riscv: Omit optimized string routines when using KASAN

The optimized string routines are implemented in assembly, so they are
not instrumented for use with KASAN. Fall back to the C version of the
routines in order to improve KASAN coverage. This fixes the
kasan_strings() unit test.
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Tested-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20240801033725.28816-2-samuel.holland@sifive.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/include/asm/string.h

@@ -19,6 +19,7 @@ extern asmlinkage void *__memcpy(void *, const void *, size_t);
 extern asmlinkage void *memmove(void *, const void *, size_t);
 extern asmlinkage void *__memmove(void *, const void *, size_t);
 
+#if !(defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS))
 #define __HAVE_ARCH_STRCMP
 extern asmlinkage int strcmp(const char *cs, const char *ct);
 
@@ -27,6 +28,7 @@ extern asmlinkage __kernel_size_t strlen(const char *);
 
 #define __HAVE_ARCH_STRNCMP
 extern asmlinkage int strncmp(const char *cs, const char *ct, size_t count);
+#endif
 
 /* For those files which don't want to check by kasan. */
 #if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)

arch/riscv/kernel/riscv_ksyms.c

@@ -12,9 +12,6 @@
 EXPORT_SYMBOL(memset);
 EXPORT_SYMBOL(memcpy);
 EXPORT_SYMBOL(memmove);
-EXPORT_SYMBOL(strcmp);
-EXPORT_SYMBOL(strlen);
-EXPORT_SYMBOL(strncmp);
 EXPORT_SYMBOL(__memset);
 EXPORT_SYMBOL(__memcpy);
 EXPORT_SYMBOL(__memmove);

arch/riscv/lib/Makefile

@@ -3,9 +3,11 @@ lib-y			+= delay.o
 lib-y			+= memcpy.o
 lib-y			+= memset.o
 lib-y			+= memmove.o
+ifeq ($(CONFIG_KASAN_GENERIC)$(CONFIG_KASAN_SW_TAGS),)
 lib-y			+= strcmp.o
 lib-y			+= strlen.o
 lib-y			+= strncmp.o
+endif
 lib-y			+= csum.o
 ifeq ($(CONFIG_MMU), y)
 lib-$(CONFIG_RISCV_ISA_V)	+= uaccess_vector.o

arch/riscv/lib/strcmp.S

@@ -120,3 +120,4 @@ strcmp_zbb:
 .option pop
 #endif
 SYM_FUNC_END(strcmp)
+EXPORT_SYMBOL(strcmp)

arch/riscv/lib/strlen.S

@@ -131,3 +131,4 @@ strlen_zbb:
 #endif
 SYM_FUNC_END(strlen)
 SYM_FUNC_ALIAS(__pi_strlen, strlen)
+EXPORT_SYMBOL(strlen)

arch/riscv/lib/strncmp.S

@@ -136,3 +136,4 @@ strncmp_zbb:
 .option pop
 #endif
 SYM_FUNC_END(strncmp)
+EXPORT_SYMBOL(strncmp)

arch/riscv/purgatory/Makefile

 # SPDX-License-Identifier: GPL-2.0
 
 purgatory-y := purgatory.o sha256.o entry.o string.o ctype.o memcpy.o memset.o
+ifeq ($(CONFIG_KASAN_GENERIC)$(CONFIG_KASAN_SW_TAGS),)
 purgatory-y += strcmp.o strlen.o strncmp.o
+endif
 
 targets += $(purgatory-y)
 PURGATORY_OBJS = $(addprefix $(obj)/,$(purgatory-y))