Re: [PATCH v2] iommu/mediatek: fix NULL pointer dereference when printing dev_name

[Robin Murphy <robin.murphy@arm.com>]

On 2022-04-25 09:24, Miles Chen via iommu wrote:
> When larbdev is NULL (in the case I hit, the node is incorrectly set
> iommus = <&iommu NUM>), it will cause device_link_add() fail and
> kernel crashes when we try to print dev_name(larbdev).
> 
> Fix it by adding a NULL pointer check before
> device_link_add/device_link_remove.
> 
> It should work for normal correct setting and avoid the crash caused
> by my incorrect setting.
> 
> Error log:
> [   18.189042][  T301] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000050
> [   18.190247][  T301] Mem abort info:
> [   18.190255][  T301]   ESR = 0x96000005
> [   18.190263][  T301]   EC = 0x25: DABT (current EL), IL = 32 bits
> [   18.192142][  T301]   SET = 0, FnV = 0
> [   18.192151][  T301]   EA = 0, S1PTW = 0
> [   18.194710][  T301]   FSC = 0x05: level 1 translation fault
> [   18.195424][  T301] Data abort info:
> [   18.195888][  T301]   ISV = 0, ISS = 0x00000005
> [   18.196500][  T301]   CM = 0, WnR = 0
> [   18.196977][  T301] user pgtable: 4k pages, 39-bit VAs, pgdp=0000000104f9e000
> [   18.197889][  T301] [0000000000000050] pgd=0000000000000000, p4d=0000000000000000, pud=0000000000000000
> [   18.199220][  T301] Internal error: Oops: 96000005 [#1] PREEMPT SMP
> [   18.343152][  T301] Kernel Offset: 0x1444080000 from 0xffffffc008000000
> [   18.343988][  T301] PHYS_OFFSET: 0x40000000
> [   18.344519][  T301] pstate: a0400005 (NzCv daif +PAN -UAO)
> [   18.345213][  T301] pc : mtk_iommu_probe_device+0xf8/0x118 [mtk_iommu]
> [   18.346050][  T301] lr : mtk_iommu_probe_device+0xd0/0x118 [mtk_iommu]
> [   18.346884][  T301] sp : ffffffc00a5635e0
> [   18.347392][  T301] x29: ffffffc00a5635e0 x28: ffffffd44a46c1d8
> [   18.348156][  T301] x27: ffffff80c39a8000 x26: ffffffd44a80cc38
> [   18.348917][  T301] x25: 0000000000000000 x24: ffffffd44a80cc38
> [   18.349677][  T301] x23: ffffffd44e4da4c6 x22: ffffffd44a80cc38
> [   18.350438][  T301] x21: ffffff80cecd1880 x20: 0000000000000000
> [   18.351198][  T301] x19: ffffff80c439f010 x18: ffffffc00a50d0c0
> [   18.351959][  T301] x17: ffffffffffffffff x16: 0000000000000004
> [   18.352719][  T301] x15: 0000000000000004 x14: ffffffd44eb5d420
> [   18.353480][  T301] x13: 0000000000000ad2 x12: 0000000000000003
> [   18.354241][  T301] x11: 00000000fffffad2 x10: c0000000fffffad2
> [   18.355003][  T301] x9 : a0d288d8d7142d00 x8 : a0d288d8d7142d00
> [   18.355763][  T301] x7 : ffffffd44c2bc640 x6 : 0000000000000000
> [   18.356524][  T301] x5 : 0000000000000080 x4 : 0000000000000001
> [   18.357284][  T301] x3 : 0000000000000000 x2 : 0000000000000005
> [   18.358045][  T301] x1 : 0000000000000000 x0 : 0000000000000000
> [   18.360208][  T301] Hardware name: MT6873 (DT)
> [   18.360771][  T301] Call trace:
> [   18.361168][  T301]  dump_backtrace+0xf8/0x1f0
> [   18.361737][  T301]  dump_stack_lvl+0xa8/0x11c
> [   18.362305][  T301]  dump_stack+0x1c/0x2c
> [   18.362816][  T301]  mrdump_common_die+0x184/0x40c [mrdump]
> [   18.363575][  T301]  ipanic_die+0x24/0x38 [mrdump]
> [   18.364230][  T301]  atomic_notifier_call_chain+0x128/0x2b8
> [   18.364937][  T301]  die+0x16c/0x568
> [   18.365394][  T301]  __do_kernel_fault+0x1e8/0x214
> [   18.365402][  T301]  do_page_fault+0xb8/0x678
> [   18.366934][  T301]  do_translation_fault+0x48/0x64
> [   18.368645][  T301]  do_mem_abort+0x68/0x148
> [   18.368652][  T301]  el1_abort+0x40/0x64
> [   18.368660][  T301]  el1h_64_sync_handler+0x54/0x88
> [   18.368668][  T301]  el1h_64_sync+0x68/0x6c
> [   18.368673][  T301]  mtk_iommu_probe_device+0xf8/0x118 [mtk_iommu]
> [   18.369840][  T301]  __iommu_probe_device+0x12c/0x358
> [   18.370880][  T301]  iommu_probe_device+0x3c/0x31c
> [   18.372026][  T301]  of_iommu_configure+0x200/0x274
> [   18.373587][  T301]  of_dma_configure_id+0x1b8/0x230
> [   18.375200][  T301]  platform_dma_configure+0x24/0x3c
> [   18.376456][  T301]  really_probe+0x110/0x504
> [   18.376464][  T301]  __driver_probe_device+0xb4/0x188
> [   18.376472][  T301]  driver_probe_device+0x5c/0x2b8
> [   18.376481][  T301]  __driver_attach+0x338/0x42c
> [   18.377992][  T301]  bus_add_driver+0x218/0x4c8
> [   18.379389][  T301]  driver_register+0x84/0x17c
> [   18.380580][  T301]  __platform_driver_register+0x28/0x38
> ...
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Fixes: 635319a4a744 ("media: iommu/mediatek: Add device_link between the consumer and the larb devices")
> Signed-off-by: Miles Chen <miles.chen@mediatek.com>
> 
> ---
> 
> Change since v1
> fix a build warning reported by kernel test robot
> https://lore.kernel.org/lkml/202204231446.IYKdZ674-lkp@intel.com/
> 
> ---
>   drivers/iommu/mtk_iommu.c    | 13 ++++++++-----
>   drivers/iommu/mtk_iommu_v1.c | 13 ++++++++-----
>   2 files changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> index 6fd75a60abd6..03e0133f346a 100644
> --- a/drivers/iommu/mtk_iommu.c
> +++ b/drivers/iommu/mtk_iommu.c
> @@ -581,10 +581,12 @@ static struct iommu_device *mtk_iommu_probe_device(struct device *dev)
>   		}
>   	}
>   	larbdev = data->larb_imu[larbid].dev;
> -	link = device_link_add(dev, larbdev,
> -			       DL_FLAG_PM_RUNTIME | DL_FLAG_STATELESS);
> -	if (!link)
> -		dev_err(dev, "Unable to link %s\n", dev_name(larbdev));
> +	if (larbdev) {

