Re: [PATCH v2 3/3] iommu/vt-d: Sanity check uapi argsz filled by users

[Jacob Pan <jacob.jun.pan@linux.intel.com>]

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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