powerpc/inst: Fix sparse detection on get_user_instr()

get_user_instr() lacks sparse detection for the __user tag.

This is because __gui_ptr is assigned with a cast.

Fix that by adding a __chk_user_ptr()
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/0320e5b41a794fd456ab8c5993bbfadcf9e1d8b4.1621516826.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/inst.h

@@ -12,6 +12,8 @@
 	unsigned long __gui_ptr = (unsigned long)ptr;			\
 	struct ppc_inst __gui_inst;					\
 	unsigned int __prefix, __suffix;				\
+									\
+	__chk_user_ptr(ptr);						\
 	__gui_ret = gu_op(__prefix, (unsigned int __user *)__gui_ptr);	\
 	if (__gui_ret == 0) {						\
 		if ((__prefix >> 26) == OP_PREFIX) {			\
@@ -29,7 +31,10 @@
 })
 #else /* !CONFIG_PPC64 */
 #define ___get_user_instr(gu_op, dest, ptr)				\
-	gu_op((dest).val, (u32 __user *)(ptr))
+({									\
+	__chk_user_ptr(ptr);						\
+	gu_op((dest).val, (u32 __user *)(ptr));				\
+})
 #endif /* CONFIG_PPC64 */
 
 #define get_user_instr(x, ptr) \