kasan, powerpc: don't rename memintrinsics if compiler adds prefixes

With appropriate compiler support [1], KASAN builds use __asan prefixed
meminstrinsics, and KASAN no longer overrides memcpy/memset/memmove.

If compiler support is detected (CC_HAS_KASAN_MEMINTRINSIC_PREFIX), define
memintrinsics normally (do not prefix '__').

On powerpc, KASAN is the only user of __mem functions, which are used to
define instrumented memintrinsics.  Alias the normal versions for KASAN to
use in its implementation.

Link: https://lore.kernel.org/all/20230224085942.1791837-1-elver@google.com/ [1]
Link: https://lore.kernel.org/oe-kbuild-all/202302271348.U5lvmo0S-lkp@intel.com/
Link: https://lkml.kernel.org/r/20230227094726.3833247-1-elver@google.comSigned-off-by: Marco Elver <elver@google.com>
Reported-by: kernel test robot <lkp@intel.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>	[powerpc]
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/powerpc/include/asm/kasan.h

@@ -2,7 +2,7 @@
 #ifndef __ASM_KASAN_H
 #define __ASM_KASAN_H
 
-#ifdef CONFIG_KASAN
+#if defined(CONFIG_KASAN) && !defined(CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX)
 #define _GLOBAL_KASAN(fn)	_GLOBAL(__##fn)
 #define _GLOBAL_TOC_KASAN(fn)	_GLOBAL_TOC(__##fn)
 #define EXPORT_SYMBOL_KASAN(fn)	EXPORT_SYMBOL(__##fn)

arch/powerpc/include/asm/string.h

@@ -30,11 +30,17 @@ extern int memcmp(const void *,const void *,__kernel_size_t);
 extern void * memchr(const void *,int,__kernel_size_t);
 void memcpy_flushcache(void *dest, const void *src, size_t size);
 
+#ifdef CONFIG_KASAN
+/* __mem variants are used by KASAN to implement instrumented meminstrinsics. */
+#ifdef CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
+#define __memset memset
+#define __memcpy memcpy
+#define __memmove memmove
+#else /* CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX */
 void *__memset(void *s, int c, __kernel_size_t count);
 void *__memcpy(void *to, const void *from, __kernel_size_t n);
 void *__memmove(void *to, const void *from, __kernel_size_t n);
-
-#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
+#ifndef __SANITIZE_ADDRESS__
 /*
  * For files that are not instrumented (e.g. mm/slub.c) we
  * should use not instrumented version of mem* functions.
@@ -46,8 +52,9 @@ void *__memmove(void *to, const void *from, __kernel_size_t n);
 #ifndef __NO_FORTIFY
 #define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
 #endif
-
-#endif
+#endif /* !__SANITIZE_ADDRESS__ */
+#endif /* CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX */
+#endif /* CONFIG_KASAN */
 
 #ifdef CONFIG_PPC64
 #ifndef CONFIG_KASAN

arch/powerpc/kernel/prom_init_check.sh

@@ -13,8 +13,13 @@
 # If you really need to reference something from prom_init.o add
 # it to the list below:
 
-grep "^CONFIG_KASAN=y$" ${KCONFIG_CONFIG} >/dev/null
-if [ $? -eq 0 ]
+has_renamed_memintrinsics()
+{
+	grep -q "^CONFIG_KASAN=y$" ${KCONFIG_CONFIG} && \
+		! grep -q "^CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX=y" ${KCONFIG_CONFIG}
+}
+
+if has_renamed_memintrinsics
 then
 	MEM_FUNCS="__memcpy __memset"
 else