RE: [PATCH v1 1/8] vfio: Add VFIO_IOMMU_PASID_REQUEST(alloc/free)

[Liu, Yi L]

Hi Alex,
> From: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Sent: Saturday, April 4, 2020 1:50 AM
> Subject: Re: [PATCH v1 1/8] vfio: Add VFIO_IOMMU_PASID_REQUEST(alloc/free)
> 
> On Fri, 3 Apr 2020 13:12:50 +0000
> "Liu, Yi L" <yi.l.liu@xxxxxxxxx> wrote:
> 
> > Hi Alex,
> >
> > > From: Alex Williamson <alex.williamson@xxxxxxxxxx>
> > > Sent: Friday, April 3, 2020 1:50 AM
> > > Subject: Re: [PATCH v1 1/8] vfio: Add VFIO_IOMMU_PASID_REQUEST(alloc/free)
> > >
> > > On Sun, 22 Mar 2020 05:31:58 -0700
> > > "Liu, Yi L" <yi.l.liu@xxxxxxxxx> wrote:
> > >
> > > > From: Liu Yi L <yi.l.liu@xxxxxxxxx>
> > > >
[...]
> > > >  static long vfio_iommu_type1_ioctl(void *iommu_data,
> > > >  				   unsigned int cmd, unsigned long arg)
> > > >  {
> > > > @@ -2276,6 +2333,53 @@ static long vfio_iommu_type1_ioctl(void
> > > *iommu_data,
> > > >
> > > >  		return copy_to_user((void __user *)arg, &unmap, minsz) ?
> > > >  			-EFAULT : 0;
> > > > +
> > > > +	} else if (cmd == VFIO_IOMMU_PASID_REQUEST) {
> > > > +		struct vfio_iommu_type1_pasid_request req;
> > > > +		unsigned long offset;
> > > > +
> > > > +		minsz = offsetofend(struct vfio_iommu_type1_pasid_request,
> > > > +				    flags);
> > > > +
> > > > +		if (copy_from_user(&req, (void __user *)arg, minsz))
> > > > +			return -EFAULT;
> > > > +
> > > > +		if (req.argsz < minsz ||
> > > > +		    !vfio_iommu_type1_pasid_req_valid(req.flags))
> > > > +			return -EINVAL;
> > > > +
> > > > +		if (copy_from_user((void *)&req + minsz,
> > > > +				   (void __user *)arg + minsz,
> > > > +				   sizeof(req) - minsz))
> > > > +			return -EFAULT;
> > >
> > > Huh?  Why do we have argsz if we're going to assume this is here?
> >
> > do you mean replacing sizeof(req) with argsz? if yes, I can do that.
> 
> No, I mean the user tells us how much data they've provided via argsz.
> We create minsz the the end of flags and verify argsz includes flags.
> Then we proceed to ignore argsz to see if the user has provided the
> remainder of the structure.

I think I should avoid using sizeof(req) as it may be variable
new flag is added. I think better to make a data[] field in struct
vfio_iommu_type1_pasid_request and copy data[] per flag. I'll
make this change in new version.

> > > > +
> > > > +		switch (req.flags & VFIO_PASID_REQUEST_MASK) {
> > > > +		case VFIO_IOMMU_PASID_ALLOC:
> > > > +		{
> > > > +			int ret = 0, result;
> > > > +
> > > > +			result = vfio_iommu_type1_pasid_alloc(iommu,
> > > > +							req.alloc_pasid.min,
> > > > +							req.alloc_pasid.max);
> > > > +			if (result > 0) {
> > > > +				offset = offsetof(
> > > > +					struct vfio_iommu_type1_pasid_request,
> > > > +					alloc_pasid.result);
> > > > +				ret = copy_to_user(
> > > > +					      (void __user *) (arg + offset),
> > > > +					      &result, sizeof(result));
> > >
> > > Again assuming argsz supports this.
> >
> > same as above.
> >
> > >
> > > > +			} else {
> > > > +				pr_debug("%s: PASID alloc failed\n", __func__);
> > >
> > > rate limit?
> >
> > not quite get. could you give more hints?
> 
> A user can spam the host logs simply by allocating their quota of
> PASIDs and then trying to allocate more, or by specifying min/max such
> that they cannot allocate the requested PASID.  If this logging is
> necessary for debugging, it should be ratelimited to avoid a DoS on the
> host.

got it. thanks for the coaching. will use pr_debug_ratelimited().

Regards,
Yi Liu