Re: x86/sgx: uapi change proposal

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>,
	Jethro Beekman <jethro@fortanix.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"x86@kernel.org" <x86@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-sgx@vger.kernel.org" <linux-sgx@vger.kernel.org>,
	Josh Triplett <josh@joshtriplett.org>,
	Haitao Huang <haitao.huang@linux.intel.com>,
	"Dr . Greg Wettstein" <greg@enjellic.com>
Subject: Re: x86/sgx: uapi change proposal
Date: Sun, 23 Dec 2018 12:42:48 -0800	[thread overview]
Message-ID: <CALCETrXhuVx3oFUUr5KRGPXrEpcUPjFXapLdHYJZ8C+91woh_Q@mail.gmail.com> (raw)
In-Reply-To: <20181223125114.GA7051@linux.intel.com>

On Sun, Dec 23, 2018 at 4:52 AM Jarkko Sakkinen
<jarkko.sakkinen@linux.intel.com> wrote:
>
> On Sat, Dec 22, 2018 at 10:25:02AM +0200, Jarkko Sakkinen wrote:
> > On Sat, Dec 22, 2018 at 10:16:49AM +0200, Jarkko Sakkinen wrote:
> > > On Thu, Dec 20, 2018 at 12:32:04PM +0200, Jarkko Sakkinen wrote:
> > > > On Wed, Dec 19, 2018 at 06:58:48PM -0800, Andy Lutomirski wrote:
> > > > > Can one of you explain why SGX_ENCLAVE_CREATE is better than just
> > > > > opening a new instance of /dev/sgx for each encalve?
> > > >
> > > > I think that fits better to the SCM_RIGHTS scenario i.e. you could send
> > > > the enclav to a process that does not have necessarily have rights to
> > > > /dev/sgx. Gives more robust environment to configure SGX.
> > >
> > > Sean, is this why you wanted enclave fd and anon inode and not just use
> > > the address space of /dev/sgx? Just taking notes of all observations.
> > > I'm not sure what your rationale was (maybe it was somewhere). This was
> > > something I made up, and this one is wrong deduction. You can easily
> > > get the same benefit with /dev/sgx associated fd representing the
> > > enclave.
> > >
> > > This all means that for v19 I'm going without enclave fd involved with
> > > fd to /dev/sgx representing the enclave. No anon inodes will be
> > > involved.
> >
> > Based on these observations I updated the uapi.
> >
> > As far as I'm concerned there has to be a solution to do EPC mapping
> > with a sequence:
> >
> > 1. Ping /dev/kvm to do something.
> > 2. KVM asks SGX core to do something.
> > 3. SGX core does something.
> >
> > I don't care what the something is exactly is, but KVM is the only sane
> > place for KVM uapi. I would be surprised if KVM maintainers didn't agree
> > that they don't want to sprinkle KVM uapi to random places in other
> > subsystems.
>
> The one option to consider to do would be to have a device driver for
> KVM if you really want this e.g. something like /dev/vsgx. With the
> current knowledge I'm not yet sure why all could not be done just
> through /dev/kvm.
>

That seems reasonable too.  I don't really care about the path to the
device node, but it does seem reasonable to me to have it be a
separate node entirely from the normal enclave interface.