Page granular curtained memory via mapping control

• US 20030200405A1
• Filed: 04/17/2002
• Published: 10/23/2003
• Est. Priority Date: 04/17/2002
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: England, Paul, Willman, Bryan Mark
• Granted Patent: US 6,986,006 B2
• Time in Patent Office: Days
• US Class Current: 711/163
• CPC Class Codes: G06F 12/145 the protection being virtual, e.g. for virtual blocks or segments before a translation mechanism
• CPC Class Codes: G06F 12/1491 in a hierarchical protection system, e.g. privilege levels, memory rings

Abstract

Methods of providing and limiting access to trusted memory are provided. Trusted memory pages are not mapped with page map pages. When a central processor is operated in a page-mapping mode, access to the trusted memory is limited. In particular, without mapping information, software and hardware modules cannot access and modify the contents of trusted memory sections.

Claims

1. A method of restricting access to memory, the method comprising:

storing data in a memory location;

determining whether the data is trusted or non-trusted data; and

mapping the memory location with at least one page map page stored in a non-trusted memory section only when the data is non-trusted data.

2. The method of claim 1, further comprising:

configuring a processor that controls access to the at least one page map page to run in a page-mapping mode.

3. The method of claim 2, further comprising:

declaring a security violation when the processor changes from the page-mapping mode.

4. The method of claim 2, further comprising:

declaring a security violation when the processor changes to another page-mapping mode.

5. The method of claim 1, further comprising:

configuring a processor that controls access to the at least one page map page to run in a segment-mapping mode.

6. The method of claim 5, further comprising:

declaring a security violation when the processor changes from the segment-mapping mode.

7. The method of claim 1, further comprising:

storing entries in the at least one page map page in read only format.

8. The method of claim 7, further including:

declaring a security violation when an attempt is made to write data to a read only page map page entry.

9. The method of claim 8, further including:

aborting the attempt when the attempt is not a legal operation.

10. The method of claim 1 wherein the data is trusted data stored in a physical memory page and further comprising:

identifying the physical memory page as trusted memory in a trusted page vector.

11. A computer-readable medium contain computer-executable instructions for causing a computer device to perform the steps comprising:

storing data in a memory location;

determining whether the data is trusted or non-trusted data; and

mapping the memory location with at least one page map page stored in a non-trusted memory section only when the data is non-trusted data.

12. The computer-readable medium of claim 11, further including computer-executable instructions for causing the computer device to perform the step comprising:

configuring a processor that controls access to the at least one page map page to run in a page-mapping mode.

13. The computer-readable medium of claim 12, further including computer-executable instructions for causing the computer device to perform the step comprising:

declaring a security violation when the processor changes from the page-mapping mode.

14. The computer-readable medium of claim 12, further including computer-executable instructions for causing the computer device to perform the step comprising:

declaring a security violation when the processor changes to another page-mapping mode.

15. The computer-readable medium of claim 12, further including computer-executable instructions for causing the computer device to perform the step comprising:

storing entries in the at least one page map page in read only format.

16. The computer-readable medium of claim 15, further including computer-executable instructions for causing the computer device to perform the step comprising:

declaring a security violation when an attempt is made to write data to a read only page map page entry.

17. The computer-readable medium of claim 12, further including computer-executable instructions for causing the computer device to perform the step comprising:

identifying the physical memory page as trusted memory in a trusted page vector when the data is trusted data.

18. A device for restricting direct memory access to a first memory, the device coupled to a central processing unit and comprising:

a second memory containing a direct memory access exclusion vector containing access values that identify physical memory pages that do not allow direct memory access;

a restriction module coupled to the central processing unit, the first memory and the second memory, the restriction module configured to perform the steps comprising;

receiving an identification of a physical memory page in the first memory;

comparing the identification to an access value for the physical memory page in the direct memory access exclusion vector; and

allowing direct memory access to the physical memory page only when the access value allows direct memory access.

19. The device of claim 18, wherein the first memory and the second memory are implemented in the same memory module.

20. The device of claim 19, wherein the identification of the physical memory page is received from a peripheral device having bus master access.

21. The device of claim 18, further including:

a third memory that contains at least one page map page mapping only physical memory pages that are identified as non-trusted.

23. The computer device of claim 20, wherein the central processor unit is operated in a page-mapping mode.

22. A computer device configured to limit access to memory, the computer device comprising:

a central processor unit configured to operate in a trusted mode and a non-trusted mode;

a first memory containing physical memory pages;

a second memory containing at least one non-trusted page map page that only maps the physical memory pages that are identified as non-trusted.