It is not known if Cole spotted the riot police guarding the red carpet with batons and shields, or if she had any idea what the film was about as she posed for photographers in a white bandage dress split to the thigh.
She is a "spokesmodel" for L'Oreal, which sponsors the festival.
Around 1,200 protesters demonstrated outside the festival hall on the Croisette and the nearby town hall, although there was no violence as police with batons and shields lined up opposite them.
Right-wing politicians have accused Bouchareb of distorting history in his emotionally-charged account of two Algerian brothers who are driven from their home by the French and grow up to fight in mainland France for the Algerian National Liberation Front (FLN).
It opens with a massacre of Algerian civilians by French soldiers in the town of Setif in 1945 -- a historical event which critics say is misrepresented.
The brothers flee and end up in an immigrant shanty town in Paris, where two of them launch a campaign of violence targeting French police but also fellow Algerians, justifying their violent tactics as a "revolution".
Ahead of the festival, some politicians criticised the film's treatment of France's role in Algeria during the colonial period and the war that led to independence in 1962.
Lawmaker Lionnel Luca of the governing UMP party said after seeing it on Friday that is was "a partisan, militant, pro-FLN film" which "compared the French to the SS and the French police to the Gestapo".
Police said 1,200 people joined the Cannes protest which involved the far-right National Front party, but no incidents were reported. Army veterans and groups representing former colonists and "harkis", Algerians who fought for France, joined the protest, with demonstrators waving French flags and singing the French national anthem.
"It is a falsification of history," said Frederic Bruno, a 62-year-old pensioner who travelled from Nice to join the rally. In Setif, "the army kept order" after Algerians killed French people, he said.
French historians estimate that some 15,000 Algerians were killed in Setif when forces fired on a pro-independence rally, but their Algerian counterparts put the figure as high as 45,000. More than 100 Europeans also died.
Bouchareb insisted after the screening: "The film isn't a battlefield. The film is not there to provoke confrontation. It is there to launch a calm debate."
