powerpc: Use barrier_nospec in copy_from_user()

Based on the x86 commit doing the same.

See commit 304ec1b0 ("x86/uaccess: Use __uaccess_begin_nospec()
and uaccess_try_nospec") and b3bbfb3f ("x86: Introduce
__uaccess_begin_nospec() and uaccess_try_nospec") for more detail.

In all cases we are ordering the load from the potentially
user-controlled pointer vs a previous branch based on an access_ok()
check or similar.

Base on a patch from Michal Suchanek.
Signed-off-by: Michal Suchanek <msuchanek@suse.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/uaccess.h

@@ -258,6 +258,7 @@ do {								\
 	__chk_user_ptr(ptr);					\
 	if (!is_kernel_addr((unsigned long)__gu_addr))		\
 		might_fault();					\
+	barrier_nospec();					\
 	__get_user_size(__gu_val, __gu_addr, (size), __gu_err);	\
 	(x) = (__typeof__(*(ptr)))__gu_val;			\
 	__gu_err;						\
@@ -269,8 +270,10 @@ do {								\
 	unsigned long  __gu_val = 0;					\
 	const __typeof__(*(ptr)) __user *__gu_addr = (ptr);		\
 	might_fault();							\
-	if (access_ok(VERIFY_READ, __gu_addr, (size)))			\
+	if (access_ok(VERIFY_READ, __gu_addr, (size))) {		\
+		barrier_nospec();					\
 		__get_user_size(__gu_val, __gu_addr, (size), __gu_err);	\
+	}								\
 	(x) = (__force __typeof__(*(ptr)))__gu_val;				\
 	__gu_err;							\
 })
@@ -281,6 +284,7 @@ do {								\
 	unsigned long __gu_val;					\
 	const __typeof__(*(ptr)) __user *__gu_addr = (ptr);	\
 	__chk_user_ptr(ptr);					\
+	barrier_nospec();					\
 	__get_user_size(__gu_val, __gu_addr, (size), __gu_err);	\
 	(x) = (__force __typeof__(*(ptr)))__gu_val;			\
 	__gu_err;						\
@@ -308,15 +312,19 @@ static inline unsigned long raw_copy_from_user(void *to,
 
 		switch (n) {
 		case 1:
+			barrier_nospec();
 			__get_user_size(*(u8 *)to, from, 1, ret);
 			break;
 		case 2:
+			barrier_nospec();
 			__get_user_size(*(u16 *)to, from, 2, ret);
 			break;
 		case 4:
+			barrier_nospec();
 			__get_user_size(*(u32 *)to, from, 4, ret);
 			break;
 		case 8:
+			barrier_nospec();
 			__get_user_size(*(u64 *)to, from, 8, ret);
 			break;
 		}
@@ -324,6 +332,7 @@ static inline unsigned long raw_copy_from_user(void *to,
 			return 0;
 	}
 
+	barrier_nospec();
 	return __copy_tofrom_user((__force void __user *)to, from, n);
 }