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

[Antonios Motakis <a.motakis-lrHrjnjw1UfHK3s98zE1ajGjJy/sRE9J@public.gmane.org>]

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-lrHrjnjw1UfHK3s98zE1ajGjJy/sRE9J@public.gmane.org>
---
 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)
+{
+	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)) {
+			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 */
+		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);
 
-- 
1.8.3.2