Messages in this thread | | | Date | Tue, 11 Jun 2019 15:02:43 -0700 | From | Sean Christopherson <> | Subject | Re: [RFC PATCH v1 2/3] LSM/x86/sgx: Implement SGX specific hooks in SELinux |
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On Tue, Jun 11, 2019 at 09:40:25AM -0400, Stephen Smalley wrote: > I haven't looked at this code closely, but it feels like a lot of > SGX-specific logic embedded into SELinux that will have to be repeated or > reused for every security module. Does SGX not track this state itself?
SGX does track equivalent state.
There are three proposals on the table (I think):
1. Require userspace to explicitly specificy (maximal) enclave page permissions at build time. The enclave page permissions are provided to, and checked by, LSMs at enclave build time.
Pros: Low-complexity kernel implementation, straightforward auditing Cons: Sullies the SGX UAPI to some extent, may increase complexity of SGX2 enclave loaders.
2. Pre-check LSM permissions and dynamically track mappings to enclave pages, e.g. add an SGX mprotect() hook to restrict W->X and WX based on the pre-checked permissions.
Pros: Does not impact SGX UAPI, medium kernel complexity Cons: Auditing is complex/weird, requires taking enclave-specific lock during mprotect() to query/update tracking.
3. Implement LSM hooks in SGX to allow LSMs to track enclave regions from cradle to grave, but otherwise defer everything to LSMs.
Pros: Does not impact SGX UAPI, maximum flexibility, precise auditing Cons: Most complex and "heaviest" kernel implementation of the three, pushes more SGX details into LSMs.
My RFC series[1] implements #1. My understanding is that Andy (Lutomirski) prefers #2. Cedric's RFC series implements #3.
Perhaps the easiest way to make forward progress is to rule out the options we absolutely *don't* want by focusing on the potentially blocking issue with each option:
#1 - SGX UAPI funkiness
#2 - Auditing complexity, potential enclave lock contention
#3 - Pushing SGX details into LSMs and complexity of kernel implementation
[1] https://lkml.kernel.org/r/20190606021145.12604-1-sean.j.christopherson@intel.com
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