How can PPP loans be used for forgiveness?

The proceeds of a PPP loan are to be used for:

• Payroll costs: gross wages and company paid retirement contributions, limited to $100k per year equivalent during the covered period
• Health Insurance: costs related to the continuation of group health care, life, disability, vision, or dental benefits during periods of paid sick, medical, or family leave, and group health care, life, disability, vision, or dental insurance premiums.
  NOTE: there are specific restrictions on retirement contribution and health insurance limits for the owners/shareholders of the business
• Mortgage interest payments (but not mortgage prepayments or principal payments), for BUSINESS related mortgage place in service prior to Feb. 15th 2020
• Rent payments: business-use office pace or equipment for contracts established prior to Feb. 15th 2020
• Utility payments
• Interest payments on any other debt obligations that were incurred before February 15, 2020
• Refinancing an SBA EIDL loan made between January 31, 2020 and April 3, 2020
• Covered operations expenditures (payments for any business software or cloud computing service that facilitates business operations, product or service delivery, the processing, payment, or tracking of payroll expenses, human resources, sales and billing functions, or accounting or tracking of supplies, inventory, records and expenses)
• Covered property damage costs (costs related to property damage and vandalism or looting due to public disturbances that occurred during 2020 that was not covered by insurance or other compensation)
• Covered supplier costs (expenditures made by a borrower to a supplier of goods for the supply of goods that
  -(A) are essential to the operations of the borrower at the time at which the expenditure is made; and
  -(B) is made pursuant to a contract, order, or purchase order—(i) in effect at any time before the covered period with respect to the applicable covered loan; or (ii) with respect to perishable goods, in effect before or at any time during the covered period with respect to the applicable covered loan)
• Covered worker protection expenditures: operating or a capital expenditures to facilitate the adaptation of the business activities of an entity to comply with requirements established or guidance issued by the Department of Health and Human Services, the Centers for Disease Control, or the Occupational Safety and Health Administration, or any equivalent requirements established or guidance issued by a State or local government, during the period beginning on March 1, 2020 and ending the date on which the national emergency with respect to the COVID– 19 expires related to the maintenance of standards for sanitation, social distancing, or any other worker or customer safety requirement related to COVID–19. Such expenditures may include: the purchase, maintenance, or renovation of assets that create or expand:
  1- a drive-through window facility
  2- an indoor, outdoor, or combined air or air pressure ventilation or filtration system
  3- a physical barrier such as a sneeze guard
  4- an expansion of additional indoor, outdoor, or combined business space;
  5- An onsite or offsite health screening capability
  6- other assets relating to the compliance with the requirements or guidance described in subparagraph (A), as determined by the Administrator in consultation with the Secretary of Health and Human Services and the Secretary of Labor; and (ii) the purchase of—(I) covered materials described in section 328.103(a) of title 44, Code of Federal Regulations, or any successor regulation; (II) particulate filtering face piece respirators approved by the National Institute for Occupational Safety and Health, including those approved only for emergency use authorization; or (III) other kinds of personal protective equipment, as determined by the Administrator in consultation with the Secretary of Health and Human Services and the Secretary of Labor; and (C) such expenditures do not include residential real property or intangible property).

From page 13 and 14 of this PDF from treasury, related to updates to PPP program as of 12/27/2020:
https://home.treasury.gov/system/files/136/Interim-Final-Rule-Paycheck-Protection-Program-as-Amended-by-Economic-Aid-Act.pdf