Subsystem firewalls

A method, comprising:

• blocking from a boot of the device, with a first configurable firewall, communication from a first input/output (IO) subsystem of the device to a first range of addresses in a memory mapped address space until the first configurable firewall has been configured with secure code from a trusted execution environment of the device;
• subsequent to the boot, configuring the first configurable firewall with the secure code from the trusted execution environment of the device while code from at least one other execution environment of the device is prevented from configuring the first configurable firewall, wherein the trusted execution environment is associated with a greater level of trust than the at least one other execution environment;
• and
• after the configuring of the first configurable firewall, selectively allowing the first IO subsystem access to the first range of addresses in the memory mapped address space based on the first range of addresses in the memory mapped address space being configured as accessible to the first IO subsystem by the secure code.

An apparatus, comprising:

• at least one hardware processor configured to operate in a trusted execution environment;
• and
• a first input/output (IO) subsystem that is configured to control at least some input/output functions of the apparatus based on secure code received from the trusted execution environment, wherein the first IO subsystem includes:
• a first hardware firewall that is configured such that communication from the first IO subsystem to a first range of addresses in a memory mapped address space is blocked from a boot of the apparatus until the first hardware firewall has been configured, and wherein the first hardware firewall is functional to:
• be configured by the secure code while non-secure code is prevented from configuring the first hardware firewall;
• and
• after configuration of the first hardware firewall, selectively allow the first IO subsystem access to the first range of addresses in the memory mapped address space based on the first range of addresses in the memory mapped address space being configured as accessible to the first IO subsystem by the configuration.