[PATCH v4.4,v4.9] vfio/type1: Limit DMA mappings per container

[PATCH v4.4,v4.9] vfio/type1: Limit DMA mappings per container

[Guenter Roeck]

From: Alex Williamson <alex.williamson@redhat.com>

commit 492855939bdb59c6f947b0b5b44af9ad82b7e38c upstream.

Memory backed DMA mappings are accounted against a user's locked
memory limit, including multiple mappings of the same memory.  This
accounting bounds the number of such mappings that a user can create.
However, DMA mappings that are not backed by memory, such as DMA
mappings of device MMIO via mmaps, do not make use of page pinning
and therefore do not count against the user's locked memory limit.
These mappings still consume memory, but the memory is not well
associated to the process for the purpose of oom killing a task.

To add bounding on this use case, we introduce a limit to the total
number of concurrent DMA mappings that a user is allowed to create.
This limit is exposed as a tunable module option where the default
value of 64K is expected to be well in excess of any reasonable use
case (a large virtual machine configuration would typically only make
use of tens of concurrent mappings).

This fixes CVE-2019-3882.

Reviewed-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
[groeck: Adjust for missing upstream commit]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 drivers/vfio/vfio_iommu_type1.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 2fa280671c1e..875634d0d020 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -53,10 +53,16 @@ module_param_named(disable_hugepages,
 MODULE_PARM_DESC(disable_hugepages,
 		 "Disable VFIO IOMMU support for IOMMU hugepages.");
 
+static unsigned int dma_entry_limit __read_mostly = U16_MAX;
+module_param_named(dma_entry_limit, dma_entry_limit, uint, 0644);
+MODULE_PARM_DESC(dma_entry_limit,
+		 "Maximum number of user DMA mappings per container (65535).");
+
 struct vfio_iommu {
 	struct list_head	domain_list;
 	struct mutex		lock;
 	struct rb_root		dma_list;
+	unsigned int		dma_avail;
 	bool			v2;
 	bool			nesting;
 };
@@ -382,6 +388,7 @@ static void vfio_remove_dma(struct vfio_iommu *iommu, struct vfio_dma *dma)
 	vfio_unmap_unpin(iommu, dma);
 	vfio_unlink_dma(iommu, dma);
 	kfree(dma);
+	iommu->dma_avail++;
 }
 
 static unsigned long vfio_pgsize_bitmap(struct vfio_iommu *iommu)
@@ -582,12 +589,18 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
 		return -EEXIST;
 	}
 
+	if (!iommu->dma_avail) {
+		mutex_unlock(&iommu->lock);
+		return -ENOSPC;
+	}
+
 	dma = kzalloc(sizeof(*dma), GFP_KERNEL);
 	if (!dma) {
 		mutex_unlock(&iommu->lock);
 		return -ENOMEM;
 	}
 
+	iommu->dma_avail--;
 	dma->iova = iova;
 	dma->vaddr = vaddr;
 	dma->prot = prot;
@@ -903,6 +916,7 @@ static void *vfio_iommu_type1_open(unsigned long arg)
 
 	INIT_LIST_HEAD(&iommu->domain_list);
 	iommu->dma_list = RB_ROOT;
+	iommu->dma_avail = dma_entry_limit;
 	mutex_init(&iommu->lock);
 
 	return iommu;
-- 
2.7.4

Re: [PATCH v4.4,v4.9] vfio/type1: Limit DMA mappings per container

[Greg Kroah-Hartman]

On Thu, May 02, 2019 at 06:33:23AM -0700, Guenter Roeck wrote:
> From: Alex Williamson <alex.williamson@redhat.com>
> 
> commit 492855939bdb59c6f947b0b5b44af9ad82b7e38c upstream.
> 
> Memory backed DMA mappings are accounted against a user's locked
> memory limit, including multiple mappings of the same memory.  This
> accounting bounds the number of such mappings that a user can create.
> However, DMA mappings that are not backed by memory, such as DMA
> mappings of device MMIO via mmaps, do not make use of page pinning
> and therefore do not count against the user's locked memory limit.
> These mappings still consume memory, but the memory is not well
> associated to the process for the purpose of oom killing a task.
> 
> To add bounding on this use case, we introduce a limit to the total
> number of concurrent DMA mappings that a user is allowed to create.
> This limit is exposed as a tunable module option where the default
> value of 64K is expected to be well in excess of any reasonable use
> case (a large virtual machine configuration would typically only make
> use of tens of concurrent mappings).
> 
> This fixes CVE-2019-3882.
> 
> Reviewed-by: Eric Auger <eric.auger@redhat.com>
> Tested-by: Eric Auger <eric.auger@redhat.com>
> Reviewed-by: Peter Xu <peterx@redhat.com>
> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> [groeck: Adjust for missing upstream commit]
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)

Nice, thanks for the backport, now queued up!

greg k-h