# Patent

## Title
Secure memory access system and method

## Abstract

A secure memory access system and method for providing secure access to Hyper Management Mode memory ranges is presented.

## Background
FIELD OF THE INVENTION
The present invention relates to the field of memory access type designations.
BACKGROUND OF THE INVENTION
Electronic devices and systems have made a significant contribution towards the advancement of modern society and are utilized in a number of applications to achieve advantageous results. Numerous electronic technologies such as digital computers, calculators, audio devices, video equipment, and telephone systems have facilitated increased productivity and reduced costs in analyzing and communicating data, ideas, and trends in most areas of business, science, education and entertainment. These electronic devices often include processors that process information stored in a memory. The information in said memory is typically accessed by read and write operations. These so-called memory accesses usually have a designated type and improperly typed memory accesses can cause problems.
SUMMARY
A secure memory access system and method for providing secure access to Hyper Management Mode memory ranges is presented.



DRAWINGS
FIG. 1 is a flow chart of an exemplary secure Hyper Management Mode method in accordance with one embodiment of the present invention.
FIG. 2 is a flow chart of an exemplary secure memory access process in accordance with one embodiment of the present invention.
FIG. 3 is a block diagram of an exemplary secure memory access system in accordance with one embodiment of the present invention



DETAILED DESCRIPTION
Reference will now be made in detail to preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications, and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be obvious to one ordinarily skilled in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as to not unnecessarily obscure aspects of the current invention.
In one embodiment of the present invention, a Hyper Management Mode (HMM) is utilized to perform a variety of special management operations. Hyper Management Mode is initiated if a certain sequence of events occurs. When said sequence of events occurs, a Hyper Management Interrupt (HMI) is generated and the processor is directed to access Hyper Management Mode instructions in memory. A portion of said memory is assigned to store the directions or instructions (e.g. a hypervisor, interrupt handler, etc.) for performing the Hyper Management Mode operations. In a system with Random Access Memory (RAM) the portion of the memory storing the Hyper Management Mode instructions is referred to as the Hyper Management Random Access Memory (HMRAM).
The locations in main memory are accessed for reading and writing contents. There are a variety of access types that define how the memory is accessed. For example, memory types determine if information is cached when it is read from or written to a memory region, if information can be accessed in order or out of order, etc. In one embodiment of the present invention, the memory types include uncached (UC), write combining (WC), write protected (WP), write through (WT) and write back (WB). Uncached means that when the memory region is accessed, information is read or written straight from the storage location without buffering in a cache. Write combining is similar in that when information is written to memory multiple times, the information is merged or combined into one large block that is written in one access, efficiently using bandwidth. Write combining is used typically for devices that transfer information in relatively large chunks, such as graphics controllers, LAN controllers, etc.
The memory types can have similarities. For example, write through and write back involve caching. For write through, when information is written it is cached and directed to write through to an end storage device. For write back, the information is written to a cache, which can write it to the end storage device whenever it is convenient.
FIG. 3 is a block diagram of an exemplary secure memory access system 400 in accordance with one embodiment of the present invention. Secure memory access system 400 includes processor 410 communicatively coupled to memory 420. In one embodiment memory 420 has multiple memory ranges including hyper management mode memory range 425 and other memory ranges (e.g., memory range 427). In one exemplary implementation processor 410 includes Memory Type Range Registers 411.
The components of secure memory access system 400 cooperatively operate to facilitate secure memory access. Hyper Management Mode memory range 426 stores information associated with Hyper Management Mode operations. Memory range 427 can include ranges used to store information related to a variety of functions. Processor 410 processes the information and processor 410 securely designates memory access types associated with the Hyper Management Mode memory range 425. In one exemplary implementation, the Memory Type Range Registers designating memory access types associated with ranges within memory 420, including Hyper Management Mode memory range 427. In one embodiment, the memory access type designation associated with Hyper Management Mode memory range 425 is hard wired to a predetermined memory access type. The hardwired memory access type can take precedence regardless of memory access type designations in a memory type range register. In one embodiment, the instructions for securely designating the memory access types are stored in said Hyper Management Mode memory range 425.
A memory region cannot be designated as more than one type at a time.
