Re: [PATCH 1/1] iommu/vtd: Fix NULL pointer dereference in prq_event_thread()

[Lu Baolu]

Hi Yi,

On 11/5/18 1:21 PM, Liu, Yi L wrote:
> Hi Baolu,
>
> > From: iommu-bounces@xxxxxxxxxxxxxxxxxxxxxxxxxx [mailto:iommu-
> > bounces@xxxxxxxxxxxxxxxxxxxxxxxxxx] On Behalf Of Lu Baolu
> > Sent: Monday, November 5, 2018 10:19 AM
> > To: Joerg Roedel <joro@xxxxxxxxxx>; David Woodhouse <dwmw2@xxxxxxxxxxxxx>
> > Cc: Raj, Ashok <ashok.raj@xxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx;
> > iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx
> > Subject: [PATCH 1/1] iommu/vtd: Fix NULL pointer dereference in prq_event_thread()
> >
> > When handling page request without pasid event, go to "no_pasid"
> > branch instead of "bad_req". Otherwise, a NULL pointer deference will happen there.
> >
> > Cc: Ashok Raj <ashok.raj@xxxxxxxxx>
> > Cc: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> > Cc: Sohil Mehta <sohil.mehta@xxxxxxxxx>
> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > ---
> >   drivers/iommu/intel-svm.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/iommu/intel-svm.c b/drivers/iommu/intel-svm.c index
> > db301efe126d..887150907526 100644
> > --- a/drivers/iommu/intel-svm.c
> > +++ b/drivers/iommu/intel-svm.c
> > @@ -595,7 +595,7 @@ static irqreturn_t prq_event_thread(int irq, void *d)
> >   			pr_err("%s: Page request without PASID: %08llx %08llx\n",
> >   			       iommu->name, ((unsigned long long *)req)[0],
> >   			       ((unsigned long long *)req)[1]);
> > -			goto bad_req;
> > +			goto no_pasid;
> >   		}
> >
> >   		if (!svm || svm->pasid != req->pasid) {
> > --
>
> I'm afraid it is still necessary to goto "bad_req". The following code behind
> "bad_req" will trigger fault_cb registered by in-kernel drivers. It is reasonable
> that PRQ without PASID can be handled by such callbacks. So I would suggest
> to keep the existing logic.

A page fault without a pasid is triggered by a DMA transfer without
PASID. It doesn't relate to the SVM functionality hence there's no
@svm or @sdev related to it. It's unnecessary to report it to the
drivers as far as I can see.

Best regards,
Lu Baolu

>                  if (sdev && sdev->ops && sdev->ops->fault_cb) {
>                          int rwxp = (req->rd_req << 3) | (req->wr_req << 2) |
>                                   (req->exe_req << 1) | (req->priv_req);
>                          sdev->ops->fault_cb(sdev->dev, req->pasid, req->addr, req->private, rwxp, result);
>                   }
>
> Thanks,
> Yi Liu