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Subject: Re: [PATCH] vfio powerpc: implemented IOMMU driver for VFIO
From: Alex Williamson <alex.williamson@redhat.com>
To: Alexey Kardashevskiy <aik@ozlabs.ru>
Date: Wed, 12 Dec 2012 07:36:13 -0700
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Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
 Paul Mackerras <paulus@samba.org>, linuxppc-dev@lists.ozlabs.org,
 David Gibson <david@gibson.dropbear.id.au>
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On Wed, 2012-12-12 at 17:59 +1100, Alexey Kardashevskiy wrote:
> On 08/12/12 04:01, Alex Williamson wrote:
> >> +	case VFIO_IOMMU_MAP_DMA: {
> >> +		vfio_iommu_spapr_tce_dma_map param;
> >> +		struct iommu_table *tbl = container->tbl;
> >> +		enum dma_data_direction direction;
> >> +		unsigned long locked, lock_limit;
> >> +
> >> +		if (WARN_ON(!tbl))
> >> +			return -ENXIO;
> >> +
> >> +		minsz = offsetofend(vfio_iommu_spapr_tce_dma_map, size);
> >> +
> >> +		if (copy_from_user(&param, (void __user *)arg, minsz))
> >> +			return -EFAULT;
> >> +
> >> +		if (param.argsz < minsz)
> >> +			return -EINVAL;
> >> +
> >> +		if ((param.flags & VFIO_DMA_MAP_FLAG_READ) &&
> >> +				(param.flags & VFIO_DMA_MAP_FLAG_WRITE))
> >> +			direction = DMA_BIDIRECTIONAL;
> >> +		else if (param.flags & VFIO_DMA_MAP_FLAG_READ)
> >> +			direction = DMA_TO_DEVICE;
> >> +		else if (param.flags & VFIO_DMA_MAP_FLAG_WRITE)
> >> +			direction = DMA_FROM_DEVICE;
> >> +		else
> >> +			return -EINVAL;
> >
> > flags needs to be sanitized too.  Return EINVAL if any unknown bit is
> > set or else sloppy users may make it very difficult to make use of those
> > flag bits later.
> 
> 
> It already returns -EINVAL on any bit set except READ/WRITE, no?

No.  I could pass flags ~0 through there to get a read/write mapping and
cause you problems if you later want to define another bit.  Thanks,

Alex