Attach IAM Policy to SNS Topic

I am trying deliver a message from an unencrypted SNS topic to an encrypted SQS queue following this guide. I was able to complete the "Configure KMS permissions for AWS services" step, but I am having trouble with the "Configure KMS permissions for producers " step. I have created the IAM role, however attaching this role to my SNS topic is where I am specifically confused. Here are some questions I have which my own research was unable to answer:

• Can an IAM role be attached to a specific item (SNS topic, SQS queue, etc...)? If not, what other way is there to grant permissions to a specific item?
• When the instructions mention "producer", is this referring to the SNS topic or the AWS account which owns the SNS topic?

Any and all help is greatly appreciated.

Edit:

Here is my current AWS KMS key policy:

{
    "Version": "2012-10-17",
    "Id": "key-consolepolicy-3",
    "Statement": [
        {
            "Sid": "Allow administration of the key",
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::${aws_account_id}:root"
            },
            "Action": "kms:*",
            "Resource": "*"
        },
        {
            "Sid": "Allow SNS to use KMS",
            "Effect": "Allow",
            "Principal": {
                "Service": "sns.amazonaws.com"
            },
            "Action": [
                "kms:GenerateDataKey",
                "kms:Decrypt"
            ],
            "Resource": "*"
        }
    ]
}

Whenever I add the following statements to my KMS key policy in the Statement list, I get the error "MalformedPolicyDocumentException - Policy contains a statement with no principal":

{
    "Effect": "Allow",
    "Action": [
        "kms:GenerateDataKey",
        "kms:Decrypt"
    ],
    "Resource": "${kms_customer_managed_key_arn}"
},
{
    "Effect": "Allow",
    "Action": [
        "sqs:SendMessage"
    ],
    "Resource": "${sqs_queue_arn}"
}