Is Trust Relationship required for both Passrole and AssumeRole to work?

The usage of IAM Passrole is well explained here but it does not explicitly say that for all Passrole and AssumeRole to work, it requires trust relationship.
https://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles_use_passrole.html

In a different scenario, there are AWS CLI commands which takes in the --role-arn parameter. If --role-arn is specified, the AWS service would assume this role to perform operations.

If I have a user account User1 with user_role who executes the command cloudformation create ... --role-arn admin_role:

• Does User1 require Passrole permission to invoke the --role-arn call to pass admin_role to CloudFormation?
• Or is a trust relationship only required for CloudFormation to assume admin_role?

I was trying to determine what is the least privilege for Passrole and AssumeRole. I wanted to find out the extent of trust relationships for these two mechanisms.