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SubjectRe: [PATCH v38 14/24] x86/sgx: Add SGX_IOC_ENCLAVE_INIT
On Mon, Sep 21, 2020 at 11:10:21AM -0700, Sean Christopherson wrote:
> On Mon, Sep 21, 2020 at 07:35:14PM +0200, Borislav Petkov wrote:
> > On Tue, Sep 15, 2020 at 02:28:32PM +0300, Jarkko Sakkinen wrote:
> > > +static int sgx_einit(struct sgx_sigstruct *sigstruct, void *token,
> > > + struct sgx_epc_page *secs, u64 *lepubkeyhash)
> > > +{
> > > + int ret;
> > > +
> > > + preempt_disable();
> > > + sgx_update_lepubkeyhash_msrs(lepubkeyhash, false);
> >
> > So this will update the cached copies *and* the MSRs itself if what's
> > cached is stale...
> >
> > > + ret = __einit(sigstruct, token, sgx_get_epc_addr(secs));
> > > + if (ret == SGX_INVALID_EINITTOKEN) {
> >
> > ... so why would it return this error here?
> >
> > Definition of this error says:
> >
> > * %SGX_INVALID_EINITTOKEN: EINITTOKEN is invalid and enclave signer's
> > * public key does not match IA32_SGXLEPUBKEYHASH.
> >
> > when you just updated them?!
> >
> > > + sgx_update_lepubkeyhash_msrs(lepubkeyhash, true);
> >
> > So why force a second time?
>
> The LE pubkey hash MSRs are special snowflakes. They get reset to Intel's
> default key on any loss of EPC, e.g. if the system does a suspend/resume
> cycle. The approach we took (obviously) is to assume the kernel's cache can
> be stale at any given time. The alternative would be to try and track loss
> of EPC conditions and emulate the reset, but that's a bit dicey on bare
> metal as any missed case would hose SGX, and in a VM it's theoretically
> impossible to handle as a particularly unhelpful VMM could emulate loss of
> EPC at will.
>
> Yes, this need a big fat comment.

Thanks, please provide one :-)

/Jarkko

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