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    SubjectRe: [PATCH v2 3/3] iommu/vt-d: Sanity check uapi argsz filled by users
    On Thu, 11 Jun 2020 14:55:18 -0600
    Alex Williamson <alex.williamson@redhat.com> wrote:

    > On Thu, 11 Jun 2020 13:02:24 -0700
    > Jacob Pan <jacob.jun.pan@linux.intel.com> wrote:
    >
    > > On Thu, 11 Jun 2020 11:08:16 -0600
    > > Alex Williamson <alex.williamson@redhat.com> wrote:
    > >
    > > > On Wed, 10 Jun 2020 21:12:15 -0700
    > > > Jacob Pan <jacob.jun.pan@linux.intel.com> wrote:
    > > >
    > > > > IOMMU UAPI data has an argsz field which is filled by user. As
    > > > > the data structures expands, argsz may change. As the UAPI data
    > > > > are shared among different architectures, extensions of UAPI
    > > > > data could be a result of one architecture which has no impact
    > > > > on another. Therefore, these argsz santity checks are performed
    > > > > in the model specific IOMMU drivers. This patch adds sanity
    > > > > checks in the VT-d to ensure argsz passed by userspace matches
    > > > > feature flags and other contents.
    > > > >
    > > > > Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
    > > > > ---
    > > > > drivers/iommu/intel-iommu.c | 16 ++++++++++++++++
    > > > > drivers/iommu/intel-svm.c | 12 ++++++++++++
    > > > > 2 files changed, 28 insertions(+)
    > > > >
    > > > > diff --git a/drivers/iommu/intel-iommu.c
    > > > > b/drivers/iommu/intel-iommu.c index 27ebf4b9faef..c98b5109684b
    > > > > 100644 --- a/drivers/iommu/intel-iommu.c
    > > > > +++ b/drivers/iommu/intel-iommu.c
    > > > > @@ -5365,6 +5365,7 @@ intel_iommu_sva_invalidate(struct
    > > > > iommu_domain *domain, struct device *dev, struct
    > > > > device_domain_info *info; struct intel_iommu *iommu;
    > > > > unsigned long flags;
    > > > > + unsigned long minsz;
    > > > > int cache_type;
    > > > > u8 bus, devfn;
    > > > > u16 did, sid;
    > > > > @@ -5385,6 +5386,21 @@ intel_iommu_sva_invalidate(struct
    > > > > iommu_domain *domain, struct device *dev, if
    > > > > (!(dmar_domain->flags & DOMAIN_FLAG_NESTING_MODE)) return
    > > > > -EINVAL;
    > > > > + minsz = offsetofend(struct iommu_cache_invalidate_info,
    > > > > padding);
    > > >
    > > > Would it still be better to look for the end of the last field
    > > > that's actually used to avoid the code churn and oversights
    > > > if/when the padding field does get used and renamed?
    > > >
    > > My thought was that if the padding gets partially re-purposed, the
    > > remaining padding would still be valid for minsz check. The
    > > extension rule ensures that there is no size change other the
    > > variable size union at the end. So use padding would avoid the
    > > churn, or i am totally wrong?
    >
    > No, it's trying to predict the future either way. I figured checking
    > minsz against the fields we actually consume allows complete use of
    > the padding fields and provides a little leniency to the user. We'd
    > need to be careful though that if those fields are later used by this
    > driver, the code would still need to accept the smaller size. If the
    > union was named rather than anonymous we could just use offsetof() to
    > avoid directly referencing the padding fields.
    >
    I will change it to named union.

    Thanks,

    > > > Per my comment on patch 1/, this also seems like where the device
    > > > specific IOMMU driver should also have the responsibility of
    > > > receiving a __user pointer to do the copy_from_user() here. vfio
    > > > can't know which flags require which fields to make a UAPI with
    > > > acceptable compatibility guarantees otherwise.
    > > >
    > > Right, VFIO cannot do compatibility guarantees, it is just seem to
    > > be that VFIO has enough information to copy_from_user sanely &
    > > safely and handle over to IOMMU. Please help define the
    > > roles/responsibilities in my other email. Then I will follow the
    > > guideline.
    >
    > We can keep that part of the discussion in the other thread. Thanks,
    >
    > Alex
    >
    > > > > + if (inv_info->argsz < minsz)
    > > > > + return -EINVAL;
    > > > > +
    > > > > + /* Sanity check user filled invalidation dat sizes */
    > > > > + if (inv_info->granularity == IOMMU_INV_GRANU_ADDR &&
    > > > > + inv_info->argsz != offsetofend(struct
    > > > > iommu_cache_invalidate_info,
    > > > > + addr_info))
    > > > > + return -EINVAL;
    > > > > +
    > > > > + if (inv_info->granularity == IOMMU_INV_GRANU_PASID &&
    > > > > + inv_info->argsz != offsetofend(struct
    > > > > iommu_cache_invalidate_info,
    > > > > + pasid_info))
    > > > > + return -EINVAL;
    > > > > +
    > > > > spin_lock_irqsave(&device_domain_lock, flags);
    > > > > spin_lock(&iommu->lock);
    > > > > info = get_domain_info(dev);
    > > > > diff --git a/drivers/iommu/intel-svm.c
    > > > > b/drivers/iommu/intel-svm.c index 35b43fe819ed..64dc2c66dfff
    > > > > 100644 --- a/drivers/iommu/intel-svm.c
    > > > > +++ b/drivers/iommu/intel-svm.c
    > > > > @@ -235,15 +235,27 @@ int intel_svm_bind_gpasid(struct
    > > > > iommu_domain *domain, struct device *dev, struct dmar_domain
    > > > > *dmar_domain; struct intel_svm_dev *sdev;
    > > > > struct intel_svm *svm;
    > > > > + unsigned long minsz;
    > > > > int ret = 0;
    > > > >
    > > > > if (WARN_ON(!iommu) || !data)
    > > > > return -EINVAL;
    > > > >
    > > > > + /*
    > > > > + * We mandate that no size change in IOMMU UAPI data
    > > > > before the
    > > > > + * variable size union at the end.
    > > > > + */
    > > > > + minsz = offsetofend(struct iommu_gpasid_bind_data,
    > > > > padding);
    > > >
    > > > Same. Thanks,
    > > >
    > > > Alex
    > > >
    > > > > + if (data->argsz < minsz)
    > > > > + return -EINVAL;
    > > > > +
    > > > > if (data->version != IOMMU_GPASID_BIND_VERSION_1 ||
    > > > > data->format != IOMMU_PASID_FORMAT_INTEL_VTD)
    > > > > return -EINVAL;
    > > > >
    > > > > + if (data->argsz != offsetofend(struct
    > > > > iommu_gpasid_bind_data, vtd))
    > > > > + return -EINVAL;
    > > > > +
    > > > > if (!dev_is_pci(dev))
    > > > > return -ENOTSUPP;
    > > > >
    > > >
    > >
    > > [Jacob Pan]
    > >
    >

    [Jacob Pan]

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