From: Li Zhe <[email protected]>
In function vfio_dma_do_unmap(), we currently prevent process to unmap
vfio dma region whose mm_struct is different from the vfio_dma->task.
In our virtual machine scenario which is using kvm and qemu, this
judgement stops us from liveupgrading our qemu, which uses fork() &&
exec() to load the new binary but the new process cannot do the
VFIO_IOMMU_UNMAP_DMA action during vm exit because of this judgement.
This judgement is added in commit 8f0d5bb95f76 ("vfio iommu type1: Add
task structure to vfio_dma") for the security reason. But it seems that
no other task who has no family relationship with old and new process
can get the same vfio_dma struct here for the reason of resource
isolation. So this patch delete it.
Signed-off-by: Li Zhe <[email protected]>
---
drivers/vfio/vfio_iommu_type1.c | 6 ------
1 file changed, 6 deletions(-)
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index c13b9290e357..a8ff00dad834 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -1377,12 +1377,6 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
if (!iommu->v2 && iova > dma->iova)
break;
- /*
- * Task with same address space who mapped this iova range is
- * allowed to unmap the iova range.
- */
- if (dma->task->mm != current->mm)
- break;
if (invalidate_vaddr) {
if (dma->vaddr_invalid) {
--
2.20.1
On Thu, Jun 23, 2022 at 07:56:03PM +0800, [email protected] wrote:
> From: Li Zhe <[email protected]>
>
> In function vfio_dma_do_unmap(), we currently prevent process to unmap
> vfio dma region whose mm_struct is different from the vfio_dma->task.
> In our virtual machine scenario which is using kvm and qemu, this
> judgement stops us from liveupgrading our qemu, which uses fork() &&
> exec() to load the new binary but the new process cannot do the
> VFIO_IOMMU_UNMAP_DMA action during vm exit because of this judgement.
>
> This judgement is added in commit 8f0d5bb95f76 ("vfio iommu type1: Add
> task structure to vfio_dma") for the security reason. But it seems that
> no other task who has no family relationship with old and new process
> can get the same vfio_dma struct here for the reason of resource
> isolation. So this patch delete it.
>
> Signed-off-by: Li Zhe <[email protected]>
> ---
> drivers/vfio/vfio_iommu_type1.c | 6 ------
> 1 file changed, 6 deletions(-)
I'm inclined to agree with this reasoning and deliberately did not
include a similar check in iommufd. Any process with access to the
container FD should be able to manipulate the IOVA space.
Reviewed-by: Jason Gunthorpe <[email protected]>
Jason