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    SubjectRe: [PATCH v5 11/11] intel_sgx: driver documentation
    On Tue, Nov 21, 2017 at 12:46:23AM +0200, Jarkko Sakkinen wrote:
    > On Wed, Nov 15, 2017 at 12:54:12PM +0100, Peter Zijlstra wrote:
    > > On Tue, Nov 14, 2017 at 10:49:48PM +0200, Jarkko Sakkinen wrote:
    > > > In these cases IA32_FEATURE_CONTROL[17] would be zeroed before locking
    > > > the feature control, which would mean that the kernel could not write
    > > > new values with wrmsr for the root key hash.
    > >
    > > > The question is whether we want to allow this or not. If the answer is
    > > > no, a check can be added to the driver initialization code whether 17 is
    > > > set, and if not, it driver would fail to initialize.
    > >
    > > That has my vote; I would not trust a firmware/BIOS key.
    >
    > Please note that it does not have a key to look inside the enclave. The
    > enclave is protected by two means:
    >
    > 1. The CPU asserts the memory accesses to it.
    > 2. The CPU encrypts/decrypts in L1 in order to protect from physical
    > attacks and peripherals that have potential spy the bus.

    The encryption key is generated for every boot cycle and it is *never*
    leaked out of the CPU package.

    After thinking what you and Borislav said I position myself to the point
    of view that even if the MSRs would be read-only the kernel could allow
    running enclaves *with a condition*.

    I propose adding an additional check to the driver initialization:

    Try to start LE. If it doesn't start i.e. is signed with a different
    root key than the one inside MSRs, then fail the initialization.

    /Jarkko

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