[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:

quoted

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

quoted

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)));

quoted

luckly that the previous and the next neighbour of "sync_count" are both aligned

/s/luckly/luckily or fortunately/

OK, thanks

quoted

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 <redacted>
---
 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.

quoted

     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;

quoted

+    } __attribute__((aligned(8)));

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

Thanks




.

-- 
Thanks!
BestRegards