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

[Robin Murphy]

On 31/10/2018 04:02, Zhen Lei wrote:
> 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.

Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>

> 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