Re: [PATCH v2 0/2] gitlab-ci.yml: Add jobs to test CFI

["Daniel P. Berrangé" <berrange@redhat.com>]

On Mon, Mar 01, 2021 at 03:39:42PM -0500, Daniele Buono wrote:
> Hi Daniel,
> 
> On 3/1/2021 10:08 AM, Daniel P. Berrangé wrote:
> > What are the unique failure scenarios for CFI that these jobs are
> > likely to expose ? Is it likely that we'll have cases where
> > CFI succeeds in say, x86_64 target, but fails in aarch64 target ?
> 
> For CFI to fail (even if it shouldn't) you'll need code that is calling a
> function pointer that was not well defined at compile time. Although
> unlikely, that could happen everywhere in the code.

What does "was not well defined" mean here ? 

> 
> So by just testing one (or few) targets we are are not covering the code in
> the TCG frontend used to compile the target ISA to tcg ops, which should be
> the in target/, and the architecture-dependent code in linux-user.
> 
> That code seems unlikely (at least to me) to cause a false positive with
> CFI. Examples that I've seen in QEMU so far are:
> - Calling code that was JIT-ed at runtime
> - Callbacks to functions that were loaded from shared libraries
> - Signal Handlers
> And none of those should happen there IMHO. But you know, corner cases are
> still possible, and it's quite difficult to predict what new code may bring.
> 
> We could also consider always testing one or two targets, and keep an
> optional job to test them all when deemed necessary. I'm thinking for
> example full testing when code in target/ or linux-user/ is considered, or
> for testing pre-release code. Would be nice to have this automated but I am
> not sure that's possible.
> 
> Regards,
> Daniele
> 

Regards,
Daniel
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