In one embodiment, input/output (I/O) devices utilize uncached and write combining memory types. In one exemplary implementation, there is a block of controllers associated with the I/O device and there is a block of main memory assigned to the device's communication buffers. Said buffers are marked as write combining so that they can be written to very quickly and efficiently, while the control registers are marked as uncached. The buffer is filled with write combining writes and then one or more control registers are written, directing the buffer to communicate the information in one large block.
The different types of memory access have various characteristics. For example, write protect is relatively secure in that it prevents information from being overwritten. The memory addresses can range from 0 to the maximum supported by a particular system. In one embodiment, memory addresses 0 to 640 KB and 1 MB to 128 MB are cachable memory. The 1 MB to 128 MB range can be assigned a write back access type, which is cachable and relatively fast. The 640 KB to 1 MB range can be segmented and assigned a variety of memory types. For example, the memory locations assigned to the (shadowed) BIOS can be write protected.
In one embodiment of the present invention, Memory Type Range Registers (MTRRs) are associated with ranges of memory, and store memory type access indications that control the type of memory accesses performed when information flows to or from memory locations within the memory range corresponding to the MTRR. There are three categories of MTRRs: generic, fixed, and variable.
A generic MTRR indicates which memory types are enabled and, if so, in which way. If nothing is enabled the generic MTRR includes an indication on how to handle the memory access.
The fixed MTRRs are a set of registers in the CPU, each of which contains a number of 8-bit fields, whereas each field corresponds to a predetermined memory region. In one exemplary implementation, each field of a fixed MTRR corresponds to a range of addresses within the 640 KB to 1 MB region. If a memory access is directed to an address, the processor checks the MTRR and whatever type of memory access is expressed in the MTRR is applied. The granularity can go down to a 4 KB page.
The variable MTRRs are a set of registers in the CPU including zero to n MTRRs. Each variable MTRR has a starting address and a range, both of which can vary. Each MTRR includes a base register and a mask register. The base register includes a starting address indication. The mask register includes a range indication, which determines how much memory is associated with the register's memory type indication.
The present invention can also be implemented in systems utilizing a Programmable Attribute Table (PAT) for controlling memory accesses and indicating memory access types. In one exemplary implementation, 3 bits per page select one of 8 memory access types from a Programmable Attribute Table Model Specific Register.
While the description of the present invention is primarily presented in terms of protecting MTRR settings from illicit tampering and/or accidental changes, it is appreciated that the present invention is readily implemented for protecting PAT settings in a similar manner.
The memory access types are assigned to particular ranges of memory to achieve certain advantages desirable for the information in that range. If the memory access types are maliciously or accidentally altered, problems can arise. For example, if a memory range is assigned a relatively fast type of memory access (e.g. a cachable memory type) because it is critical that information in that range be available quickly, and the memory access type is changed to a relatively slow memory access type (e.g. an uncachable one), then problems can arise if the critical information is not available in time. Also, if a memory location that has to be updated (e.g. the address is associated with a count value that has to be updated) is changed to write protected, critical updates may be prevented from occurring. Another problem can arise if the there is sequencing information that needs to be saved, but is prevented from, because a memory range is being changed to a write protect access type. For example, if the special HMM trigger events occur, and addresses associated with what a program was doing and where in a process it stopped are written, but their memory type is changed to write protected, then the processor will not be able to return to the correct point in the interrupted process because the write protect will have prevented the storage of the requisite information.
The present invention is directed to preventing intentional and accidental corruption of the memory access type assignment for the HMRAM range.
FIG. 1 is a flow chart of a secure Hyper Management Mode method 100 in accordance with one embodiment of the present invention. Secure Hyper Management Mode method 100 enables protected Hyper Management Mode operations. In one exemplary implementation, method 100 prevents malicious and/or accidental manipulation of Hyper Management Mode information and operations.
In step 110, information processing is performed. Information processing associated with a variety of applications can be performed. In one embodiment, the information processing includes code morphing of instructions into very long instruction words. It is appreciated that the present invention is also readily adapted to non-code morphing systems.
In step 120, a determination is made if a Hyper Management Mode trigger event occurs. There are a variety of events that can trigger a Hyper Management Mode initiation.
In step 130, a secured Hyper Management Mode operation is performed. In one embodiment, the secured Hyper Management Mode operation includes securing a memory type designation associated with the Hyper Management Mode memory space. The designation can be stored in a Memory Type Range Register and/or a Programmable Attribute Table. In one exemplary implementation the secure memory access process prevents unauthorized alteration of a memory type associated with the Hyper Management Mode memory space. A memory access operation can be executed as part of the secured Hyper Management Mode operation. In one exemplary implementation, the memory access operation is directed to a write operation. In another exemplary implementation, the memory access operation is directed to a read operation.
