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

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Date:   Tue, 28 Mar 2023 08:48:55 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>
Cc:     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>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v2 7/8] iommu: Export iommu_get_dma_domain

Hi Baolu,

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? 

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


Thanks,

Jacob