Messages in this thread | | | Subject | Re: [PATCH v6 5/5] x86/tdx: Add Quote generation support | From | Kai Huang <> | Date | Wed, 18 May 2022 11:06:26 +1200 |
| |
On Tue, 2022-05-17 at 13:08 -0700, Sathyanarayanan Kuppuswamy wrote: > > 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("e_lock); > quote_hdr = (struct tdx_quote_hdr *)entry->buf->vmaddr; > if (quote_hdr->status == GET_QUOTE_IN_FLIGHT) {
What prevents VMM from updating quote_hdr->status from IN_FLIGHT to DONE _after_ this check?
If you want to add such check, you should check against GET_QUOTE_DONE, but not IN_FLIGHT. Only after status is DONE, VMM will not update the buffer. Perhaps something like below:
mutex_lock("e_lock); /* Skip invalidate the buffer if VMM has done with the buffer */ if (quote_hdr->status == GET_QUOTE_DONE) { mutex_unlock("e_lock); return 0; }
And in the IOCTL, you can perhaps to choose to return 0, instead of -EINTR in this case, as the Quote has been finished already.
But I am not sure whether this is necessary. The worst case is one finished Quote is wasted I guess.
> entry->valid = false; > mutex_unlock("e_lock); > return; > } > _del_quote_entry(entry); > mutex_unlock("e_lock); > } > >
-- Thanks, -Kai
| |