JPH01279343A - Main memory protection system for computer system - Google Patents

Abstract

PURPOSE:To reduce overhead and to facilitate the production of a program by setting the lock value of a main memory to receive an access to each key of a control register at the head of a program which has accesses to plural areas having different lock values. CONSTITUTION:A control register 1 holds a 1st key 2 and a 2nd key 3. A lock register 4 holds a lock 18 for each page of a main memory as well as an F flag 19. Then the lock 18 of the corresponding page and the flag 19 are selected via an address line 5 which selects a page to receive an access. The lock 18 of the register 4 and the flag 19 selected by the line 5 as well as both keys 2 and 3 of the register 1 are inputted to two comparators 9 respectively. Then the reading and writing plates set to each key are outputted as the reading and writing permission signals 20 and 22 respectively.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a main memory protection method for a computer system.

[Conventional technology]

Conventionally, regarding main memory protection methods for computer systems, 1, for example, Madnick and Tonopan co-authored, Ikeda method.

Operating Systems, Computer Association of Japan Publishing, pp. 48-51 (MADNICK.

A key-and-lock system described in ``DONOVAN Co-authored'' is known.

[Problem to be solved by the invention]

According to the above-mentioned conventional technology, keys assigned to each program are held in a control register of the computer system.

On the other hand, a lock is held for each fixed capacity (hereinafter referred to as a page) in the main storage device. When a program attempts to access a page in main memory, the key in the control register is compared with the lock of the page to be accessed.

If the key and lock match, both reading and writing to that page is possible. In addition to the lock, the above-mentioned conventional technology includes a bit in the main memory that indicates read permission for each page when the key and lock do not match.

Therefore, even if the key and lock do not match, only reading may be possible depending on the state of the bit. As a result of the above access right determination, if access to the page is prohibited, an exception interrupt occurs and control is transferred to the operating system, where abnormal processing is performed.

Here, we will discuss storage protection for user programs stored in different pages and service programs called from the user programs.

Different values A and B are set to the locks of the main memory where the user program and the service program are stored, respectively, and A is set to the key value of the control register when the user program is executed.

It is assumed that writing from the user program is permitted to the white area of the main memory, but writing to the service program area is prohibited. Furthermore, the instruction to change the key of the control register is a privileged instruction that can only be executed by the operating system, so that the user program or service program cannot directly change the key. Now, assuming that a user program calls a service program and the service program writes to both the data area of the white area and the data area of the calling user program, the service program calls the service program from the user program. The key value of the control register at the time of
It is not possible to write to the white area as it is. Therefore.

Before writing data to the white area, the service program issues a system call asking the operating system to change the key to B. The operating system checks the validity of the key change value, changes the key to B, and returns control to the service program.

After this, when writing data processed by the service program to the calling user program area, the system call must be issued again to return the key to eight.

[Problem to be solved by the invention]

In this way, in the conventional technology, when one program writes data alternately to multiple areas with different protection lock values, a system call is issued each time to change the lock value of the main storage area to which the key value is written. There is a problem that the overhead is large. In addition, it is necessary to be aware of whether the writing area is a white area and change the key as necessary, which makes it difficult to create a program and may cause an error in forgetting to change the key.

The first object of the present invention is to solve the second problem.

[Means to solve the problem]

The above object is achieved by providing an area in the control register to store the second and subsequent keys, and calculating the sum of the comparison results between each key and the lock of the main memory to be accessed.

In other words, by setting each key in the control register to the lock value of the main memory to be accessed at the beginning of a program that accesses multiple areas with different lock values, there is no need to change the key each time the access area changes. Overhead is reduced and programming becomes easier.

[Effect]

In the present invention, access rights such as read rights and write rights are obtained for each comparison between a plurality of keys provided in a control register and a lock of the main memory to be accessed, and each access right is obtained as a result of the comparison. Let the sum be the access right to the main memory of the access target. It is checked whether or not access to the main memory is permitted based on the access rights determined by the above operations. If permission is granted, access is permitted; if not, an exception interrupt is generated and control is transferred to the operating system.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

The first @ is FIG. 1 showing the configuration of a main memory protection circuit.

In FIG. 1, the control register 1 includes the first . The lock register 4 is a register that holds the key 2 and the second key 3, and the lock register 4 is a lock for each page of the main memory.The lock register 4 is a register that holds the B and F flags 19, and the corresponding page is locked 18 by the address line 5, which selects the page to be accessed. The 62 comparators 9 in which the F flag 19 is selected are each controlled to lock the lock register 4 selected by the first key 2 and the second key 3 in the generator 1 and the address line 5. 18
and■? The flags 19 are input and compared, and the read permission and write permission for each key are determined by a read permission signal 20. It is output as a write permission signal 22. Here, each read permission signal 20 indicates that reading is possible when it is 1'', and indicates that reading is prohibited when it is 0.Similarly, the write permission signal 22 indicates that writing is enabled when it is LL I II, and that it is prohibited to write when it is It Q II. , the OR gate 11 takes the logical sum of the read permission signals 20 output from the two comparators 9 and outputs the read permission sum signal 24.Similarly, the OR gate 12 takes the logical sum of the read permission signals 20 output from the two comparators 9 and outputs the read permission sum signal 24. 22 and outputs a write permission sum signal 25.The comparator 13 receives the read permission sum signal 24, the write permission sum signal 25, and a read request signal indicating a read request to the main memory to be accessed. 14. Similarly, a write request signal 15 indicating a write request is input.

