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Protection Scheme for Non-Key Storage Systems

IP.com Disclosure Number: IPCOM000060316D
Original Publication Date: 1986-Mar-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Boguski, MJ: AUTHOR [+5]

Abstract

In various systems having small work stations in which storage keys are not implemented, the possibility exists of accessing and destroying the supervisor software by the user software. A scheme is provided which generates an exception to the user software accessing the supervisor software by flagging the supervisor for error correction. The supervisor program resides contiguously at the high end 1 (Fig. 1) of the virtual space, and user programs 2 reside below the supervisor program 3. The supervisor program size may vary from 64 Kb to 16 Meg minus 128 Kb in 64 Kb increments, as seen in the virtual memory map (Fig. 1). The supervisor boundary register 4 (Fig. 2) is initialized to X'FF' when the system is powered on, thus bypassing the protection mechanism.

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Protection Scheme for Non-Key Storage Systems

In various systems having small work stations in which storage keys are not implemented, the possibility exists of accessing and destroying the supervisor software by the user software. A scheme is provided which generates an exception to the user software accessing the supervisor software by flagging the supervisor for error correction. The supervisor program resides contiguously at the high end 1 (Fig. 1) of the virtual space, and user programs 2 reside below the supervisor program 3. The supervisor program size may vary from 64 Kb to 16 Meg minus 128 Kb in 64 Kb increments, as seen in the virtual memory map (Fig.
1). The supervisor boundary register 4 (Fig. 2) is initialized to X'FF' when the system is powered on, thus bypassing the protection mechanism. The mechanism is invoked by the supervisor with a special "Diagnose" command. The command passes the last 64 Kb virtual address segment of the user memory space and one control bit information to select the protection for "write only" or "read and write" accesses. The microcode uses this information to load the appropriate hardware registers. Whenever the program in problem state makes an attempt to access the supervisor memory, the access is blocked by the hardware and an error is generated to notify the supervisor. The error-handling routine may obtain the address of the illegal access, and type of access (read or write) for further processing.

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