In one embodiment, memory addresses of a computer system are assigned to various functional activities, including a region or Hyper Management Mode memory range for storing information associated with Hyper Management Mode operations. A processor performs the instructions associated with the Hyper Management Mode operations when it receives a Hyper Management Mode Interrupt. When the processor enters Hyper Management Mode, the addresses assigned to the Hyper Management Mode memory range become “visible” or accessible to the processor. The processor securely designates memory access types associated with said Hyper Management Mode memory range.
FIG. 2 is a flow chart of a secure memory access process 300 in accordance with one embodiment of the present invention. Secure memory access process 300 enables secure access of a memory while minimizing threats to memory information manipulation. In one exemplary implementation, memory access method 300 prevents malicious and/or accidental manipulation of memory access types.
In step 310, memory addresses are associated with memory ranges. It is appreciated that a maximum memory amount supported by a system can be divided up in a variety of ways. In one exemplary implementation, addresses 0 to 640 KB are dedicated memory, and there are fragmented memory spaces from 640 KB to 1 MB that store various legacy information, such as information associated with various cards (e.g. a video graphics card, interface connection cards, etc.) and other basic input output information (e.g. BIOS information). The region above 1 MB is utilized for various other main memory operations. Hyper Management Random Access Memory is assigned to a portion of the region between 1 MB and the maximum supported by the system's main memory (e.g. 1 MB up to 128 MB). The region between the end of RAM and top-of-memory can be used for peripherals.
In step 320, an analysis is made to determine if a memory access request is directed to an address within a Hyper Management Mode memory range. The memory access request can be directed to addresses from a variety of regions within a memory. For example, the memory access request can be directed to addresses in the main memory region or in memory regions associated with various other memory devices. In one embodiment, the memory access request is directed to a Hyper Management Mode memory space. If the memory access request is not directed to an address within the Hyper Management Mode memory range, then the request is handled in a traditional way. If the memory access request is directed to an address within the Hyper Management Mode memory range the process proceeds to step 330.
In step 330, a secure memory operation directed at the address is performed if the address is within the Hyper Management Mode memory range. In one embodiment, memory type designations associated with the Hyper Management Mode memory range are secured if the memory access request is directed to an address within the Hyper Management Mode memory range. Securing the memory type designations associated with the Hyper Management Mode range ensures that when the Hyper Management Mode is exited the appropriate memory type designations are still associated with the Hyper Management Mode memory range.
In one embodiment, the memory type designations associated with the Hyper Management Mode memory range are stored in a secure location before permitting access to the memory Hyper Management Mode memory range. The memory designations are restored when exiting the Hyper Management Mode memory range. This can be done explicitly or implicitly. In an explicit implementation the first few instructions executed upon entry into HMM direct saving, while the last few instructions before exit from HMM direct restoring. In an implicit implementation, the processor—upon receiving a HMI—saves the MTRR settings associated with HMRAM elsewhere as part of entering HMM, before it writes or changes anything in HMRAM. It saves all the “old” states and sets the MTRRs to a suitable state. In one exemplary implementation, a snapshot of the old values is included as part of the HSM; said snapshot is restored during exit from HMM. There are various optimizations; e.g. only the valid MTRRs can be saved, or only MTRRs that deal with HMRAM addresses but not MTRRs associated with other memory regions.
There are various ways in which the restore of the variable MTRRs can be implemented. All MTRRs can be written back or just the variable MTRRs can be written back. It is also possible to write only the previously saved ones back. In one exemplary implementation, the restoring includes enabled memory type range register information.
In another embodiment, a determination is made if the processor is in Hyper Management Mode, e.g. by examining a Hyper Management Mode indication bit. Memory designations are set to a predetermined type if the processor is in Hyper Management Mode. In one exemplary implementation, the Hyper Management Mode memory access type is set to a write back designation when exiting the memory access operations.
The present invention can also include intercepting accesses to MTRRs and/or the PAT MSR, and preventing changes to their true values, alternatively setting those true values to a predetermined default memory access type.
Thus, the present invention facilitates efficient and secure Hyper Management Mode operations. Adverse impacts associated with malicious or accidental unauthorized manipulations of memory access types associated with Hyper Management Mode memory space are reduced.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.

