linux-hardening - Re: [PATCH v4 2/2] selftests/powerpc: Add a test for execute-only memory

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Date:   Sat, 20 Aug 2022 16:30:18 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Nicholas Miehlbradt <nicholas@...ux.ibm.com>,
        Jordan Niethe <jniethe5@...il.com>,
        Russell Currey <ruscur@...sell.cc>,
        linuxppc-dev@...ts.ozlabs.org
Cc:     ajd@...ux.ibm.com, anshuman.khandual@....com,
        aneesh.kumar@...ux.ibm.com, npiggin@...il.com,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v4 2/2] selftests/powerpc: Add a test for execute-only
 memory

Nicholas Miehlbradt <nicholas@...ux.ibm.com> writes:
> On 17/8/2022 4:15 pm, Jordan Niethe wrote:
>> On Wed, 2022-08-17 at 15:06 +1000, Russell Currey wrote:
>>> From: Nicholas Miehlbradt <nicholas@...ux.ibm.com>
>>>
>>> This selftest is designed to cover execute-only protections
>>> on the Radix MMU but will also work with Hash.
>>>
>>> The tests are based on those found in pkey_exec_test with modifications
>>> to use the generic mprotect() instead of the pkey variants.
>> 
>> Would it make sense to rename pkey_exec_test to exec_test and have this test be apart of that?
>> 
> I think might make it unnecessarily complex. The checks needed when 
> testing with pkeys would mean that it would be necessary to check if 
> pkeys are enabled and choose which set of tests to run depending on the 
> result. The differences are substantial enough that it would be 
> challenging to combine them into a single set of tests.

Yeah I think I agree. Having each test stand on its own is nice for
debugging also.

In general I'm less bothered about code duplication in tests. We should
try and share code where we can, but it's more important that we have
tests at all, rather than blocking new tests because they duplicate some
code from another test.

So I'm inclined to merge this as-is, we can always refactor it to share
code in future if we think there's enough commonality to warrant it.

cheers