Messages in this thread | | | Subject | Re: [PATCH v23 12/24] x86/sgx: Linux Enclave Driver | From | Stephen Smalley <> | Date | Fri, 1 Nov 2019 09:28:17 -0400 |
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On 11/1/19 9:16 AM, Stephen Smalley wrote: > On 10/31/19 5:17 PM, Jarkko Sakkinen wrote: >> On Wed, Oct 30, 2019 at 09:45:05AM -0400, Stephen Smalley wrote: >>> On 10/28/19 5:03 PM, Jarkko Sakkinen wrote: >>>> Intel Software Guard eXtensions (SGX) is a set of CPU instructions that >>>> can be used by applications to set aside private regions of code and >>>> data. The code outside the SGX hosted software entity is disallowed to >>>> access the memory inside the enclave enforced by the CPU. We call these >>>> entities as enclaves. >>>> >>>> This commit implements a driver that provides an ioctl API to construct >>>> and run enclaves. Enclaves are constructed from pages residing in >>>> reserved physical memory areas. The contents of these pages can only be >>>> accessed when they are mapped as part of an enclave, by a hardware >>>> thread running inside the enclave. >>>> >>>> The starting state of an enclave consists of a fixed measured set of >>>> pages that are copied to the EPC during the construction process by >>>> using ENCLS leaf functions and Software Enclave Control Structure >>>> (SECS) >>>> that defines the enclave properties. >>>> >>>> Enclave are constructed by using ENCLS leaf functions ECREATE, EADD and >>>> EINIT. ECREATE initializes SECS, EADD copies pages from system >>>> memory to >>>> the EPC and EINIT check a given signed measurement and moves the >>>> enclave >>>> into a state ready for execution. >>>> >>>> An initialized enclave can only be accessed through special Thread >>>> Control >>>> Structure (TCS) pages by using ENCLU (ring-3 only) leaf EENTER. >>>> This leaf >>>> function converts a thread into enclave mode and continues the >>>> execution in >>>> the offset defined by the TCS provided to EENTER. An enclave is exited >>>> through syscall, exception, interrupts or by explicitly calling another >>>> ENCLU leaf EEXIT. >>>> >>>> The permissions, which enclave page is added will set the limit for >>>> maximum >>>> permissions that can be set for mmap() and mprotect(). This will >>>> effectively allow to build different security schemes between >>>> producers and >>>> consumers of enclaves. Later on we can increase granularity with LSM >>>> hooks >>>> for page addition (i.e. for producers) and mapping of the enclave >>>> (i.e. for >>>> consumers) >>> >>> Where do things stand wrt to ensuring that SGX cannot be used to >>> introduce >>> executable mappings that were never authorized by the LSM (or never >>> measured >>> by IMA)? >> >> This was the latest discussion about that subject: >> >> https://lore.kernel.org/linux-sgx/CALCETrWDLX68Vi4=9Dicq9ATmJ5mv36bzrc02heNYaHaBeWumQ@mail.gmail.com/ >> > > So, IIUC, that means that merging the driver will create a regression > with respect to LSM control over executable mappings that will only be > rectified at some future point in time if/when someone submits LSM hooks > or calls to existing hooks to restore such control. That doesn't seem > like a good idea. Why can't you include at least that basic level of > control now? It is one thing to defer finer grained control or > SGX-specific access controls to the future - that I can understand. But > introducing a regression in the existing controls is not really ok.
Unless you are arguing that the existing checks on mmap/mprotect of /dev/sgx/enclave are a coarse-grained approximation (effectively requiring WX to the file or execmem for any user of SGX).
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