On Mon, Mar 14, 2022 at 10:39:36AM -0500, Haitao Huang wrote:
> 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.
>ar
> 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.
The #PF handler should do unconditionally EMODPR with PROT_READ.
