CloudFormation is not authorized to perform: iam:PassRole on resource

While I can't say specifically what happened in your situation, the error message means that the Role/User that CloudFormation used to deploy resources did not have appropriate iam:PassRole permissions.

The iam:PassRole permission is used when assigning a role to resources. For example, when an Amazon EC2 instance is launched with an IAM Role, the entity launching the instance requires permission to specify the IAM Role to be used. This is done to prevent users gaining too much permission. For example, a non-administrative user should not be allowed to launch an instance with an Administrative role, since they would then gain access to additional permissions to which they are not entitled.

In the case of your template, it would appear that CloudFormation is creating a function and is assigning the FnRole permission to that function. However, the CloudFormation template has not been given permission to assign this role to the function.

When a CloudFormation template is launched, it either provisions resources as the user who is creating the stack, or using an IAM Role specified when the stack is launched. It is that User/Role that requires the iam:PassRole permissions to use FnRole.

User: arn:aws:sts::156478935478:assumed-role/CodeStarWorker-AppConfig-CloudFormation/AWSCloudFormation is not authorized to perform: iam:PassRole on resource: arn:aws:iam::156478935478:role/service-role/FnRole(Service: AWSLambda; Status Code: 403; Error Code: AccessDeniedException; Request ID: 129f601b-a425-11e8-9659-410b0cc8f4f9)

From this log you can tell what policy (iam:PassRole) needs to be assigned to the CloudFormation role for your stack (CodeStarWorker-AppConfig-CloudFormation).

You should:

• Go IAM > Roles
• Type in search CodeStarWorker-AppConfig-CloudFormation
• Open that role and go to Permissions
• Find CodeStarWorkerCloudFormationRolePolicy, expand it, go Edit policy
• In this following section under resources add ARN of your role (arn:aws:iam::579913947261:role/FnRole), if you don't have that section just copy and paste this, but under Resources use yours ARNs.

Policy:

{
    "Action": [
        "iam:PassRole"
    ],
    "Resource": [
        "arn:aws:iam::156478935478:role/CodeStarWorker-AppConfig-Lambda",
        "arn:aws:iam::579913947261:role/FnRole"
    ],
    "Effect": "Allow"
}

If you want to assign that permission to all resources ("Resource": "*") find this following section and above under actions add the permission you want to assign:

"Resource": "*",
"Effect": "Allow"

You can do apply this for all others permissions you want to assign to CloudFormation for your resources.