Re: [PATCH] x86/sgx: Free backing memory after faulting the enclave page
From: Jarkko Sakkinen
Date: Thu Nov 04 2021 - 11:25:09 EST
On Thu, 2021-11-04 at 08:13 -0700, Dave Hansen wrote:
> On 11/4/21 8:04 AM, Jarkko Sakkinen wrote:
> > > Do we also need to deal with truncating the PCMD? (For those watching
> > > along at home, there are two things SGX swaps to RAM: the actual page
> > > data and also some metadata that ensures page integrity and helps
> > > prevent things like rolling back to old versions of swapped pages)
> > Yes.
> >
> > This can be achieved by iterating through all of the enclave pages,
> > which share the same shmem page for storing their PCMD's, as the one
> > being faulted back. If none of those pages is swapped, the PCMD page can
> > safely truncated.
>
> I was thinking we could just read the page. If it's all 0's, truncate it.
Hmm... did ELDU zero PCMD as a side-effect?
It should be fairly effecient just to check the pages by using
encl->page_tree.
/Jarkko