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

Leizhen (ThunderTown)
2018-10-16T09:19:28Z

On 2018/10/15 19:17, John Garry wrote:
> 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?

OK

>
>> 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".

OK, I will use "struct" in v2.

+ struct {
u32 sync_count;
+ u32 padding;
+ } __attribute__((aligned(8)));

>
>> luckly that the previous and the next neighbour of "sync_count" are both aligned
>
> /s/luckly/luckily or fortunately/

OK, thanks

>
>> 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@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 */
>
> I think that a more detailed comment is required.

OK, I will try to describe it more clearly.

>
>> 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.

These indent is inherited, to keep aligning with other members.

There is no endian issue, I have tested it on both little-endian and big-endian.

$gdb vmlinux
......
(gdb) p &((struct arm_smmu_device *)0)->sync_count
$1 = (u32 *) 0x4178
(gdb) p &((struct arm_smmu_device *)0)->tst1
$2 = (int *) 0x4170
(gdb) p &((struct arm_smmu_device *)0)->tst2
$3 = (int *) 0x4180

------------testcase--------

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 5059d09..7c6f7ac 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -586,7 +586,14 @@ struct arm_smmu_device {

struct arm_smmu_strtab_cfg strtab_cfg;

+ int tst1;
+
+ union {
+ u64 padding;
u32 sync_count;
+ } __attribute__((aligned(8)));
+
+ int tst2;

/* IOMMU core code handle */
struct iommu_device iommu;

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

--
Thanks!
BestRegards