Re: [Xen-devel] c/s 24425:053a44894279 (xsm: add checks on PCI configuration access)

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

On 06/21/2012 11:13 AM, Jan Beulich wrote:
>>>> On 21.06.12 at 16:19, Daniel De Graaf <dgdegra@xxxxxxxxxxxxx> wrote:
>> On 06/21/2012 09:20 AM, Jan Beulich wrote:
>>> The mmconfig part of this is seriously broken: These operations,
>>> even when carried out by Dom0, are MMIO accesses, and hence
>>> are invisible to the hypervisor without extra handling. Putting
>>> the checks into pci_mmcfg_{read,write}() has the effect of
>>> potentially denying the _hypervisor_ access. So I think at least
>>> that part needs to be reverted.
>>
>> I agree - the XSM checks are intended to be done only when the hypervisor
>> is accessing on behalf of the domain, which looks to be covered by the
>> traps part of the patch. These checks are currently intended to deny a
>> domain with IS_PRIV but without full hardware access - in particular,
>> without access to the PCI configuration MMIO area - from using legacy 
>> register access to reconfigure PCI devices.
>>
>> While it may be useful to extend this access check to include the PCI 
>> configuration MMIO pages, this would require emulating both reads and
>> writes to any page that has entries that a particular domain does not
>> have access to. The existing pciback/pcifront configuration access model
>> already handles these issues without changes to the hypervisor.
> 
> So do I read correctly that you agree to revert that part of said
> c/s?
> 
> Jan
> 

Yes.

-- 
Daniel De Graaf
National Security Agency



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