Re: [PATCH v5 11/11] intel_sgx: driver documentation

Jarkko Sakkinen
2017-11-24T17:26:21Z

On Fri, Nov 17, 2017 at 01:43:10PM -0800, Darren Hart wrote:
> This series will need to be updated per the comments received so far, as
> well as with commit messages and a complete Cc list *per patch* giving
> all required parties an opportunity to review.
>
> With respect to the obvious security nature of this series, who from the
> kernel security folks are going to be reviewing this?
> security@kernel.org?

I think it would make sense to CC this to linux-security module.

> Cc updated for this thread, and specifically the question regarding
> location below:
>
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
> > ---
> > Documentation/index.rst | 1 +
> > Documentation/x86/intel_sgx.rst | 131 ++++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 132 insertions(+)
> > create mode 100644 Documentation/x86/intel_sgx.rst
> >
>
> ...
>
> > diff --git a/Documentation/x86/intel_sgx.rst b/Documentation/x86/intel_sgx.rst
> > new file mode 100644
> > index 000000000000..34bcf6a2a495
> > --- /dev/null
> > +++ b/Documentation/x86/intel_sgx.rst
> > @@ -0,0 +1,131 @@
> > +===================
> > +Intel(R) SGX driver
> > +===================
> > +
> > +Introduction
> > +============
> > +
> > +Intel(R) SGX is a set of CPU instructions that can be used by applications to
> > +set aside private regions of code and data. The code outside the enclave is
> > +disallowed to access the memory inside the enclave by the CPU access control.
> > +In a way you can think that SGX provides inverted sandbox. It protects the
> > +application from a malicious host.
> > +
> > +There is a new hardware unit in the processor called Memory Encryption Engine
> > +(MEE) starting from the Skylake microarchitecture. BIOS can define one or many
> > +MEE regions that can hold enclave data by configuring them with PRMRR registers.
> > +
> > +The MEE automatically encrypts the data leaving the processor package to the MEE
> > +regions. The data is encrypted using a random key whose life-time is exactly one
> > +power cycle.
> > +
> > +You can tell if your CPU supports SGX by looking into ``/proc/cpuinfo``:
> > +
> > + ``cat /proc/cpuinfo | grep sgx``
>
> Is SGX considered architectural or not? A quick search of the SDM
> includes it in Volume 3:
>
> Volume 3: Includes the full system programming guide, parts 1, 2, 3, and
> 4. Describes the operating-system support environment of Intel® 64 and
> IA-32 architectures, including: memory management, protection, task
> management, interrupt and exception handling, multi-processor support,
> thermal and power management features, debugging, performance
> monitoring, system management mode, virtual machine extensions (VMX)
> instructions, Intel® Virtualization Technology (Intel® VT), and Intel®
> Software Guard Extensions (Intel® SGX).
>
> https://software.intel.com/en-us/articles/intel-sdm
>
> Depending on the answer, this impacts whether this belongs in
> drivers/platform/x86 or arch/x86/platform per our recent agreement with
> Thomas.
>
> Thomas, Mingo, HPA, do you wish to see this organized/located
> differently than it is here in v5?

The code is made easily relocatable. I just wanted to keep it as an
encapsulated driver up until I hear the maintainer feedback. I'll submit
v6 with code otherwise fixed according to the feedback that I've heard
up until that point and relocate it in v7 based on your feedback.

> > +Launch control
> > +==============
> > +
> > +For launching an enclave, two structures must be provided for ENCLS(EINIT):
> > +
> > +1. **SIGSTRUCT:** a signed measurement of the enclave binary.
> > +2. **EINITTOKEN:** the measurement, the public key of the signer and various
> > + enclave attributes. This structure contains a MAC of its contents using
> > + hardware derived symmetric key called *launch key*.
> > +
> > +The hardware platform contains a root key pair for signing the SIGTRUCT
> > +for a *launch enclave* that is able to acquire the *launch key* for
> > +creating EINITTOKEN's for other enclaves. For the launch enclave
> > +EINITTOKEN is not needed because it is signed with the private root key.
> > +
> > +There are two feature control bits associate with launch control
>
> Nit: missing colon at the end of the line above ^

Yes. Thanks for spotting that out :-)

/Jarkko