x86: introduce copy_user_handle_tail() routine
Introduce generic C routine for handling necessary tail operations after
protection fault in copy_*_user on x86.
Signed-off-by: Vitaly Mayatskikh <v.mayatskih@gmail.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c
index 0c89d1b..f4df6e7 100644
--- a/arch/x86/lib/usercopy_64.c
+++ b/arch/x86/lib/usercopy_64.c
@@ -158,3 +158,26 @@
}
EXPORT_SYMBOL(copy_in_user);
+/*
+ * Try to copy last bytes and clear the rest if needed.
+ * Since protection fault in copy_from/to_user is not a normal situation,
+ * it is not necessary to optimize tail handling.
+ */
+unsigned long
+copy_user_handle_tail(char *to, char *from, unsigned len, unsigned zerorest)
+{
+ char c;
+ unsigned zero_len;
+
+ for (; len; --len) {
+ if (__get_user_nocheck(c, from++, sizeof(char)))
+ break;
+ if (__put_user_nocheck(c, to++, sizeof(char)))
+ break;
+ }
+
+ for (c = 0, zero_len = len; zerorest && zero_len; --zero_len)
+ if (__put_user_nocheck(c, to++, sizeof(char)))
+ break;
+ return len;
+}