On Tue, 13 Dec 2022 07:46:56 -0800
Steve Sistare <steven.sistare@xxxxxxxxxx> wrote:
> When a vfio container is preserved across exec using the VFIO_UPDATE_VADDR
> interfaces, locked_vm of the new mm becomes 0. If the user later unmaps a
> dma mapping, locked_vm underflows to a large unsigned value, and a
> subsequent dma map request fails with ENOMEM in __account_locked_vm.
>
> To fix, when VFIO_DMA_MAP_FLAG_VADDR is used and the dma's mm has changed,
> add the mapping's pinned page count to the new mm->locked_vm, subject to
> the rlimit. Now that mediated devices are excluded when using
> VFIO_UPDATE_VADDR, the amount of pinned memory equals the size of the
> mapping.
>
> Underflow will not occur when all dma mappings are invalidated before exec.
> An attempt to unmap before updating the vaddr with VFIO_DMA_MAP_FLAG_VADDR
> will fail with EINVAL because the mapping is in the vaddr_invalid state.
Where is this enforced?
> Underflow may still occur in a buggy application that fails to invalidate
> all before exec.
>
> Signed-off-by: Steve Sistare <steven.sistare@xxxxxxxxxx>
> ---
> drivers/vfio/vfio_iommu_type1.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index f81e925..e5a02f8 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -100,6 +100,7 @@ struct vfio_dma {
> struct task_struct *task;
> struct rb_root pfn_list; /* Ex-user pinned pfn list */
> unsigned long *bitmap;
> + struct mm_struct *mm;
> };
>
> struct vfio_batch {
> @@ -1174,6 +1175,7 @@ static void vfio_remove_dma(struct vfio_iommu *iommu, struct vfio_dma *dma)
> vfio_unmap_unpin(iommu, dma, true);
> vfio_unlink_dma(iommu, dma);
> put_task_struct(dma->task);
> + mmdrop(dma->mm);
> vfio_dma_bitmap_free(dma);
> if (dma->vaddr_invalid) {
> iommu->vaddr_invalid_count--;
> @@ -1622,6 +1624,13 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
> dma->vaddr = vaddr;
> dma->vaddr_invalid = false;
> iommu->vaddr_invalid_count--;
> + if (current->mm != dma->mm) {
> + mmdrop(dma->mm);
> + dma->mm = current->mm;
> + mmgrab(dma->mm);
> + ret = vfio_lock_acct(dma, size >> PAGE_SHIFT,
> + 0);
What does it actually mean if this fails? The pages are still pinned.
lock_vm doesn't get updated. Underflow can still occur. Thanks,
Alex
> + }
> wake_up_all(&iommu->vaddr_wait);
> }
> goto out_unlock;
> @@ -1679,6 +1688,8 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
> get_task_struct(current->group_leader);
> dma->task = current->group_leader;
> dma->lock_cap = capable(CAP_IPC_LOCK);
> + dma->mm = dma->task->mm;
> + mmgrab(dma->mm);
>
> dma->pfn_list = RB_ROOT;
>
