Re: [Xen-devel] EPT question - XENMEM_get_access_op

[Balbir Singh <bsingharora@xxxxxxxxx>]

On Fri, Feb 20, 2015 at 4:19 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>> On 20.02.15 at 05:47, <bsingharora@xxxxxxxxx> wrote:
>> I'm trying to use the memevent channel to extract the permission for a
>> particular text section. I expect to see rx as the permission, instead
>> I am seeing rwx. I have not spent a whole lot of time looking at
>> memaccess[] and p2m-ept.c, but I am puzzled. The OS definitely has
>> this text segment marked as COPY-ON-WRITE, I am a little confused with
>> the permissions returned. Is there a way to get the right thing?
>
> What the guest OS specifies doesn't matter here - EPT is not OS
> (L1) but hypervisor (L2) paging, and hence the permissions there
> are controlled by the hypervisor. Of course guest memory
> accesses have to pass both paging levels' access checks in order
> to be carried out (and not fault).


Thanks Jan! Is there a way for a memevents channel consumer to get
access to the L1 (OS Page tables). I presume we'll need to walk the
page tables, I suspect the current access_op is broken without it and
may not be returning anything meaningful in most of the cases

Balbir Singh

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