linux-kernel - Re: [PATCH v2 7/8] iommu: Export iommu_get_dma

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Date:   Wed, 29 Mar 2023 14:28:51 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     baolu.lu@...ux.intel.com, LKML <linux-kernel@...r.kernel.org>,
        iommu@...ts.linux.dev, Jason Gunthorpe <jgg@...dia.com>,
        Joerg Roedel <joro@...tes.org>, dmaengine@...r.kernel.org,
        vkoul@...nel.org, Robin Murphy <robin.murphy@....com>,
        Will Deacon <will@...nel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Raj Ashok <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>
Subject: Re: [PATCH v2 7/8] iommu: Export iommu_get_dma_domain

On 3/28/23 11:48 PM, Jacob Pan wrote:
> On Tue, 28 Mar 2023 14:04:15 +0800, Baolu Lu<baolu.lu@...ux.intel.com>
> wrote:
> 
>> On 3/28/23 7:21 AM, Jacob Pan wrote:
>>> Devices that use ENQCMDS to submit work needs to retrieve its DMA
>>> domain. It can then attach PASID to the DMA domain for shared mapping
>>> (with RID) established by DMA API.
>>>
>>> Signed-off-by: Jacob Pan<jacob.jun.pan@...ux.intel.com>
>>> ---
>>>    drivers/iommu/iommu.c | 1 +
>>>    include/linux/iommu.h | 5 +++++
>>>    2 files changed, 6 insertions(+)
>>>
>>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>>> index 10db680acaed..c51d343a75d2 100644
>>> --- a/drivers/iommu/iommu.c
>>> +++ b/drivers/iommu/iommu.c
>>> @@ -2118,6 +2118,7 @@ struct iommu_domain *iommu_get_dma_domain(struct
>>> device *dev) {
>>>    	return dev->iommu_group->default_domain;
>>>    }
>>> +EXPORT_SYMBOL_GPL(iommu_get_dma_domain);
>> Directly exporting this function for external use seems unsafe. If the
>> caller is the kernel driver for this device, it's fine because default
>> domain remains unchanged during the life cycle of the driver. Otherwise,
>> using this function may cause UAF. Keep in mind that group's default
>> domain could be changed through sysfs.
> don't you have to unload the driver?

Yes, of cause.

Hence, the getting domain interfaces are only safe to be used in the
driver of the device.

Best regards,
baolu