riscv: implement __get_kernel_nofault and __put_user_nofault

Implement the non-faulting kernel access helpers directly instead of
abusing the uaccess routines under set_fs(KERNEL_DS).
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/include/asm/uaccess.h

@@ -486,6 +486,26 @@ unsigned long __must_check clear_user(void __user *to, unsigned long n)
 	__ret;							\
 })
 
+#define HAVE_GET_KERNEL_NOFAULT
+
+#define __get_kernel_nofault(dst, src, type, err_label)			\
+do {									\
+	long __kr_err;							\
+									\
+	__get_user_nocheck(*((type *)(dst)), (type *)(src), __kr_err);	\
+	if (unlikely(__kr_err))						\
+		goto err_label;						\
+} while (0)
+
+#define __put_kernel_nofault(dst, src, type, err_label)			\
+do {									\
+	long __kr_err;							\
+									\
+	__put_user_nocheck(*((type *)(dst)), (type *)(src), __kr_err);	\
+	if (unlikely(__kr_err))						\
+		goto err_label;						\
+} while (0)
+
 #else /* CONFIG_MMU */
 #include <asm-generic/uaccess.h>
 #endif /* CONFIG_MMU */