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

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Date:   Mon, 15 Oct 2018 14:52:33 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Zhen Lei <thunder.leizhen@...wei.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>, nd@....com
Subject: Re: [PATCH 1/1] iommu/arm-smmu-v3: eliminate a potential memory
 corruption on Hi16xx soc

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?

Robin.

> 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 */
>   	u32				sync_count;
> +	} __attribute__((aligned(8)));
>   
>   	/* IOMMU core code handle */
>   	struct iommu_device		iommu;
>