Re: [PATCH V1 1/1] iommu: Make sure device's ID array elements are unique

[Tomasz Nowicki]

On 19.12.2017 17:37, Alex Williamson wrote:
> On Tue, 19 Dec 2017 16:20:21 +0100
> Tomasz Nowicki <tomasz.nowicki@xxxxxxxxxxxxxxxxxx> wrote:
>
> > While iterating over DMA aliases for a PCI device, for some rare cases
> > (i.e. PCIe-to-PCI/X bridges) we may get exactly the same ID as initial child
> > device. In turn, the same ID may get registered for a device multiple times.
> > Eventually IOMMU  driver may try to configure the same ID within domain
> > multiple times too which for some IOMMU drivers is illegal and causes kernel
> > panic.
> >
> > Rule out ID duplication prior to device ID array registration.
> >
> > CC: stable@xxxxxxxxxxxxxxx	# v4.14+
>
> You've identified a release, is there a specific commit this fixes?

Yes, it was triggered by converting drm_pci_init() to 
pci_register_driver() in ast_drv.c

Fixes: 10631d724def ("drm/pci: Deprecate drm_pci_init/exit completely
")

> > Signed-off-by: Tomasz Nowicki <tomasz.nowicki@xxxxxxxxxxxxxxxxxx>
> > ---
> >   drivers/iommu/iommu.c | 28 ++++++++++++++++++++++++++++
> >   1 file changed, 28 insertions(+)
> >
> > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > index 3de5c0b..9b2c138 100644
> > --- a/drivers/iommu/iommu.c
> > +++ b/drivers/iommu/iommu.c
> > @@ -1945,6 +1945,31 @@ void iommu_fwspec_free(struct device *dev)
> >   }
> >   EXPORT_SYMBOL_GPL(iommu_fwspec_free);
> >   
> > +static void iommu_fwspec_remove_ids_dup(struct device *dev, u32 *ids,
> > +					int *num_ids)
> > +{
> > +	struct iommu_fwspec *fwspec = dev->iommu_fwspec;
> > +	int i, j, k, valid_ids = *num_ids;
> > +
> > +	for (i = 0; i < valid_ids; i++) {
> > +		for (j = 0; j < fwspec->num_ids; j++) {
> > +			if (ids[i] != fwspec->ids[j])
> > +				continue;
> > +
> > +			dev_info(dev, "found 0x%x ID duplication, skipped\n",
> > +				 ids[i]);
> > +
> > +			for (k = i + 1; k < valid_ids; k++)
> > +				ids[k - 1] = ids[k];
>
> Use memmove()?

Right.

> > +
> > +			valid_ids--;
> > +			break;
>
> At this point ids[i] is not the ids[i] that we tested for dupes, it's
> what was ids[i + 1], but we're going to i++ on the next iteration and
> we therefore never test that entry.

Good point.

Now the fundamental question is where we should put the patch, here or 
in SMMUv3 driver as per Robin suggestion.

Thanks,
Tomasz