x86: kasan: kmsan: support CONFIG_GENERIC_CSUM on x86, enable it for KASAN/KMSAN

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.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Alexander Potapenko <[e-mail]>
Cc: Alexander Viro <[e-mail]>
Cc: Alexei Starovoitov <[e-mail]>
Cc: Andrey Konovalov <[e-mail]>
Cc: Andrey Konovalov <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Cc: Christoph Lameter <[e-mail]>
Cc: David Rientjes <[e-mail]>
Cc: Dmitry Vyukov <[e-mail]>
Cc: Eric Biggers <[e-mail]>
Cc: Eric Biggers <[e-mail]>
Cc: Eric Dumazet <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Herbert Xu <[e-mail]>
Cc: Ilya Leoshkevich <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jens Axboe <[e-mail]>
Cc: Joonsoo Kim <[e-mail]>
Cc: Kees Cook <[e-mail]>
Cc: Marco Elver <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Michael S. Tsirkin <[e-mail]>
Cc: Pekka Enberg <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Petr Mladek <[e-mail]>
Cc: Stephen Rothwell <[e-mail]>
Cc: Steven Rostedt <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Vasily Gorbik <[e-mail]>
Cc: Vegard Nossum <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

arch/x86/Kconfig

···
 	def_bool y
 	depends on ISA_DMA_API
 
+config GENERIC_CSUM
+	bool
+	default y if KMSAN || KASAN
+
 config GENERIC_BUG
 	def_bool y
 	depends on BUG

arch/x86/include/asm/checksum.h

···
 /* SPDX-License-Identifier: GPL-2.0 */
-#define  _HAVE_ARCH_COPY_AND_CSUM_FROM_USER 1
-#define HAVE_CSUM_COPY_USER
-#define _HAVE_ARCH_CSUM_AND_COPY
-#ifdef CONFIG_X86_32
-# include <asm/checksum_32.h>
+#ifdef CONFIG_GENERIC_CSUM
+# include <asm-generic/checksum.h>
 #else
-# include <asm/checksum_64.h>
+# define  _HAVE_ARCH_COPY_AND_CSUM_FROM_USER 1
+# define HAVE_CSUM_COPY_USER
+# define _HAVE_ARCH_CSUM_AND_COPY
+# ifdef CONFIG_X86_32
+#  include <asm/checksum_32.h>
+# else
+#  include <asm/checksum_64.h>
+# endif
 #endif

arch/x86/lib/Makefile

···
 endif
 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