Messages in this thread | | | Subject | Re: [PATCH v23 12/24] x86/sgx: Linux Enclave Driver | From | Stephen Smalley <> | Date | Fri, 1 Nov 2019 09:16:16 -0400 |
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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.
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