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

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Message-ID: <e7d53d04-6b7f-05a4-3077-42470c6d2823@linux.intel.com>
Date:   Tue, 28 Mar 2023 14:04:15 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jacob Pan <jacob.jun.pan@...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
Cc:     baolu.lu@...ux.intel.com, 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 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.

However, iommu_get_domain_for_dev() has already done so and has been
exported. Maybe I'm worried too much. :-)

Best regards,
baolu