linux-kernel - Re: [PATCH v4 8/9] iommu: Remove unused argument in is_attach

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Date:   Wed, 30 Mar 2022 23:40:19 -0700
From:   Drew Fustini <dfustini@...libre.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Tony Lindgren <tony@...mide.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Ben Skeggs <bskeggs@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@....de>, linux-omap@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, regressions@...ts.linux.dev
Subject: Re: [PATCH v4 8/9] iommu: Remove unused argument in
 is_attach_deferred

On Wed, Mar 30, 2022 at 02:33:23PM -0300, Jason Gunthorpe wrote:
> On Wed, Mar 30, 2022 at 08:19:37PM +0300, Tony Lindgren wrote:
> 
> > > > __iommu_probe_device from probe_iommu_group+0x2c/0x38
> > > > probe_iommu_group from bus_for_each_dev+0x74/0xbc
> > > > bus_for_each_dev from bus_iommu_probe+0x34/0x2e8
> > > > bus_iommu_probe from bus_set_iommu+0x80/0xc8
> > > > bus_set_iommu from omap_iommu_init+0x88/0xcc
> > > > omap_iommu_init from do_one_initcall+0x44/0x24c
> > > > 
> > > > Any ideas for a fix?
> > > > 
> > > > It would be good to fix this quickly so we don't end up with a broken
> > > > v5.18-rc1..
> > > > 
> > > > For reference, this is mainline commit 41bb23e70b50 ("iommu: Remove unused
> > > > argument in is_attach_deferred").
> > > 
> > > Are you confident in the bisection? I don't see how that commit could
> > > NULL deref..
> > 
> > Oops sorry you're right, the breaking commit is a different patch, it's
> > 3f6634d997db ("iommu: Use right way to retrieve iommu_ops") instead. I must
> > have picked the wrong commit while testing.
> 
> That makes alot more sense
>  
> > > Can you find the code that is the NULL deref?
> > 
> > I can debug a bit more tomorrow.
> 
> Looks like omap's omap_iommu_probe_device() is buggy, it returns 0 on
> error paths:
> 
> 	num_iommus = of_property_count_elems_of_size(dev->of_node, "iommus",
> 						     sizeof(phandle));
> 	if (num_iommus < 0)
> 		return 0;
> 
> This function needs to return an errno -ENODEV
> 
> Otherwise it causes a NULL dev->iommu->iommu_dev and dev_iommu_ops() will
> crash.
> 
> Jason

I tried to boot current mainline (787af64d05cd) on am57xx-evm and it
failed to boot. I made the change you suggested and it boots okay now:
https://gist.github.com/pdp7/918eefe03b5c5db3b5d28d819f6a27f6

thanks,
drew

diff --git a/drivers/iommu/omap-iommu.c b/drivers/iommu/omap-iommu.c
index 4aab631ef517..d9cf2820c02e 100644
--- a/drivers/iommu/omap-iommu.c
+++ b/drivers/iommu/omap-iommu.c
@@ -1661,7 +1661,7 @@ static struct iommu_device *omap_iommu_probe_device(struct device *dev)
        num_iommus = of_property_count_elems_of_size(dev->of_node, "iommus",
                                                     sizeof(phandle));
        if (num_iommus < 0)
-               return 0;
+               return ERR_PTR(-ENODEV);

        arch_data = kcalloc(num_iommus + 1, sizeof(*arch_data), GFP_KERNEL);
        if (!arch_data)