RE: [Xen-devel] VCPU Structure

["Nimgaonkar, Satyajeet" <SatyajeetNimgaonkar@xxxxxxxxxx>]

Hi Kaushik,
                 Here is what I wish to do.
                 I have implemented a custom hypercall in xen. Now i need to access the memory pages that are being assigned to a particular process. I intend to do this from the hypercall handler itself. Once I have these memory pages, I will compute the hash (Memory Integrity block) of it and store it in the VCPU structure. This will help me save the state of the memory for a particular process. Later I can check if some modification have been done to the process by computing and matching the hash value with the one saved in the VCPU.
                It would be great if you could give me some insight on how to achieve this. Any sample code or examples on this would help a lot.
                Thanks a lot.

Regards,
Satyajeet

---

From: Kaushik Barde [kbarde@xxxxxxxxxx]
Sent: Thursday, November 11, 2010 4:47 PM
To: 'Dan Magenheimer'; Nimgaonkar, Satyajeet; 'Xen Devel'
Subject: RE: [Xen-devel] VCPU Structure

Satyajeet

 

I think, describing exact details of “memory integrity block” and its relevance to VCPU modification would help the conversation.

 

-Kaushik

 

From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Dan Magenheimer
Sent: Monday, November 08, 2010 5:43 AM
To: Nimgaonkar, Satyajeet; Xen Devel
Subject: RE: [Xen-devel] VCPU Structure

 

I’m not asking you to describe the Xen functionality.  I am asking you to describe in more detail the modification to the processor functionality/behavior that you are trying to achieve.  I don’t know what a “simple memory integrity block” does and searching for it doesn’t find anything helpful.

Nearly all instructions in the VCPU are executed directly in hardware (by the physical CPU == PCPU).  The only way to change the VCPU behavior is to cause some kind of trap or fault or exception to occur on the PCPU, which gets intercepted by the processor and then control is turned over to privileged software (in this case Xen).  Xen has a lot of code that handles many many different kinds of traps/faults/exceptions.  Your VCPU will need to execute an instruction that causes a trap or fault or exception and then you will need to add code to Xen to recognize your special one and do something special with it.

Does that help?

Dan

 

From: Nimgaonkar, Satyajeet [mailto:SatyajeetNimgaonkar@xxxxxxxxxx]
Sent: Sunday, November 07, 2010 10:14 PM
To: Dan Magenheimer; Xen Devel
Subject: RE: [Xen-devel] VCPU Structure

 

Hi,
   I am sorry if I have not provided provided enough information about the functionality that I want to implement. But my problem is that even I new to Xen and trying to understand my way around it. With regards to the functionality that I want to implement, I wish to modify the behavior of the VCPU in xen. As a starting point, I just want to add simple memory integrity block within the VCPU. I am really not sure what would be the best way to do this so I need some suggestions on that too.
   Thanks. I hope that helps too.

Regards,
Satyajeet

---

From: Dan Magenheimer [dan.magenheimer@xxxxxxxxxx]
Sent: Thursday, November 04, 2010 7:25 PM
To: Nimgaonkar, Satyajeet; Xen Devel
Subject: RE: [Xen-devel] VCPU Structure

I think nobody is responding because you haven’t provided enough information about what it is you are trying to do... and resending the same message doesn’t help.

For example, if you are “extending” the instruction set (e.g. using an illegal opcode to do something useful), that would be very different than trapping memory accesses that meet a certain criteria.

 

From: Nimgaonkar, Satyajeet [mailto:SatyajeetNimgaonkar@xxxxxxxxxx]
Sent: Thursday, November 04, 2010 2:52 PM
To: Xen Devel; Dan Magenheimer
Subject: [Xen-devel] VCPU Structure

 

 Hi,
    I want to modify the VCPU structure to implement memory integrity functionality (i.e. memory hash function), such that the VCPU functionality incorporates memory integrity. Also once this is done, I want make sure that the VMs i create (Dom0 and Domu) run on this modified VCPU itself.
    Can anyone please tell me where should I look for to implement this.
    Thank you very much.

Regards,
Satyajeet

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