Re: [PATCH v6 5/5] x86/tdx: Add Quote generation support

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

On 5/16/22 7:58 PM, Kai Huang wrote:
> On Fri, 2022-05-13 at 12:29 -0700, Sathyanarayanan Kuppuswamy wrote:
>>>
>>>
>>>> +
>>>> +	/* Wait for attestation completion */
>>>> +	ret = wait_for_completion_interruptible(&entry->compl);
>>>> +	if (ret < 0) {
>>>> +		/*
>>>> +		 * For premature termination, since VMM still owns the
>>>> +		 * shared buffer, mark the request invalid to let
>>>> +		 * quote_callback_handler() handle the memory cleanup
>>>> +		 * function.
>>>> +		 */
>>>> +		invalidate_quote_request(entry);
>>>
>>> Interrupt can arrive after signal interrupt.  So invalidate_quote_request()
>>> should check if the request is already processed, and return 0 or -EINTR.
>>> Probably check the state always and del_list under single lock/unlock pair.
>>
>> Agree. But I think we should return -EINTR for the interrupted case
>> irrespective of the processed status (so no return 0).
>>
>> I will hold the lock and handle the cleanup for the processed
>> status.
> 
> Even if we check the buffer status in invalidate_quote_request(), there's no
> guarantee the VMM won't change the buffer status _after_ we do the check, so
> looks such check isn't necessary.
> 

Consider the case where we get a callback interrupt, and before we
complete the processing for it, user terminates the request. In this
scenario,  quote_callback_handler() will consider the request is
still valid and no do the memory cleanup. To handle this case,
we need to check the status in invalidate_quote_request() and do
the cleanup if required.

/* Handles early termination of GetQuote requests */
void invalidate_quote_request(struct quote_entry *entry)
{
         struct tdx_quote_hdr *quote_hdr;

         /*
          * For early termination, if the request is not yet
          * processed by VMM (GET_QUOTE_IN_FLIGHT), the VMM
          * still owns the shared buffer, so mark the request
          * invalid to let quote_callback_handler() handle the
          * memory cleanup function. If the request is already
          * processed, then do the cleanup and return.
          */

         mutex_lock(&quote_lock);
         quote_hdr = (struct tdx_quote_hdr *)entry->buf->vmaddr;
         if (quote_hdr->status == GET_QUOTE_IN_FLIGHT) {
                 entry->valid = false;
                 mutex_unlock(&quote_lock);
                 return;
         }
         _del_quote_entry(entry);
         mutex_unlock(&quote_lock);
}


-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer