JPH0833832B2 - Information processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention is intended to protect resources in an information processing apparatus having a microprocessor operating in a privileged state, a user state and a special state and a specific resource accessed in the special state. Of the execution states, state holding means for holding information on the user state and privileged state, and when the execution state held by the state holding means is the user state when the processor is in the special state, access to a specific resource is prohibited. And a prohibition unit for prohibiting access to resources when the processor changes from the user state to the special state.

[Industrial applications]

The present invention relates to an information processing apparatus, and in particular, changes a privileged state that permits the use of a privileged instruction that changes the system state, a user state that prohibits the use of this privileged instruction and uses a user program, and a state of a specific resource. The present invention relates to a microprocessor that operates in a plurality of states including a special state for outputting, and externally outputs state information indicating which operating state is currently operating, and an information processing device having the above-mentioned specific resource.

[Conventional technology]

In general, there are the following information processing apparatuses that connect resources such as an input / output device and a memory to a microprocessor via a bus to execute data communication. This is the third
As shown in the figure, a microprocessor 10 is connected with resources such as an input / output device 12 and a memory 13 via a bus 11 so that data communication and processing can be performed between the respective devices.

In such an information processing apparatus, if the operating environment of the system is changed carelessly, the entire system malfunctions or adversely affects other user programs. Privileged instructions that enable the use of user programs only in the user mode, prohibit the use of privileged instructions that change the system state, and operate the microprocessor's system state, segment registers, stack pointer, etc. in the privileged mode only. Is feasible.

[Problems to be solved by the invention]

By the way, in an information processing apparatus, the internal state of a resource with which a microprocessor exchanges data cannot be rewritten in a normal privileged state. Therefore, in order to rewrite the internal state of this resource, the processor is There are things that are designed to be a special state according to the state.

The following information processing device is available. As shown in FIG. 4, it is possible to select an address signal, a status signal indicating a state of the operation mode, a strobe signal, a microprocessor 20 for reading and writing data, and a status signal for decoding. Decoder 21 that raises the signal of the mode in which it is activated, the address signal, the special state selection signal from the decoder 21,
It is composed of a decode circuit 22 for outputting a select signal, an input / output control device for receiving / selecting a select signal, an address signal, a strobe signal, and a control signal from the decode circuit 22, and putting data in / out, and a resource 23 such as a memory. It is a thing.

However, in such an information processing apparatus, when accessing in a special state, the status signal indicates a special state indicating that the processor is in the special state. Access that prohibits changing the internal state of the resource 23 is prohibited, or access that changes the internal state of the resource is possible because the processor 20 has switched from the privileged state to the special state. It is impossible to judge whether or not the resource cannot be protected in the user state, and it is desired to protect the resource.

[Means for solving problems]

In the present invention, means for solving the above problems are, as shown in FIG. 1, a privileged state that permits the use of a privileged instruction that changes the state of the system and a user program that prohibits the use of the privileged instruction. A microprocessor which operates in a plurality of states including a user state in which it is used and a special state for changing the state of a specific resource 1, and which outputs to the outside state information indicating in which operating state it is currently operating. Two
In the information processing device having the specific resource 1 and the specific resource 1, the state holding means 3 that holds only the privileged state and the user state among the state information including the privileged state, the user state, and the special state output from the microprocessor 2. And the prohibiting means 4 for prohibiting data communication when the microprocessor 2 is in the special state and the state held by the state holding means 3 is the user state, and the processor is switched from the user state to the special state. In case of specific resource 1
Access is prohibited, and when the processor switches from the privileged state to the special state, the access to the specific resource 1 is permitted.

[Action]

According to the present invention, when the microprocessor of the information processing device is set from the user state or the privileged state to the special state, the state holding means holds the set user state or privileged state, and the prohibiting means holds the state. When the state held by the means is the user state, data communication is prohibited, and when the processor switches from the privileged state to the special state, access to the above specific resource is permitted. Access to specific resources is prohibited except when switching.

〔Example〕

An embodiment of the information processing apparatus according to the present invention will be described below.
FIG. 2 shows an embodiment of the information processing apparatus according to the present invention.

In this embodiment, as shown in FIG. 2, the information processing apparatus has a microprocessor 30 similar to the conventional one, a memory management unit 33 as a resource, and a decoder 31 for decoding a status signal from the microprocessor 30.
And a decoding circuit 32 that sends a select signal to the memory management unit according to the signal from this decoder 31.
Consists of And in the present embodiment, the decoder 31
A state holding circuit 34 as a state holding means is provided on the output lines of the user mode and the privileged mode of the state holding circuit 34.
Is provided with an access prohibition circuit 35 as prohibition means for prohibiting data communication, and enables / prohibits input of a strobe signal input to the memory management unit 33 to prohibit writing of data to the memory management unit 33. In this embodiment, a memory management unit (MMU) that executes address exchange between memories is used as a resource. Normal memory exchange is executed in the user state, but privileged state is used to change the internal state. Rather, it must be done in a special condition.

Therefore, in this embodiment, when the microprocessor 30 is in the privileged state and the data is rewritten by changing the internal state of the memory management unit 33 to the special state, the microprocessor 30 is set to the special state and the data can be transmitted. Good. Then the state holding circuit
34 holds state information that the decoder 31 has output the privileged state, and the access prohibition circuit 35 does not operate.
Strobe signal is normally in memory management unit
It is possible to change the state inside the memory management unit 33 by inputting to 33.

On the other hand, it is assumed that when the microprocessor 30 is in the user state, a program is activated to bring the microprocessor 30 into a special state to access the inside of the memory management unit 33. At this time, the state holding device 34
Holds a status signal from the decoder 31 indicating that the microprocessor 30 is in the user status, the access prohibition circuit 35 operates to invalidate the strobe signal and prohibit the output to the memory management unit 33.
Data is not written in the memory management unit 33, and the memory management unit 33, which is a resource, is protected.

In the above-mentioned embodiment, the prohibiting means prohibits the input of the strobe signal. However, if the writing to the resource is impossible, another signal such as a select signal generated by the decoding circuit is used. Input of a signal may be prohibited.

〔The invention's effect〕

As described above, according to the information processing apparatus of the present invention, information processing including a microprocessor operating in a plurality of states including a privileged state, a user state, and a special state, and a specific resource accessed in the special state In the device, in order to protect resources, state holding means for holding only the privileged state and the user state among the state information consisting of the privileged state, the user state, and the special state output by the microprocessor, and the microprocessor are in the special state. Since the state holding means holds a user state, a prohibiting means for prohibiting data communication is provided. Therefore, when the state of the microprocessor is the user state, the program operates and the microprocessor operates. Even if the processor is in a special state and tries to access the inside of the resource, the holding means is the microprocessor. Since holding the state signal indicating that the service is a user state, data not is written in the resource, there is an effect that it is possible to protect the resources.

[Brief description of drawings]

1 is a principle diagram of the present invention, FIG. 2 is a block diagram showing an embodiment of an information processing apparatus according to the present invention, FIG. 3 is a block diagram showing an information processing apparatus according to the present invention, and FIG. 3 is a block diagram showing an example of the information processing apparatus of FIG. 1 ... Resource 2 ... Microprocessor 3 ... Holding means 4 ... Prohibition means

Claims (1)

[Claims] 1. A privilege state for permitting the use of a privileged instruction for changing a system state, a user state for prohibiting the use of the privileged instruction and a user program, and a state for changing a specific resource (1). A microprocessor (2) that operates in a plurality of states including a special state and outputs to the outside state information indicating which operating state is currently operating
And the specific resource (1), the information processing device holds only the privileged state and the user state among the state information including the privileged state, the user state, and the special state output from the microprocessor (2). State holding means (3)
And a prohibiting means (4) for prohibiting data communication when the microprocessor (2) is in the special state and the state held by the state holding means (3) is the user state. When the processor is switched to the special state, access to the specific resource (1) is prohibited, and when the processor is switched from the privileged state to the special state, the access to the specific resource (1) is permitted. An information processing device characterized by the above.