How to Fix AWS Managed Key Issues When Restoring Backups

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If you’re trying to restore an AWS Elastic File System (EFS) and encounter the error saying you don’t have permission to use the specified KMS key, don’t worry—you’re not alone. This issue often happens even when your IAM policies seem to be set correctly, especially when dealing with AWS managed keys.

Here’s a straightforward way to troubleshoot and fix this problem:

First, review your IAM policy. Make sure it grants all the necessary KMS permissions, like Encrypt, Decrypt, ReEncrypt, GenerateDataKey, DescribeKey, and CreateGrant. Your current policy includes those actions, which is good. However, because the KMS key is managed by AWS, you can’t change its policy directly.

The key point is that AWS managed keys are designed to be used automatically with AWS services, but sometimes you still need to give your IAM role explicit permission to use them. To do this, you should link your role directly to the specific AWS managed key. Normally, AWS handles this, but in some cases, explicit permissions are required.

Here’s what you can do:

Check the KMS key for your resource: Since it’s an AWS Managed Key, verify if the service (EFS in this case) has the necessary permissions. These permissions are usually granted automatically, but sometimes additional policies are needed on your IAM role.
Attach a policy to your IAM role explicitly allowing use of the AWS managed key: Even though the key is managed by AWS, ensure your IAM role has the correct permissions to use it during restore operations.
Use the correct KMS Key ID: Make sure the KmsKeyId you’re specifying matches the AWS managed key that the service uses automatically. Usually, AWS managed keys have a specific format or ID, and using the right one is crucial.
Add a policy statement for AWS managed keys: To be safe, add a statement allowing your role to perform KMS actions on the specific AWS managed key. For example:

json
{
“Effect”: “Allow”,
“Action”: [
“kms:Encrypt”,
“kms:Decrypt”,
“kms:ReEncrypt“,
“kms:GenerateDataKey“,
“kms:DescribeKey”
],
“Resource”: “arn:aws:kms:your-region:aws:alias/aws/efs”
}

Replace "your-region" with your actual region. This specifies the correct AWS-managed key for EFS.

Test after updating policies: Once you add this permission, try the restore operation again.

Remember, even with a broad IAM policy, issues with AWS managed keys often come down to explicit permissions or correct resource identifiers. Ensuring your role has permission to use the specific AWS managed key linked to your EFS should resolve the issue.

By following these steps, you should be able to restore your EFS without hitting the access denied error.