[Xen-devel] Scan guests' page to seek specific instructions

[Wen QI <qiwen@xxxxxxxxxx>]

Hi,

I am trying to scan guests' pages and check whether they contain specific 
instructions (e.g., LOCK). I summarize how I did it as follows. Could you 
please give some suggestions about whether am I on the right direction? Thank 
you.

In my testing environment, XEN 4.4.0 is deployed. Both Domain-0 and guests are 
using Ubuntu 14.4 64-bit. The guests are in HVM mode.

1. In the page fault handler sh_page_fault(), we first judge #PF 
(regs->error_code), if it contains PFEC_insn_fetch && PFEC_user_mode, then 
continue to next step.

2. The virtual address (va, which is from CR3) is converted to MFN.

3. If the MFN is valid, we get the page address via mfn_to_virt().

4. Then scan the page's data to check whether specific instructions exist in 
the page.

To simplify the testing, I temporarily disabled all shadow optimizations by 
setting SHADOW_OPTIMIZATIONS as 0x0F.

My observations are as follows:
- In step 2, some virtual addresses can be converted to valid MFN, some cannot.

- In the HVM guest, I run a piece of C code which contains the LOCK 
instructions. However, in step 4, the instructions cannot be detected.

Looking forward to your suggestions. Thanks again.

Best Regards
Wen



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