Re: [RFC PATCH v3 04/12] x86/sgx: Require userspace to define enclave pages' protection bits

From: Andy Lutomirski <luto@kernel.org>
To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	"Schaufler, Casey" <casey.schaufler@intel.com>,
	James Morris <jmorris@namei.org>,
	linux-sgx@vger.kernel.org, Dave Hansen <dave.hansen@intel.com>,
	Cedric Xing <cedric.xing@intel.com>,
	Jethro Beekman <jethro@fortanix.com>,
	"Dr . Greg Wettstein" <greg@enjellic.com>,
	Stephen Smalley <sds@tycho.nsa.gov>,
	LSM List <linux-security-module@vger.kernel.org>
Subject: Re: [RFC PATCH v3 04/12] x86/sgx: Require userspace to define enclave pages' protection bits
Date: Mon, 5 Aug 2019 14:30:22 -0700	[thread overview]
Message-ID: <CALCETrVcaL5KfR0V2fiHzQtyQdEC7d9iFNDKp9yBj7QZQsdXyw@mail.gmail.com> (raw)
In-Reply-To: <20190805205104.6ylxomqq37deqb3v@linux.intel.com>

On Mon, Aug 5, 2019 at 1:51 PM Jarkko Sakkinen
<jarkko.sakkinen@linux.intel.com> wrote:
>
> On Sun, Aug 04, 2019 at 03:20:24PM -0700, Andy Lutomirski wrote:
> > On Thu, Aug 1, 2019 at 9:38 AM Jarkko Sakkinen
> > <jarkko.sakkinen@linux.intel.com> wrote:
> > >
> > > On Mon, Jul 15, 2019 at 03:29:23PM -0700, Andy Lutomirski wrote:
> > > > I would say it differently: regardless of exactly how /dev/sgx/enclave
> > > > is wired up under the hood, we want a way that a process can be
> > > > granted permission to usefully run enclaves without being granted
> > > > permission to execute whatever bytes of code it wants.  Preferably
> > > > without requiring LSMs to maintain some form of enclave signature
> > > > whitelist.
> > >
> > > Would it be better to have a signer whitelist instead or some
> > > combination? E.g. you could whiteliste either by signer or
> > > enclave signature.
> > >
> >
> > I'm not sure, and also don't really think we need to commit to an
> > answer right now.  I do think that the eventual solution should be
> > more flexible than just whitelisting the signers.  In particular, it
> > should be possible to make secure enclaves, open-source or otherwise,
> > that are reproducibly buildable.  This more or less requires that the
> > signing private key not be a secret, which means that no one would
> > want to whitelist the signing key.  The enclave would be trusted, and
> > would seal data, on the basis of its MRENCLAVE, and the policy, if
> > any, would want to whitelist the MRENCLAVE or perhaps the whole
> > SIGSTRUCT.
> >
> > But my overall point is that it should be possible to have a conherent
> > policy that allows any enclave whatsoever to run but that still
> > respects EXECMEM and such.
>
> So could kernel embed a fixed signing key that would be made available
> through sysfs for signing? Already have one for my selftest.
>

Do you mean a public and private key?  I was imagining that someone
would just create a key pair and publish it for the case of SGX
programs that don't depend on MRSIGNER.  There doesn't have to be just
one.

But I may be misunderstanding you.