Messages in this thread | | | Subject | Re: [PATCH v2] iommu: Check dev->iommu in iommu_dev_xxx functions | From | Robin Murphy <> | Date | Tue, 16 Feb 2021 13:45:10 +0000 |
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On 2021-02-12 17:28, Shameerali Kolothum Thodi wrote: > > >> -----Original Message----- >> From: Shameerali Kolothum Thodi >> Sent: 12 February 2021 16:45 >> To: 'Robin Murphy' <robin.murphy@arm.com>; linux-kernel@vger.kernel.org; >> iommu@lists.linux-foundation.org >> Cc: joro@8bytes.org; jean-philippe@linaro.org; will@kernel.org; Zengtao (B) >> <prime.zeng@hisilicon.com>; linuxarm@openeuler.org >> Subject: RE: [PATCH v2] iommu: Check dev->iommu in iommu_dev_xxx functions >> >> >> >>> -----Original Message----- >>> From: Robin Murphy [mailto:robin.murphy@arm.com] >>> Sent: 12 February 2021 16:39 >>> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>; >>> linux-kernel@vger.kernel.org; iommu@lists.linux-foundation.org >>> Cc: joro@8bytes.org; jean-philippe@linaro.org; will@kernel.org; Zengtao (B) >>> <prime.zeng@hisilicon.com>; linuxarm@openeuler.org >>> Subject: Re: [PATCH v2] iommu: Check dev->iommu in iommu_dev_xxx >> functions >>> >>> On 2021-02-12 14:54, Shameerali Kolothum Thodi wrote: >>>> Hi Robin/Joerg, >>>> >>>>> -----Original Message----- >>>>> From: Shameer Kolothum >> [mailto:shameerali.kolothum.thodi@huawei.com] >>>>> Sent: 01 February 2021 12:41 >>>>> To: linux-kernel@vger.kernel.org; iommu@lists.linux-foundation.org >>>>> Cc: joro@8bytes.org; robin.murphy@arm.com; jean-philippe@linaro.org; >>>>> will@kernel.org; Zengtao (B) <prime.zeng@hisilicon.com>; >>>>> linuxarm@openeuler.org >>>>> Subject: [Linuxarm] [PATCH v2] iommu: Check dev->iommu in >>> iommu_dev_xxx >>>>> functions >>>>> >>>>> The device iommu probe/attach might have failed leaving dev->iommu >>>>> to NULL and device drivers may still invoke these functions resulting >>>>> in a crash in iommu vendor driver code. Hence make sure we check that. >>>>> >>>>> Also added iommu_ops to the "struct dev_iommu" and set it if the dev >>>>> is successfully associated with an iommu. >>>>> >>>>> Fixes: a3a195929d40 ("iommu: Add APIs for multiple domains per >> device") >>>>> Signed-off-by: Shameer Kolothum >>> <shameerali.kolothum.thodi@huawei.com> >>>>> --- >>>>> v1 --> v2: >>>>> -Added iommu_ops to struct dev_iommu based on the discussion with >>> Robin. >>>>> -Rebased against iommu-tree core branch. >>>> >>>> A gentle ping on this... >>> >>> Is there a convincing justification for maintaining yet another copy of >>> the ops pointer rather than simply dereferencing iommu_dev->ops at point >>> of use? >>> >> >> TBH, nothing I can think of now. That was mainly the way I interpreted your >> suggestion >> from the v1. Now it looks like you didn’t mean it :). I am Ok to rework it to >> dereference >> it from iommu_dev. Please let me know. > > So we can do something like this, > > index fd76e2f579fe..5fd31a3cec18 100644 > --- a/drivers/iommu/iommu.c > +++ b/drivers/iommu/iommu.c > @@ -2865,10 +2865,12 @@ EXPORT_SYMBOL_GPL(iommu_fwspec_add_ids); > */ > int iommu_dev_enable_feature(struct device *dev, enum iommu_dev_features feat) > { > - const struct iommu_ops *ops = dev->bus->iommu_ops; > + if (dev->iommu && dev->iommu->iommu_dev && dev->iommu->iommu_dev->ops) > + struct iommu_ops *ops = dev->iommu->iommu_dev->ops; > > - if (ops && ops->dev_enable_feat) > - return ops->dev_enable_feat(dev, feat); > + if (ops->dev_enable_feat) > + return ops->dev_enable_feat(dev, feat); > + } > > return -ENODEV; > } > > Again, not sure we need to do the checking for iommu->dev and ops here. If the > dev->iommu is set, is it safe to assume that we have a valid iommu->iommu_dev > and ops always? (May be it is safer to do the checking in case something > else breaks this assumption in future). Please let me know your thoughts.
I think it *could* happen that dev->iommu is set by iommu_fwspec_init() but iommu_probe_device() later refuses the device for whatever reason, so we would still need to check iommu->iommu_dev to be completely safe. We can assume iommu_dev->ops is valid, since if the IOMMU driver has returned something bogus from .probe_device then it's a major bug in that driver and crashing is the best indicator :)
Robin.
> > Thanks, > Shameer > > > _______________________________________________ > iommu mailing list > iommu@lists.linux-foundation.org > https://lists.linuxfoundation.org/mailman/listinfo/iommu >
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