Visa question about take a cruise

Hello,
I am traveling to Honk Kong from Mexico to take a cruise that starts in Hong Kong. My flight leaves Mexico City and arrives in Shanghai. That same day I take a flight to Hong Kong. I will board the ship that day (Dec 21) and the ship leaves on the 22nd to Vietnam.
The ship ends in Singapur on Jan 3. I fill fly from Singapore on Dec 4th to Shanghai and then to Mexico City on that same day.

Do I need a permit? I am confused since I was told I don't need it for Hong Kong, but I am going through Shanghai.

Please let me know if I need it and if so which type.

Thanks,
Kathia Contreras