linux-kernel - Re: [PATCH v3 09/14] iommu/arm-smmu: Prevent forced unbinding of Arm SMMU drivers

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Date:   Tue, 26 Nov 2019 09:13:20 +0000
From:   John Garry <john.garry@...wei.com>
To:     Will Deacon <will@...nel.org>, <iommu@...ts.linuxfoundation.org>,
        <linux-kernel@...r.kernel.org>
CC:     Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Saravana Kannan" <saravanak@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Isaac J. Manjarres" <isaacm@...eaurora.org>,
        Robin Murphy <robin.murphy@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH v3 09/14] iommu/arm-smmu: Prevent forced unbinding of Arm
 SMMU drivers

On 21/11/2019 11:49, Will Deacon wrote:
> Forcefully unbinding the Arm SMMU drivers is a pretty dangerous operation,
> since it will likely lead to catastrophic failure for any DMA devices
> mastering through the SMMU being unbound. When the driver then attempts
> to "handle" the fatal faults, it's very easy to trip over dead data
> structures, leading to use-after-free.
> 
> On John's machine, he reports that the machine was "unusable" due to
> loss of the storage controller following a forced unbind of the SMMUv3
> driver:
> 
>    | # cd ./bus/platform/drivers/arm-smmu-v3
>    | # echo arm-smmu-v3.0.auto > unbind
>    | hisi_sas_v2_hw HISI0162:01: CQE_AXI_W_ERR (0x800) found!
>    | platform arm-smmu-v3.0.auto: CMD_SYNC timeout at 0x00000146
>    | [hwprod 0x00000146, hwcons 0x00000000]
> 
> Prevent this forced unbinding of the drivers by setting "suppress_bind_attrs"
> to true.

This seems a reasonable approach for now.

BTW, I'll give this series a spin this week, which again looks to be 
your iommu/module branch, excluding the new IORT patch.

Cheers,
John

> 
> Link: https://lore.kernel.org/lkml/06dfd385-1af0-3106-4cc5-6a5b8e864759@huawei.com
> Reported-by: John Garry <john.garry@...wei.com>
> Signed-off-by: Will Deacon <will@...nel.org>
> ---
>   drivers/iommu/arm-smmu-v3.c | 5 +++--
>   drivers/iommu/arm-smmu.c    | 7 ++++---
>   2 files changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> index 2ad8e2ca0583..3fd75abce3bb 100644
> --- a/drivers/iommu/arm-smmu-v3.c
> +++ b/drivers/iommu/arm-smmu-v3.c
> @@ -3700,8 +3700,9 @@ MODULE_DEVICE_TABLE(of, arm_smmu_of_match);
>   
>   static struct platform_driver arm_smmu_driver = {
>   	.driver	= {
> -		.name		= "arm-smmu-v3",
> -		.of_match_table	= of_match_ptr(arm_smmu_of_match),
> +		.name			= "arm-smmu-v3",
> +		.of_match_table		= of_match_ptr(arm_smmu_of_match),
> +		.suppress_bind_attrs	= true,
>   	},
>   	.probe	= arm_smmu_device_probe,
>   	.remove	= arm_smmu_device_remove,
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 53bbe0663b9e..d6c83bd69555 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -2237,9 +2237,10 @@ static const struct dev_pm_ops arm_smmu_pm_ops = {
>   
>   static struct platform_driver arm_smmu_driver = {
>   	.driver	= {
> -		.name		= "arm-smmu",
> -		.of_match_table	= of_match_ptr(arm_smmu_of_match),
> -		.pm		= &arm_smmu_pm_ops,
> +		.name			= "arm-smmu",
> +		.of_match_table		= of_match_ptr(arm_smmu_of_match),
> +		.pm			= &arm_smmu_pm_ops,
> +		.suppress_bind_attrs    = true,
>   	},
>   	.probe	= arm_smmu_device_probe,
>   	.remove	= arm_smmu_device_remove,
>