On Mon, Jun 29, 2020 at 06:02:42PM +0200, Borislav Petkov wrote: > On Thu, Jun 18, 2020 at 01:08:34AM +0300, Jarkko Sakkinen wrote: > > Provisioning Certification Enclave (PCE), the root of trust for other > > enclaves, generates a signing key from a fused key called Provisioning > > Certification Key. PCE can then use this key to certify an attestation key > > of a QE, e.g. we get the chain of trust down to the hardware if the Intel > > What's a QE? > > I don't see this acronym resolved anywhere in the whole patchset. Quoting Enclave. > > signed PCE is used. > > > > To use the needed keys, ATTRIBUTE.PROVISIONKEY is required but should be > > only allowed for those who actually need it so that only the trusted > > parties can certify QE's. > > > > Obviously the attestation service should know the public key of the used > > PCE and that way detect illegit attestation, but whitelisting the legit > > users still adds an additional layer of defence. > > > > Add new device file called /dev/sgx/provision. The sole purpose of this > > file is to provide file descriptors that act as privilege tokens to allow > > to build enclaves with ATTRIBUTE.PROVISIONKEY set. A new ioctl called > > SGX_IOC_ENCLAVE_SET_ATTRIBUTE is used to assign this token to an enclave. > > So I'm sure I'm missing something here: what controls which > enclave can open /dev/sgx/provision and thus pass the FD to > SGX_IOC_ENCLAVE_SET_ATTRIBUTE? /dev/sgx/provision is root-only by default, the expectation is that the admin will configure the system to grant only specific enclaves access to the PROVISION_KEY. > And in general, how does that whole flow look like: what calls > SGX_IOC_ENCLAVE_SET_ATTRIBUTE when? The basic gist is that the host process of an enclave that needs/wants access to the PROVISION_KEY will invoke SGX_IOC_ENCLAVE_SET_ATTRIBUTE when building the enclave. Any enclave can request access to PROVISION_KEY, but practically speaking only the PCE and QE (or their non-Intel equivalents) actually need access to the key. KVM (future series) will also respect /dev/sgx/provision, i.e. require a similar ioctl() to expose the PROVISION_KEY to a guest. E.g. for my own personal testing, I never do anything attestation related, so none of the enclaves I run request PROVISION_KEY, but I do expose it to VMs to test the KVM paths. In this series, access is fairly binary, i.e. there's no additional kernel infrastructure to help userspace make per-enclave decisions. There have been more than a few proposals on how to extend the kernel to help provide better granularity, e.g. LSM hooks, but it was generally agreed to punt that stuff to post-upstreaming to keep things "simple" once we went far enough down various paths to ensure we weren't painting ourselves into a corner. If you want super gory details, Intel's whitepaper on attestation in cloud environments is a good starting point[*], but I don't recommended doing much more than skimming unless you really like attestation stuff or are masochistic, which IMO amount to the same thing :-) [*] https://download.01.org/intel-sgx/dcap-1.0/docs/SGX_ECDSA_QuoteGenReference_DCAP_API_Linux_1.0.pdf
