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-rw-r--r--arch/x86/lib/usercopy_64.c23
1 files changed, 23 insertions, 0 deletions
diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c
index 0c89d1bb028..f4df6e7c718 100644
--- a/arch/x86/lib/usercopy_64.c
+++ b/arch/x86/lib/usercopy_64.c
@@ -158,3 +158,26 @@ unsigned long copy_in_user(void __user *to, const void __user *from, unsigned le
}
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;
+}