## Claims

1. A secure Hyper Management Mode method comprising:
performing information processing;
determining if a Hyper Management Mode trigger event occurs during said information processing; and
performing a secured Hyper Management Mode operation if said Hyper Management Mode trigger event occurs.

2. The secure memory access method of claim 1 wherein said secured Hyper Management Mode operations include securing a memory type designation associated with a Hyper Management Mode memory space.

3. The secure memory access method of claim 2 wherein said memory type designation is stored in a Memory Type Range Register.

4. The secure memory access method of claim 2 wherein said memory type designation is stored in a Programmable Attribute Table.

5. The secure memory access method of claim 1 wherein instructions for performing said secured Hyper Management Mode are stored in a Hyper Management Mode memory space associated with said Hyper Management Mode.

6. The secure memory access method of claim 1 wherein unauthorized alteration of a memory type associated with a Hyper Management Mode memory space is prevented.

7. The secure memory access method of claim 1 wherein a Memory Type Range Register is restored to an original designation.

8. A secure memory access system comprising:
a memory for storing information including a Hyper Management Mode memory range for storing information associated with Hyper Management Mode operations; and
a processor for processing said information, wherein said processor securely designates memory access types associated with said Hyper Management Mode memory range.

9. The secure memory access system of claim 8 wherein said processor includes Memory Type Range Registers for designating memory access types associated with ranges within said memory, including said Hyper Management Mode memory range.

10. The secure memory access system of claim 8 wherein said memory access type designation associated with said Hyper Management Mode memory range is hard wired to a predetermined memory access type.

11. The secure memory access system of claim 10 wherein said hardwired memory access type takes precedence regardless of memory access type designations in a memory type range register.

12. The secure memory access system of claim 10 wherein said instructions for securely designating said memory access types are stored in said Hyper Management Mode memory range.

13. A secure memory access process comprising:
associating memory addresses with ranges;
analyzing if a memory access request is directed to an address within a Hyper Management Mode memory range; and
performing a secure memory operation directed at said address if said address is within said Hyper Management Mode memory range.

14. The secure memory access process of claim 13 wherein memory type designations associated with said Hyper Management Mode memory range are secured if said memory access request is directed to an address within said Hyper Management Mode memory range.

15. The secure memory access process of claim 13 further comprising:
storing said memory type designations associated with said Hyper Management Mode memory range in a secure location before permitting access to said memory Hyper Management Mode memory range; and
restoring said memory designations when exiting said Hyper Management Mode memory range.

16. The secure memory access process of claim 13 wherein said restoring includes enabled Memory Type Range Register information.

17. The secure memory access process of claim 13 further comprising:
determining if the processor is in Hyper Management Mode; and
setting memory designations to a predetermined type when executing a memory access if said processor is in said Hyper Management Mode.

18. The secure memory access process of claim 17 wherein said determining includes examining a Hyper Management Mode indication bit.

19. The secure memory access process of claim 13 further comprising intercepting accesses to a Memory Type Range Register and preventing changes to said Memory Type Range Register.

20. The secure memory access process of claim 13 further comprising intercepting accesses to a Programmable Attribute Table and preventing changes to said Programmable Attribute Table.

21. The secure memory access process of claim 13 further comprising setting said memory designation to a predetermined default memory access type.

22. The secure memory access process of claim 13 further comprising assigning said Hyper Management Mode memory access type to a write back designation when executing said memory access operations.