On Sat, 2018-06-09 at 22:32 -0700, Andy Lutomirski wrote:
> On Fri, Jun 8, 2018 at 10:22 AM Jarkko Sakkinen
> <jarkko.sakkinen@xxxxxxxxxxxxxxx> wrote:
> >
> >
> > SGX has a set of data structures to maintain information about the enclaves
> > and their security properties. BIOS reserves a fixed size region of
> > physical memory for these structures by setting Processor Reserved Memory
> > Range Registers (PRMRR). This memory area is called Enclave Page Cache
> > (EPC).
> >
> >
> > +/**
> > + * sgx_einit - EINIT an enclave with the appropriate LE pubkey hash
> > + * @sigstruct: a pointer to the enclave's sigstruct
> > + * @token: a pointer to the enclave's EINIT token
> > + * @secs_page: a pointer to the enclave's SECS EPC page
> > + * @le_pubkey_hash: the desired LE pubkey hash for EINIT
> > + */
> > +int sgx_einit(struct sgx_sigstruct *sigstruct, struct sgx_einittoken *token,
> > + struct sgx_epc_page *secs_page, u64 le_pubkey_hash[4])
> > +{
> > + u64 __percpu *cache;
> > + void *secs;
> > + int i, ret;
> > +
> > + secs = sgx_get_page(secs_page);
> > +
> > + if (!sgx_lc_enabled) {
> I'm confused. What does this code path do? It kind of looks like the
> driver will load and just malfunction if we don't have write access to
> the MSRs. What is the intended behavior?
The driver will also allow itself to load if the MSRs are read-only,
but only if the MSRs' pubkey hash matches that of its launch enclave,
i.e. the system has been pre-configured for the kernel's LE. Whether
or not that is a valid scenario is probably a different discussion.
> > + ret = __einit(sigstruct, token, secs);
> > + goto out;
> > + }
> > +
> > + cache = per_cpu(sgx_le_pubkey_hash_cache, smp_processor_id());
> > +
> > + preempt_disable();
> > + for (i = 0; i < 4; i++) {
> > + if (le_pubkey_hash[i] == cache[i])
> > + continue;
> > +
> > + wrmsrl(MSR_IA32_SGXLEPUBKEYHASH0 + i, le_pubkey_hash[i]);
> > + cache[i] = le_pubkey_hash[i];
> > + }
> > + ret = __einit(sigstruct, token, secs);
> > + preempt_enable();
> > +
> > +out:
> > + sgx_put_page(secs);
> > + return ret;
> > +}
> > +EXPORT_SYMBOL(sgx_einit);
> > +
