Null pointer dereference occurs due to a race between smmu
driver probe and client driver probe, when of_dma_configure()
for client is called after the iommu_device_register() for smmu driver
probe has executed but before the driver_bound() for smmu driver
has been called.
Following is how the race occurs:
T1:Smmu device probe T2: Client device probe
really_probe()
arm_smmu_device_probe()
iommu_device_register()
really_probe()
platform_dma_configure()
of_dma_configure()
of_dma_configure_id()
of_iommu_configure()
iommu_probe_device()
iommu_init_device()
arm_smmu_probe_device()
arm_smmu_get_by_fwnode()
driver_find_device_by_fwnode()
driver_find_device()
next_device()
klist_next()
/* null ptr
assigned to smmu */
/* null ptr dereference
while smmu->streamid_mask */
driver_bound()
klist_add_tail()
When this null smmu pointer is dereferenced later in
arm_smmu_probe_device, the device crashes.
Fix this by deferring the probe of the client device
until the smmu device has bound to the arm smmu driver.
Fixes: 021bb8420d44 ("iommu/arm-smmu: Wire up generic configuration support")
Cc: stable@xxxxxxxxxxxxxxx
Co-developed-by: Prakash Gupta <quic_guptap@xxxxxxxxxxx>
Signed-off-by: Prakash Gupta <quic_guptap@xxxxxxxxxxx>
Signed-off-by: Pratyush Brahma <quic_pbrahma@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20241004090428.2035-1-quic_pbrahma@xxxxxxxxxxx
[will: Add comment]
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
index 8321962b3714..14618772a3d6 100644
--- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
@@ -1437,6 +1437,17 @@ static struct iommu_device *arm_smmu_probe_device(struct device *dev)
goto out_free;
} else {
smmu = arm_smmu_get_by_fwnode(fwspec->iommu_fwnode);
+
+ /*
+ * Defer probe if the relevant SMMU instance hasn't finished
+ * probing yet. This is a fragile hack and we'd ideally
+ * avoid this race in the core code. Until that's ironed
+ * out, however, this is the most pragmatic option on the
+ * table.
+ */
+ if (!smmu)
+ return ERR_PTR(dev_err_probe(dev, -EPROBE_DEFER,
+ "smmu dev has not bound yet\n"));
}
ret = -EINVAL;
