Re: [PATCH 5/5] vfio/iommu_type1: implement the VFIO_DMA_MAP_FLAG_NOEXEC flag

[Antonios Motakis]

On Mon, Oct 20, 2014 at 11:13 PM, Alex Williamson
<alex.williamson@xxxxxxxxxx> wrote:
> On Mon, 2014-10-13 at 15:09 +0200, Antonios Motakis wrote:
>> Some IOMMU drivers, such as the ARM SMMU driver, make available the
>> IOMMU_NOEXEC flag, to set the page tables for a device as XN (execute never).
>> This affects devices such as the ARM PL330 DMA Controller, which respects
>> this flag and will refuse to fetch DMA instructions from memory where the
>> XN flag has been set.
>>
>> The flag can be used only if all IOMMU domains behind the container support
>> the IOMMU_NOEXEC flag. Also, if any mappings are created with the flag, any
>> new domains with devices will have to support it as well.
>>
>> Signed-off-by: Antonios Motakis <a.motakis@xxxxxxxxxxxxxxxxxxxxxx>
>> ---
>>  drivers/vfio/vfio_iommu_type1.c | 25 ++++++++++++++++++++++++-
>>  1 file changed, 24 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index 8b4202a..e225e8f 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -569,6 +569,12 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
>>       if (map->flags & VFIO_DMA_MAP_FLAG_READ)
>>               prot |= IOMMU_READ;
>>
>> +     if (map->flags & VFIO_DMA_MAP_FLAG_NOEXEC) {
>> +             if (!vfio_domains_have_iommu_cap(iommu, IOMMU_CAP_NOEXEC))
>> +                     return -EINVAL;
>> +             prot |= IOMMU_NOEXEC;
>> +     }
>> +
>>       if (!prot || !size || (size | iova | vaddr) & mask)
>>               return -EINVAL;
>
> I think this test needs to move above adding the NOEXEC flag, otherwise
> we now allow mappings without read or write, which is an ABI change.
>

Ack.

>>
>> @@ -662,6 +668,14 @@ static int vfio_iommu_replay(struct vfio_iommu *iommu,
>>               dma = rb_entry(n, struct vfio_dma, node);
>>               iova = dma->iova;
>>
>> +             /*
>> +              * if any of the mappings to be replayed has the NOEXEC flag
>> +              * set, then the new iommu domain must support it
>> +              */
>> +             if ((dma->prot | IOMMU_NOEXEC) &&
>
> I think you mean
>
> & IOMMU_NOEXEC

Ack.

>
>> +                             !(domain->caps & IOMMU_CAP_NOEXEC))
>> +                     return -EINVAL;
>> +
>
> In patch 2/5 you stated:
>
>         The IOMMU_NOEXEC flag needs to be available for all the IOMMUs
>         of the container used.
>
> But here you'll create heterogeneous containers so long as there are no
> NOEXEC mappings.  Is that intentional or a side effect of the above
> masking bug?
>

Yeah, my intention was to not stop the user of having heterogeneous
containers, as long as he doesn't care about using the NOEXEC flag. As
soon as the user tries to apply this flag however, then it should be
supported by all the IOMMUs behind the container - otherwise it is not
enforceable.

Do you think we should change this behavior? I think most users will
not care about using this flag, and we should not stop them from
mixing containers.

>>               while (iova < dma->iova + dma->size) {
>>                       phys_addr_t phys = iommu_iova_to_phys(d->domain, iova);
>>                       size_t size;
>> @@ -749,6 +763,9 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
>>       if (iommu_capable(bus, IOMMU_CAP_CACHE_COHERENCY))
>>               domain->caps |= IOMMU_CAP_CACHE_COHERENCY;
>>
>> +     if (iommu_capable(bus, IOMMU_CAP_NOEXEC))
>> +             domain->caps |= IOMMU_CAP_NOEXEC;
>> +
>>       /*
>>        * Try to match an existing compatible domain.  We don't want to
>>        * preclude an IOMMU driver supporting multiple bus_types and being
>> @@ -900,6 +917,11 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>>                               return 0;
>>                       return vfio_domains_have_iommu_cap(iommu,
>>                                                 IOMMU_CAP_CACHE_COHERENCY);
>> +             case VFIO_DMA_NOEXEC_IOMMU:
>> +                     if (!iommu)
>> +                             return 0;
>> +                     return vfio_domains_have_iommu_cap(iommu,
>> +                                                        IOMMU_CAP_NOEXEC);
>>               default:
>>                       return 0;
>>               }
>> @@ -923,7 +945,8 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>>       } else if (cmd == VFIO_IOMMU_MAP_DMA) {
>>               struct vfio_iommu_type1_dma_map map;
>>               uint32_t mask = VFIO_DMA_MAP_FLAG_READ |
>> -                             VFIO_DMA_MAP_FLAG_WRITE;
>> +                             VFIO_DMA_MAP_FLAG_WRITE |
>> +                             VFIO_DMA_MAP_FLAG_NOEXEC;
>>
>>               minsz = offsetofend(struct vfio_iommu_type1_dma_map, size);
>>
>
>
>



-- 
Antonios Motakis
Virtual Open Systems
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