Re: [PATCHv7 06/26] vfio/iommu_type1: implement the VFIO_DMA_MAP_FLAG_NOEXEC flag

[Antonios Motakis]

On Wed, Sep 24, 2014 at 12:40 AM, Alex Williamson
<alex.williamson@xxxxxxxxxx> wrote:
> On Tue, 2014-09-23 at 16:46 +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 | 38 +++++++++++++++++++++++++++++++++++++-
>>  1 file changed, 37 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index 0734fbe..09e5064 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -81,6 +81,26 @@ struct vfio_group {
>>  };
>>
>>  /*
>> + * This function returns true only if _all_ domains support the capability.
>> + */
>> +static int vfio_all_domains_have_iommu_noexec(struct vfio_iommu *iommu)
>
> Rename to vfio_domains_have_iommu_noexec() for consistency with the
> cache version.
>

The logic here is a slightly different logic between the two. For
IOMMU_CACHE we generally check if any domain includes it, for NOEXEC
in contract we need all domains to support it, otherwise we can't
expose the capability. Hence the _all_ addition in the name of the
function.

>> +{
>> +     struct vfio_domain *d;
>> +     int ret = 1;
>> +
>> +     mutex_lock(&iommu->lock);
>> +     list_for_each_entry(d, &iommu->domain_list, next) {
>> +             if (!iommu_domain_has_cap(d->domain, IOMMU_CAP_NOEXEC)) {
>
> Should we cache this in domain->prot like we do for IOMMU_CACHE?
>
>> +                     ret = 0;
>> +                     break;
>> +             }
>> +     }
>> +     mutex_unlock(&iommu->lock);
>> +
>> +     return ret;
>> +}
>> +
>> +/*
>>   * This code handles mapping and unmapping of user data buffers
>>   * into DMA'ble space using the IOMMU
>>   */
>> @@ -546,6 +566,11 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
>>               prot |= IOMMU_WRITE;
>>       if (map->flags & VFIO_DMA_MAP_FLAG_READ)
>>               prot |= IOMMU_READ;
>> +     if (map->flags & VFIO_DMA_MAP_FLAG_NOEXEC) {
>> +             if (!vfio_all_domains_have_iommu_noexec(iommu))
>> +                     return -EINVAL;
>> +             prot |= IOMMU_NOEXEC;
>> +     }
>>
>>       if (!prot || !size || (size | iova | vaddr) & mask)
>>               return -EINVAL;
>> @@ -636,6 +661,12 @@ 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 */
>
> nit, please fix the comment style to match the rest of the file.
>

Ack

>> +             if ((dma->prot | IOMMU_NOEXEC) &&
>> +                 !iommu_domain_has_cap(domain->domain, IOMMU_CAP_NOEXEC))
>> +                     return -EINVAL;
>> +
>>               while (iova < dma->iova + dma->size) {
>>                       phys_addr_t phys = iommu_iova_to_phys(d->domain, iova);
>>                       size_t size;
>> @@ -890,6 +921,10 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>>                       if (!iommu)
>>                               return 0;
>>                       return vfio_domains_have_iommu_cache(iommu);
>> +             case VFIO_IOMMU_PROT_NOEXEC:
>> +                     if (!iommu)
>> +                             return 0;
>> +                     return vfio_all_domains_have_iommu_noexec(iommu);
>>               default:
>>                       return 0;
>>               }
>> @@ -913,7 +948,8 @@ 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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