Hi Jarkko
On Sun, 13 Mar 2022 21:58:51 -0500, Jarkko Sakkinen <jarkko@xxxxxxxxxx>
wrote:
> On Mon, Mar 14, 2022 at 04:50:56AM +0200, Jarkko Sakkinen wrote:
> > On Mon, Mar 14, 2022 at 04:49:37AM +0200, Jarkko Sakkinen wrote:
> > > On Fri, Mar 11, 2022 at 09:53:29AM -0800, Reinette Chatre wrote:
> > >
> > > > I saw Haitao's note that EMODPE requires "Read access permitted
> > by enclave".
> > > > This motivates that EMODPR->PROT_NONE should not be allowed
> > since it would
> > > > not be possible to relax permissions (run EMODPE) after that.
> > Even so, I
> > > > also found in the SDM that EACCEPT has the note "Read access
> > permitted
> > > > by enclave". That seems to indicate that EMODPR->PROT_NONE is
> > not practical
> > > > from that perspective either since the enclave will not be able
to
> > > > EACCEPT the change. Does that match your understanding?
> > >
> > > Yes, PROT_NONE should not be allowed.
> > >
> > > This is however the real problem.
> > >
> > > The current kernel patch set has inconsistent API and EMODPR
ioctl is
> > > simply unacceptable. It also requires more concurrency management
> > from
> > > user space run-time, which would be heck a lot easier to do in the
> > kernel.
> > >
> > > If you really want EMODPR as ioctl, then for consistencys sake,
> > then EAUG
> > > should be too. Like this when things go opposite directions, this
> > patch set
> > > plain and simply will not work out.
> > >
> > > I would pick EAUG's strategy from these two as it requires half
> > the back
> > > calls to host from an enclave. I.e. please combine mprotect() and
> > EMODPR,
> > > either in the #PF handler or as part of mprotect(), which ever
> > suits you
> > > best.
> > >
> > > I'll try demonstrate this with two examples.
> > >
> > > mmap() could go something like this() (simplified):
> > > 1. Execution #UD's to SYSCALL.
> > > 2. Host calls enclave's mmap() handler with mmap() parameters.
> > > 3. Enclave up-calls host's mmap().
> > > 4. Loops the range with EACCEPTCOPY.
> > >
> > > mprotect() has to be done like this:
> > > 1. Execution #UD's to SYSCALL.
> > > 2. Host calls enclave's mprotect() handler.
> > > 3. Enclave up-calls host's mprotect().
> > > 4. Enclave up-calls host's ioctl() to SGX_IOC_ENCLAVE_PERMISSIONS.
I assume up-calls here are ocalls as we call them in our implementation,
which are the calls enclave make to untrusted side via EEXIT.
If so, can your implementation combine this two up-calls into one, then
host
side just do ioctl() and mprotect to kernel? If so, would that address
your
concern about extra up-calls?
> > > 3. Loops the range with EACCEPT.
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > 5. Loops the range with EACCEPT + EMODPE.
> >
> > > This is just terrible IMHO. I hope these examples bring some
insight.
>
> E.g. in Enarx we have to add a special up-call (so called enarxcall in
> intermediate that we call sallyport, which provides shared buffer to
> communicate with the enclave) just for reseting the range with
PROT_READ.
> Feel very redundant, adds ugly cruft and is completely opposite
strategy
> to
> what you've chosen to do with EAUG, which is I think correct choice as
> far
> as API is concerned.
The problem with EMODPR on #PF is that kernel needs to know what
permissions
requested from enclave at the time of #PF. So enclave has to make at
least
one call to kernel (again via ocall in our case, I assume up-call in
your
case) to make the change.
