Re: [PATCH v6 04/11] x86: define IA32_FEATUE_CONTROL.SGX_LC

[Jarkko Sakkinen]

On Tue, Nov 28, 2017 at 10:53:24PM +0200, Jarkko Sakkinen wrote:
> > So, maybe something like this?
> > 
> >     After SGX is activated[1] the IA32_SGXLEPUBKEYHASHn MSRs are writable
> >     if and only if SGX_LC is set in the IA32_FEATURE_CONTROL MSR and the
> >     IA32_FEATURE_CONTROL MSR is locked, otherwise they are read-only.
> > 
> >     For example, firmware can allow the OS to change the launch enclave
> >     root key by setting IA32_FEATURE_CONTROL.SGX_LC, and thus give the
> >     OS complete control over the enclaves it runs.  Alternatively,
> >     firmware can clear IA32_FEATURE_CONTROL.SGX_LC to lock down the root
> >     key and restrict the OS to running enclaves signed with the root key
> >     or whitelisted/trusted by a launch enclave (which must be signed with
> >     the root key).
> > 
> >     [1] SGX related bits in IA32_FEATURE_CONTROL cannot be set until SGX
> >         is activated, e.g. by firmware.  SGX activation is triggered by
> >         setting bit 0 in MSR 0x7a.  Until SGX is activated, the LE hash
> >         MSRs are writable, e.g. to allow firmware to lock down the LE
> >         root key with a non-Intel value.
> 
> Thanks I'll use this as a basis and move most of the crappy commit
> message to the commit (with some editing) that defines the MSRs.

Not sure after all if I'm following this.

IA32_FEATURE_CONTROL[17] contols whether the MSRs are writable or not
after the feature control MSR is locked. SGX_LC means just that the
CPU supports the launch configuration.

/Jarkko