RE: [PATCH v6 8/8] iommu/vt-d: Disallow read-only mappings to nest parent domain

[Liu, Yi L]

> From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Saturday, October 21, 2023 11:24 AM
> 
> On 10/20/23 5:32 PM, Yi Liu wrote:
> > From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> >
> > When remapping hardware is configured by system software in scalable mode
> > as Nested (PGTT=011b) and with PWSNP field Set in the PASID-table-entry,
> > it may Set Accessed bit and Dirty bit (and Extended Access bit if enabled)
> > in first-stage page-table entries even when second-stage mappings indicate
> > that corresponding first-stage page-table is Read-Only.
> >
> > As the result, contents of pages designated by VMM as Read-Only can be
> > modified by IOMMU via PML5E (PML4E for 4-level tables) access as part of
> > address translation process due to DMAs issued by Guest.
> >
> > This disallows read-only mappings in the domain that is supposed to be used
> > as nested parent. Reference from Sapphire Rapids Specification Update [1],
> > errata details, SPR17. Userspace should know this limitation by checking
> > the IOMMU_HW_INFO_VTD_ERRATA_772415_SPR17 flag reported in the
> IOMMU_GET_HW_INFO
> > ioctl.
> >
> > [1] https://www.intel.com/content/www/us/en/content-details/772415/content-
> details.html
> >
> > Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx>
> > ---
> >   drivers/iommu/intel/iommu.c  |  9 +++++++++
> >   drivers/iommu/intel/iommu.h  |  1 +
> >   include/uapi/linux/iommufd.h | 12 +++++++++++-
> >   3 files changed, 21 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> > index c7704e7efd4a..a0341a069fbf 100644
> > --- a/drivers/iommu/intel/iommu.c
> > +++ b/drivers/iommu/intel/iommu.c
> > @@ -2193,6 +2193,11 @@ __domain_mapping(struct dmar_domain *domain,
> unsigned long iov_pfn,
> >   	if ((prot & (DMA_PTE_READ|DMA_PTE_WRITE)) == 0)
> >   		return -EINVAL;
> >
> > +	if (!(prot & DMA_PTE_WRITE) && domain->is_nested_parent) {
> > +		pr_err_ratelimited("Read-only mapping is disallowed on the domain
> which serves as the parent in a nested configuration, due to HW errata
> (ERRATA_772415_SPR17)\n");
> > +		return -EINVAL;
> > +	}
> > +
> >   	attr = prot & (DMA_PTE_READ | DMA_PTE_WRITE | DMA_PTE_SNP);
> >   	attr |= DMA_FL_PTE_PRESENT;
> >   	if (domain->use_first_level) {
> > @@ -4101,6 +4106,9 @@ intel_iommu_domain_alloc_user(struct device *dev, u32
> flags,
> >   		domain = iommu_domain_alloc(dev->bus);
> >   		if (!domain)
> >   			return ERR_PTR(-ENOMEM);
> > +		container_of(domain,
> > +			     struct dmar_domain,
> > +			     domain)->is_nested_parent = request_nest_parent;
> 
> How about
> 		to_dmar_domain(domain)->is_nested_parent = ...;
> ?

Yes.

> 
> I would also prefer to introduce is_nested_parent_domain to the user
> domain allocation patch (patch 7/8). This field should be checked when
> allocating a nested user domain.

A ctually, no need. This should be a common check, so iommufd core already
has the check. So the parent should be a nest parent domain, otherwise already
returned in iommufd.

+	if (!parent->nest_parent)
+		return ERR_PTR(-EINVAL);

https://lore.kernel.org/linux-iommu/20231020091946.12173-8-yi.l.liu@xxxxxxxxx/

> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 8f81a5c9fcc0..d3f6bc1f6590 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -4121,6 +4121,8 @@ intel_iommu_domain_alloc_user(struct device *dev,
> u32 flags,
>                  return ERR_PTR(-EINVAL);
>          if (request_nest_parent)
>                  return ERR_PTR(-EINVAL);
> +       if (!to_dmar_domain(parent)->is_nested_parent)
> +               return ERR_PTR(-EINVAL);
> 
>          return intel_nested_domain_alloc(parent, user_data);
>   }
> 
> Best regards,
> baolu