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

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