[PATCH RFC 11/17] iommu: Hold iommu_probe_device_lock while calling ops->of_xlate

[Jason Gunthorpe <jgg@xxxxxxxxxx>]

This resolves the race around touching dev->iommu while generating the OF
fwspec on the of_iommu_configure() flow:

     CPU0                                     CPU1
of_iommu_configure()                iommu_device_register()
 ..                                   bus_iommu_probe()
  iommu_fwspec_of_xlate()              __iommu_probe_device()
                                        iommu_init_device()
   dev_iommu_get()
                                          .. ops->probe fails, no fwspec ..
                                          dev_iommu_free()
   dev->iommu->fwspec    *crash*

CPU1 is holding the iommu_probe_device_lock for iommu_init_device(),
holding it around the of_xlate() and its related manipulation of
dev->iommu will close it.

The approach also closes a similar race for what should be a successful
probe where the above basic construction results in ops->probe observing a
partially initialized fwspec.

Reported-by: Zhenhua Huang <quic_zhenhuah@xxxxxxxxxxx>
Closes: https://lore.kernel.org/linux-arm-kernel/20231017163337.GE282036@xxxxxxxx/T/#mee0d7bdc375541934a571ae69f43b9660f8e7312
Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
---
 drivers/iommu/iommu.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 9cfba9d12d1400..62c82a28cd5db3 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -41,6 +41,7 @@
 static struct kset *iommu_group_kset;
 static DEFINE_IDA(iommu_group_ida);
 static DEFINE_IDA(iommu_global_pasid_ida);
+static DEFINE_MUTEX(iommu_probe_device_lock);
 
 static unsigned int iommu_def_domain_type __read_mostly;
 static bool iommu_dma_strict __read_mostly = IS_ENABLED(CONFIG_IOMMU_DEFAULT_DMA_STRICT);
@@ -498,7 +499,6 @@ static int __iommu_probe_device(struct device *dev,
 	struct iommu_fwspec *fwspec = caller_fwspec;
 	const struct iommu_ops *ops;
 	struct iommu_group *group;
-	static DEFINE_MUTEX(iommu_probe_device_lock);
 	struct group_device *gdev;
 	int ret;
 
@@ -3002,8 +3002,11 @@ int iommu_fwspec_of_xlate(struct iommu_fwspec *fwspec, struct device *dev,
 	if (!fwspec->ops->of_xlate)
 		return -ENODEV;
 
-	if (!dev_iommu_get(dev))
+	mutex_lock(&iommu_probe_device_lock);
+	if (!dev_iommu_get(dev)) {
+		mutex_unlock(&iommu_probe_device_lock);
 		return -ENOMEM;
+	}
 
 	/*
 	 * ops->of_xlate() requires the fwspec to be passed through dev->iommu,
@@ -3015,6 +3018,7 @@ int iommu_fwspec_of_xlate(struct iommu_fwspec *fwspec, struct device *dev,
 	ret = fwspec->ops->of_xlate(dev, iommu_spec);
 	if (dev->iommu->fwspec == fwspec)
 		dev->iommu->fwspec = NULL;
+	mutex_unlock(&iommu_probe_device_lock);
 	return ret;
 }
 
@@ -3044,6 +3048,8 @@ int iommu_fwspec_init(struct device *dev, struct fwnode_handle *iommu_fwnode,
 	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
 	int ret;
 
+	lockdep_assert_held(&iommu_probe_device_lock);
+
 	if (fwspec)
 		return ops == fwspec->ops ? 0 : -EINVAL;
 
@@ -3097,6 +3103,8 @@ int iommu_fwspec_add_ids(struct device *dev, u32 *ids, int num_ids)
 {
 	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
 
+	lockdep_assert_held(&iommu_probe_device_lock);
+
 	if (!fwspec)
 		return -EINVAL;
 	return iommu_fwspec_append_ids(fwspec, ids, num_ids);
-- 
2.42.0