Re: [PATCH v2 4/6] virtio: Initialize authorized attribute for confidential guest

["Kuppuswamy, Sathyanarayanan" <sathyanarayanan.kuppuswamy@linux.intel.com>]

On 10/1/21 12:00 PM, Alan Stern wrote:
> On Fri, Oct 01, 2021 at 11:09:52AM -0700, Dan Williams wrote:
>> On Fri, Oct 1, 2021 at 9:47 AM Alan Stern <stern@rowland.harvard.edu> wrote:
>>>
>>> On Fri, Oct 01, 2021 at 09:13:54AM -0700, Dan Williams wrote:
>>>> Bear with me, and perhaps it's a lack of imagination on my part, but I
>>>> don't see how to get to a globally generic "authorized" sysfs ABI
>>>> given that USB and Thunderbolt want to do bus specific actions on
>>>> authorization toggle events. Certainly a default generic authorized
>>>> attribute can be defined for all the other buses that don't have
>>>> legacy here, but Thunderbolt will still require support for '2' as an
>>>> authorized value, and USB will still want to base probe decisions on
>>>> the authorization state of both the usb_device and the usb_interface.
>>>
>>> The USB part isn't really accurate (I can't speak for Thunderbolt).
>>> When a usb_device is deauthorized, the device will be unconfigured,
>>> deleting all its interfaces and removing the need for any probe
>>> decisions about them.  In other words, the probe decision for a
>>> usb_device or usb_interface depends only on the device's/interface's
>>> own authorization state.
>>>
>>> True, the interface binding code does contain a test of the device's
>>> authorization setting.  That test is redundant and can be removed.
>>>
>>> The actions that USB wants to take on authorization toggle events for
>>> usb_devices are: for authorize, select and install a configuration;
>>> for deauthorize, unconfigure the device.  Each of these could be
>>> handled simply enough just by binding/unbinding the device.  (There
>>> is some special code for handling wireless USB devices, but wireless
>>> USB is now defunct.)
>>
>> Ah, so are you saying that it would be sufficient for USB if the
>> generic authorized implementation did something like:
>>
>> dev->authorized = 1;
>> device_attach(dev);
>>
>> ...for the authorize case, and:
>>
>> dev->authorize = 0;
>> device_release_driver(dev);
>>
>> ...for the deauthorize case?
> 
> Yes, I think so.  But I haven't tried making this change to test and
> see what really happens.
> 

For thunderbolt driver, it looks much more complicated. Unless you
define some callbacks in struct bus_type, we cannot easily generalize
it (but such callbacks are not recommended because it brings bus specific
operations to core layer).

sysfs_read()
-> simple read

sysfs_write()
-> tb_switch_set_authorized()
   -> disapprove_switch()
      -> tb_domain_disapprove_switch()
         -> tb->cm_ops->disapprove_switch() (product specific call)
   -> tb_domain_approve_switch_key()
      -> tb->cm_ops->add_switch_key
      -> tb->cm_ops->approve_switch() (product specific call)
   -> tb_domain_approve_switch()
      -> tb->cm_ops->approve_switch() (product specific call)
   -> tb_domain_challenge_switch_key()
      -> tb->cm_ops->challenge_switch_key()
      -> crypto_alloc_shash()
      -> crypto_shash_setkey()
      -> crypto_shash_digest()
      -> tb->cm_ops->approve_switch() (product specific call)


> Alan Stern
> 

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer