Basic law

Basic Law is not constitution by itself. It is a law made according to PRC constitution article 31. This is the text:

第三十一條
國家在必要時得設立特別行政區。在特別行政區內實行的制度按照具體情況由全國人民代表大會以法律規定。
(Sorry for unable to provide English translation for you)

Therefore, Hongkong Basic Law is strictly under PRC constitution, at least depends on survivability of article 31. Without article 31, Basic law is nothing. The root is not from DOJ, but PRC constitution (but probably DOJ may add the text related to the article in future).

We should understand that Hongkong Basic Law is not truly a basic Law, which is designed to supersede a suspended constitution. Moreover, even a true basic law is not a constitution by itself.
(For reader: note for my usage of case, "Basic Law" is not "basic law")

However, Hongkong Basic Law is special constitutional status, and it is different from ordinance and other Hongkong law. It is correct to say an enforcement/legistration of law is unconstitutional if it violates Basic Law.

Hong Kong is not a country but a special administrative region. The Basic Law could not therefore be regarded as the constitution of Hong Kong. However, having regard to the the nature of Basic Law, it has been referred to as the "mini constitution (小憲法）" of Hong Kong, meaning that it is the highest law of Hong Kong only subject to the PRC's constitution.

More information could be found from these books from public libraries：
1"Hong Kong New Constitutional Order" by Yash Ghai
2“香港基本法簡釋”楊靜輝 等著