The Hunger plan was a plan of the Nazis to feed their army and population at the expense of the population of the occupied territories in the east. From the minutes of a meeting in May '42:
1) The war can only be continued if the entire Wehrmacht is fed from Russia in the third year of the war.
2) If we take what we need out of the country, there can be no doubt that tens of millions of people will die of starvation.
A commonly named figure is that the Nazis planned the death of 30 million people in this context.
In keeping with the hunger plan, the Nazis starved soviet POW and Jews in concentration camps and Getthos. They also attempted to isolate the cities from the countryside in the occupied territories, but ultimately lacked the manpower to do so. Another aspect of the hunger plan was the Siege of Leningrad/Petrograd, here the Nazis attempted to cut off the city. Between 700,000 and one million people died during the Siege of Leningrad. This city was also a target for the Nazis, as it had been a hotbed of the Russian Revolutions.
The soviets certainly knew about the blockade against Leningrad (and did what they could to alleviate its effects). It seems likely that they knew how the Nazis treated their POW, and about the death of two million POW in less than a year. It also seems likely that they knew about the attempts to cut of the cities from the countryside in the occupied areas, as they likely had contact to partisans there. They could also have had other intelligence (orders to Wehrmacht staff to feed themselves off the land etc.).
Did the Soviet Union know, from inferring or other intelligence, that the Nazis wanted to starve tens of millions? Are there soviet sources that clearly state what they knew?
Götz Aly: Vordenker der Vernichtung (I think Aly draws a few unwarranted conclusions, but this book introduced me to the Hunger Plan a few years back)
Felix Wemheuer: Der große Hunger - Hungerkatastrophen unter Stalin und Mao, an excerpt (in German) on the Hunger Plan can be found here.