Re: [PATCH v2 1/1] iommu/arm-smmu-v3: eliminate a potential memory corruption on Hi16xx soc

["Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>]

On 2018/10/30 1:59, Will Deacon wrote:
> On Sat, Oct 20, 2018 at 03:36:54PM +0800, 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:
>> 1. Add gcc __attribute__((aligned(8))) to make sure that "sync_count" is
>>    always aligned by 8 bytes.
>> 2. Add a "int" struct member to make sure the 4 bytes padding is always
>>    exist.
>>
>> There is no functional change.
>>
>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>> ---
>>  drivers/iommu/arm-smmu-v3.c | 15 ++++++++++++++-
>>  1 file changed, 14 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
>> index 5059d09..624fdd0 100644
>> --- a/drivers/iommu/arm-smmu-v3.c
>> +++ b/drivers/iommu/arm-smmu-v3.c
>> @@ -586,7 +586,20 @@ struct arm_smmu_device {
>>  
>>  	struct arm_smmu_strtab_cfg	strtab_cfg;
>>  
>> -	u32				sync_count;
>> +	/*
>> +	 * The alignment and padding is required by Hi16xx of Hisilicon.
>> +	 * Because the ITS hardware on Hi16xx 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|
>> +	 */
>> +	struct {
>> +		u32			sync_count;
>> +		int			padding;
>> +	} __attribute__((aligned(8)));
> 
> I thought the conclusion after reviewing your original patch was to maintain
> the union and drop the alignment directive? e.g.
> 
> 	union {
> 		u32	sync_count;
> 		u64	padding; /* Hi16xx writes an extra 32 bits of goodness */
> 	};
OK, I will sent v3.

> 
> Will
> 
> .
> 

-- 
Thanks!
BestRegards