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SubjectRe: [PATCH 1/1] iommu/arm-smmu-v3: eliminate a potential memory corruption on Hi16xx soc
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On 2018/10/15 21:52, Robin Murphy wrote:
> On 15/10/18 09:36, Zhen Lei wrote:
>> ITS translation register map:
>> 0x0000-0x003C Reserved
>> 0x0040 GITS_TRANSLATER
>> 0x0044-0xFFFC Reserved
>>
>> 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
>> luckly that the previous and the next neighbour of "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 "u64" union member to make sure the 4 bytes padding is always exist.
>
> Surely the u64 member inherently makes the union, and thus the u32 member as well, 64-bit-aligned anyway?

Yes, we really only need one step, "1." or "2.". As John Garry suggested, I will change it to "struct" mode.

>
> Robin.
>
>> There is no functional change.
>>
>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>> ---
>> 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 */
>> u32 sync_count;
>> + } __attribute__((aligned(8)));
>> /* IOMMU core code handle */
>> struct iommu_device iommu;
>>
>
>

--
Thanks!
BestRegards

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