On Fri, Jun 14, 2019 at 10:16:55AM -0700, Xing, Cedric wrote: > > From: Christopherson, Sean J > > Sent: Thursday, June 13, 2019 5:46 PM > > > > On Thu, Jun 13, 2019 at 01:02:17PM -0400, Stephen Smalley wrote: > > > On 6/11/19 6:02 PM, Sean Christopherson wrote: > > > >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.christopherso > > > >n@xxxxxxxxx > > > > > > Given the complexity tradeoff, what is the clear motivating example > > > for why > > > #1 isn't the obvious choice? That the enclave loader has no way of > > > knowing a priori whether the enclave will require W->X or WX? But > > > aren't we better off requiring enclaves to be explicitly marked as > > > needing such so that we can make a more informed decision about > > > whether to load them in the first place? > > > > Andy and/or Cedric, can you please weigh in with a concrete (and > > practical) use case that will break if we go with #1? The auditing > > issues for #2/#3 are complex to say the least... > > How does enclave loader provide per-page ALLOW_* flags? Unchanged from my RFC, i.e. specified at SGX_IOC_ENCLAVE_ADD_PAGE(S). > And a related question is why they are necessary for enclaves but > unnecessary for regular executables or shared objects. Because at mmap()/mprotect() time we don't have the source file of the enclave page to check SELinux's FILE__EXECUTE or AppArmor's AA_EXEC_MMAP. > What's the story for SGX2 if mmap()'ing non-existing pages is not allowed? Userspace will need to invoke an ioctl() to tell SGX "this range can be EAUG'd". > > What's the story for auditing? It happens naturally when security_enclave_load() is called. Am I missing something? > After everything above has been taken care of properly, will #1 still be > simpler than #2/#3? The state tracking of #2/#3 doesn't scare me, it's purely the auditing. Holding an audit message for an indeterminate amount of time is a nightmare. Here's a thought. What if we simply require FILE__EXECUTE or AA_EXEC_MAP to load any enclave page from a file? Alternatively, we could add an SGX specific file policity, e.g. FILE__ENCLAVELOAD and AA_MAY_LOAD_ENCLAVE. As in my other email, SELinux's W^X restrictions can be tied to the process, i.e. they can be checked at mmap()/mprotect() without throwing a wrench in auditing.
