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

[Daniele Buono]

On 3/2/2021 5:30 AM, Daniel P. Berrangé wrote:
> 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 ?

At high level, the compiler creates metadata for every function. Before
jumping to a function pointer, it makes sure that the pointer and the
pointee have matching types.
Not well defined means one of these two cases:
1. The function has a different type than the pointer -> Most likely an
error
2. The function was not available at compile time so the compiler could
not create the related metadata -> Most likely a false positive.

Thanks,
Daniele