An access permission signal 16 indicating permission to access the main memory of the access target (when it is "1", access to the main memory is possible), or similarly, to notify the operating system that access is not permitted by generating an exception interrupt. The exception interrupt signal 17 (an exception interrupt occurs when it is "1") is output.

FIG. 2 is a table showing the relationship between the input and output of the comparator 9 of FIG. 1. As shown in the figure, when the key 2 or 3 matches the lock 18, the read permission signal 20 and the write permission signal 22 both become "1" regardless of the value of the F flag 19, and the key 2 or 3 and the lock 18 match. lock 18
If they do not match, the write permission signal 22 is always “0”.
”, the read permission signal 20 indicates that the value of the F flag 19 is “1”.
'', it becomes II II II.

FIG. 3 is a table showing the relationship between the input and output of the comparator 13 shown in FIG.

FIG. 4 shows the lock 18 and F flag 19 of the lock register 4 for each page of the area where the user programmer 11 and service program of the main memory are stored.
This is a table showing the values of .

Here, the user blockrum shown in Figure 4 is the service block.
The operation of this embodiment will be explained by taking as an example a case where a program is called and the service program writes data into a white area and a user program area of the caller.

When the user program is executed, the first key 2 and second key 3 of the control register 1 are each set to ``3'' by the operating system waiting for the user program to start. Therefore, the main memory shown in FIG. The protection circuit is
When the user program requests reading and writing to the white area, the read permission signals 20. of the two comparators 9 are activated. The write permission signal 22 and write permission signal 22 are both 11111 under the conditions shown in FIG. In both read and write requests, the access permission signal 16 becomes 1", and the user program can read and write to the white area. On the other hand, when accessing the service program area from the user program, there are two The read permission signal 20 of the comparator 9 becomes ``1'', but the write permission signal 22 becomes ``0'', so the access permission signal of the comparator 13 becomes 11 in the case of a read request.
177, but in the case of a write request, it becomes ``O'''', and the user program can read into the service program area, but cannot write to it. This prevents the service program area from being accidentally destroyed by a user program.

Next, when the user program calls the service program and control is transferred to the service program, at this point both the first key 2 and the second key 3 of control register 1 remain II 3 PI, and the service program becomes white. Unable to write data to the area. Therefore, the service block issues a system call to tell the operating system to set the second key 3 of control register 1 to "2".
This is because the instruction that changes the contents of control register 1 is a privileged instruction and can only be executed by the operating system.The operating system sets the second key 3 of control register 1 to rz
211 and returns control to the changed service program.

As a result, the first key 2 of the control register 1 is N 311
．． The second key 3 becomes 112 II. As a result, the access to the white area of the service program is as follows:
The read permission signal 20 and write permission signal 22 of the comparator 9 for key 3 match the value "2" of the second key 3 and the value "2" of the lock 18 of the lock register 4 in the service program area. Both become 1'', and the access permission signal 16 of the comparator 13 becomes II II II for read requests and write requests, and the service program can both read and write to the white area. On the other hand, in order to access the user program area of the service program caller, the read permission signal 20 and write permission signal 22 of the comparator 9 for the first key 2 on the right side of FIG. ;3'' and the value II 3 II of lock 18 of lock register 4 for the user program area match, so both u l
n, and the access permission signal 16 of the comparator 13 also responds to read requests and write requests.
The service program is User Progera lN.
It becomes possible to both read and write to the area.

After the service BU [1 Gram] completes its processing, it issues a system call again, returns the value of the second key 3 of the control register 1 to #:3 II, and returns control to the user BLOGRANO.

As mentioned above, the service program uses the system call to set the first key 2 of the control register 1 to a value that matches the lock 18 in the user program area, and to the second key 3 to set a value that matches the lock 18 in the white area. This makes it possible to read and write to both areas.

In this embodiment, since two keys can be set in the control register 1, it is possible to read and write two areas with different locks by setting the keys at -degrees.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, among a plurality of programs in which different lock values are set, one program changes the value of the second and subsequent keys to the same value as the lock of the program area that it wants to access. By doing this, you can access other ProGuerra 11 from the same program at any time.
Since the area can be accessed, there is no need to switch keys while being aware of the access area, which reduces overhead and facilitates program creation.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the configuration of the main memory protection circuit, and Figure 2 is a diagram showing the configuration of the main memory protection circuit.
FIG. 3 is a diagram for explaining the relationship between the input and output of comparator 9 in FIG. 1, FIG. 4 is a diagram for explaining the relationship between the input and output of comparator 13 in FIG. Seki with the lock and flag ~ Toki! ■

Claims (1)

[Claims] 1. In a computer system that determines a program's access right to main memory by comparing keys and locks,
In addition to the above key, a second and subsequent keys are provided, each key is compared with a lock of the main memory to be accessed, and the right to access the main memory is determined by the sum of the comparison results. A main memory protection method for computer systems.