JPS6220583B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides a memory protection method in a data processing device that protects a system from rewriting the memory of a user program, discovers program errors, and facilitates debugging. It is related to.

[Conventional technology and problems]

Memory protection methods in conventional data processing devices can be broadly classified into the following two types.

The first type divides the memory into fixed or variable sizes and has a register for each unit that indicates whether the memory can be rewritten or not. To explain with reference to Figure 1A, the memory 0~
Address 10 is an area that should not be rewritten, and this is stored at the beginning of the register. Memory addresses 11 to 20 are rewritable, and this is stored in the next register. By providing such a register, it is possible to indicate which area of the memory cannot be rewritten.

The second is to separate the range that can be referenced logically from the physical memory, and the memory that is logically hidden cannot be rewritten or referenced. 1st
To explain with reference to Figure B, logical memory 0 to
If address 100 has a base address of 100 and a length of 100, addresses 100 to 200 of the physical memory can be rewritten and referenced, but the other shaded areas cannot be rewritten or referenced.

Some of the first methods have just a write-protect bit, some have a read-only bit, some have a key and cannot be accessed if it does not match the key in the program status word, and some have a key with a level There are some that have.

The second method includes supervisor mode, user mode, etc., with different logical access ranges for each mode, map register method, and virtual memory method, which uses segment tables and One that distinguishes the space that can be accessed by a page table, one that has a list that shows the range that can be accessed by program unit,
and so on.

Usually these methods are used in combination.

Some of the conventional memory protection methods described above are not suitable for protection at each level of software, and even if they are suitable, some require special hardware or are difficult to handle by software. It was a lot.

[Purpose of the invention]

In view of the above-mentioned conventional problems, the present invention provides a memory protection method that requires a small amount of hardware, is easy to handle with software, and can implement strong protection for each software level. The purpose is to

[Structure of the invention]

According to the present invention, this purpose is to arrange various programs in memory in order of need for protection, and for all instructions that have operands that need to be accessed in main memory, address in memory where the instruction is located. and the address in memory where the operand accessed by the instruction is located, and if the latter is larger than the former, the instruction is made executable, and if not, a program check is performed. This is achieved by providing a memory protection method using address comparison, which is characterized by:

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a diagram showing the configuration of the memory protection system according to the present invention, and FIG. 3 is a diagram showing the program arrangement in the memory according to the present invention.

In FIG. 2, 1 is a data processing device, 2 is a memory having a specific program arrangement, 3 is an instruction counter register ICR, 4 is an operand address register OAR, and 5 is a comparator.

As shown in FIG. 2, the instruction counter register ICR3 stores the address (instruction address) at which the instruction to be executed in the memory 2 is located. Next, calculate the memory address (operand address) to be accessed by this instruction, and write it to the operand address register OAR.
Accumulate to 4. Then, the contents of ICR3 and OAR4 are compared using a comparator, and the operand is determined from the instruction address.
If the address is large, the instruction is executed normally, but if it is not, an interrupt is generated as a program check.

As shown in FIG. 3, the software to be arranged in the memory 2 is composed of modules at several levels, which are arranged in order of logically small addresses (high need for protection).
For example, the software is arranged in the following order: OS core software, input/output management section software, file management section software, user-common software, and each user's software. Therefore, since lower level programs cannot access higher level areas, protection between levels of programs can be achieved.

Further, the comparison can be performed only on the upper n bits of the address, and the magnitude relationship between the instruction address and the operand address can also be reversed. If the addresses are equal as a result of the address comparison, processing can be normalized, or only one of writing and reading can be prohibited. Furthermore, it can also be used in conjunction with various conventional memory protection schemes.

〔Effect of the invention〕

As explained above in detail, the memory protection method using address comparison according to the present invention requires a small amount of hardware, is easy to handle with software, and can realize powerful protection at each software level. can.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the conventional memory protection method, FIG. 2 is a diagram showing the configuration of the memory protection method according to the present invention, and FIG. 3 is a diagram showing the software arrangement in the memory according to the present invention. FIG. DESCRIPTION OF SYMBOLS 1...Data processing device, 2...Memory, 3...Instruction counter register ICR, 4...Operand address register OAR, 5...Comparator.

Claims (1)

[Claims] 1 Arrange various programs in memory in order of need for protection, and for all instructions that have operands that should be accessed in main memory, write the address in memory where the instruction is located and the operands accessed by the instruction. A memory device based on address comparison that compares the address on the memory where the instruction is located, and if the latter is larger than the former, the instruction is determined to be executable, and if not, a program check is performed.・Protection method.