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

[Huang, Kai]

On Thu, 2025-07-24 at 21:14 +0000, Huang, Kai wrote:
> > 
> > > 
> > > > 
> > > > 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.

Side topic, just out of curiosity, do you know why Intel decided to re-
generate CR_BASE_KEY even SVN is found to be up-to-date?