xdr-terraform-modules/submodules/kms/ami-key/main.tf

resource "aws_kms_key" "key" {
  description         = var.description
  enable_key_rotation = true
  policy              = data.aws_iam_policy_document.kms_policy.json
  tags = merge(
    var.standard_tags,
    { "Name" = var.name },
    var.tags
  )
}

resource "aws_kms_alias" "alias" {
  name          = var.alias
  target_key_id = aws_kms_key.key.key_id
}

data "aws_iam_policy_document" "kms_policy" {
  policy_id = "${var.name}-policy"

  statement {
    sid    = "Enable IAM User Permissions"
    effect = "Allow"
    principals {
      type = "AWS"
      identifiers = [
        # The 'root' account is the entire account, we don't want that
        #"arn:${var.aws_partition}:iam::${var.aws_account_id}:root" 
        "arn:${var.aws_partition}:iam::${var.aws_account_id}:user/MDRAdmin",            # MDRAdmin as a break glass
        "arn:${var.aws_partition}:iam::${var.aws_account_id}:role/user/mdr_terraformer" # Terraformer always gets full access
      ]
    }
    actions   = ["kms:*"]
    resources = ["*"]
  }

  statement {
    sid    = "Allow access for Key Administrators"
    effect = "Allow"
    principals {
      type        = "AWS"
      identifiers = concat(var.key_admin_arns, ["arn:${var.aws_partition}:iam::${var.aws_account_id}:role/user/mdr_terraformer"])
    }

    actions = [
      "kms:Create*",
      "kms:Describe*",
      "kms:Enable*",
      "kms:List*",
      "kms:Put*",
      "kms:Update*",
      "kms:Revoke*",
      "kms:Disable*",
      "kms:Get*",
      "kms:Delete*",
      "kms:TagResource",
      "kms:UntagResource",
      "kms:ScheduleKeyDeletion",
      "kms:CancelKeyDeletion"
    ]
    resources = ["*"]
  }

  statement {
    sid    = "Allow use of the key"
    effect = "Allow"
    principals {
      type        = "AWS"
      identifiers = concat(var.key_user_arns, ["arn:${var.aws_partition}:iam::${var.aws_account_id}:role/user/mdr_terraformer"])
    }
    actions = [
      "kms:Encrypt",
      "kms:Decrypt",
      "kms:ReEncrypt*",
      "kms:GenerateDataKey*",
      "kms:DescribeKey"
    ]
    resources = ["*"]
  }

  statement {
    sid    = "Allow attachment of persistent resources"
    effect = "Allow"
    principals {
      type        = "AWS"
      identifiers = concat(var.key_attacher_arns, ["arn:${var.aws_partition}:iam::${var.aws_account_id}:role/user/mdr_terraformer"])
    }
    actions = [
      "kms:CreateGrant",
      "kms:ListGrants",
      "kms:RevokeGrant"
    ]
    resources = ["*"]
    # This condition is great, but means terraformer can't grant to the asg service
    #    condition {
    #  test = "Bool"
    #  variable =  "kms:GrantIsForAWSResource"
    #  values = [ "true" ]
    #}
  }

  #statement {
  # sid = "Allow vmimport to decrypt SSE-KMS key"
  # effect = "Allow"
  # principals {
  #   type = "AWS"
  #   identifiers = [ "arn:${var.aws_partition}:iam::${var.aws_account_id}:role/vmimport" ]
  # }
  # actions = [ "kms:*" ]
  # resources = [ "*" ]
  #}

  statement {
    sid    = "Allow use of the key by external accounts"
    effect = "Allow"
    principals {
      type        = "AWS"
      identifiers = var.remote_account_arns
    }
    actions = [
      "kms:ReEncryptFrom",
      "kms:DescribeKey"
    ]
    resources = ["*"]
  }
}