Re: [PATCH v9 6/6] x86/sgx: Enable automatic SVN updates for SGX enclaves

["Huang, Kai" <kai.huang@intel.com>]

> 
> > 
> > > 
> > > Attempt to execute ENCLS[EUPDATESVN] every time the first file descriptor
> > > is obtained via sgx_(vepc_)open(). In the most common case the microcode
> > > SVN is already up-to-date, and the operation succeeds without updating SVN.
> > 
> > (Sorry I forgot to say this in the previous versions):
> > 
> > If I read the pseudo code correctly, when the SVN is already up-to-date,
> > the EUPDATESVN doesn't update SVN but it re-generates crypto assets
> > anyway.
> > 
> > This is no harm per the pseudo code, since the "crypto assets" is actually
> > the CR_BASE_KEY which is only used by EWB/ELDU flow per the SDM.
> > 
> > In other words, it doesn't impact other enclave visible keys (those from
> > EGETKEY) such as sealing key.
> > 
> > I think this is important.  Because if enclave visible keys such as
> > sealing key are lost on EUPDATESVN when SVN is already up-to-date (which
> > is the most common case), it will bring significant visible impact to
> > enclave.  E.g., one enclave could find its secret encrypted by sealing key
> > could never be retrieved after it restarts.
> > 
> > Assuming I didn't miss anything, can we also mention this in the
> > changelog?
> 
> Yes, you are right, anything like above behaviour would be a nightmare
> in practice. So would smth like this work as an additional text:
> 
> "Note that in cases when SVN is already up-to-date and EUPDATESVN
> is executed, it does not affect enclaves' visible keys obtained via EGETKEY
> instruction."
> 
> ?
> 

Yes works for me.  Thanks.