linux-kernel - Re: [PATCH -next] iommu/of: Check for valid fwspec after of_pci_iommu

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Message-ID: <f697df05-9048-18ef-511a-24d3dc32f693@arm.com>
Date:   Wed, 2 Aug 2017 17:43:01 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Robin Murphy <robin.murphy@....com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Cc:     Sudeep Holla <sudeep.holla@....com>, Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH -next] iommu/of: Check for valid fwspec after
 of_pci_iommu_init



On 02/08/17 17:39, Robin Murphy wrote:
> On 02/08/17 17:11, Sudeep Holla wrote:
>> The successful return from of_pci_iommu_init doesn't ensure valid
>> fwspec if it's IOMMU is disabled.
>>
>> Accessing dev->iommu_fwspec->ops without checking dev->iommu_fwspec
>> could result in NULL pointer dereference.
>>
>> Unable to handle kernel NULL pointer dereference at virtual address 00000000
>> task: ffff800976880000 task.stack: ffff800976888000
>> PC is at of_iommu_configure+0x130/0x138
>> LR is at of_iommu_configure+0x118/0x138
>>  of_iommu_configure+0x130/0x138
>>  of_dma_configure+0xa8/0x190
>>  dma_configure+0x40/0xe8
>>  driver_probe_device+0x190/0x2d0
>>  __device_attach_driver+0x9c/0xf8
>>  bus_for_each_drv+0x58/0x98
>>  __device_attach+0xc4/0x138
>>  device_attach+0x10/0x18
>>  pci_bus_add_device+0x4c/0xa8
>>  pci_bus_add_devices+0x44/0x90
>>  pci_bus_add_devices+0x74/0x90
>>  pci_host_common_probe+0x14c/0x3a8
>>  gen_pci_probe+0x2c/0x38
>>  platform_drv_probe+0x58/0xc0
>>  driver_probe_device+0x214/0x2d0
>>  __driver_attach+0xac/0xb0
>>  bus_for_each_dev+0x60/0xa0
>>  driver_attach+0x20/0x28
>>  bus_add_driver+0x110/0x230
>>  driver_register+0x60/0xf8
>>  __platform_driver_register+0x44/0x50
>>  gen_pci_driver_init+0x18/0x20
>>  do_one_initcall+0x38/0x120
>>  kernel_init_freeable+0x184/0x224
>>  kernel_init+0x10/0x100
>>
>> This patch adds the check for dev->iommu_fwspec and fixes the above.
>>
>> Fixes: d87beb749281 ("iommu/of: Handle PCI aliases properly")
>> Cc: Robin Murphy <robin.murphy@....com>
>> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
>> ---
>>  drivers/iommu/of_iommu.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> Hi Robin,
>>
>> I see this crash on Juno with linux-next. Enabling PCIe SMMU fixes the
>> issue, but we may need to handle the disabled SMMU case to continue to
>> work with old DTBs.
> 
> Ugh, a disabled IOMMU should be conceptually the same as no IOMMU, but I
> guess the phandle chasing fails to fail. Per the design intent, the most
> correct fix should be this:
> 
> ----->8-----
> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> index be8ac1ddec06..9bc83f94bc10 100644
> --- a/drivers/iommu/of_iommu.c
> +++ b/drivers/iommu/of_iommu.c
> @@ -163,6 +163,8 @@ static int of_pci_iommu_init(struct pci_dev *pdev,
> u16 alias, void *data)
> 
>         if (IS_ERR(ops))
>                 return PTR_ERR(ops);
> +       if (!ops)
> +               return 1;
> 
>         return info->np == pdev->bus->dev.of_node;
>  }
> -----8<-----
> 
> But looking again, I think an even better fix involves ripping out much
> of the PTR_ERR shenanigans with ops that leads to this confusion in the
> first place. Give me a moment...
> 

Sure, I will leave it to you then ;)

-- 
Regards,
Sudeep