[PATCH v3 1/1] iommu/arm-smmu-v3: eliminate a potential memory corruption on hi1620 and earlier

[Zhen Lei]

The standard GITS_TRANSLATER register in ITS is only 4 bytes, but
Hisilicon expands the next 4 bytes to carry some IMPDEF information. That
means, total 8 bytes data will be written to MSIAddress each time.

MSIAddr: |----4bytes----|----4bytes----|
	 |    MSIData   |    IMPDEF    |

There is no problem for ITS, because the next 4 bytes space is reserved
in ITS. But it will overwrite the 4 bytes memory following "sync_count".
It's very fortunately that the previous and the next neighbour of the
"sync_count" are both aligned by 8 bytes, so no problem is met now.

It's good to explicitly add a workaround. Let's enclose the "sync_count"
into a union and companion with a new member "padding" of type u64.

There is no functional change.

Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
---
 drivers/iommu/arm-smmu-v3.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 6947ccf..4e94730 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -576,7 +576,23 @@ struct arm_smmu_device {

 	struct arm_smmu_strtab_cfg	strtab_cfg;

-	u32				sync_count;
+	/*
+	 * The member "padding" is used to make sure the member "sync_count" to
+	 * be aligned at 8 bytes boundary, and 4 bytes padding memory followed.
+	 *
+	 * These are required by hi1620 and earlier of Hisilicon. Because the
+	 * ITS hardware on hi1620 and earlier will truncate the MSIAddress(Here
+	 * it's the address of "sync_count") to 8 bytes boundary first, then
+	 * write 32 bits MSIdata at offset 0, and 32 bits IMPDEF data at offset
+	 * 4. Without this workaround, the adjacent member maybe overwritten.
+	 *
+	 *                    |---4bytes---|---4bytes---|
+	 * MSIAddress & (~0x7):   MSIdata  | IMPDEF data|
+	 */
+	union {
+		u32			sync_count;
+		u64			padding;
+	};

 	/* IOMMU core code handle */
 	struct iommu_device		iommu;
--
1.8.3