Until the MT8195 infra MMU support lands, is there ever a case where 
it's actually valid for larbdev to be NULL? If not, I think it would be 
a lot clearer to explicitly fail the probe here, rather than silently 
continue and risk fatal errors, hangs, or other weird behaviour if 
there's no guarantee that the correct LARB is powered up (plus then the 
release callbacks wouldn't need to worry about it either).

Robin.

> +		link = device_link_add(dev, larbdev,
> +				       DL_FLAG_PM_RUNTIME | DL_FLAG_STATELESS);
> +		if (!link)
> +			dev_err(dev, "Unable to link %s\n", dev_name(larbdev));
> +	}
>   	return &data->iommu;
>   }
>   
> @@ -601,7 +603,8 @@ static void mtk_iommu_release_device(struct device *dev)
>   	data = dev_iommu_priv_get(dev);
>   	larbid = MTK_M4U_TO_LARB(fwspec->ids[0]);
>   	larbdev = data->larb_imu[larbid].dev;
> -	device_link_remove(dev, larbdev);
> +	if (larbdev)
> +		device_link_remove(dev, larbdev);
>   
>   	iommu_fwspec_free(dev);
>   }
> diff --git a/drivers/iommu/mtk_iommu_v1.c b/drivers/iommu/mtk_iommu_v1.c
> index ecff800656e6..18365c73eeb2 100644
> --- a/drivers/iommu/mtk_iommu_v1.c
> +++ b/drivers/iommu/mtk_iommu_v1.c
> @@ -467,10 +467,12 @@ static struct iommu_device *mtk_iommu_probe_device(struct device *dev)
>   	}
>   
>   	larbdev = data->larb_imu[larbid].dev;
> -	link = device_link_add(dev, larbdev,
> -			       DL_FLAG_PM_RUNTIME | DL_FLAG_STATELESS);
> -	if (!link)
> -		dev_err(dev, "Unable to link %s\n", dev_name(larbdev));
> +	if (larbdev) {
> +		link = device_link_add(dev, larbdev,
> +				       DL_FLAG_PM_RUNTIME | DL_FLAG_STATELESS);
> +		if (!link)
> +			dev_err(dev, "Unable to link %s\n", dev_name(larbdev));
> +	}
>   
>   	return &data->iommu;
>   }
> @@ -502,7 +504,8 @@ static void mtk_iommu_release_device(struct device *dev)
>   	data = dev_iommu_priv_get(dev);
>   	larbid = mt2701_m4u_to_larb(fwspec->ids[0]);
>   	larbdev = data->larb_imu[larbid].dev;
> -	device_link_remove(dev, larbdev);
> +	if (larbdev)
> +		device_link_remove(dev, larbdev);
>   
>   	iommu_fwspec_free(dev);
>   }
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