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

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Date:   Tue, 16 Oct 2018 17:19:14 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     John Garry <john.garry@...wei.com>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will.deacon@....com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
CC:     LinuxArm <linuxarm@...wei.com>
Subject: Re: [PATCH 1/1] iommu/arm-smmu-v3: eliminate a potential memory
 corruption on Hi16xx soc



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@...wei.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