Re: [PATCH 1/1] iommu/arm-smmu-v3: eliminate a potential memory corruption on Hi16xx soc

[John Garry]

On 15/10/2018 09:36, Zhen Lei wrote:
> ITS translation register map:
> 0x0000-0x003C	Reserved
> 0x0040		GITS_TRANSLATER
> 0x0044-0xFFFC	Reserved

Can you add a better opening than the ITS translation register map?

> 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, 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

I think arm_smmu_device.sync_count is better, or "sync_count member in 
the the smmu driver control struct".

> luckly that the previous and the next neighbour of "sync_count" are both aligned

/s/luckly/luckily or fortunately/

> by 8 bytes, so no problem is met now.
>
> It's good to explicitly add a workaround:
> 1. Add gcc __attribute__((aligned(8))) to make sure that "sync_count" is always
>    aligned by 8 bytes.
> 2. Add a "u64" union member to make sure the 4 bytes padding is always exist.
>
> There is no functional change.
>
> Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
> ---
>  drivers/iommu/arm-smmu-v3.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> index 5059d09..a07bc0d 100644
> --- a/drivers/iommu/arm-smmu-v3.c
> +++ b/drivers/iommu/arm-smmu-v3.c
> @@ -586,7 +586,10 @@ struct arm_smmu_device {
>
>  	struct arm_smmu_strtab_cfg	strtab_cfg;
>
> +	union {
> +	u64				padding; /* workaround for Hisilicon */

I think that a more detailed comment is required.

>  	u32				sync_count;

Can you indent these 2 members? However - as discussed internally - this 
may have endian issue so better to declare full 64b struct.

> +	} __attribute__((aligned(8)));
>
>  	/* IOMMU core code handle */
>  	struct iommu_device		iommu;
Thanks