RDSで始まる場合にIAMロールをEC2に割り当てることができるポリシー

{
    "Version": "2012-10-17",
    "Id": "Secret Policy",
    "Statement": [
        {
            "Sid": "EC2",
            "Effect": "Allow",
            "Action": "ec2:*",
            "Resource": "*"
        },
        {
            "Sid": "Passrole",
            "Effect": "Allow",
            "Action": [
                "iam:PassRole"
            ],
            "Resource": "arn:aws:iam:::role/RDS-*"
        }
    ]
}

参照
https://docs.aws.amazon.com/ja_jp/IAM/latest/UserGuide/id_roles_use_passrole.html