Re: [PATCH v14 09/19] x86/mm: x86/sgx: Signal SEGV_SGXERR for #PFs w/ PF_SGX

From: Dave Hansen
Date: Thu Sep 27 2018 - 10:59:52 EST

On 09/27/2018 06:42 AM, Jarkko Sakkinen wrote:
>> This flag is 1 if the exception is unrelated to paging and
>> resulted from violation of SGX-specific access-control
>> requirements. ... such a violation can occur only if there
>> is no ordinary page fault...
>> This is pretty important. It means that *none* of the other
>> paging-related stuff that we're doing applies.
>> We also need to clarify how this can happen. Is it through something
>> than an app does, or is it solely when the hardware does something under
>> the covers, like suspend/resume.
> When you change page permissions lets say with mprotect after the and
> try to do an invalid access according to the EPCM permissions this can
> happen.

So, there are pages that are non-executable, non-readable, or
non-writable both via the page tables and via underlying SGX
permissions. Then, we allow an mprotect() and a later access will
result in one of these SGX faults?

What permissions are these, exactly? Is it even a good idea to let that
mprotect() go through in the first place?

Either way, it sounds like we have some new conditions to spell out in
that comment.