On 3/31/21 5:53 PM, Dave Hansen wrote: > On 3/31/21 5:50 AM, Raoul Strackx wrote: >> The sgx driver can only load enclaves whose pages are fully measured. >> This may exclude existing enclaves from running. This patch adds a >> new ioctl to measure 256 byte chunks at a time. > > The changelogs here are pretty sparse. Could you explain in a bit more > detail what's going on? > > A review of the relevant pieces of the SGX architecture would be > appreciated. > Yes the explanation was very succinct. A more elaborate explanation: BACKGROUND Creation of an SGX enclave consists of three steps. First, a new enclave environment is created by the ECREATE leaf function. Some enclave settings are specified at this step by passing an SGX Enclave Control Structure (SECS) that contains the enclave MRENCLAVE, MRSIGNER, etc. This instruction also starts a cryptographic log of the enclave being built. (This log should eventually result in the MRENCLAVE.) Second, pages are added to the enclave. The EADD leaf function copies 4KB data to an empty EPC page. The cryptographic log records (among other properties) the location and access rights of the page being added. It _does not_ include a measurement of the page content. When the enclave writer wishes to ensure the content of the enclave page as well, she must use the EEXTEND leaf function. Extending the enclave cryptographic log can only be done per 256 bytes. Extending the log with a full 4K page thus requires 16 invocations of the EEXTEND leaf function. Finally, the enclave is finalized by the EINIT leaf function. Any new invocations of the EADD or EEXTEND leaf functions will result in a fault. With EINIT a number of checks are performed as well. A cryptographic hash is computed over the final cryptographic log and compared to the MRENCLAVE field of the SECS structure passed to the ECREATE leaf function (see step one). The signature (MRSIGNER) over this MRENCLAVE is verified as well. When all checks pass, the enclave enters an executable state. PROBLEM STATEMENT The SGX driver currently only supports extending the cryptographic log as part of the EADD leaf function and _must_ measure full 4K pages. Not all enclaves may have been constructed within these constraints. Such enclaves currently cannot be build on the Linux platform. Trying to do so will result in a different cryptographic log; the MRENCLAVE specified at enclave creation time will not match the cryptographic log kept by the processor and EINIT will fail. SOLUTION OF THIS PATCH This patch adds a new ioctl to enable userspace to execute EEXTEND leaf functions per 256 bytes of enclave memory. This enables enclaves to be build as specified by enclave providers. I'm still very new to how Linux kernel patches are handled. Where would such a more elaborate description usually go: the cover page, the commit that introduces the ioctl or both? Regards, Raoul
