[PATCH v2 4/9] drivers/iommu: Take a ref to the IOMMU driver prior to ->add_device()

Will Deacon
2019-11-08T15:16:29Z

To avoid accidental removal of an active IOMMU driver module, take a
reference to the driver module in 'iommu_probe_device()' immediately
prior to invoking the '->add_device()' callback and hold it until the
after the device has been removed by '->remove_device()'.

Suggested-by: Joerg Roedel <joro@8bytes.org>
Signed-off-by: Will Deacon <will@kernel.org>
---
drivers/iommu/iommu.c | 19 +++++++++++++++++--
include/linux/iommu.h | 2 ++
2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index c1aadb570145..4bfecfbbe2cf 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -22,6 +22,7 @@
#include <linux/bitops.h>
#include <linux/property.h>
#include <linux/fsl/mc.h>
+#include <linux/module.h>
#include <trace/events/iommu.h>

static struct kset *iommu_group_kset;
@@ -185,10 +186,21 @@ int iommu_probe_device(struct device *dev)
if (!iommu_get_dev_param(dev))
return -ENOMEM;

+ if (!try_module_get(ops->owner)) {
+ ret = -EINVAL;
+ goto err_free_dev_param;
+ }
+
ret = ops->add_device(dev);
if (ret)
- iommu_free_dev_param(dev);
+ goto err_module_put;
+
+ return 0;

+err_module_put:
+ module_put(ops->owner);
+err_free_dev_param:
+ iommu_free_dev_param(dev);
return ret;
}

@@ -199,7 +211,10 @@ void iommu_release_device(struct device *dev)
if (dev->iommu_group)
ops->remove_device(dev);

- iommu_free_dev_param(dev);
+ if (dev->iommu_param) {
+ module_put(ops->owner);
+ iommu_free_dev_param(dev);
+ }
}

static struct iommu_domain *__iommu_domain_alloc(struct bus_type *bus,
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 29bac5345563..d9dab5a3e912 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -245,6 +245,7 @@ struct iommu_iotlb_gather {
* @sva_get_pasid: Get PASID associated to a SVA handle
* @page_response: handle page request response
* @pgsize_bitmap: bitmap of all possible supported page sizes
+ * @owner: Driver module providing these ops
*/
struct iommu_ops {
bool (*capable)(enum iommu_cap);
@@ -308,6 +309,7 @@ struct iommu_ops {
struct iommu_page_response *msg);

unsigned long pgsize_bitmap;
+ struct module *owner;
};

/**