Re: [PATCH for-next 0/4] RDMA/hns: Introduce delay-destruction mechanism

[Leon Romanovsky <leon@kernel.org>]

On Thu, Feb 20, 2025 at 04:45:54PM +0800, Junxian Huang wrote:
> 
> 
> On 2025/2/20 15:32, Leon Romanovsky wrote:
> > On Thu, Feb 20, 2025 at 11:48:49AM +0800, Junxian Huang wrote:
> >>
> >>
> >> On 2025/2/19 22:35, Leon Romanovsky wrote:
> >>> On Wed, Feb 19, 2025 at 09:07:36PM +0800, Junxian Huang wrote:
> >>>>
> >>>>
> >>>> On 2025/2/19 20:14, Leon Romanovsky wrote:
> >>>>> On Mon, Feb 17, 2025 at 03:01:19PM +0800, Junxian Huang wrote:
> >>>>>> When mailboxes for resource(QP/CQ/SRQ) destruction fail, it's unable
> >>>>>> to notify HW about the destruction. In this case, driver will still
> >>>>>> free the resources, while HW may still access them, thus leading to
> >>>>>> a UAF.
> >>>>>
> >>>>>> This series introduces delay-destruction mechanism to fix such HW UAF,
> >>>>>> including thw HW CTX and doorbells.
> >>>>>
> >>>>> And why can't you fix FW instead?
> >>>>>
> >>>>
> >>>> The key is the failure of mailbox, and there are some cases that would
> >>>> lead to it, which we don't really consider as FW bugs.
> >>>>
> >>>> For example, when some random fatal error like RAS error occurs in FW,
> >>>> our FW will be reset. Driver's mailbox will fail during the FW reset.
> >>>
> >>> I don't understand this scenario. You said at the beginning that HW can
> >>> access host memory and this triggers UAF. However now, you are presenting 
> >>> case where driver tries to access mailbox.
> >>>
> >>
> >> No, I'm saying that mailbox errors are the reason of HW UAF. Let me
> >> explain this scenario in more detail.
> >>
> >> Driver notifies HW about the memory release with mailbox. The procedure
> >> of a mailbox is:
> >> 	a) driver posts the mailbox to FW
> >> 	b) FW writes the mailbox data into HW
> >>
> >> In this scenario, step a) will fail due to the FW reset, HW won't get
> >> notified and thus may lead to UAF.
> > 
> > Exactly, FW performed reset and didn't prevent from HW to access it.
> > 
> 
> Yes, but the problem is that our HW doesn't provide a method to prevent
> the access. There's nothing FW can do in this scenario, so we can only
> prevent UAF by adding these codes in driver.

Somehow HW doesn't access mailbox if destroy was successful, so why
can't FW use same "method" to inform HW before reset?

Thanks