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

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Date:   Mon, 15 Oct 2018 16:36:16 +0800
From:   Zhen Lei <thunder.leizhen@...wei.com>
To:     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:     Zhen Lei <thunder.leizhen@...wei.com>,
        LinuxArm <linuxarm@...wei.com>
Subject: [PATCH 1/1] iommu/arm-smmu-v3: eliminate a potential memory corruption on Hi16xx soc

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.

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;
-- 
1.8.3