linux-kernel - Re: [PATCH v2] iommu/arm-smmu: Defer probe of clients after smmu device bound

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Message-ID: <d4a52579-0e2a-4df3-a1fa-e8e154ff1e90@quicinc.com>
Date: Tue, 15 Oct 2024 19:01:30 +0530
From: Pratyush Brahma <quic_pbrahma@...cinc.com>
To: <will@...nel.org>
CC: <robin.murphy@....com>, <joro@...tes.org>, <jgg@...pe.ca>,
        <jsnitsel@...hat.com>, <robdclark@...omium.org>,
        <quic_c_gdjako@...cinc.com>, <dmitry.baryshkov@...aro.org>,
        <linux-arm-kernel@...ts.infradead.org>, <iommu@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>, <quic_charante@...cinc.com>,
        <stable@...r.kernel.org>, Prakash Gupta
	<quic_guptap@...cinc.com>
Subject: Re: [PATCH v2] iommu/arm-smmu: Defer probe of clients after smmu
 device bound


On 10/4/2024 2:34 PM, Pratyush Brahma wrote:
> Null pointer dereference occurs due to a race between smmu
> driver probe and client driver probe, when of_dma_configure()
> for client is called after the iommu_device_register() for smmu driver
> probe has executed but before the driver_bound() for smmu driver
> has been called.
>
> Following is how the race occurs:
>
> T1:Smmu device probe		T2: Client device probe
>
> really_probe()
> arm_smmu_device_probe()
> iommu_device_register()
> 					really_probe()
> 					platform_dma_configure()
> 					of_dma_configure()
> 					of_dma_configure_id()
> 					of_iommu_configure()
> 					iommu_probe_device()
> 					iommu_init_device()
> 					arm_smmu_probe_device()
> 					arm_smmu_get_by_fwnode()
> 						driver_find_device_by_fwnode()
> 						driver_find_device()
> 						next_device()
> 						klist_next()
> 						    /* null ptr
> 						       assigned to smmu */
> 					/* null ptr dereference
> 					   while smmu->streamid_mask */
> driver_bound()
> 	klist_add_tail()
>
> When this null smmu pointer is dereferenced later in
> arm_smmu_probe_device, the device crashes.
>
> Fix this by deferring the probe of the client device
> until the smmu device has bound to the arm smmu driver.
>
> Fixes: 021bb8420d44 ("iommu/arm-smmu: Wire up generic configuration support")
> Cc: stable@...r.kernel.org
> Co-developed-by: Prakash Gupta <quic_guptap@...cinc.com>
> Signed-off-by: Prakash Gupta <quic_guptap@...cinc.com>
> Signed-off-by: Pratyush Brahma <quic_pbrahma@...cinc.com>
> ---
> Changes in v2:
>   Fix kernel test robot warning
>   Add stable kernel list in cc
>   Link to v1: https://lore.kernel.org/all/20241001055633.21062-1-quic_pbrahma@quicinc.com/
>
>   drivers/iommu/arm/arm-smmu/arm-smmu.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> index 723273440c21..7c778b7eb8c8 100644
> --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> @@ -1437,6 +1437,9 @@ static struct iommu_device *arm_smmu_probe_device(struct device *dev)
>   			goto out_free;
>   	} else {
>   		smmu = arm_smmu_get_by_fwnode(fwspec->iommu_fwnode);
> +		if (!smmu)
> +			return ERR_PTR(dev_err_probe(dev, -EPROBE_DEFER,
> +						"smmu dev has not bound yet\n"));
>   	}
>   
>   	ret = -EINVAL;


Hi
Can someone please review this patch? Let me know if any further 
information is required.

Thanks
Pratyush