From mboxrd@z Thu Jan 1 00:00:00 1970 From: thunder.leizhen@huawei.com (Leizhen (ThunderTown)) Date: Tue, 16 Oct 2018 17:41:14 +0800 Subject: [PATCH 1/1] iommu/arm-smmu-v3: eliminate a potential memory corruption on Hi16xx soc In-Reply-To: <20181015172146.GD31305@brain-police> References: <1539592576-24352-1-git-send-email-thunder.leizhen@huawei.com> <20181015172146.GD31305@brain-police> Message-ID: <5BC5B23A.5040003@huawei.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 2018/10/16 1:21, Will Deacon wrote: > On Mon, Oct 15, 2018 at 04:36:16PM +0800, 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. >> >> There is no functional change. >> >> Signed-off-by: Zhen Lei >> --- >> 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))); > > Won't this already be aligned by the ABI? > > Anyway, you'll need to swizzle things for big-endian, I suspect. Maybe you > can do something clever like making sync_count an array of two elements > and determining the offset based on the endianness. Or just keep it simple > like we do for things like struct qrwlock and struct qspinlock and use > #ifdefs. This workaround is a special case, the sync_count is only written by ITS hardware, and is only read by software. Although Hisilicon ITS will write 8 bytes at MSIAddress(required it aligned by 8 bytes), but it can sure that the value of MSIdata will be written at the lower 4 bytes(the start address of sync_count). Because the type of sync_count is u32, so that CPU is also read the 4 bytes at the lower address. > > Also -- you need a comment to explain this insanity :) > > Will > > . > -- Thanks! BestRegards