[RFC PATCH v4 10/12] security/selinux: Add enclave_load() implementation

[Sean Christopherson]

On Mon, Jul 01, 2019 at 01:03:51PM -0700, Xing, Cedric wrote:
> > From: Andy Lutomirski [mailto:luto at kernel.org]
> > Sent: Monday, July 01, 2019 12:33 PM
> > 
> > It does make sense, but I'm not sure it's correct to assume that any LSM
> > policy will always allow execution on enclave source pages if it would
> > allow execution inside the enclave.  As an example, here is a policy
> > that seems reasonable:
> > 
> > Task A cannot execute dynamic non-enclave code (no execmod, no execmem,
> > etc -- only approved unmodified file pages can be executed).
> > But task A can execute an enclave with MRENCLAVE == such-and-such, and
> > that enclave may be loaded from regular anonymous memory -- the
> > MRENCLAVE is considered enough verification.
> 
> You are right. That's a reasonable policy. But I still can't see the need for
> SGX_EXECUNMR, as MRENCLAVE is considered enough verification.

That assumes the enclave/loader developer will never make a mistake, and
that policy owners are going to do a deep dive on the EEXTEND values for
an enclave (and will never make a mistake).

User errors aside, EXECUNMR would also be useful in conjunction with
MRSIGNER, e.g. allow all enclaves signed by X, but disallow unmeasured
code.