Paged memory management unit having stack change control register
First Claim
1. In a paged memory management unit (PMMU) which cooperates with a processor to provide access by a calling module to called module, each of said modules having a selected one of a plurality of access levels and being allocated a new stack area by the processor in response to the processor receiving a change stack signal, the improvement comprising:
- storage means for selectively storing a stack change indicator for each of said access levels, each of said indicators being selectively set in response to a respective signal from said processor; and
control means, responsive to said storage means, for providing said change stack signal to said processor if any stack change indicator in said storage means corresponding to an access level between the access level of the calling module and the access level of the called module, including the access level of the called module, is set.
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Accused Products
Abstract
A paged memory management unit (PMMU) adapted to prevent unauthorized access by a calling module executing in a data processor to a called module having a higher access level. A Stack Change Control Register in the PMMU has a bit corresponding to each valid access level. If the PMMU determines that any bit in the Stack Change Control Register corresponding to an access level between the access level of the calling module and the called module, including the access level of the called module, is set, a Change Stack bit in a Status Register is set to indicate that the processor should allocate a new stack for the called module. Both the Stack Change Control Register and the Status Register are accessible to the processor.
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Citations
11 Claims
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1. In a paged memory management unit (PMMU) which cooperates with a processor to provide access by a calling module to called module, each of said modules having a selected one of a plurality of access levels and being allocated a new stack area by the processor in response to the processor receiving a change stack signal, the improvement comprising:
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storage means for selectively storing a stack change indicator for each of said access levels, each of said indicators being selectively set in response to a respective signal from said processor; and control means, responsive to said storage means, for providing said change stack signal to said processor if any stack change indicator in said storage means corresponding to an access level between the access level of the calling module and the access level of the called module, including the access level of the called module, is set. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. In a paged memory management unit (PMMU) which cooperates with a processor to provide access by a calling module to a called module, each of said modules having a selected one of a plurality of access levels and being allocated a new stack area by the processor in response to the processor receiving a change stack signal, the method comprising the steps of:
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selecting storing a stack change indicator for each of said access levels, each of said indicators being selectively set in response to a respective signal from said processor; and providing said change stack signal to said processor if any stack change indicator in said storage means corresponding to an access level between the access level of the calling module and the access level of the called module, including the access level of the called module, is set. - View Dependent Claims (9, 10, 11)
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Specification