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

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Date:   Wed, 30 Mar 2022 11:23:40 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Tony Lindgren <tony@...mide.com>
Cc:     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 05:00:39PM +0300, Tony Lindgren wrote:
> Hi,
> 
> * Lu Baolu <baolu.lu@...ux.intel.com> [700101 02:00]:
> > The is_attach_deferred iommu_ops callback is a device op. The domain
> > argument is unnecessary and never used. Remove it to make code clean.
> 
> Looks like this causes a regression for at least drivers/iommu/omap-iommu.c.
> 
> To me it seems the issue is there is no is_attach_deferred implemented, so
> we get a NULL pointer dereference at virtual address 00000008:
> 
> __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..

Can you find the code that is the NULL deref?

Jason