Messages in this thread | | | Subject | Re: [PATCH v2] s390/vfio-ap: fix memory leak in mdev remove callback | From | Tony Krowiak <> | Date | Tue, 18 May 2021 09:42:05 -0400 |
| |
On 5/18/21 5:30 AM, Christian Borntraeger wrote: > > > On 17.05.21 21:10, Halil Pasic wrote: >> 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? > > Would it help, if the code in priv.c would read the hook once > and then only work on the copy? We could protect that with rcu > and do a synchronize rcu in vfio_ap_mdev_unset_kvm after > unsetting the pointer?
I'll look into this.
>> >> 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 >>
| |