On Tue, Dec 3, 2019 at 3:17 PM Marco Elver <elver@xxxxxxxxxx> wrote:
>
> On Fri, 22 Nov 2019 at 12:28, <glider@xxxxxxxxxx> 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?
Not sure :/
I'll probably replace it with "x86:", as other patches to this file
don't mention "net".
> > Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
> > To: Alexander Potapenko <glider@xxxxxxxxxx>
> > Cc: Arnd Bergmann <arnd@xxxxxxxx>
> > Cc: Michal Simek <monstr@xxxxxxxxx>
> > Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> > Cc: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
> > Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> > Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> > Cc: linux-mm@xxxxxxxxx
> > ---
> >
> > 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.
There is already a similar option for MIPS and m68k, so I think it's
better to be consistent with them.
> > 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
--
Alexander Potapenko
Software Engineer
Google Germany GmbH
Erika-Mann-Straße, 33
80636 München
Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
