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

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Date:   Tue, 30 Oct 2018 22:02:51 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     John Garry <john.garry@...wei.com>,
        Will Deacon <will.deacon@....com>
CC:     Joerg Roedel <joro@...tes.org>, LinuxArm <linuxarm@...wei.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        Robin Murphy <robin.murphy@....com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 1/1] iommu/arm-smmu-v3: eliminate a potential memory
 corruption on Hi16xx soc



On 2018/10/30 17:26, John Garry wrote:
> On 30/10/2018 01:52, Leizhen (ThunderTown) wrote:
>>
>>
>> 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@...wei.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.
> 
> Nit: I know that there is no functional change related to this bug which depends on the chip version, but how about "hi1620 and earlier"? hi16xx is very broad.

OK, I will update it.

> 
> Thanks
> 
>>>> +     * 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