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

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Message-ID: <9990d737-9b9c-911f-3850-c9f3bc43c29b@intel.com>
Date:   Thu, 16 Sep 2021 08:30:05 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Reinette Chatre <reinette.chatre@...el.com>,
        linux-sgx@...r.kernel.org, jarkko@...nel.org, shuah@...nel.org
Cc:     seanjc@...gle.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 12/14] selftests/sgx: Add page permission and exception
 test

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.  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.