riscv: Add ARCH_HAS_FORTIFY_SOURCE

FORTIFY_SOURCE could detect various overflows at compile and run time.
ARCH_HAS_FORTIFY_SOURCE means that the architecture can be built and
run with CONFIG_FORTIFY_SOURCE. Select it in RISCV.

See more about this feature from commit 6974f0c4
("include/linux/string.h: add the option of fortified string.h functions").
Signed-off-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NPalmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/Kconfig

@@ -20,6 +20,7 @@ config RISCV
 	select ARCH_HAS_DEBUG_VM_PGTABLE
 	select ARCH_HAS_DEBUG_VIRTUAL if MMU
 	select ARCH_HAS_DEBUG_WX
+	select ARCH_HAS_FORTIFY_SOURCE
 	select ARCH_HAS_GCOV_PROFILE_ALL
 	select ARCH_HAS_GIGANTIC_PAGE
 	select ARCH_HAS_KCOV

arch/riscv/include/asm/string.h

@@ -23,5 +23,10 @@ extern asmlinkage void *__memmove(void *, const void *, size_t);
 #define memcpy(dst, src, len) __memcpy(dst, src, len)
 #define memset(s, c, n) __memset(s, c, n)
 #define memmove(dst, src, len) __memmove(dst, src, len)
+
+#ifndef __NO_FORTIFY
+#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
+#endif
+
 #endif
 #endif /* _ASM_RISCV_STRING_H */