Re: [PATCH v2] s390/vfio-ap: fix memory leak in mdev remove callback

[Halil Pasic <pasic@linux.ibm.com>]

On Mon, 17 May 2021 09:37:42 -0400
Tony Krowiak <akrowiak@linux.ibm.com> wrote:

> >
> > Because of this, I don't think the rest of your argument is valid.  
> 
> Okay, so your concern is that between the point in time the
> vcpu->kvm->arch.crypto.pqap_hook pointer is checked in
> priv.c and the point in time the handle_pqap() function
> in vfio_ap_ops.c is called, the memory allocated for the
> matrix_mdev containing the struct kvm_s390_module_hook
> may get freed, thus rendering the function pointer invalid.
> While not impossible, that seems extremely unlikely to
> happen. Can you articulate a scenario where that could
> even occur?

Malicious userspace. We tend to do the pqap aqic just once
in the guest right after the queue is detected. I do agree
it ain't very likely to happen during normal operation. But why are
you asking?

I'm not sure I understood correctly what kind of a scenario are
you asking for. PQAP AQIC and mdev remove are independent
events originated in userspace, so AFAIK we may not assume
that the execution of two won't overlap, nor are we allowed
to make assumptions on how does the execution of these two
overlap (except for the things we explicitly ensure -- e.g.
some parts are made mutually exclusive using the matrix_dev->lock
lock).

Regards,
Halil