[Qemu-devel] Asking about QEMU's process in memory address space of host

[Qemu-devel] Asking about QEMU's process in memory address space of host

[Piyawath Boukom]

Dear peoples in mailing-list,

My name is Piyawath Boukom, I’m a student from Tokyo Tech.
I hope you can enlighten me about this.

Below are things that those I would like to perform.

- I want to identify where guest kernel lives in QEMU’s process on host machine, is it possible to find a set of logical address space of guest kernel on host machine ? (which part of memory space is being used by guest kernel)

- If I can specify where QEMU’s process lives in host memory address space then I know where stack, heap, data, text, etc. of QEMU live. So, can I determine where guest machine’s physical memory lives ? (in host logical address)

- If above are possible to do, can I write those things into a file ? (ex. data in guest machine’s memory, binary data, etc.)

*Host and guest are Linux.

Any comments are very welcome.

Looking forward to hearing back from you.
Piyawath Boukom

Re: [Qemu-devel] Asking about QEMU's process in memory address space of host

[Christopher Covington]

On 07/08/2015 07:14 AM, Piyawath Boukom wrote:
> Dear peoples in mailing-list,
> 
> My name is Piyawath Boukom, I’m a student from Tokyo Tech.
> I hope you can enlighten me about this.
> 
> Below are things that those I would like to perform.
> 
> - I want to identify where guest kernel lives in QEMU’s process on host machine, is it possible to find a set of logical address space of guest kernel on host machine ? (which part of memory space is being used by guest kernel)
> 
> - If I can specify where QEMU’s process lives in host memory address space then I know where stack, heap, data, text, etc. of QEMU live. So, can I determine where guest machine’s physical memory lives ? (in host logical address)
> 
> - If above are possible to do, can I write those things into a file ? (ex. data in guest machine’s memory, binary data, etc.)
> 
> *Host and guest are Linux.

The "savevm" monitor command dumps pretty much all the state to a file,
although you have to use QCOW2 format disk images.

https://en.wikibooks.org/wiki/QEMU/Monitor#savevm

Once the snapshot/checkpoint has been saved, you can dig into it to get
specific memory contents. You'll have to write your own scripts for this as
far as I know.

For kernel virtual addresses, check the guest's dmesg. `dmesg | sed -nr
'/Virtual kernel memory/,/\[/ p'` does that for me on AArch64.

If there's a particular user space process you're interested in, run `cat
/proc/$PID/maps` in the guest immediately before or after saving the
checkpoint to get its virtual addresses.

Chris

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