[PATCH v4 10/16] iommu/arm-smmu: Prevent forced unbinding of Arm SMMU drivers

[Will Deacon]

Forcefully unbinding the Arm SMMU drivers is a pretty dangerous operation,
since it will likely lead to catastrophic failure for any DMA devices
mastering through the SMMU being unbound. When the driver then attempts
to "handle" the fatal faults, it's very easy to trip over dead data
structures, leading to use-after-free.

On John's machine, he reports that the machine was "unusable" due to
loss of the storage controller following a forced unbind of the SMMUv3
driver:

  | # cd ./bus/platform/drivers/arm-smmu-v3
  | # echo arm-smmu-v3.0.auto > unbind
  | hisi_sas_v2_hw HISI0162:01: CQE_AXI_W_ERR (0x800) found!
  | platform arm-smmu-v3.0.auto: CMD_SYNC timeout at 0x00000146
  | [hwprod 0x00000146, hwcons 0x00000000]

Prevent this forced unbinding of the drivers by setting "suppress_bind_attrs"
to true.

Link: https://lore.kernel.org/lkml/06dfd385-1af0-3106-4cc5-6a5b8e864759@xxxxxxxxxx
Reported-by: John Garry <john.garry@xxxxxxxxxx>
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
---
 drivers/iommu/arm-smmu-v3.c | 5 +++--
 drivers/iommu/arm-smmu.c    | 7 ++++---
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 68163b1d680d..9d4c9de6172d 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -3700,8 +3700,9 @@ MODULE_DEVICE_TABLE(of, arm_smmu_of_match);
 
 static struct platform_driver arm_smmu_driver = {
 	.driver	= {
-		.name		= "arm-smmu-v3",
-		.of_match_table	= of_match_ptr(arm_smmu_of_match),
+		.name			= "arm-smmu-v3",
+		.of_match_table		= of_match_ptr(arm_smmu_of_match),
+		.suppress_bind_attrs	= true,
 	},
 	.probe	= arm_smmu_device_probe,
 	.remove	= arm_smmu_device_remove,
diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index 7c768f771001..5cbee88a3b83 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -2268,9 +2268,10 @@ static const struct dev_pm_ops arm_smmu_pm_ops = {
 
 static struct platform_driver arm_smmu_driver = {
 	.driver	= {
-		.name		= "arm-smmu",
-		.of_match_table	= of_match_ptr(arm_smmu_of_match),
-		.pm		= &arm_smmu_pm_ops,
+		.name			= "arm-smmu",
+		.of_match_table		= of_match_ptr(arm_smmu_of_match),
+		.pm			= &arm_smmu_pm_ops,
+		.suppress_bind_attrs    = true,
 	},
 	.probe	= arm_smmu_device_probe,
 	.remove	= arm_smmu_device_remove,
-- 
2.24.1.735.g03f4e72817-goog