uITRON4.0 Specification Memory Protection Extension (Page12)

(4)   Memory object

 

The sequence of memory area which becomes target of kernel memory protection is called memory object. Memory object is one type of kernel object and identified using the starting address. Moreover, memory object is sometimes specified using the arbitrary address inside the memory area.

 

The start address and size of the memory object are restricted to have the boundary and unit that can be used by memory protection through hardware. Moreover, the memory objects do not overlap each other.

In this specification, except the operation of memory block acquisition/release, there is no dynamic unit/split of memory object.

(5)   Kernel Domain, System Domain, User Domain

The protection domain which has the access rights equal to kernel, in other words, which can perform all kind of operations/access over all kernel objects is called kernel domain. The processing units belonging to kernel domain executes in privileged mode of processor. In a system, only one kernel domain exists.

 

The protection domain, which has operation/access restrictions over kernel objects, but the processing units belonging to that executes in privileged mode, is called system domain. Using the processing units executed in privileged mode, the access rights of memory area can be changed without any restrictions. Therefore, malicious programs cannot use system domain for protection. Inside a system, there can be multiple system domains.

The protection domain in which processing units execute in unprivileged mode and there are restrictions in operating/accessing kernel objects is called user domain. Inside a system, there can be multiple user domains.

(6)   Independent Objects

Kernel objects excluding the processing units, can be made not to belong to any protection domain. These kernel objects are called independent objects and can be operated/accessed from all protection domains by default. Similar to kernel objects belonging to protection domain, it is possible to setup a set of protection domains which can operate/access each kernel object.

2.2 Protection Domain Management and setting of belonging Protection Domain

2.2.1 Protection Domain ID number

Protection Domain is a kernel object identified by ID number. The ID number of protection domain will be called as Protection Domain ID.

System Domain and user domain will have positive ID number. (the rule that distinguishes the system objects by defining the negative ID number in uITRON4.0 specification is not adopted here) Kernel Domain will have special ID number (-1).