powerpc: Use barrier_nospec in copy_from_user()

BugLink: https://bugs.launchpad.net/bugs/1830176

commit ddf35cf3 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

arch/powerpc/include/asm/uaccess.h

@@ -269,6 +269,7 @@ 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;						\
@@ -283,6 +284,7 @@ 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) = (__force __typeof__(*(ptr)))__gu_val;			\
 	__gu_err;						\
@@ -295,8 +297,10 @@ do {								\
 	unsigned long  __gu_val = 0;					\
 	__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;							\
 })
@@ -307,6 +311,7 @@ do {								\
 	unsigned long __gu_val;					\
 	__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;						\
@@ -323,8 +328,10 @@ extern unsigned long __copy_tofrom_user(void __user *to,
 static inline unsigned long copy_from_user(void *to,
 		const void __user *from, unsigned long n)
 {
-	if (likely(access_ok(VERIFY_READ, from, n)))
+	if (likely(access_ok(VERIFY_READ, from, n))) {
+		barrier_nospec();
 		return __copy_tofrom_user((__force void __user *)to, from, n);
+	}
 	memset(to, 0, n);
 	return n;
 }
@@ -359,21 +366,27 @@ static inline unsigned long __copy_from_user_inatomic(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;
 		}
 		if (ret == 0)
 			return 0;
 	}
+
+	barrier_nospec();
 	return __copy_tofrom_user((__force void __user *)to, from, n);
 }
 
@@ -400,6 +413,7 @@ static inline unsigned long __copy_to_user_inatomic(void __user *to,
 		if (ret == 0)
 			return 0;
 	}
+
 	return __copy_tofrom_user(to, (__force const void __user *)from, n);
 }