[PATCH] iommu: Check return of __iommu_attach_device()

[Will Deacon]

On Thu, Nov 19, 2020 at 04:58:46PM +0000, Shameer Kolothum wrote:
> Currently iommu_create_device_direct_mappings() is called
> without checking the return of __iommu_attach_device(). This
> may result in failures in iommu driver if dev attach returns
> error.
> 
> Fixes: ce574c27ae27("iommu: Move iommu_group_create_direct_mappings() out of iommu_group_add_device()")
> Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi at huawei.com>
> ---
> Crash log:
> [   31.353605] hns3 0000:7d:00.3: Adding to iommu group 10
> [   31.358822] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000018
> [   31.367567] Mem abort info:
> [   31.370350]   ESR = 0x96000004
> [   31.373391]   EC = 0x25: DABT (current EL), IL = 32 bits
> [   31.378680]   SET = 0, FnV = 0
> [   31.381720]   EA = 0, S1PTW = 0
> [   31.384847] Data abort info:
> [   31.387716]   ISV = 0, ISS = 0x00000004
> [   31.391535]   CM = 0, WnR = 0
> [   31.394491] [0000000000000018] user address but active_mm is swapper
> [   31.400818] Internal error: Oops: 96000004 [#1] PREEMPT SMP
> [   31.406365] Modules linked in:
> [   31.409409] CPU: 21 PID: 1 Comm: swapper/0 Not tainted 5.10.0-rc4-00008-gdd5aba9d719-dirty #79
> [   31.417980] Hardware name: Huawei TaiShan 200 (Model 2280)/BC82AMDD, BIOS 2280-V2 CS V3.B220.01 03/19/2020
> [   31.427588] pstate: 00c00009 (nzcv daif +PAN +UAO -TCO BTYPE=--)
> [   31.433566] pc : arm_smmu_tlb_inv_range+0x178/0x1f0
> [   31.438422] lr : arm_smmu_tlb_inv_range+0x5c/0x1f0
> [   31.443190] sp : ffff80001043b4e0
> ...
> [   31.531175] Call trace:
> [   31.533613]  arm_smmu_tlb_inv_range+0x178/0x1f0
> [   31.538122]  arm_smmu_iotlb_sync+0x2c/0x38
> [   31.542200]  iommu_unmap+0x60/0x90
> [   31.545585]  __iommu_map+0x110/0x1f0
> [   31.549144]  iommu_create_device_direct_mappings.isra.34+0x1ac/0x250
> [   31.555468]  iommu_probe_device+0x6c/0x110
> [   31.559551]  iort_iommu_configure_id+0x114/0x218
> [   31.564148]  acpi_dma_configure_id+0x94/0xe0
> [   31.568402]  pci_dma_configure+0xc8/0xf0
> [   31.572310]  really_probe+0xd4/0x3e0
> [   31.575871]  driver_probe_device+0x5c/0xc0
> 
> ---
>  drivers/iommu/iommu.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index b53446bb8c6b..0f4dc25d46c9 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -264,16 +264,18 @@ int iommu_probe_device(struct device *dev)
>  	 */
>  	iommu_alloc_default_domain(group, dev);
>  
> -	if (group->default_domain)
> +	if (group->default_domain) {
>  		ret = __iommu_attach_device(group->default_domain, dev);
> +		if (ret) {
> +			iommu_group_put(group);
> +			goto err_release;
> +		}
> +	}

This looks sensible to me, but what I don't understand is where that
NULL pointer is coming from in the first place. iommu_map() operates
on the domain, so why does it matter if the attach fails? What is being
accessed at arm_smmu_tlb_inv_range+0x178/0x1f0 ?

Will