linux-kernel - Re: [PATCH v4] tty: serial: jsm: allocate queue buffer at probe time

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Date:   Fri, 9 Jul 2021 22:55:42 +0800
From:   Zheyu Ma <zheyuma97@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jiri Slaby <jirislaby@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] tty: serial: jsm: allocate queue buffer at probe time

On Fri, Jul 9, 2021 at 10:20 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Fri, Jul 09, 2021 at 10:00:32PM +0800, Zheyu Ma wrote:
> > On Thu, Jul 8, 2021 at 3:13 AM Jiri Slaby <jirislaby@...nel.org> wrote:
> > >
> > > On 07. 07. 21, 14:52, Andy Shevchenko wrote:
> > > > On Wed, Jul 7, 2021 at 10:50 AM Jiri Slaby <jirislaby@...nel.org> wrote:
> > > >> On 05. 07. 21, 14:53, Zheyu Ma wrote:
> > > >
> > > >> So how it comes an interrupt came before
> > > >> neo_param() in jsm_tty_open was called?
> > > >
> > > > If IRQ is shared we have a special debug feature to test shared IRQs
> > > > on freeing IRQ stage (*).
> > > > But it doesn't matter, the IRQ handler must survive at any stage after
> > > > the action has been listed.
> > >
> > > Yes, but IRQ_NONE is returned from the ISR in that case.
> > >
> > > The issue the patch is fixing is for a "malicious" device and I am not
> > > sure we want to fix this -- if I can put in a malicious device, I can
> > > use hammer to kill the box too…
> >
> > Well, this threat assumption is indeed strong, but this attack may be
> > real. For example, some programmable USB devices (such as FaceDancer)
> > may exploit vulnerabilities in the USB device driver to attack. Of
> > course, there has not been such an attack in the real world for PCI
> > devices. Or, some devices with DMA functions may also send malicious
> > data and some previous kernel commits have also fixed such bugs.
> >
> > Anyway, thanks for your patient comments.
>
> Right now, yes, we treat USB devices as "possibly malicious".  We do not
> do so for PCI devices yet.  If we want to do that, then we need to do a
> lot of work, not just "this one call in this one driver" type of thing
> as there are much bigger issues involved here.
>
> If you wish to take on this work, as you feel PCI devices should be
> treated this way, please do so!  But start in the PCI core at the very
> least, before worrying about the thousands of individual drivers.

Alright, I understand.

Thank you for your valuable suggestions, I will continue to learn and
make more contributions to the kernel.

Regards,
Zheyu Ma