* Reading guest page flags
@ 2018-09-13 17:29 Spencer Michaels
2018-09-13 17:47 ` Razvan Cojocaru
0 siblings, 1 reply; 4+ messages in thread
From: Spencer Michaels @ 2018-09-13 17:29 UTC (permalink / raw)
To: xen-devel
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Hello,
I'm writing an application that can read/write guest memory, and as part of
that I need to check whether the page being manipulated is
readable/writable by the guest itself. Does Xen have an API that would
allow me to read the flags of an arbitrary page on a guest, given either
its address or its PFN? I've only been able to find functions that update
the existing memory mappings, but none to read them.
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* Re: Reading guest page flags
2018-09-13 17:29 Reading guest page flags Spencer Michaels
@ 2018-09-13 17:47 ` Razvan Cojocaru
2018-09-13 18:45 ` Tamas K Lengyel
2018-09-14 8:01 ` Spencer Michaels
0 siblings, 2 replies; 4+ messages in thread
From: Razvan Cojocaru @ 2018-09-13 17:47 UTC (permalink / raw)
To: Spencer Michaels, xen-devel
On 9/13/18 8:29 PM, Spencer Michaels wrote:
> I'm writing an application that can read/write guest memory, and as part
> of that I need to check whether the page being manipulated is
> readable/writable by the guest itself. Does Xen have an API that would
> allow me to read the flags of an arbitrary page on a guest, given either
> its address or its PFN? I've only been able to find functions that
> update the existing memory mappings, but none to read them.
If you mean EPT, yes: look at xc_get_mem_access() in xenctrl.h / libxc.
If you mean "regular" PTEs, no - you'd have to write your own code to
retrieve that.
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* Re: Reading guest page flags
2018-09-13 17:47 ` Razvan Cojocaru
@ 2018-09-13 18:45 ` Tamas K Lengyel
2018-09-14 8:01 ` Spencer Michaels
1 sibling, 0 replies; 4+ messages in thread
From: Tamas K Lengyel @ 2018-09-13 18:45 UTC (permalink / raw)
To: Razvan Cojocaru; +Cc: sxmichaels, Xen-devel
On Thu, Sep 13, 2018 at 11:48 AM Razvan Cojocaru
<rcojocaru@bitdefender.com> wrote:
>
> On 9/13/18 8:29 PM, Spencer Michaels wrote:
> > I'm writing an application that can read/write guest memory, and as part
> > of that I need to check whether the page being manipulated is
> > readable/writable by the guest itself. Does Xen have an API that would
> > allow me to read the flags of an arbitrary page on a guest, given either
> > its address or its PFN? I've only been able to find functions that
> > update the existing memory mappings, but none to read them.
>
> If you mean EPT, yes: look at xc_get_mem_access() in xenctrl.h / libxc.
> If you mean "regular" PTEs, no - you'd have to write your own code to
> retrieve that.
LibVMI does that for guest PTEs:
https://github.com/libvmi/libvmi/blob/master/libvmi/libvmi.h#L936
Tamas
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* Re: Reading guest page flags
2018-09-13 17:47 ` Razvan Cojocaru
2018-09-13 18:45 ` Tamas K Lengyel
@ 2018-09-14 8:01 ` Spencer Michaels
1 sibling, 0 replies; 4+ messages in thread
From: Spencer Michaels @ 2018-09-14 8:01 UTC (permalink / raw)
To: Razvan Cojocaru; +Cc: xen-devel
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Thanks! Sorry, I should have been more specific - I do indeed mean the
regular guest PTEs (and I'm using PV guests which as I understand don't use
EPT anyway). So, it seems I'll have to write my own code for this. I'll
take a look at libvmi's implementation; if anyone knows any other libraries
/ programs that read guest PTEs, that would be helpful to know as well.
On Thu, Sep 13, 2018, 10:47 AM Razvan Cojocaru <rcojocaru@bitdefender.com>
wrote:
> On 9/13/18 8:29 PM, Spencer Michaels wrote:
> > I'm writing an application that can read/write guest memory, and as part
> > of that I need to check whether the page being manipulated is
> > readable/writable by the guest itself. Does Xen have an API that would
> > allow me to read the flags of an arbitrary page on a guest, given either
> > its address or its PFN? I've only been able to find functions that
> > update the existing memory mappings, but none to read them.
>
> If you mean EPT, yes: look at xc_get_mem_access() in xenctrl.h / libxc.
> If you mean "regular" PTEs, no - you'd have to write your own code to
> retrieve that.
>
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2018-09-13 17:29 Reading guest page flags Spencer Michaels
2018-09-13 17:47 ` Razvan Cojocaru
2018-09-13 18:45 ` Tamas K Lengyel
2018-09-14 8:01 ` Spencer Michaels
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