Re: [PATCH 12/14] selftests/sgx: Add page permission and exception test

[Reinette Chatre]

Hi Dave,

On 9/16/2021 8:30 AM, Dave Hansen wrote:
> On 9/15/21 1:31 PM, Reinette Chatre wrote:
> > Add a test to ensure that (1) PTE permissions can be changed as long as
> > they do not exceed EPCM permissions, and (2) even if EPCM permissions
> > allow a page to be written to, if the PTE permissions do not then a #PF
> > should be generated when attempting to write to a (from PTE perspective)
> > read-only page.
>
> It took me a minute to figure out what this was trying to say.

The goal was to describe what features/functionalities are being tested. 
You accurately point out that it is not clear how the test implemented 
in the patch matches with these test goals.

>  Maybe
> breaking it down into these three steps would help:
>
> Add a test that:
>   (1) Creates an SGX enclave page with writable EPCM permission
>   (2) Changes the PTE permission on the page to read-only.  This should
>       be permitted because the permission does not exceed the EPCM
>       permission.
>   (3) Attempts a write to the page and generate a page fault (#PF)
>       because of the read-only PTE.

Thank you for the suggestion. What I understand from your feedback is 
that I should mix the description of the actual test with what 
features/functionalities are being tested. You do so in your suggestion 
for (2) and to do the same for (3) I now plan to expand it to:

   (3) Attempts a write to the page. This should generate a page fault
       (#PF) because of the read-only PTE even though the EPCM
       permissions allow the page to be written to.

Reinette