  config GENERIC_BUG
>         def_bool y
>         depends on BUG
> diff --git a/arch/x86/include/asm/checksum.h b/arch/x86/include/asm/checksum.h
> index d79d1e622dcf..ab3464cbce26 100644
> --- a/arch/x86/include/asm/checksum.h
> +++ b/arch/x86/include/asm/checksum.h
> @@ -1,6 +1,10 @@
>  /* SPDX-License-Identifier: GPL-2.0 */
> -#ifdef CONFIG_X86_32
> -# include <asm/checksum_32.h>
> +#ifdef CONFIG_GENERIC_CSUM
> +# include <asm-generic/checksum.h>
>  #else
> -# include <asm/checksum_64.h>
> +# ifdef CONFIG_X86_32
> +#  include <asm/checksum_32.h>
> +# else
> +#  include <asm/checksum_64.h>
> +# endif
>  #endif
> diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
> index 5246db42de45..bca9031de9ff 100644
> --- a/arch/x86/lib/Makefile
> +++ b/arch/x86/lib/Makefile
> @@ -55,7 +55,9 @@ endif
>          lib-$(CONFIG_X86_USE_3DNOW) += mmx_32.o
>  else
>          obj-y += iomap_copy_64.o
> +ifneq ($(CONFIG_GENERIC_CSUM),y)
>          lib-y += csum-partial_64.o csum-copy_64.o csum-wrappers_64.o
> +endif
>          lib-y += clear_page_64.o copy_page_64.o
>          lib-y += memmove_64.o memset_64.o
>          lib-y += copy_user_64.o

Thanks,
-- Marco