mm/usercopy: Switch to using lm_alias

The usercopy checking code currently calls __va(__pa(...)) to check for
aliases on symbols. Switch to using lm_alias instead.
Reviewed-by: NMark Rutland <mark.rutland@arm.com>
Tested-by: NMark Rutland <mark.rutland@arm.com>
Acked-by: NKees Cook <keescook@chromium.org>
Signed-off-by: NLaura Abbott <labbott@redhat.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

mm/usercopy.c

@@ -108,13 +108,13 @@ static inline const char *check_kernel_text_object(const void *ptr,
 	 * __pa() is not just the reverse of __va(). This can be detected
 	 * and checked:
 	 */
-	textlow_linear = (unsigned long)__va(__pa(textlow));
+	textlow_linear = (unsigned long)lm_alias(textlow);
 	/* No different mapping: we're done. */
 	if (textlow_linear == textlow)
 		return NULL;
 
 	/* Check the secondary mapping... */
-	texthigh_linear = (unsigned long)__va(__pa(texthigh));
+	texthigh_linear = (unsigned long)lm_alias(texthigh);
 	if (overlaps(ptr, n, textlow_linear, texthigh_linear))
 		return "<linear kernel text>";